Upcycling waste polyoxymethylene to value-added chemicals using reusable polymeric acid catalysts at ppm levels

Abstract

Waste polyoxymethylene (POM) plastic was upcycled using m-phenolsulfonic acid-formaldehyde resin, a polymeric heterogeneous catalyst, to afford multiple value-added chemicals, including solvents, insecticides, herbicides, and pillar[5]arenes using biomass-derived alcohols, amines or water as reactants. The acid catalyst exhibited stable and reliable performance at a 260 mol ppm S loading and remained active after five reuse cycles without any loss of catalytic efficiency. The upcycling process was effective even at a 40-gram scale. Under acid-catalyzed conditions, the POM moiety in carbon-fiber-reinforced polymers (CFRPs; 360 mg–5 g scale) was selectively depolymerized, yielding carbon fibers free of POM residues, as confirmed by solid-state NMR and SEM. This process also mitigates environmental concerns by converting microplastics into value-added chemicals. Additionally, microwave irradiation proved more effective (up to 99% upcycling) than conventional heating methods (73%). Life cycle assessment analysis results indicate that this upcycling process is sustainable and helps reduce environmental pollution.

---

Green foundation

1. Plastic pollution is escalating. Our new upcycling strategy for waste polyoxymethylene utilizes a reusable polymeric acid catalyst, overcoming previous methods that relied on non-recyclable catalysts and high energy demands.

2. We have successfully developed a method for upcycling waste polyoxymethylene using biomass-derived diols, alcohol, or water, with a recyclable polymeric acid catalyst at ppm levels and synthesize value-added chemicals. This methodology was effectively demonstrated at the 40 g scale and applied to microplastics and carbon fiber-reinforced polymers (CFRPs). Using microwave irradiation as an energy source enables selective, energy-efficient heating. A life-cycle assessment indicates that our approach is sustainable. This method contributes to SDG 7 (clean energy), SDG 12 (responsible consumption), and SDGs 14 and 15 (protecting life underwater and on land).

3. Further studies utilizing solar energy instead of grid electricity for upcycling waste polyoxymethylene will make the process greener.

Introduction

Plastics are ubiquitous in contemporary life owing mainly to their widespread availability and low cost: however, most plastic materials are non-degradable and non-reusable, resulting in significant plastic waste, which adversely affects both terrestrial and aquatic ecosystems and thus places a considerable burden on the environment.¹ Incinerating plastic is not a viable waste management solution because this process emits copious greenhouse gases.² The chemical upcycling of plastic waste has therefore attracted increasing attention.^3–19 Plastic upcycling aims to transform waste materials into value-added chemicals in accordance with the Sustainable Development Goals (SDGs), a global framework for environmental, social, and economic sustainability set up by the United Nations.

Polyoxymethylene (POM), also known as polyacetal and commonly referred to as engineered thermoplastic, is a versatile plastic used in various everyday items, including buckles, kitchen utensils, motor gears, joints, lighters, and coffee brewers.²⁰ It is known for its high mechanical strength, stiffness, and water-repellency. Hence, the demand for POM has increased, with the current global production capacity reaching approximately 1900 kilotons annually.²¹ However, POM materials are difficult to recycle and exacerbate environmental pollution. POM can be treated using various methods such as mechanical recycling,²² electrochemical depolymerization,^23,24 and pyrolysis;²⁵ however, mechanical recycling typically does not reconvert the polymeric plastic into monomers and thus downgrades the polymer, while pyrolysis aggravates greenhouse gas emissions. Although electrochemical depolymerization produces small molecules, the reaction is non-selective.²⁴ Electrochemical depolymerization also requires solvents and electrolytes and is therefore less atom-efficient. To address these issues, several studies have investigated the chemical upcycling of POM.^26–31 A method using formic acid and manganese catalysts produces methanol via POM upcycling; however, this method produces CO₂ and requires high reaction temperatures and long reaction times.²⁶ The synthesis of cyclic acetals such as 1,3-dioxane²⁷ or 1,3-dioxolane²⁸ from waste POM using Bi(OTf)₃ or 4-chlorobenzenesulfonic acid (4-ClC₆H₄SO₃H) catalysis has been achieved using diol derivatives (Fig. 1A). These cyclic acetals act as both solvents and reagents in the synthesis of 7- and 8-membered cyclic molecules;³² they are also used in solid-state batteries³³ and for the storage of natural gas.³⁴ Despite yielding valuable cyclic acetals from waste POM, the reaction requires high catalyst loadings (0.2–5 mol%). In contrast, the alcoholysis of POM catalyzed by Bi(OTf)₃ affords valuable dialkoxymethanes; however, the process does not occur in water, necessitating the use of additional solvents.²⁹ The catalysts used in existing POM upcycling methods, including formic acid, Bi(OTf)₃, and 4-chlorobenzenesulfonic acid, are homogeneous and not reusable. Proton-exchanged montmorillonite-catalyzed POM upcycling has been reported.³⁰ However, this strategy requires a high catalyst loading (12.5 mg of catalyst for 50 mg of POM) and organic solvents. Similarly, a nano-H-beta-15-zeolite catalyzed POM upcycling has also been documented.³¹ Unfortunately, this method also demands high catalyst loading (20 mg of catalyst for 30 mg of POM). Therefore, efficient processes are required to upcycle waste POM plastic with reusable catalysts to produce cyclic acetals and dialkoxymethanes under solvent-free conditions. Moreover, depolymerizing POM using water as a reactant offers several advantages, improving atom economy and enhancing sustainability.

