Confined polymerization: multidimensional regulation, advanced measurements and cutting-edge applications

Abstract

Confined polymerization, as an innovative polymerization strategy, achieves precise control over the reaction pathway and microscopic structure of the product by confining the polymerization reaction within the physical space of a micro-nano scale. Compared with traditional large-scale or solution polymerization, confined polymerization is carried out in confined spaces, such as nanochannels, layered intermediate layers, or porous material pores, significantly altering properties such as the polymerization rate, molecular weight distribution, glass transition temperature, and product morphology. This review systematically classifies the limited-domain polymerization strategies in different dimensional spaces, clarifies their mechanism differences, and emphasizes the progress in characterisation techniques, including in situ microscopy, spectroscopy, and computational simulation. Additionally, we discuss confined polymerization in cutting-edge applications, such as water purification, medical diagnosis and treatment, energy storage, catalysis, and composite coatings. By combining fundamental principles with functional innovation, we identify the key challenges, such as real-time mechanism detection and scalable synthesis, and propose future directions, including dynamic limitations, biomimetic design, and AI-driven optimization. The aim of this article is to stimulate the attention of more scholars to the field of confined polymerization, thereby accelerating breakthrough progress in this field and providing innovative material solutions for global challenges such as climate change, disease treatment, and clean energy.

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Lushan Sun

Lushan Sun is currently a Master's student at the Petrochemicals College of Jilin University of Chemical Technology. Her research focuses include the polymerization methods of active small molecules within the confined space of hydrogels.

Jian Sun

Jian Sun is currently an Associate Professor at the Institute of Petrochemical Engineering, Jilin University of Chemical Technology. He earned his PhD from Dalian University of Technology in 2016 and conducted his postdoctoral research at Jilin Chemical Fiber Group Co., Ltd. His research is focused on the performance regulation of composite materials and the structural design of ionic liquid cross-linked hydrogels.

Mingqiong Tong

Mingqiong Tong graduated from the School of Chemistry, Beijing Normal University, with a major in Physical Chemistry. Presently, she is a Lecturer at the School of Health and Medicine at Dezhou University. She mainly engages in research in theoretical and computational chemistry, traditional Chinese medicine, and biomedical fields. She has published more than 20 academic papers and 6 SCI-indexed papers as the first author in internationally renowned professional journals, such as Journal of Chemical Information and Modeling, International Journal of Hydrogen Energy, Langmuir, and Journal of Molecular Recognition.

Yanyan Zhao

Yanyan Zhao received her BSc in Applied Chemistry from Qingdao University of Science and Technology in 2017 and her PhD from the Institute of Chemistry, Chinese Academy of Sciences in 2022. Presently, she is a lecturer at the School of Health and Medicine at Dezhou University. Her research focuses on the preparation and application of fluorescent functional materials.

Xiangling Gu

Xiangling Gu graduated from Shandong University with a PhD in Polymer Chemistry and Physics in June 2010. He currently serves as the Dean and Professor at the School of Health and Medicine, Dezhou University. As a Visiting Scholar under the EU Erasmus Programme and a China-Finland cooperation project, he specialises in soft matter research related to hydrogels. He serves as an Editorial Board Member of the Journal of Biomedical Engineering Research (in Chinese) and as a young Editorial Board Member for several international English-language journals, including Exploration, Polymer Science and Technology, and Wearable Electronics.

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Wider impact

Constrained polymerization achieves precise control over polymerization pathways, kinetics, and product structures through micro-/nano-scale spatial confinement, breaking the thermodynamic equilibrium limitations of traditional polymerization. It can synthesize novel materials, such as cyclic polymers and double-stranded topological structures, and significantly optimize molecular weight distribution, crystallinity, and functional properties. The core of this field of interest lies in its disruptive potential, providing innovative solutions for water treatment, healthcare, energy, and catalysis. We propose that future research should focus on in situ mechanistic analysis. For instance, advanced techniques such as ultrafast spectroscopy and single-molecule tracking should be developed to capture transient reaction intermediates in real time within confined spaces. Furthermore, integrating biomimetic designs (such as microfluidics) with stimulus-responsive templates (light/magnetic regulation) would enable dynamic switching of polymerization pathways. Ultimately, establishing a “spatial confinement-property” relationship database will accelerate the development of new materials to address climate and energy challenges. These breakthroughs will drive material science to a paradigm shift towards atomic-level programming and functional intelligent integration.

1. Introduction

Controlled polymerization, as a central strategy in modern polymer materials science, aims to achieve the design of polymer chain structures or morphologies by regulating the polymerization process. Traditional controlled polymerization methods (e.g., living radical polymerization, living anionic polymerization, and coordination polymerization) primarily rely on reaction condition optimization or specific catalytic systems to achieve control objectives, yet their controllability exhibits moderate limitations. Conversely, “confined polymerization” represents an innovative strategy for overcoming the constraints of traditional systems, enabling precise control over the reaction pathways and product microstructures. Unlike conventional bulk polymerization or solution polymerization that occurs in an open space, confined polymerization usually restricts the synthesis process to physical domains at the micro and nanometre levels, such as nanopores, micelle microphases, layered intermediate layers or microemulsion droplets. This confinement creates a comparatively isolated environment with strictly limited mass exchange between the reaction system and the external surroundings, potentially inducing distinct polymerization mechanisms and kinetic behaviors compared with conventional conditions.^1–5 For instance, confined polymerization within nanopores has confirmed alterations in reaction rates,^6,7 molecular weight distributions,⁸ glass transition temperatures,⁹ and morphologies, among other properties,¹⁰ Notably, this strategy enables the synthesis of novel polymer architectures,^11,12 which are inaccessible under conventional conditions, thereby offering a transformative technological platform for modulating polymerization kinetics, molecular structures, and material performances.^13,14

As a pivotal approach for modulating polymerization reactions, spatial confinement effects have garnered extensive research attention within the academic community. Through the synergistic integration of chemical synthesis, theoretical modeling, and advanced characterisation techniques, this field has developed distinct interdisciplinary characteristics. Elucidating the physicochemical mechanisms underlying polymerization reactions within diverse confined spaces not only clarifies the structure–property relationships governed by spatial constraints but also advances polymer science toward precision engineering and functional innovation. However, systematic reviews of “confined polymerization” remain scarce in the current literature. Therefore, the basic concept of confined spaces is first elaborated in this review. Subsequently, research progress in “confined polymerization” is systematically reviewed based on the classification framework encompassing one-dimensional (1D) longitudinal confined spaces, two-dimensional (2D) interfacial confinement systems, three-dimensional (3D) porous confinement architectures, and other specialized confined space systems (Fig. 1a). Finally, the application potential of this technology in frontier fields, such as water treatment, drug delivery systems, and energy storage materials, is systematically summarized (Fig. 1b). Future developmental directions are primarily focused on, with theoretical support and innovative methodologies that are required to be continuously provided for advancing research in this field.

Fig. 1 (a) Common carriers for confined polymerization in 1D, 2D, 3D and special confined spaces. (b) Application fields of confined polymerization.

2. Confined spaces

2.1. Definition of confined spaces

A confined space is defined as a micro/nano-scale region where the chemical and physical behaviors of molecules are confined within a volume comparable to the characteristic dimension of individual molecules. Such confinement typically arises from geometric constraints, dimensionality, and environmental conditions inherent in nanoscale domains.^15,16 Within these confined spaces, the arrangement, interactions, and phase transitions of matter may exhibit behaviors distinct from those observed at macroscopic scales, endowing materials with novel physical, chemical, and biological properties. Through precise control of spatial dimensions, morphological features, and boundary constraints, fundamental principles underlying nanoscale phenomena are systematically investigated, and unique physical mechanisms along with chemical processes governing matter at this frontier are elucidated.^17–20

2.2. Classification and synthesis of confined spaces

Confined spaces, which exist ubiquitously across inorganic,²¹ organic²² and polymeric materials,²³ provide uniquely confined microenvironments for mass transport and chemical reactions. Based on geometric dimensionality, these spaces can be categorized into four classes: (I) 1D confined spaces, (ii) 2D confined spaces, (iii) 3D confined spaces, and (iv) specialized confined spaces.

1D confined spaces typically refer to the reaction environments within nanotubes or nanoporous channels. Such spaces restrict the conformational freedom of the polymer chains, inducing unique aggregate states and microstructures in the resulting polymers. The fabrication of these 1D channels commonly employs template-assisted methodologies, wherein pre-patterned architectures dictate the spatial organisation and dimensional constraints of the confined environment. For instance, a hard-template-directed growth strategy utilizing CEO nanowires as structural sacrificial templates was proposed by Wang et al.²⁴ Using coordination etching-in situ precipitation synergy, they achieved the controlled synthesis of 1D Eoh hollow tubes, as illustrated in Fig. 2a. On this basis, the dimension of the template-based method was expanded by Wang et al. through the development of a dual-silicon template-assisted strategy (Fig. 2f).²⁵ This approach involved the co-deposition of dopamine and silica onto silica nanowire templates, followed by carbonization and silica removal. Monodisperse silica nanowires (Siow₂ NWs) served as rigid templates for hollow tubular pore formation, while silica nanoparticles (Sion₂ NPs) generated via sol–gel processing of tetraethyl orthosilicate (TEOS) acted as porogens to create mesopores. A hierarchical template system was constructed by leveraging silica nanowire templates as substrates, enabling the dual regulation of both pore architecture and morphological contours in the target material. This strategy successfully yielded nitrogen-doped carbon nanotubes (NMCTs) with hierarchical pore structures that integrated the open mesopores and tubular macropores.

Fig. 2 (a) Schematic and reaction procedure for the preparation of FeOOH sheets using Cu₂O wires as sacrificial templates. Reproduced with permission from ref. 24. Copyright 2023, Springer Nature. (b) Scanning electron microscopy (SEM) image of mesoporous nanofibres. Reproduced with permission from ref. 26. Copyright 2023, Springer Nature. (c) Synthetic scheme for porous spherical carbon materials. Reproduced with permission from ref. 27. Copyright 2024, Elsevier. (d) Experimental procedure for liquid metal exfoliation of h-BN. Reproduced with permission from ref. 29. Copyright 2025, John Wiley and Sons. (e) Atomic force microscopy (AFM) images of ZnO thin films grown via the sol–gel method and annealed at different temperatures. Reproduced with permission from ref. 28. Copyright 2022, Springer Nature. (f) Schematic of the synthesis process for NMCT. Reproduced with permission from ref. 25. Copyright 2023, John Wiley and Sons.

An alternative approach to synthesize 1D nanoconfined spaces involves construction through self-assembly mechanisms. Zhao et al.²⁶ showed the self-assembly of single micelles into mesoporous nanoellipsoids in solution, which subsequently grew into uniform mesoporous nanofibers, as illustrated in Fig. 2b. An innovative soft-template-induced self-assembly strategy was invented by Wang et al. by employing poly(ethylene glycol)-block-poly(propylene glycol) (F127) as the soft template and N-allylthiourea as the heteroatom doping source.²⁷ Through hydrogen bonding interactions and solvent evaporation-driven self-assembly processes (Fig. 2c), they successfully synthesized porous spherical carbon materials exhibiting ordered microporous structures with controlled interlayer spacings. These materials possess elongated 1D architectures that maintain internal material confinement while providing defined spatial limitations.

The emergence of 1D nanomaterials (e.g., nanotubes and nanofibers) with confined spaces has enabled the fabrication of nanostructures with unique morphologies and properties. Furthermore, it has laid the groundwork for developing 2D and 3D materials. For 2D confined systems, chemical reactions occurring within these spaces are significantly influenced by surface effects and interfacial interactions, which in turn modulate the morphology and performance of the resulting compounds. Thin films are canonical examples of materials with 2D confinement characteristics. Taking doped zinc oxide (ZnO) thin films as an illustrative case, the sol–gel method has become the predominant synthesis approach due to the ability of ZnO to form homogeneous films through solution-based deposition processes. This methodology leverages the controlled precipitation of ZnO precursors from solution, enabling precise thickness regulation and uniform film formation across substrates.^30,31 Zou et al.³² proposed a straightforward strategy that employs the polar solvent dimethylformamide (DMF) as a cosolvent in the sol–gel method for fabricating high-quality DMF-ZnO thin films. Zinc acetate dihydrate was used as the precursor, and a mixed solvent of 2-methoxyethanol and DMF was employed to form the ZnO sol. The resulting ZnO sol was spin-coated onto the substrate and annealed at a high temperature to achieve crystallization, leading to the formation of high-quality films with a wurtzite structure. Furthermore, when annealing treatment is carried out at different temperatures, the structure and properties of the zinc oxide film are changed, as shown in Fig. 2e.²⁸ Beyond the conventional swelling-gel method, a liquid metal exfoliation approach was developed by Yu et al.²⁹ inspired by adhesive-assisted exfoliation techniques for fabricating 2D nanosheets. Hexagonal boron nitride (h-BN) was selected as a model material, where shear forces generated through mechanical agitation acted synergistically with the intercalation of liquid metal gallium to achieve successful exfoliation of boron nitride nanosheets, as illustrated in Fig. 2d. An inherently confined 2D environment was thus established between nanosheet planes, restricting molecular motion within nanoscale spatial boundaries.

3D confined spaces primarily involve materials with porous architectures, such as mesoporous silica spheres, metal–organic frameworks (MOFs), and other polymeric porous materials. In hydrogel-based polymeric systems, 3D network spaces are typically constructed using monomer polymerization techniques. For instance, anisotropic polyvinyl alcohol-polyaniline (PVA-PANI) hydrogels were designed and fabricated by Liu et al. using a vertical gradient freezing approach combined with a cryopolymerization strategy.³³ In this process, PVA chains, aniline monomers, and initiators self-assembled into a 3D ordered honeycomb architecture, followed by confined polymerization of aniline to gradually form a polyaniline nanofibre scaffold (Fig. 3a). Furthermore, a hydrogel system composed of tannic acid-modified ZIF@P1 nanoparticles (TA-ZIF@P1) and phenylboronic acid-functionalized gelatin (GP hydrogel) was investigated by Li et al.³⁴ This composite hydrogel exhibits a 3D network structure with pore sizes ranging from 50 to 130 μm (Fig. 3b). The resulting 3D confinement spaces provide multiple reaction pathways and unique spatial constraints that enhance polymer diversity and functionality. The establishment of such confined spatial environments creates a specialized platform for chemical reactions and introduces innovative design paradigms for polymeric materials.

Fig. 3 (a) Schematic of the fabrication process of anisotropic polyvinyl alcohol/polyaniline hydrogels (APPH). Reproduced with permission from ref. 33. Copyright 2020, Springer Nature. (b) Scanning electron microscopy (SEM) images of the 3D network structures in lyophilized GP and GPTP hydrogels. Reproduced with permission from ref. 34. Copyright 2025, the American Chemical Society. (c) and (e) SEM micrographs showing intracellular aggregates of B₃–Te. Reproduced with permission from ref. 39. Copyright 2023, the American Chemical Society. (d) Schematic depicting confined spatial environments. Reproduced with permission from ref. 36. Copyright 2023, John Wiley and Sons.

Special confined spaces mainly refer to non-rigid, physically confined spaces with adjustable boundaries. Their confined dimensions can be dynamically reconfigured in real time using external stimuli (such as light, heat, and pH) or internal chemical feedback. A special soft confinement space was synthesized by Lu et al. using amphiphilic microspheres (ADMs) and deep eutectic solvents (DESs).³⁵ The confined structure was formed through hydrogen bonding interactions between sulfonic acid groups (–SO₃H) on the microsphere surface and acrylic acid components within the DES matrix. The hydrogen bond network, combined with dynamic intermolecular electrostatic interactions, enables supramolecular interaction reconstruction via molecular chain relaxation. Unlike conventional confinement systems, this architecture demonstrates the dynamic expansion capabilities of a confined space under applied stimuli. The unique combination of hydrogen bonding and electrostatic effects has been shown to facilitate reversible structural adaptation, distinguishing it from the static confinement mechanisms typically observed in traditional systems. Li et al. revealed the construction of confinement spaces with tailored spatial limitations by exploiting differential hydration behavior between salts and polymer chains.³⁶ Through regulation of the free water-to-bound water ratio and precise control over interchain distances, the dimensions of these confinement spaces were systematically modulated (Fig. 3d). Living cells are also used to construct special enclosed spaces. The specific confined spaces within the cells integrate multi-scale structural levels, metabolic activities and autonomous regulatory mechanisms, making them different from synthetic enclosed systems.^37,38 A novel strategy was employed by Xu et al., leveraging the intracellular redox microenvironment in combination with the hypersensitive oxidizability of organotellurium compounds to trigger oxidative polymerization reactions.³⁹ This approach enabled the realization of hyperbranched polymerization within living cells, as shown in Fig. 3c and e. The special constraints emphasize the dynamic biological micro-environment and self-limitation at the molecular level, while the general confined space focuses on the static porous structure.

3. Confined polymerization

The seminal concept of “Über Polymerization” (“on polymerization”), through which the notion of macromolecules composed of repeating units connected by covalent bonds was elucidated, was pioneered by Hermann Staudinger.⁴⁰ Currently, the majority of monomer polymerization reactions occur in open reaction environments, where reactant molecules undergo frequent collisions within extensive volumes, thereby promoting enhanced reaction rates and conversion efficiencies.^41–43 With the deepening understanding of polymerization mechanisms and continuous advancements in technological innovations, however, increasing attention has been directed toward the development of more efficient and controllable polymerization systems by scientists—a shift driven by the escalating demands for advanced polymeric materials with tailored performance characteristics.⁴⁴ Against this backdrop, confined polymerization has garnered growing attention. This review will subsequently explore polymerization processes conducted under various dimensional constraints and in specialized confined environments.

Confined polymerization involves restricting reactants within the limited spatial domain of a host material to guide the fabrication of substances with tailored properties. The concept of confined polymerization emerged in scientific research three decades ago, as exemplified by the pioneering work of Aida. Leveraging mesoporous silica fibres with tubular pore structures as reaction matrices for ethylene polymerization, Aida successfully synthesized polyethylene (PE) nanofibres exhibiting specific diametres (30–50 nm) and ultra-high molecular weights (up to 6 200 000 g mol⁻¹).⁴⁵ The spatial confinement imposed by the pore dimensions prevented PE chains from adopting conventional lamellar structures, compelling them to form extended-chain crystals within the confined geometry. This unique structural confinement endowed the PE nanofibres with exceptional physical and chemical attributes. The transformative concept of “extrusion polymerization” was introduced by Aida, building upon this phenomenon. Since this seminal contribution, confined polymerization has gained significant traction as a methodology for producing high-performance polymeric nanomaterials, and has attracted sustained interest from the scientific community.

3.1. Polymerization in one-dimensional confined spaces

Polymerization reactions conducted within 1D confined spaces represent a specialized chemical process that strictly constrains molecular motion to linear channels or tubular architectures. Such reactions typically occur in nanoconfined systems, including the interior of carbon nanotubes, molecular sieve channels, or other sub-nanometre to micrometre-scale tubular structures. Polymerization in 1D confined environments completely restricts the lateral mobility of molecules, compelling the reaction to proceed along a singular axial direction. This spatial constraint fundamentally alters polymer chain propagation, conformational arrangements, and entropic effects and ultimately influences the physical properties and performance characteristics of the resulting polymeric materials.