Fig. 1 Representative examples of POM upcycling using alcohol. (A) Upcycling of POM using homogeneous catalysts. (B) Upcycling of POM using a reusable polymeric acid catalyst (this study).

A highly active, stable, and heterogeneous acid catalyst, m-phenolsulfonic acid-formaldehyde resin (PAFR II) was previously developed for continuous-flow esterification³⁵ and Ritter reactions.³⁶ The acid catalyst remained stable for more than two weeks of continuous use in both continuous-flow esterification and Ritter reactions, demonstrating excellent stability. Therefore, solid PAFR II was hypothesized to facilitate the upcycling of POM materials into value-added chemicals owing to its high stability and acidity. Additionally, using microwave irradiation as a heating source may enhance the efficiency of the reaction by selectively heating the heterogeneous catalyst.^37,38 The selective heating properties of microwaves can save electricity and thus contribute to achieving carbon neutrality by minimizing CO₂ emissions.³⁹ Thus, in this study, we developed a microwave-assisted reusable polymeric acid-catalyzed process for upcycling waste POM plastics (Fig. 1B). To the best of our knowledge, this is the first reported instance of waste plastic upcycling catalyzed by a reusable polymeric catalyst. This microwave-assisted plastic upcycling contributes to SDG 7 (clean and affordable energy via the use of microwaves as a heating source), SDG 12 (responsible consumption and production using biomass-derived alcohols, amines, and water), and SDGs 14 and 15 (life underwater and life on land via the decomposition of waste plastics and microplastics).

Results and discussion

Reaction development and optimization

Initial optimization of the reaction conditions was conducted using polyoxymethylene 1. The reaction of 1 and 1,3-propanediol (2a) in the presence of the PAFR II catalyst (260 mol ppm S) was performed under microwave irradiation for 2 h, yielding 1,3-dioxane (3a) in 99% yield (Table 1, entry 1). Microwave heating was more effective than conventional methods, which afforded 3a in only 73% yield even after an extended reaction time (entry 2). The high catalytic activity of the PAFR II catalysts under microwave irradiation was attributed to the presence of polar functional groups, which more efficiently absorb microwaves. The catalyst remained effective even at a sulfur loading of 100 mol ppm, producing 3a in 79% yield (entry 3). This result indicates that the PAFR II catalyst is highly effective for POM depolymerization. An evaluation of several acid catalysts for POM degradation demonstrated the superior catalytic performance of PAFR II (entries 4–10). The polymeric acid catalyst poly(4-styrenesulfonic acid) (PSS, Fig. 2) afforded 3a in 71% yield (entry 4). The use of p-toluenesulfonic acid (PTSA), p-chlorosulfonic acid (PCSA) and phenol as catalysts afforded 3a in low yields of 19%, 40%, and 4%, respectively (entries 5–7). Interestingly, the monomeric m-phenolsulfonic acid was less effective than the polymeric PAFR II catalyst, affording 3a in 34% yield (entry 8). Formic acid and sulfuric acid catalysts afforded 3a in 75% and 64% yields, respectively (entries 9 and 10), and the reaction intermediate 1,3,5-trioxane (4) (Fig. 2) was detected in 31% and 9% yields, respectively (entries 9 (31%) and 10); moreover, polymer 1 was consumed. In all other reactions using homogeneous acid catalysts, unreacted polymer 1 remained. No reaction was observed in the absence of a catalyst (entry 11).