Carbon nanotubes (CNTs) possess one-dimensional hollow channels with a definite diameter, providing an ideal platform for achieving confined polymerization at an extreme scale. The inner cavities of CNTs can be regarded as a ‘rigid nano-reactor’, with their nanoscale diameters (typically 0.5–10 nm) imposing strict physical constraints on the conformation and chain movement of polymers. The sp² carbon surface of CNTs may have strong π–π interactions with monomers or polymers, further guiding the directional growth and arrangement of polymers. A confined polymerization strategy was successfully implemented on the surface of multi-walled carbon nanotubes (MWCNTs) by Campisciano et al. using a polymerizable deep eutectic solvent (DEM).⁴⁶ Within this system, polymerization was localized in proximity to the nanotube surfaces, where spatial confinement effects were demonstrated to significantly suppress the free expansion of polymer chains, thereby inducing the formation of more compact and ordered polymeric architectures. Compared to conventional polymerization conducted in ethanol solutions, the DEM-mediated system exhibited elevated local monomer concentrations. When coupled with the physical confinement imposed by nanotube surfaces and the interfacial guiding effects of the DEM, the directional growth of polymer chains along the nanotube surfaces was facilitated under constrained conditions. This ultimately resulted in the formation of thinner (approximately 50 nm), denser, and more stable coatings, as opposed to the thicker (approximately 150 nm) and loosely structured layers formed in unconstrained environments. Zeolites are a representative class of inorganic porous framework materials, and their precisely tunable pore size distributions, achievable through controlled synthesis, can accommodate monomer diffusion and reaction requirements across diverse length scales.^47–49 Their pore walls are rich in silanol and aluminol active sites, which not only allow post-synthetic modification with functional groups (e.g., amino and sulfonic acid) to tailor pore polarity and hydrophilicity/hydrophobicity but also serve as catalytic centres for direct participation in polymerization reactions. This dual functionality enables “confinement-induced catalytic polymerization”. An experiment by Hu et al. showed the confinement of Suzuki coupling polymerization of flexible monomers within the nanopores of catalyst-embedded SBA-15 molecular sieves.⁵⁰ Leveraging the spatial confinement effects of the nanoreactor, they suppressed the formation of ultra-long linear polymers at high monomer conversion while promoting end-to-end (ete) intramolecular cyclization reactions (Fig. 4). This approach yielded cyclic polyesters with exceptional purity and remarkably low polymer dispersity (Đ < 1.35).

Fig. 4 Schematic of cyclic polymer synthesis via nanoconfinement-induced macrocyclization of propagating chains. Reproduced with permission from ref. 50. Copyright 2023, the American Chemical Society.

MOFs and covalent-organic frameworks (COFs), as organic–inorganic hybrid porous materials, offer ideal platforms for constructing polymer architectures with precise topological control by virtue of their highly ordered nanoporous architectures, precisely tunable pore size distributions, and surface functionalizability. These crystalline frameworks serve as exceptional nanoreactors for confinement-induced polymerization, enabling spatial organisation of reactive species and directional growth of polymer chains within their well-defined pores.⁵⁵ Uemura et al. revealed the realization of double-strand topological architectures through crosslinked confinement polymerization within MOF nanopores.⁵¹ In this approach, vinyl monomers confined in 1D MOF channels undergo polymerization with a tailored crosslinking agent that specifically encapsulates and connects two growing polymer chains. The geometric constraints of the 1D confinement environment force the polymer chains to adopt extended linear conformations along the channel axis (Fig. 5a), enabling the formation of precisely crosslinked polymer networks. This confinement strategy effectively prevents undesirable inter-pore crosslinking events while ensuring that highly controlled crosslinking reactions occur exclusively between paired chains within individual channels. The successful synthesis of double-stranded polymers with predefined structural features is illustrated in Fig. 5b. High-efficiency photoinitiated flow polymerization of phenyl acrylate monomers within the 1D nanochannels of zinc porphyrin-based MOF membranes was demonstrated by Zhang et al.⁵² The dimensional matching between monomer molecules and channel geometries, combined with π–π interactions from periodic benzene rings within the channels and size-exclusion effects, significantly enhanced polymerization stereoselectivity. This confinement strategy yielded heterotactic poly(phenyl acrylate) with precisely controlled tacticity in contrast to the atactic polymers produced through conventional bulk polymerization (Fig. 5c). The confined polymerization products exhibit superior molecular weights and stereoregularity compared to their bulk counterparts, resulting in marked improvements in crystallinity, shear stress resistance, and ionic conductivity.

Fig. 5 (a) Synthesis of double-stranded polymers through crosslinking polymerization within MOF 1D channels. Reproduced with permission from ref. 51. Copyright 2023, the American Chemical Society. (b) Comparative schematic of bulk photopolymerization (producing atactic polymers) versus enzyme-mimetic photoflow polymerization through Zn-PMOF membranes with specific AB atomic layer stacking, yielding heterotactic polymers. Reproduced with permission from ref. 52. Copyright 2025, the American Chemical Society. (c) Monomer encapsulation and polymer formation within SURMOF-2 nanochannels. Reproduced with permission from ref. 53. Copyright 2020, the American Chemical Society. (d) Molecular dynamics simulations showing AAM monomer diffusion and hydrogen-bonding formation in TpPa-1 nanochannels (water molecules are omitted for clarity). Time progression is denoted as T. Reproduced with permission from ref. 54. Copyright 2023, Springer Nature.

Porous framework materials, through their unique confined spatial architectures, not only induce significant alterations in the physicochemical properties of encapsulated monomers but also enable complex reciprocal interactions between the evolving polymer networks and host frameworks during ongoing polymerization reactions. As monomer conversion progresses within the framework pores, the growing polymer chains dynamically interact with the framework structure, leading to feedback-driven modifications in the framework's pore geometry, mechanical stability, and surface chemical environment. This bidirectional relationship creates adaptive hybrid materials where confinement effects and polymer-framework interactions collectively govern the evolution of material properties at multiple length scales. For instance, Mario Ruben et al. showed the incorporation of mono-substituted alkynes into the 1D channels of MOFs, followed by electro-polymerization to achieve confinement polymerization within the pores. The resulting polyacetylene-infilled MOF thin films exhibited an eight-order-of-magnitude enhancement in electrical conductivity compared to pristine MOFs.⁵³ Similarly, A nanoconfinement polymerization strategy was developed by Yan et al., utilizing the aligned nanochannels of covalent-organic frameworks or molecular sieves to achieve spatially controlled polymerization.⁵⁴ This confinement approach effectively immobilizes polymer segments while leveraging the abundant hydroxyl, carbonyl, and imine groups within COF frameworks to significantly amplify hydrogen-bonding interactions (Fig. 5d), thereby enabling precise structural control and enhanced intermolecular interactions within the confined polymer networks.

1D confined polymerization can also occur within surface or slit-like nanospaces. For example, the creation of nanoscale 1D channels with a width of 1.22 nm on gold surfaces was presented by Chi et al., achieved through molecular adsorption and annealing-induced reconstruction.⁵⁶ These confined channels exert strong spatial constraints on polymerization pathways, with their confinement effects synergistically interacting with surface catalytic functions to significantly reduce activation energy barriers. The combination of entropic activation control and anisotropic chain propagation kinetics suppresses side reactions while enabling the directional alignment of alkane monomers along the 1D axis. This results in the formation of polymer chains with atomic-level structural order, as the confinement environment enforces strict linear growth trajectories and minimizes conformational disorders.

3.2. Polymerization in two-dimensional confined spaces

2D confined polymerization represents a unique chemical process in which molecular motion is strictly constrained within planar dimensions. Such reactions typically occur in nanoscale confinement environments, including thin-film interfaces, interlayer spaces of layered materials, or self-assembled monolayers. The spatial geometric constraints inherent in these 2D systems not only fundamentally alter reactant diffusion behaviors but also induce distinct kinetic pathways and product topological architectures compared to conventional bulk polymerization.^57,58

Pang et al. employed poly(aryl ether ketone) (PEEKt) thin films as reaction substrates to confined polymerization reactions occurring within the membrane matrix, which enabled the co-growth of two polymers in confined space (Fig. 6a), resulting in the fabrication of polyaniline/poly(ether ketone) composite membranes.⁵⁹ Within this structure, interpenetrating PEEK chains effectively mitigate excessive hydrogen-bonding-induced polymerization of polyaniline, demonstrating that confined polymerization strategies enable effective integration of rigid or insoluble polymers.

Fig. 6 (a) Schematic of intramembrane reactions. Reproduced with permission from ref. 59. Copyright 2021, John Wiley and Sons. (b) Confined photopolymerization process for hydrogel formation. Reproduced with permission from ref. 60. Copyright 2024, John Wiley and Sons. (c) Mechanistic illustration of living supramolecular polymer (LSP) formation. Reproduced with permission from ref. 62. Copyright 2021, John Wiley and Sons. Springer Nature. (d) LDH confinement-mediated size regulation of the LSP. Scanning electron micrographs (a)–(d) of LSM prepared using SG7-LDHs with varying dimensions. Reproduced with permission from ref. 62. Copyright 2021, Springer Nature. (e) Synthetic scheme for nitrogen-doped amorphous carbon materials (NAMCs). Reproduced with permission from ref. 61. Copyright 2024, Springer Nature.

Notably, the unique molecular structures of such rigid/insoluble polymers, exemplified by poly dodecyl glycerol itaconate(pDGI), serve as templates for 2D confined polymerization systems. pDGI with rigid layered structures was prepared by Chen et al. using shear-flow-induced self-assembly (as illustrated in Fig. 6b), and the resulting structures provided confinement spaces for monomer polymerization.⁶⁰ This enabled the confined polymerization of acrylamide (AAm) and N,N′-methylenebisacrylamide (DMA) to form bilayer hydrogels. Similarly, NiAl-layered double hydroxide (NiAl-LDH) with its inherent 2D lamellar structure was adopted by Guo et al. as a template for the confinement synthesis of nitrogen-doped amorphous carbon materials (NAMCs).⁶¹ By intercalating pyrrole monomers between LDH host layers and conducting confined polymerization, followed by acid leaching to remove the template, they successfully obtained NAMC (Fig. 6e). The universality of this spatial confinement strategy was further validated through the synthesis of 2D monolayer materials, including polythiophene and polycarbazole. LDH nanomaterials were also leveraged by Lv et al. to create confined environments, with a living supramolecular polymerization (LSP) strategy developed based on LDH confinement effects (Fig. 6c).⁶² By intercalating simple monomers into the interlayer spaces of LDH, the ordered arrangement and confinement effects were utilized to suppress spontaneous nucleation, and living supramolecular seeds (LSM) were thus formed (Fig. 6d). Subsequent solvent adjustment triggered the chain polymerization reaction, thereby achieving active polymerization with a high polymerization degree and a narrow distribution range.

Interfacial confined polymerization represents another paradigmatic approach within 2D confined spatial environments. Through synergistic regulation of interfacial interactions, this method not only governs the kinetic characteristics of polymerization reactions and the formation patterns of product topological structures but also induces significant alterations in reaction energy barrier distributions via reconfiguration of molecular packing behaviors. The confined spatial environment thus triggers multidimensional regulatory effects on both the thermodynamic equilibrium states and kinetic pathways of polymerization systems.⁶³ An ice-confined interfacial polymerization (IC-IP) strategy was created by Shao et al., utilizing ice/water phase transitions induced by ice melting for the synthesis of 3D quasi-lamellar polyamide membranes.⁶⁴ This IC-IP synthesis occurs at the interface between frozen m-phenylenediamine (MPD) solids and an n-hexane solution containing trimesoyl chloride (TMC) (Fig. 7a). The polymerization process is synergistically controlled by the reaction kinetics and thermodynamics of ice melting, resulting in the formation of polymer structures exhibiting 3D quasi-lamellar architectures (Fig. 7b). A Janus substrate was constructed by Xu et al. through the unilateral deposition of polydopamine/polyethyleneimine (PDA/PEI) on a polypropylene microfiltration membrane (PPMM), with the thickness of the hydrophilic layer being regulated by deposition time, while the hydrophobic layer maintained the intrinsic properties of the original PPMM.⁶⁵ This asymmetric structure created a physically confined space, with the hydrophilic layer serving as a monomer reservoir and the hydrophobic layer preventing excessive solution penetration. The aqueous-phase piperazine (PIP) and organic-phase trimesoyl chloride (TMC) monomers underwent polycondensation at the hydrophilic layer surface (as illustrated in Fig. 7c), forming a polyamide thin film. The confined space provided by the Janus substrate enabled a high PIP concentration within the hydrophilic layer, promoting the rapid formation of a dense, defect-free initial polyamide layer. This design not only enhanced local concentration and reaction efficiency but also precisely controlled the total monomer amount, avoiding the issue of excessive film thickness caused by monomer overload in conventional substrates.

Fig. 7 (a) Ice-constrained interfacial polymerization. Reproduced with permission from ref. 64. Copyright year 2023, The American Association for the Advancement of Science. (b) Scanning electron microscopy (SEM) image of the polyamide membrane formed by interfacial polymerization. Reproduced with permission from ref. 65. Copyright 2024, Research. (c) Schematic of nanofilm growth during interfacial polymerization. Reproduced with permission from ref. 65. Copyright 2024, Research. (d) Nano-confined hydrogel with entangled polyacrylamide (PAAm) polymers within nanosheet scaffolds. Reproduced with permission from ref. 66. Copyright 2025, Springer Nature.

The confined polymerization of monomers within a 2D space is commonly achieved by introducing nanosheet materials with a high aspect ratio, utilizing their unique geometric confinement effect and spatial arrangement characteristics to enable monomer confined polymerization in nanoscale 2D environments. A confined environment was constructed by Zhang et al. using synthetic hectorite nanosheets exhibiting an ultra-high aspect ratio (AR ≈ 20 000) with a thickness of merely 1 nm and a diametre of approximately 20 μm, as illustrated in Fig. 7d.⁶⁶ Through shear flow-induced orientational alignment, they formed a macroscopically monodomain coplanar nano-confined structure, where the interlayer spacing was adjustably controlled within the range of 50–200 nm. Within this homogeneous nanoscale confined environment, acrylamide underwent ultraviolet (UV)-initiated radical polymerization, and coupled with the confinement effect of the nanosheets, it polymerized into polyacrylamide (PAAm) hydrogels. The coplanar confinement environment provided by the hectorite nanosheets, combined with the high-concentration polymerization of acrylamide, synergistically enhanced the mechanical properties of the hydrogels through the interplay of physical entanglement and spatial confinement.

Confined assembly has emerged as a viable strategy for fabricating two-dimensional ordered polymer architectures. A programmable assembly approach combining directional confined polymerization was proposed by Yu et al., as depicted in Fig. 8a.⁶⁷ Under confined conditions, silver nanowires (AgNWs) and sodium alginate (SA) were subjected to bidirectional freeze-casting assembly within silicon molds, resulting in the formation of an aerogel (ASAA) scaffold with a layered morphology. This structured scaffold exhibits a layer thickness of 2 μm and an interlayer spacing of approximately 50 μm. Adjacent lamellae were interconnected by AgNW/SA nanocolumns (Fig. 8b) that penetrated through the layer interfaces. Subsequently, a polymerizable precursor solution containing n-isopropylacrylamide (NIPAM) and CNTs was infiltrated into the pre-structured ASAA matrix. Unidirectional freeze-polymerization was then executed parallel to the ASAA lamellae using ice-templating techniques, enabling the formation of a PNIPAM/CNT hydrogel network that replicated the layered architecture of ASAA. The interlayer spacing expanded marginally to ∼60 μm, while the resultant ASPC hydrogel exhibited a three-dimensionally interconnected open-pore honeycomb network with uniformly distributed pores (10–25 μm) embedded within its layered framework. In addition to inorganic membranes, organic frameworks, or polymers, which serve as confined spaces to induce structural transformations in polymer assemblies, a confined polymerization method utilizing ice crystals as templates was developed by Geng et al., as illustrated in Fig. 8c.⁶⁸ In this approach, the monomer 3,4-ethylenedioxythiophene (EDOT) is initially encapsulated within sodium dodecyl sulfate (SDS) micelles, followed by the initiation of oxidative polymerization. The growth and morphology of ice crystals spatially confine the polymerization reaction, directing the ordered arrangement of EDOT polymer chains within two-dimensional interfacial planes during freezing. This confinement-induced ordering facilitates the formation of highly crystalline two-dimensional polymer sheets with controllable morphologies.

Fig. 8 (a) Schematic of the fabrication process for ASPC hydrogels with ASAA frameworks via lamellar confinement and freeze-assembly-assisted polymerization. Reproduced with permission from ref. 67. Copyright 2024, Springer Nature. (b) Highly aligned AgNW/SA nanocolumns interpenetrating between the adjacent lamellae of the ASAA scaffold. Reproduced with permission from ref. 67. Copyright 2024, Springer Nature. (c) Schematic of ice-templated fabrication of 2D PEDOT sheets. Reproduced with permission from ref. 68. Copyright 2023, John Wiley and Sons.

3.3. Polymerization in three-dimensional confined spaces

Polymerization reactions conducted within 3D confined spaces represent a specialized chemical process wherein molecular motion is spatially confined within stereoscopic lattices or enclosed cavities. Such reactions typically occur within the porous networks of materials, including mesoporous silica, MOFs, porous organic polymers (POPs), hydrogels, and other confined systems.^69–73 In contrast to 1D linear or 2D planar confinement, these 3D constraints force polymerization to proceed within nanocages or microcapsules, with kinetic behavior and product morphology being synergistically regulated by factors such as pore size, solvent permeability, and spatial confinement effects.

The utilisation of nitrogen-enriched porous materials as confined reaction spaces to guide the spatially controlled growth of zinc oxide (ZnO) was demonstrated by Lu et al.⁷⁴ As illustrated in Fig. 9a, ZnO particles with an average crystallite size of ∼9 nm were uniformly embedded within the mesopores of spherical carbon scaffolds, where the mesopores exhibit diametres ranging from 10 to 15 nm. This hierarchical architecture, featuring nanoscale confinement effects, significantly reduces the propensity for agglomeration and fracture in zinc-based materials. Furthermore, the interconnected foam-like mesoporous spherical structure of the material facilitates efficient ion diffusion (as shown in Fig. 9a), providing abundant independent confinement spaces for the growth of small ZnO crystallites. Beyond their direct involvement in confining polymerization reactions, porous polymers can also serve as catalyst supports for confined catalytic processes. Porous polymer microspheres (PPMs) with interconnected trimodal pore architectures were employed by Guang et al. as catalyst carriers, as illustrated in Fig. 9b.⁷⁵ By leveraging the independent pore compartments of PPMs, they investigated the influence of three distinct catalysts (Cp₂ZrCl₂, Cp₂TiCl₂, and TiCl₄) on the confined polymerization of ethylene. Experimental observations revealed that polymerization swelling behavior varied significantly across catalysts, thereby modulating the confinement state of the support and the properties of the final polymer products. These findings indirectly demonstrate that the degree of confinement experienced during polymerization directly impacts the resultant material properties. Specifically, higher confinement levels increase local monomer concentrations while reducing diffusion rates: a dual effect in which elevated monomer concentrations accelerate polymerization kinetics, whereas suppressed diffusion rates retard the overall reaction rate.