Fig. 2 Structure of the acid catalysts and the reaction intermediate in Table 1.

Table 1 Synthesis of 1,3-dioxane from polyoxymethylene (1)

Entry	Deviations from standard conditions	Yield of 3a (%)
Reaction conditions: 1 (400 mg, 13.3 mmol (based on monomer), 1 mol equiv.), 2a (1.2 mol equiv., 16 mmol), PAFR II (260 mol ppm S), 130 °C (microwave heating), 2 h under aerobic conditions.a Reaction time: 6 h.b Reaction scale: 28 mmol.
1	None	99
2^a	130 °C conventional heating	73
3	100 mol ppm of PAFR II	79
4	PSS catalyst	71
5	PTSA catalyst	19
6	PCSA catalyst	40
7	Phenol catalyst	4
8	m-Phenolsulfonic acid catalyst	34
9	Formic acid catalyst	75
10^b	H2SO4 catalyst	64
11	No catalyst	0

---

Reactivity of diols and diamines

Under the optimal reaction conditions, the reactivity of 1 with various biomass-derived diols and diamines was explored (Fig. 3). The reaction of 1 with 1,3-propanediol (2a) afforded 1,3-dioxane (3a) in 99% yield. The degradation of 1 was performed using butane-1,3-diol (2b), pentane-2,4-diol (2c), ethane-1,2-diol (2d), propane-1,2-diol (2e), and pinacol (2f) to afford the corresponding 1,3-dioxacyclic compounds 3b–g. The observed trend indicates that primary alcohols demonstrate higher reactivity than sterically hindered secondary and tertiary alcohols. The formation of thermodynamically stable six-membered rings resulted in more efficient POM upcycling than the formation of five- or seven-membered rings. Interestingly, the diamines also produced aminals under this polymeric acid-catalyzed POM upcycling. When reaction was performed using 2,2-dimethyl-1,3-propanediamine (2h), the corresponding 3h was observed in 99% yield.

Fig. 3 POM depolymerization of 1 with various diols and diamines (3a–h).

Reactivity of alcohols and water

Common and environmentally sustainable alcohols such as ethanol and methanol facilitated the depolymerization of 1 (Fig. 4). The reaction of 1 with ethanol required a slightly higher catalyst loading (0.1 mol% S), but afforded diethoxymethane (5) in a relatively high 87% yield (Fig. 4A). Moreover, reacting a POM-based joint clip with ethanol under optimal reaction conditions gave 5 in 84% yield. The reaction of 1 with methanol in the presence of PAFR II at 123 °C, which reached the pressure limit of 10 bar, afforded dimethoxymethane (6) in 66% yield (Fig. 4B). The use of water as a nucleophile resulted in complete conversion; however, the desired product was not detected, likely owing to its volatility. To address this issue, formaldehyde was trapped using acetophenone (7) via a PAFR II-catalyzed aldol condensation, affording 8 in 46% yield (Fig. 4C).

Fig. 4 Reaction of 1 with ethanol, methanol, and water. ^a Polymer 1 originates from a joint clip made from POM. (A) Depolymerization of POM using ethanol. (B) Depolymerization of POM using methanol. (C) Depolymerization of POM using water.

Reactivity of different waste plastics

The formation of 3a was achieved by upcycling various POM plastic products over 6 h (Fig. 5). A laboratory joint clip readily reacted with 2a in the presence of PAFR II, affording 3a in 88% yield (entry 1). The reaction of plastic buckles obtained from a backpack and a polyacetal gear gave 3a in yields of 67% and 82%, respectively (entries 2 and 3). Similarly, the depolymerization of a black joint and white tube made from POM afforded 3a in 95% and 56% yields, respectively (entries 4 and 5).

Fig. 5 Upcycling of plastic materials made from POM. Reaction conditions: plastics (400 mg, 13.3 mmol, considered as pure POM material), 2a (1.2 mol equiv.), PAFR II (260 mol ppm S) under microwave irradiation (80 W) at 130 °C for 6 h. All yields are NMR yields using 1,3,5-trimethoxybeneze as an internal standard. ^a Catalyst loading: 1 mol%.