Fig. 9 (a) Schematic of the formation process of spherical carbon frameworks. Reproduced with permission from ref. 74. Copyright 2017, Elsevier. (b) Impact of different supported catalysts on confined spaces. Reproduced with permission from ref. 75. Copyright 2017, John Wiley and Sons. (c) Schematic of confined polymerization. Reproduced with permission from ref. 79. Copyright 2024, Elsevier. (d) Schematic of the CCOF-templated controlled synthesis of OACPs with supramolecular imprinted chirality and their chiral memory processes. Reproduced with permission from ref. 84. Copyright 2024, John Wiley and Sons. (e) Schematic of confined polymerization of pyrrole. Reproduced with permission from ref. 85. Copyright 2022, the Royal Society of Chemistry. (f) Schematic of the in situ polymerization of SPA monomers within hydrogels. Reproduced with permission from ref. 33. Copyright 2020, Springer Nature.

Mesoporous silica, renowned for its ordered structural architecture, high specific surface area, tunable porosity, and controllable synthesis, has been widely adopted as a carrier material for confined synthesis processes.^76–78 The utilisation of SiO₂ spheres of varying sizes as templates to fabricate conjugated microporous polymers (CMPs) with highly ordered structures and superior performance through a template-confined polymerization strategy was revealed by Xu et al., as illustrated in Fig. 9c.⁷⁹ Notably, the confined synthesis approach enabled the formation of uniformly spherical CMPs in contrast to irregular morphologies observed in template-free counterparts. Crucially, the spherical morphology was retained even after template removal, with particle dimensions precisely adjustable according to the template size. Additionally, Sindee et al. investigated the confined free-radical polymerization of benzyl methacrylate (BzMA) within mesoporous silica, controlled-pore glass (CPG), and ordered mesoporous carbon.⁸⁰ Distinct confinement effects were observed across various media. Polymerization rates increased by approximately 30% in CPG pores and approximately 20% in mesoporous silica, whereas it decreased by approximately 15% in mesoporous carbon compared with bulk polymerization. This demonstrated the media-dependent nature of confinement effects on polymerization kinetics.

Porous framework materials, renowned for their exceptional flexibility, high porosity, and tunable pore sizes, serve as ideal host matrices for confined synthesis.^81–83 Cui et al. demonstrated the utilisation of three-dimensional chiral covalent organic frameworks (CCOFs) featuring π-rich porous surfaces for chiral-imprinted synthesis of conjugated polymers.⁸⁴ Achromiral monomers were selected as polymerization precursors, with the nanoconfined spaces of chiral CCOFs acting as templates to induce chiral arrangement and polymerization of monomers through supramolecular interactions (Fig. 9d). The resultant polymers inherited the chirality of the CCOF templates, retaining chiral information even after template removal. This approach successfully achieves cross-scale chiral information transfer by leveraging the spatial confinement and templating effects of porous frameworks. The confined polymerization of pyrrole (Py) within MOFs exhibiting well-dispersed, uniformly spherical morphologies was shown by Li et al.⁸⁵ Monomeric pyrrole was introduced into the MOF pores for in situ polymerization, where steric hindrance effects within the confined spaces suppressed disorderly chain stacking (Fig. 9e). This confinement strategy significantly enhanced electron delocalization within the conjugated polymer network, leading to improved photothermal conversion efficiency. Notably, the structural integrity of MOFs was maintained throughout the polymerization process.

Hydrogels, with their 3D networked crosslinked structures, porosity, and structural tunability, provide confined growth spaces for small monomer molecules, enabling the formation of composite materials with tailored morphologies and architectures.^86–88 In 2022, Shen et al. utilized the three-dimensional network of calcium alginate hydrogels to encapsulate p-phenylenediamine (SPA) monomers and horseradish peroxidase (HRP), yielding hydrogels with enhanced tissue adhesivity and low-molecular-weight poly(p-phenylenediamine) (PSPA).⁸⁹ The improved adhesive performance stems from hydrogen bonding between hydroxyl (–OH) and carboxylate (–COO⁻) groups within the hydrogel matrix, coupled with interactive forces involving –OH, –NH₂, and –COO⁻ functional groups on tissue surfaces (Fig. 9f). However, the confined polymerization environment imposed by the hydrogel's three-dimensional network impeded SPA monomer diffusion, resulting in reduced polymerization efficiency compared to bulk aqueous solutions. Liu et al. developed a low-temperature polymerization strategy to fabricate anisotropic polyvinyl alcohol-polyaniline hydrogels with a tailored structural hierarchy.³³ As illustrated in Fig. 2a, an aqueous solution containing PVA, aniline, and an initiator was subjected to unidirectional freezing along a vertical temperature gradient, inducing the formation of a three-dimensionally ordered honeycomb-like architecture. Aniline monomers underwent localized nucleation and confined polymerization at the interfaces between vertically aligned ice crystals and PVA cell walls, yielding a polyaniline nanofibre scaffold. The resultant three-dimensional network exhibits microscale vertical porosity along with densely packed, periodically arranged honeycomb-like pores. Increasing the initial aniline monomer concentration systematically reduces the diameter of these honeycomb pores, notably demonstrating a concentration-dependent modulation of the final pore architecture. Beyond hydrogels, aerogels composed of crosslinked graphene sheets can also serve as scaffolds for confined reaction spaces. For instance, Pan et al. demonstrated that nanoconfined spaces within graphene aerogels enhance local reactant concentrations through confinement effects, thereby promoting oligomerization reaction pathways and achieving a remarkable 208-fold acceleration in reaction rates.⁹⁰

3.4. Polymerization in specific confined spaces

Special confined spaces are different from traditional confined spaces. Their boundaries can be dynamically reconfigured in real time through external stimuli (temperature, pH, and light) or internal chemical feedback, thereby dynamically regulating the mass transfer process, chain growth path, and topological evolution of the polymerization reaction. Polymerization in special confined spaces also plays a crucial role in biological systems. The important biological macromolecules within cells, such as nucleic acids, proteins and polysaccharides, are all formed by polymerizing small molecule building blocks in specific regions within the cells.^91–94

Building on the universal strategy for intracellular polymerization, the in situ polymerization of low-IC50 monomers, including N-hydroxypropyl acrylamide (HPMA) and sodium p-styrenesulfonate (NASS), within living cells under 365 nm UV irradiation was initiated by Bradley et al. using the biocompatible photoinitiator 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959), as illustrated in Fig. 10a.⁹⁵ This approach achieved high intracellular monomer concentration enrichment, enabling the modulation of cell migration efficiency through controlled polymerization reactions. Furthermore, the methodology provided stable fluorescent labelling of cells, facilitating precise manipulation, tracking, and control of cellular behaviors.

Fig. 10 (a) Intracellular polymerization strategy in living cells: HPMA monomers and Irgacure 2959 initiator were introduced into the cell culture medium, followed by a 365 nm light irradiation to initiate photopolymerization. Reproduced with permission from ref. 95. Copyright 2019, Springer Nature. (b) Schematic of Aot-directed photopolymerization of NaSS. Reproduced with permission from ref. 100. Copyright 2023, Springer Nature.¹⁰⁰ (c) Intracellular hyperbranched polymerization of B3–Te in cancer cells. Reproduced with permission from ref. 39. Copyright 2023, the American Chemical Society. (d) Molecular structures of macrocycles 1a and 1b. Reproduced with permission from ref. 102. Copyright 2023, Springer Nature. (e) Energy-minimized structure of macrocycle 1b. Reproduced with permission from ref. 102. Copyright 2023, Springer Nature. (f) Schematic of macrocycle 1a with spatially distributed self-assembling functional groups. Reproduced with permission from ref. 102. Copyright 2023, Springer Nature.

As highly complex biological entities, living cells initiate polymerization reactions in situ by leveraging cell-permeable functional monomers under the co-regulation of endogenous metabolic cues and exogenous stimuli. Upon perceiving intracellular signals or external interventions, monomers undergo precise molecular recognition, guided by supramolecular non-covalent interactions or covalent bond formation via specific functional groups, to assemble into polymeric networks. This dynamic polymerization process transcends the physical barriers of cellular membranes and enables intelligent responses to cellular microenvironments through bioorthogonal reaction mechanisms.^96–99

A reactive oxygen species (ROS)-triggered hyperbranched polymerization strategy executed within living cells was reported by Xu et al.³⁹ Leveraging the hypersensitive oxidative properties of organotellurium compounds and the intracellular redox microenvironment, they achieved ROS-initiated hyperbranched polymerization in situ (Fig. 10b). A tellurium-containing B3-Te monomer responsive to ROS levels was synthesized, which underwent hyperbranched polymerization within live cells. The resulting Te–O polymers effectively suppressed cellular antioxidant systems through interactions between the Te(+4) species and selenoproteins, thereby inducing selective apoptosis in cancer cells. Additionally, the hyperbranched polymers self-assembled into branched nanostructures within the cells, circumventing drug efflux pump mechanisms in cancer cells and prolonging intracellular retention for sustained therapeutic efficacy. The aforementioned confined-space polymerization strategies utilize cellular compartments as regulatory environments. The implementation of diverse polymerization reactions within biological systems using a nanocompartment confinement strategy was demonstrated by Zhu et al.¹⁰⁰ They employed sodium bis(2-ethylhexyl)sulfosuccinate vesicles as confined environments, forming nanocompartments with diametres of approximately 80 nm via solvent injection (Fig. 10c). This structure provided a physical confinement space for monomers, thereby promoting local enrichment, significantly increasing collision frequencies, and accelerating the polymerization rate. Nico et al. utilized Escherichia coli (E. coli) as a host to conduct polymerization reactions involving acrylamide, acrylate, and methacrylate monomers via atom transfer radical polymerization initiators.¹⁰¹ Their study results indicate that the conversion rate of polymerization reaction monomers within living cells is as high as 90%, and the dispersion degree reaches 1.4. The unique confined environment within the cells limits the expansion and termination rates of the chains, thereby leading to an increase in chain initiation and a shortening of the polymer chains.