Depolymerization of CFRPs and microplastics

Depolymerizing the POM moiety of carbon-fiber-reinforced polymers (CFRPs), which are known for their strength, water repellency, and corrosion resistance, is crucial for recovering high-value carbon fibers via POM upcycling. The POM moiety is depolymerized by PAFR II acid catalysis (Fig. 6A). The reaction of CFRP (10% carbon-fiber-reinforced polymer) with 2a under the standard reaction conditions afforded 3a in 71% yield, and reinforced carbon fiber was recovered in 83% yield. The solid-state ¹³C-NMR spectra indicated that the recovered carbon fibers contained no POM (SI). The Scanning Electron Microscopy (SEM) analysis of the recovered carbon fiber showed needle-like materials. Microplastics are potentially hazardous to human health and pose a significant risk of environmental pollution. To address this, we investigated the acid-catalyzed decomposition of microplastics (Fig. 6B). The reaction of microplastics prepared from black polyacetal joints via ball milling and with 2a under the optimized catalytic conditions afforded 3a in 88% yield. These results demonstrate the efficacy of this approach in facilitating the degradation of microplastics, offering a potential solution to this pressing environmental challenge.

Fig. 6 Upcycling of 10% CFRP and POM microplastics. Reaction conditions: plastics (400 mg, 13.3 mmol, considered as pure POM material), 2a (1.2 mol equiv.), PAFR II (260 mol ppm S) under microwave irradiation (80 W) at 130 °C for 6 h. All yields are NMR yields using 1,3,5-trimethoxybeneze as an internal standard. ^a 10% carbon fiber was considered the only additive. ^b Microplastic was prepared by ball-milling of black polyacetal joints. (A) Upcycling of carbon-fiber-reinforced polymer (CFRP). (B) Upcycling of POM microplastics.

Scale-up upcycling of waste plastics

The upcycling of polyoxymethylene was effective on a 5-gram scale without an increase in catalyst loading. The conversion of waste polyacetal joints (5 g) afforded 3a in 89% yield (Fig. 7A). Similarly, the upcycling of 10% carbon-fiber-reinforced POM (5 g) containing 500 mg of carbon fibers gave 3a in 68% yield (Fig. 7B). The carbon fibers were recovered from the reaction mixture in 96% yield, demonstrating the efficiency of this approach for both polymer depolymerization and carbon fiber recovery. Interestingly, our method also successfully upcycled waste polyacetal joints on a 40-gram scale, yielding 89% of 3a (Fig. 7C). Even this 40-gram scale reaction does not demand increased catalyst loading or higher reaction temperature.

Fig. 7 Scale-up for POM and CFRP upcycling. (A) 5 g-scale depolymerization of polyacetal joints. (B) 5 g-scale upcycling of POM-C-10 (10% carbon-fiber-reinforced polymer, CFRP), (C) 40 g-scale upcycling of waste polyacetal joints.

Reusability of PAFR II catalyst

The reusability of the PAFR II catalyst was also investigated (Fig. 8). The catalyst was recovered by filtration; it was washed and dried under vacuum prior to reuse (SI). The catalyst was used six times without any loss of activity, affording 3a in 97–99% yields. Elemental analysis confirmed the exceptional stability of the PAFR II catalyst under optimal reaction conditions. After six cycles, the recovered catalyst retained a sulfur content of 10.4%, similar to the 11.2% sulfur content of the fresh catalyst, indicating minimal loss of active components. SEM analysis revealed no morphological differences between the fresh and the recovered catalysts (Fig. S10). Likewise, FT-IR spectra indicated that the structural features of the PAFR II catalyst remained unchanged after reuse (Fig. S11). PAFR II retained its catalytic activity during the upcycling of POM-based joint clips (Table S2), confirming its high reusability. Notably, after three cycles, the reused catalyst PAFR-II afforded 3a in 88% yield, which was identical to the yield obtained using the fresh catalyst. These results highlight the remarkable durability and sustained catalytic activity of PAFR II in the upcycling of plastic waste, thereby demonstrating its potential for sustainable chemical recycling.

Fig. 8 Reusability of PAFR II in the reaction of 1 with 2a.

The synthetic utility of the upcycled products obtained using PAFR II was also explored (Fig. 9). The reaction of ethylal (formaldehyde diethyl acetal) (5) with 1,4-dimethoxybenzene (9) in the presence of PAFR II (1 mol% S), afforded DMpillar[5]arene 10, an important molecule in host–guest chemistry,⁴⁰ in 63% yield (Fig. 9A, top). The insecticide chlorfenapyr (12)⁴¹ was obtained in 55% yield via the reaction of 5 and 11 (Fig. 9A, bottom). In addition, we also synthesize compound 14 in one-pot with 81% yield, which is a herbicide (Fig. 9B).⁴² Thus, the PAFR II-catalyzed POM upcycling strategy converted waste plastic materials into value-added chemicals.