Beyond cellular systems, monomers with spatially segregated interactive domains can also create novel confined spaces at the molecular scale, enabling topological control over supramolecular assembly pathways. A regional-confined amphiphilic supramolecular polymerization (RASP) strategy was developed to synthesize cyclic supramolecular polymers (CASPs) based on intramolecular hydrophilic–hydrophobic microdomain segregation.¹⁰² They designed a 48-membered pyridine-oxadiazole alternating macrocycle with a structured hydrophilic–hydrophobic zonal distribution (Fig. 10d–f). The rigid intramolecular segregation of these domains imposed molecular-scale spatial constraints on the self-assembly process, forcing polymerization to proceed exclusively through specific interaction zones (e.g., π–π stacking and amphiphilic interactions) while preventing disordered polymerization. The resulting CASPs achieved diametres of up to 10 micrometres with polymerization degrees exceeding 10⁴, demonstrating the profound potential of confined polymerization in controlling higher-order supramolecular architectures. A special confined polymerization strategy based on the dynamic hydrogen bond-induced confinement effect (DHBCE) was developed by Fu et al.¹⁰³ This system employs a biobased polyether polyol (PO3G) as the soft segment and 2,5-furan diacetyl hydrazide (FDHA) as the hard segment dynamic crosslinking unit. A reversible dynamic hydrogen bond network was constructed at the molecular level, achieving a continuous gradient distribution of soft and hard segments. This dynamic hydrogen bond network serves as a dynamic spatial constraint with dual functionalities in polymerization and microphase separation processes. The acyl carbazolium (ASC) units in FDHA form multiple hydrogen bonds with exceptionally high bond energy (−23.19 kcal mol⁻¹), acting as robust physical crosslinking points to create nanoscale hard domains. These domains significantly restrict the mobility of soft segment molecular chains. Concurrently, weaker hydrogen bonds function as sacrificial bonds that dynamically rupture and reform under external mechanical stimuli, enabling effective energy dissipation. Through dynamic and reversible non-covalent interactions, this specialized confined space achieves intelligent control and adaptive limitation of polymer chain arrangement, polymerization structure, and mechanical response at the molecular scale.

4. Advanced measurement for confined polymerization

4.1. Surface topography

Advanced microscopy techniques, valued for their intuitive visualization and high-resolution capabilities, have emerged as indispensable tools for elucidating confined spaces and polymer surface morphologies.^104,105 In confined environments, such as nanopores, layered materials, or microcapsules, polymerization reactions exhibit markedly distinct thermodynamic and kinetic behaviors compared to bulk systems. These confined regimes give rise to unique polymer morphologies, which are ultimately exhibited in specific topological features, internal architectures, and molecular arrangements. The multiscale imaging capabilities of advanced microscopy techniques provide an indispensable perspective for systematically elucidating how confinement effects shape polymer morphologies across different spatial scales—from surface topography to intramolecular ordering.

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) can directly capture the overall and local surface morphology of confined polymers (such as those synthesized in nanopores or layered structures). These techniques provide multiscale imaging capabilities, allowing not only macroscopic observation of sample morphology but also nanoscale structural analysis with atomic-level resolution.^106–108 SEM is adept at presenting the overall topological features of the sample surface and can clearly reveal the specific protrusion structures formed on the surface of the confined polymer products.¹⁰⁹ TEM can penetrate the sample and reveal its internal structure and element distribution (often accompanied by EDS element distribution maps). By combining TEM and EDS, we can confirm the in situ formation of polymers in the target confined space (such as inside pores or interlayer gaps) and visualize the interface interaction between the polymer and the host material.

However, although SEM and TEM provide high-resolution 2D/3D projection morphology information, they have limitations in precisely quantifying the evolution of surface roughness or the thickness distribution of interface layers. To accurately depict the three-dimensional nano-morphology dynamics of polymer growth on confined substrates and the kinetic processes it reflects, Hu et al. quantitatively measured the gradient changes in polymer height using atomic force microscopy (AFM) and verified the results with a spectroscopic ellipsometre (SE).¹¹⁰ The progressive increase in polymer height with position/time observed using both techniques directly visualizes and quantifies the significant hindrance of monomer diffusion by confined spaces, converting the kinetic restriction effect into clear morphological evidence. Further pushing the characterisation to the atomic/molecular scale, scanning tunneling microscopy (STM) directly images the arrangement of individual polymer chains at atomic resolution and precisely manipulates molecules through the probe tip.^111–113 Chen et al. utilized STM imaging to directly observe the highly ordered 1D linear arrangement of polymer chains within nanogrooves formed by gold atoms, which is a unique apparent structure induced by strict geometric confinement.⁵⁶ Using the STM nanomanipulation technique, they successfully extracted polymer chain fragments from the grooves and demonstrated their sliding behavior along the grooves. It is notable that the lengths of these manipulated chain segments generally exceed 200 nanometres or contain more than 50 monomer units. This extremely long chain structure, which forms and maintains integrity under extreme one-dimensional confinement conditions, and its mobility are unique apparent features that are difficult to achieve in bulk polymerization. This directly confirms the profound influence of the confined environment on chain growth dynamics and chain conformation.

From the macroscopic surface topography revealed by SEM, the internal structure and interface interactions shown by TEM/EDS, and the quantitative 3D nano-scale morphology dynamics depicted by AFM, to the molecular-level arrangement imaging and manipulation achieved by STM, the continuous and coordinated evolution of microscopy techniques has transformed the unique thermodynamic and kinetic differences in confined polymers into intuitive, quantifiable, and controllable multi-dimensional morphological evidence. This not only systematically reveals the synergistic mechanism of space limitations, interface effects, and diffusion limitations but also provides an indispensable multi-scale analytical capability for a deeper understanding of how the confined space shapes the structure and properties of polymers from the molecular level to the macroscopic scale.

4.2. Structure and composition

Confined polymerization products often differ fundamentally from their bulk polymerization counterparts, as their structural parametres and performance characteristics are profoundly influenced by the geometric constraints and interfacial interactions imposed by physical or chemical microenvironments. Within confined spaces (e.g., nanopores, interfacial layers, or template cavities), monomer diffusion rates, radical concentration profiles, and chain propagation kinetics undergo significant alterations, resulting in narrower molecular weight distributions, reduced chain branching, and the induction of unique topological architectures. Therefore, accurately analyzing the chemical and structural characteristics of a confined space and its products is vital for elucidating the unique influences of these microenvironments. This requires characterisation techniques not only to have conventional analytical capabilities but also to be able to meet the specific needs of confined systems (such as high sensitivity, surface/interface specificity, and micro-area analysis capabilities) and even to drive the development of new methods.

For the chemical structure characterisation of confined polymers, the application of conventional techniques often requires a combination of their specific advantages or the development of targeted approaches. Fourier Transform Infrared Spectroscopy (FT-IR) is a fundamental technique for analyzing the functional groups of polymers. Its surface-sensitive mode (such as ATR-FTIR) is particularly important in the study of confined polymers, as it enables the identification of characteristic vibration peaks (such as C=O, C–O–C stretching) to elucidate the chemical structure of polymers.^114,115 For instance, Liu et al. applied diffusion-confined polymerization synthesis, applied FT-IR (in combination with other techniques) to confirm the chemical structure of the synthesized polymer under confined conditions, and verified the possible influence of the microenvironment on the reaction pathway.¹¹⁶ To address the challenge of accurately analyzing trace polymers from complex and confined matrices (such as porous materials, templates), matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) has demonstrated significant value. Its high sensitivity and precise molecular weight determination capability make it possible to analyze the molecular weight distribution, end group structure and repeat units of polymers under confined conditions at the nanoscale.¹¹⁷ It was through the use of MALDI-TOF MS that researchers were able to directly detect highly polymerized products with an average molecular weight of approximately 1174 Da within a confined space of 20 nanometres. This discovery provided crucial evidence for the hypothesis that confined spaces can promote the formation of specific molecular weight products.¹¹⁸ In the field of crystal structure analysis, X-ray diffraction (XRD) is the key method for revealing the internal orderliness of polymers.¹¹⁹ It is particularly suitable for studying the polymerization process that takes place in confined environments with periodic structures (such as MOFs and COFs). For instance, Cui et al. conducted monomer polymerization within chiral covalent organic frameworks (CCOFs). Nitrogen adsorption–desorption isotherm (BET) measurements revealed a significant reduction in specific surface area post-polymerization (from 844 m² g⁻¹ to 92 m² g⁻¹), indicating intra-pore polymerization. XRD analysis further confirmed that the crystalline integrity of the composite material was preserved post-polymerization, with no observable crystallographic disruption.⁸⁴ To obtain more direct information on the molecular/groove arrangement, the development of low-dose high-resolution transmission electron microscopy technology provides a complementary solution, enabling the direct visualization of the molecular arrangement and crystal structure of confined polymers (especially the crystalline part).^120,121 Surface chemical analysis is crucial for understanding the interfacial interactions in confined polymerization. X-ray photoelectron spectroscopy (XPS), with its surface sensitivity (probe depth of 1–10 nm) and chemical state resolution capabilities (such as distinguishing C–C and C=O bonds), has become an ideal tool for precisely analyzing the elemental chemical environment and functional group evolution at confined interfaces.¹²² Surface chemical analysis is crucial for understanding the interfacial interactions in confined polymerization. X-ray photoelectron spectroscopy (XPS), with its surface sensitivity (probe depth of 1–10 nm) and chemical state resolution capabilities (such as distinguishing C–C, C=O bonds), has become an ideal tool for precisely analyzing the elemental chemical environment and functional group evolution at confined interfaces.^123,124

The emergence of the constrained polymerization model has continuously driven the innovation of characterisation methods. Sha et al. pioneered the development of a time-resolved fluorescence resonance energy transfer (Tr-FRET) method, which is specifically used for quantitative analysis of the conformational dynamics of polymer chains in nano-sized confined spaces.¹²⁵ The successful application of this technology not only fills the gap in traditional methods for real-time monitoring of conformational changes within confined spaces but also demonstrates its great potential for exploring the chain behavior of different polymer types and complex confined geometric configurations in the future.

4.3. Polymerization reaction kinetics

Characterisation of polymerization kinetics within confined spaces necessitates the integration of thermodynamic analyses and microscopic simulation techniques to elucidate the unique effects of confinement. A multiscale combinatorial strategy should be constructed by selecting complementary technologies based on the specific characteristics of the system, with a focus on the influence of “confined polymerization” effects on reaction rates, product topological architectures, and related parametres.

The combination of differential scanning calorimetry (DSC) and molecular dynamics (MD) simulation perfectly demonstrates the powerful complementarity of this approach in the study of confined dynamics. DSC provides a macroscopic, time-resolved thermodynamic panorama (such as a reaction enthalpy change and activation energy), directly reflecting the overall reaction process and energy barriers. Complementary to this, MD simulations provide a dynamic atomic-scale perspective by solving Newton's equations to track particle trajectories and accurately analyze the diffusion behavior of monomers in confined spaces (such as calculating the diffusion coefficient), interface interactions (such as adsorption energy E_ads and binding free energy ΔG_binding), and molecular mechanisms. By correlating the anomalous activation energy measured in DSC experiments with the confined diffusion coefficient revealed by MD simulations, researchers were able to jointly interpret the non-classical polymer dynamics observed in nanopores or interface layers. This synergy of macroscopic and microscopic data is the core approach to understanding the confinement effect.^126,127 For instance, Shao et al. elucidated the interface polymerization mechanism in the specific confined environment of the ice/water interface. They jointly employed MD simulation and DSC/in situ monitoring. The MD simulation revealed the significant diffusion limitation effect of the key monomer, m-phenylenediamine (MPD), at the ice/water interface as well as the dynamic anchoring behavior of the crosslinking agent, triacetyl chloride (TMC).⁶³ Meanwhile, DSC quantified the key influence of the ice crystalline state (a physical confined state) on the release kinetics of MPD. The in situ release kinetic experiment monitored the dynamic changes in the monomer concentration during the ice melting process, directly correlating the microscopic simulation predictions with the macroscopic/mesoscopic experimental observations.⁶⁴ The technological advancements in molecular dynamics simulation have significantly enhanced its application depth and result reliability in the study of confined polymerization. Polymerization kinetics under pore-confined environments were analyzed using MD simulations by Michael et al.⁸ Their findings demonstrated that monomers freely diffused within two distinct pore sizes and became enriched at the pore walls, with polymer chain diffusion exhibiting pronounced pore-size-dependent behavior. It visually demonstrates the decisive influence of confined spaces on the dynamics of chain growth at a later stage. Similarly, the alignment mechanisms, interfacial interactions, and mechanical reinforcement principles of nanosheets under dual-scale confinement were elucidated using MD simulations by Yu et al., thereby providing a microscopic mechanistic interpretation of confined polymerization kinetics.¹²⁸

The development of fluorescence technology is of vital importance for in situ and real-time monitoring of polymerization behavior in dynamic confined spaces, such as physiological or complex chemical microenvironments. Its high sensitivity, non-invasive nature, and spatiotemporal resolution make it an ideal probe for tracking reaction processes within confined systems. The thiazole orange T fluorescence assay method was innovatively applied by Rao et al., enabling the successful real-time tracking of polymer hydrophobic polymerization dynamics within living cells. The kinetic process of polymer reactions in the confined cytoplasmic environment was directly reflected through changes in fluorescence intensity, and the regulatory role of specific factors (such as glutathione) in intracellular polymer reactions was effectively verified.¹²⁹ In combination with the parallel characterisation of the particle size distribution of intracellular polymer aggregates by dynamic light scattering (DLS), the influence of concentration dependence on the size evolution of aggregates in confined spaces was further revealed. Furthermore, Nico et al. developed an integrated multi-technology strategy utilizing nuclear magnetic resonance spectroscopy, gel permeation chromatography for polymer extraction, and specific fluorescence labelling for the characterisation of intracellular polymers. This approach enabled multi-angle cross-validation of the confined polymerization process occurring within living cells, highlighting the urgent need for complex confined environment characterisation in technological innovation and integration.¹⁰¹

5. Cutting-edge applications for confined polymerization

In recent years, with the deepening exploration of “confined spaces” strategies, scientists have discovered that nanoconfinement enables the precise modulation of polymer molecular configurations and topological architectures, transcending traditional spatial limitations in polymerization. By leveraging steric hindrance and oriented alignment, polymers form ordered systems that combine structural programmability with anisotropic arrangement and precise functional regulation. This dual mechanism of physical confinement and chemical synergy has propelled the widespread adoption of “confined polymerization” across diverse scientific and industrial domains.^130–134

5.1. Water purification

The escalating pace of global industrialization has exacerbated water pollution and freshwater scarcity, which now stand as critical bottlenecks impeding the sustainable development of human society.^135,136 Against this backdrop, innovative strategies based on confined polymerization have delivered breakthrough solutions for advancing water purification technologies. A ZIF-8-derived glass-composite catalytic platform was created by Li et al. to address the bottlenecks of conventional persulfate-based advanced oxidation processes. These bottlenecks include excessive oxidant consumption—manifested by hydrogen peroxide utilisation efficiency below 40%—and elevated carbon footprints exceeding 2.1 kg CO₂ per ton of treated water.¹³⁷ By exploiting the confinement effect of MOF nanopores with a 1.16 nm aperture, they spatially anchored organic pollutants such as bisphenol A near Fe–O active sites, achieving a 3.7-fold enhancement in proton-coupled electron transfer efficiency. This spatially confined reaction pathway reorganisation enabled the conversion of >80% of organic carbon into recoverable polymers with a number-average molecular weight (Mn) of 5800 g mol⁻¹, achieving >95% total organic carbon removal while reducing carbon emissions by 62%. This innovation establishes a synergistic “pollution control-resource recovery” paradigm.

Equally groundbreaking is the revolutionary advancement by Shao et al. in membrane separation technology. Their ice-confined interfacial polymerization strategy involves freezing MPD monomer solutions to create ice templates, enabling precise control over monomer diffusion kinetics with a release rate of 0.12 mmol m⁻² s⁻¹ through ice phase transitions.⁶⁴ Upon contact with trimesoyl chloride/n-hexane organic phases, the confined reaction interface induces the formation of polyamide membranes featuring three-dimensional quasi-lamellar structures and an exceptionally high ionization density. Synchrotron small-angle X-ray scattering confirms that this unique architecture arises from an ice crystal growth-driven molecular orientation. The resultant nanofiltration membrane demonstrates extraordinary performance: >98.5% Na₂SO₄ rejection and 21.5 L m⁻² h⁻¹ bar⁻¹ permeability, nearly triple that of conventional interfacial polymerization membranes, with a breakthrough Cl⁻/SO₄²⁻ selectivity coefficient of 18. This innovation provides transformative solutions for heavy metal wastewater treatment and valuable ion resource recovery.

5.2. Medical diagnosis

The “confined polymerization” technology shows significant potential in disease diagnostics, where its unique spatially confined reaction characteristics offer novel paradigms for developing highly sensitive and specific diagnostic tools. By enabling precise control over polymerization reactions at the nanoscale or within microenvironments, confined polymerization facilitates the fabrication of functionalized nanomaterials, biosensors, and smart probes. These materials exhibit exceptional performance in disease biomarker detection, early-stage diagnosis, and real-time monitoring applications. The MOF-confined phototheranostic platform was invented by Li et al.⁸⁵ They employed ZIF-8 with 2.3 nm pores as a reaction vessel to synthesize uniform polypyrrole@MOF nanoparticles (with a pore size of 48.7 ± 2.1 nm) via confined polymerization of pyrrole monomers within the channels. XPS revealed that the confined environment increased the conjugation length of polypyrrole by 32%, resulting in a photothermal conversion efficiency of 68.7% under 808 nm laser irradiation—a 1.8-fold enhancement compared to free-polymerization systems. Concurrently, the confined growth of polypyrrole generated a strong fluorescence signal, enabling cancer cell targeting through folate receptor modification. In tumor-bearing mouse models, this platform demonstrated synergistic theranostic effects: fluorescence imaging-guided precise photodynamic therapy reduced tumor volumes by 87%, while real-time temperature monitoring ensured therapeutic safety. Expanding to infectious disease diagnostics, an H₂O₂-responsive smart hydrogel system was engineered by Shen et al.⁸⁹ Calcium-crosslinked hyaluronic acid-alginate hydrogels (pore size 15–25 μm) loaded with horseradish peroxidase (HRP) and the aniline derivative (SPA) were designed. Upon exposure to H₂O₂ (50–200 μM) in infected microenvironments, ˙OH generation was catalyzed by HRP, leading to confined polymerization of SPA into conductive PSPA networks. This process generated dual-responsive signals: a colourimetric change from transparent to dark blue and a 14-fold increase in photoacoustic signal intensity, enabling a visual quantitative assessment of infection severity. These breakthroughs signify that confined polymerization technologies are propelling disease diagnostics toward “precision–visualization–intelligence” paradigms.