Fig. 9 Synthesis of value-added chemicals. (A) Stepwise synthesis of DMpillar[5]arene (top) and stepwise synthesis of chlorfenapyr (bottom). (B) One-pot synthesis of herbicide (14).

Plausible catalytic pathway

The chemical kinetic studies suggest that the POM upcycling process follows a first-order dependence for the polymer (1) (Fig. S15) and the catalyst (Fig. S13), whereas it follows a zero-order dependence for 1,3-propanediol (2a) (Fig. S14). Thus, based on chemical kinetics, the interaction between two solid materials (PAFR II catalysts and polymer) is the rate-determining step for this conversion. A plausible catalytic pathway (Fig. 10) is proposed based on mechanistic studies (SI, Section S11) and chemical kinetics. Initially, PAFR II interacts with polyoxymethylene (1) to form an oxonium ion intermediate B. Formation of this oxonium ion intermediate is also observed by IR (Fig. S16). Next, 1,3-propanediol (2a) acts as a nucleophile and forms intermediate B. A proton exchange generates intermediate C from intermediate B. Next, intermediate D is generated via an intermolecular cyclization, followed by another proton exchange to regenerate the catalyst and produce 1,3-dioxane (3a) as a product.

Fig. 10 Plausible catalytic pathway for POM upcycling.

Life cycle assessment analysis

The life cycle assessment (LCA) analysis reveals that our POM upcycling strategy results in significantly lower greenhouse gas emissions (1.88 kg CO₂-eq per kg) compared to traditional methods of 1,3-dioxane synthesis (6.08 kg CO₂-eq per kg), indicating that our method is more environmentally friendly and sustainable (see SI, Section 12). Moreover, the incineration of polyoxymethylene can be avoided by directly converting the plastics to value-added chemicals, which also makes the upcycle strategy sustainable.

Conclusions

In this study, we successfully achieved the upcycling of waste polyoxymethylene (POM) plastics using a novel polymeric heterogeneous catalyst. This approach enabled the efficient depolymerization of POM in the presence of diols, ethanol, methanol, or water, with a remarkably low catalyst loading of 260 mol ppm. The PAFR II catalyst exhibited outstanding stability and maintained essentially 100% catalytic activity for at least six cycles. This method is a powerful and scalable strategy for the upcycling of waste polyacetal plastics into value-added chemicals and demonstrates versatility across both small- and large-scale applications. Moreover, the catalytic system exhibits broad utility, enabling the synthesis of high-value pillar[5]arenes, insecticides, and herbicides. Building on this success, ongoing research in our laboratory continues to expand the frontier of plastic upcycling and explore the potential of PAFR II catalysts in a wide range of sustainable polymer transformations. Additionally, we plan to design a new sulfur-bearing catalyst for more efficient plastic upcycling.

Author contributions

A. S. and Y. M. A. Y. designed the experiments and wrote the manuscript. A. S. performed the experiments. A. O. performed SEM and IR measurements and analyses. A. C., Y. X., J. Z., N. M., J. T. C. performed LCA analysis. All the authors approved the final version of the manuscript.

Conflicts of interest

There are no conflicts to declare.

Data availability

The data supporting this article have been included as part of the supplementary information (SI). Supplementary information (experimental procedures, product characterization, catalyst reusability, life cycle assessments, ¹H-NMR, ¹³C-NMR, ¹³C-CPMAS, IR spectra, GC and GC-MS, MALDI-MS spectra) is available. See DOI: https://doi.org/10.1039/d5gc06065f.

Acknowledgements

We are grateful to Mitsubishi Chemicals for providing the Carbon Fiber-Reinforced Polymer CFRPs. We thank the materials characterization support team, CEMS, and RIKEN for their assistance with elemental analysis. We thank Ms. Eman Soliman (our team) for preparing the PAFR II. We thank Dr Takehiro Suzuki (RIKEN Center for Sustainable Resource Science). We gratefully acknowledge financial support from JSPS (Grant-in-Aid for Scientific Research (B) 21H01979, Grant-in-Aid for Transformative Research Areas (A) JP21A204 and 24H01102, Digitalization-driven Transformative Organic Synthesis (Digi-TOS)), The Naito Foundation, RIKEN (RIKEN Intensive Research Project), and the Project “Acceleration of Social Implementation and Dissemination of Components and Materials for Realizing Innovative CO₂ Emission Reduction” by Ministry of the Environment, Japan.