5.3. Energy storage

The advancement of novel energy storage devices, including high-performance batteries and supercapacitors, is fundamentally contingent upon the innovative exploration of emerging materials. Porous materials with architecturally distinctive configurations have been systematically identified as optimal matrices for attaining exceptional electrochemical properties. Nevertheless, the performance limitations exhibited by conventional energy storage materials necessitate the strategic exploitation of the inherent spatial confinement effects of porous frameworks, which has been rigorously substantiated as an efficacious methodology for augmenting the functional capabilities of electrode materials. A hierarchical nanostructured solid-state electrolyte characterized by environmental benignity and inherent hydroxide ion conduction capability was innovatively constructed through the nano-confined polymerization of dicationic ionic liquids within 3D porous cationic cellulose nanofibre frameworks, as revealed by Chen et al.¹³⁸ The flexible zinc–air battery assembled with this electrolyte demonstrates excellent electrochemical performance and an ultra-long cycle life. This electrolyte system ingeniously integrates the advantages of aqueous electrolytes and solid-state electrolytes, achieving significant improvements in preventing safety hazards, such as leakage and short circuits, thereby further enhancing its overall safety and reliability. A novel electrolyte architecture employing spatial confinement polymerization has been successfully developed for high-performance lithium metal batteries, as systematically reported by Wang et al.¹³⁹ Experimental results reveal that the polymeric matrix, when integrated with Li⁺-conductive ceramic fillers and optimized lithium salts, not only effectively mitigates inhomogeneous impregnation risks and liquid leakage phenomena but also demonstrates exceptional ionic conductivity of 1.1 × 10⁻¹ S cm⁻¹ at 30 °C and 1.0 × 10⁻¹ S cm⁻¹ at 80 °C. Crucially, superior interfacial compatibility with lithium metal anodes has been achieved, enabling stable operation of Li||Li symmetric cells and lithium metal full cells incorporating LiFePO₄ or LiCoO₂ cathodes under ambient conditions, with capacity retention rates exceeding 92.4% after 500 cycles at a 1C rate, as validated by galvanostatic cycling measurements.

5.4. Catalyst

The confinement polymerization strategy enables the construction of highly dispersed, stable, and functionally integrated catalytic materials at the nanoscale or molecular level through its unique spatially constrained effects. By precisely regulating the microenvironment and spatial distribution of catalytically active sites, this methodology provides an innovative solution to the long-standing challenge of simultaneously achieving high activity, stability, and selectivity in conventional catalytic systems, which has been persistently hindered by the intrinsic trade-off effects amongst these critical performance metrics. A self-polymerization confinement strategy was innovatively created by Xing et al. through the synergistic modulation of precursor directional assembly and carbonization processes. This methodology enabled the precise fabrication of nitrogen-doped carbon nanosheet-encapsulated ultrafine metal nanoparticle composites with atomic-level structural control.¹⁴⁰ The engineered Fe@NC Fenton catalyst demonstrated exceptional pH adaptability, exhibiting an ultrahigh apparent rate constant of 0.818 min⁻¹ for phenol degradation, which is two orders of magnitude higher than those of conventional Fe-based catalysts, while achieving 84.1% H₂O₂ utilisation efficiency through quantum tunneling-enhanced electron transfer mechanisms. Synchrotron-based X-ray absorption fine structure spectroscopy conclusively revealed that the Fe–N₄ coordination configuration formed within the confinement domains significantly reduced the reaction activation energy from 1.24 eV to 0.68 eV, with density functional theory calculations further confirming a 73.6% decrease in the energy barrier for ˙OH radical generation compared to non-confined systems. Building upon this foundation, plant polyphenols were strategically introduced as spatial directing agents by Li et al., enabling the construction of advanced catalysts featuring asymmetric FeN₄–CoN₃ diatomic sites.¹⁴¹ The unique coordination architecture was conclusively verified through in situ Raman spectroscopy and electron paramagnetic resonance analysis to selectively steer persulfate activation pathways toward singlet oxygen generation, which achieves tetracycline removal rates exceeding 98.7% in complex aqueous systems containing 20 mg L⁻¹ humic acid, thereby surmounting the long-standing technical limitation of conventional catalysts in anti-interference capacity. A 3D network-confined ruthenium catalyst was innovatively invented through the strategic incorporation of ionic liquids into confined polymerization systems by Zang et al.¹⁴² A covalently crosslinked network constructed through in situ polymerization enabled the formation of highly dispersed 2.1 nm Ru nanoparticles during thermal reduction at 600 °C from ruthenium precursors. The engineered catalyst presented exceptional electrochemical performance, achieving an ultralow overpotential of 16 mV at 10 mA cm⁻² and a mass activity of 3.2 A mg⁻¹, with negligible degradation observed after 10 000 accelerated durability cycles. Notably, this synthetic strategy has been successfully extended to multiple metallic systems, including Ag, Ni, and Co, demonstrating a 89.7% universality success rate across the 12 transition metals tested, as systematically validated through combinatorial high-throughput screening.

5.5. Composite coatings

Confined polymerization technology has also been innovatively incorporated into composite coating systems through which the spatial dimension of polymerization reactions is precisely controlled. This approach effectively enhances the interface bonding strength, mechanical properties, and synergistic effect of multi-component functionalities within the coating layers. Consequently, a novel technical pathway has been provided for the development of high-performance composite coatings. A pioneering study on the fabrication of allomelanin (AM) coatings on MOF surfaces was conducted by Gianneschi et al.¹⁴³ In this work, 1,8-dihydroxynaphthalene was selected as the precursor, and critical parametres, including temperature and precursor concentration, were systematically optimized to achieve spatially confined oxidative polymerization on MOF substrates. Notably, this spatially confined polymerization process enabled the formation of AM@MOF composites featuring hierarchically porous architectures. More importantly, the microporous channels inherent in the MOF substrate were fully preserved throughout the coating process, thereby circumventing the common issue of pore blockage observed in conventional coating methodologies. Such a strategy provides a novel paradigm for developing advanced functional composites with maintained substrate accessibility. Furthermore, the confined polymerization strategy was further developed and applied by Pan et al.¹⁰⁹ Polysilsesquioxane (PSQ) was adopted as an interfacial stabilizer to enable self-assembly at the oil–water interface, forming a mesoporous PSQ shell layer with a controlled thickness of approximately 50 nm. Spatial confinement of styrene and short-chain fluorinated alkane comonomers within this shell was achieved for subsequent free-radical polymerization, resulting in the successful fabrication of multifunctional hierarchical hybrid particles (HHPs) with core–shell architectures. Notably, compositing these HHPs with aqueous polyurethane yielded intelligent coatings that demonstrated remarkable functional integration: a superhydrophobic surface with a water contact angle of 162 degrees, thermally insulating properties marked by low thermal conductivity, and optical features exhibiting intense blue emission under 365 nm ultraviolet excitation. Such multidimensional synergistic effects fully exemplify the unique advantages of confined polymerization strategies in functional material design.

6. Summary and outlook

Confined polymerization transcends the kinetic and thermodynamic equilibrium limitations of conventional bulk polymerization by manipulating molecular motion dimensions and spatial chemical microenvironments, enabling precise control over reaction pathways, kinetic behaviors, and product structures. This review systematically categorizes confinement strategies across 1D, 2D, 3D, and specialized spatial architectures, elucidating the distinctive mechanistic features of polymerization under dimensional constraints. From helical chain conformation regulation in 1D nanotubes and anisotropic assembly in 2D interlayers to networked growth in 3D porous supports, the confined polymerization effect imparts unique topological architectures to polymers. Specialized confinement systems further push the boundaries of traditional chemical synthesis. At the application level, confined polymerization technologies have illustrated breakthroughs across multiple domains: in water purification, spatial confinement enables efficient pollutant conversion and resource recovery; in medical diagnostics, nano-confinement effects facilitate the development of ultrasensitive probes and integrated theranostic platforms; in energy storage, porous confinement designs enhance electrode material stability and ion transport efficiency; and in catalysis, confined microenvironments optimize active site distribution to overcome the activity-stability-selectivity trade-off. These advancements signify that confined polymerization is progressing from foundational research toward functional and precision-engineered applications.

Looking ahead, the evolution of confined polymerization will hinge on deep interdisciplinary integration across chemistry, materials science, and engineering, with the potential to overcome current technological barriers and drive the transition of “confined polymerization” effects from foundational research to scalable functional material manufacturing. However, practical applications of the confined polymerization effect still face significant challenges: the microscopic mechanisms underlying confined polymerization remain difficult to observe in real time, as conventional analytical techniques are constrained by technical bottlenecks in temporal and spatial resolution. In situ dynamic monitoring technologies, such as ultrafast spectroscopy and single-molecule fluorescence tracking, must be created to elucidate transient intermediates and reaction pathway evolution under confinement. This enables the mapping of a holistic “spatial confinement-reaction pathway-material performance” atlas, guiding molecular-level precision design. Bridging the laboratory-to-industry gap requires integrating biomimetic strategies, like biomineralization and microfluidic chips, with dynamic covalent chemistry, allowing the “growth” of porous confinement systems with high precision and low cost under mild conditions—akin to how biological organisms construct biominerals. Functionally, future confined polymerization systems may transcend static spatial constraints. Light-responsive templates could dynamically switch polymerization pathways, magnetic nanocages could remotely manipulate monomer transport, and supramolecular dynamic networks might even mimic the self-healing and adaptive capabilities of living systems, enabling intelligent communication between atomic arrangements and macroscopic properties. For biomedical applications, scientists envision constructing “molecular operating rooms” within living cells to precisely target pathological sites with polymerization reactions, while designing metabolizable monomers and triggerable switches for diagnostic polymers that degrade quietly post-task; these advancements could catalyze deep integration between chemistry and synthetic biology. The power of rapidly advancing artificial intelligence should be harnessed to transform vast datasets on confinement effects into predictive models, enabling the simulation of optimal solutions amongst trillions of polymerization pathways for developing materials that address climate change, disease treatment, and clean energy needs. This review aims to galvanize attention and inspire greater scholarly investment in this field, accelerating transformative breakthroughs.

Author contributions

Lushan Sun: writing – original draft, writing – review & editing, visualization. Jian Sun: supervision, writing – review & editing. Ming Tong: writing – review & editing, project administration. Yanyan Zhao: writing – review & editing, project administration. Xiangling Gu: conceptualization, writing – review & editing, Funding acquisition.

Conflicts of interest

The authors have no conflicts of interest to declare.

Data availability

No primary research results, software or code have been included and no new data were generated or analysed as part of this review.

Acknowledgements

This work is financially supported by the National Natural Science Foundation of China (22375028), and Natural Science Foundation of Shandong Province (ZR2023QB247).

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