References

1. C. M. Rochman, The story of plastic pollution: From the distant ocean gyres to the global policy stage, Oceanography, 2020, 33, 60–70,  DOI:10.5670/oceanog.2020.308.
2. L. Cabernard, S. Pfister, C. Oberschelp and S. Hellweg, Growing environmental footprint of plastics driven by coal combustion, Nat. Sustainability, 2021, 5, 139–148,  DOI:10.1038/s41893-021-00807-2.
3. L. Li, M. Leutzsch, P. Hesse, C. Wang, B. Wang and F. Schüth, Polyethylene recycling via water activation by ball milling, Angew. Chem., Int. Ed., 2025, 64, e202413132,  DOI:10.1002/anie.202413132 , PubMed: 39435641.
4. C. Xia and B. Han, Plastics upcycling made more sustainable and practical, Nat. Sustainability, 2023, 6, 1518–1519,  DOI:10.1038/s41893-023-01215-4.
5. D. Sajwan, A. Sharma, M. Sharma and V. Krishnan, Upcycling of plastic waste using photo-, electro-, and photoelectrocatalytic approaches: A way toward a circular economy, ACS Catal., 2024, 14, 4865–4926,  DOI:10.1021/acscatal.4c00290.
6. Y. Zhao, E. M. Rettner, M. E. Battson, Z. Hu, J. Miscall, N. A. Rorrer and G. M. Miyake, Tailoring the properties of chemically recyclable polyethylene-like multiblock polymers by modulating the branch structure, Angew. Chem., Int. Ed., 2024, 64, e202415707,  DOI:10.1002/anie.202415707.
7. R. J. Conk, S. Hanna, X. Jake, Y. Ji, N. R. Ciccia, L. Qi, B. J. Bloomer, S. Heuvel, T. Wills, J. Su, A. T. Bel and J. F. Hartwig, Catalytic deconstruction of waste polyethylene with ethylene to form propylene, Science, 2022, 377, 1561–1566,  DOI:10.1126/science.add1088 , PubMed: 36173865.
8. B. Lu, K. Takahashi, J. Zhou, S. Nakagawa, Y. Yamamoto, T. Katashima, N. Yoshie and K. Nozaki, Mild catalytic degradation of crystalline polyethylene units in a solid state assisted by carboxylic acid groups, J. Am. Chem. Soc., 2024, 146, 19599–19608,  DOI:10.1021/jacs.4c07458 , PubMed: 38952064.
9. C. Li, X. Y. Kong, M. Lyu, X. T. Tay, M. Đokic, K. F. Chin, C. T. Yang, E. K. X. Lee, J. Zhang, C. Y. Tham, W. X. Chan, W. J. Lee, T. T. Lim, A. Goto, M. B. Sullivan and H. S. Soo, Upcycling of non-biodegradable plastics by base metal photocatalysis, Chem, 2023, 9, 2683–2700,  DOI:10.1016/j.chempr.2023.07.008.
10. J. E. Rorrer, G. T. Beckham and Y. Román-Leshkov, Conversion of polyolefin waste to liquid alkanes with Ru-based catalysts under mild conditions, JACS Au, 2021, 1, 8–12,  DOI:10.1021/jacsau.0c00041 , PubMed: 34467267.
11. Z. Xu, F. Pana, M. Suna, J. Xub, N. E. Munyanezaa, Z. L. Crofta, G. G. Caid and G. Liua, Cascade degradation and upcycling of polystyrene waste to high-value chemicals, Proc. Natl. Acad. Sci. U. S. A., 2022, 119, e2203346119,  DOI:10.1073/pnas.2203346119 , PubMed: 35969757.
12. Q. Lai, A. H. Mason, A. Agarwal, W. C. Edenfield, X. Zhang, T. Kobayashi, Y. Kratish and T. J. Marks, Rapid polyolefin hydrogenolysis by a single-site organo-tantalum catalyst on a super-acidic support: Structure and mechanism, Angew. Chem., Int. Ed., 2023, 60, e202312546,  DOI:10.1002/anie.202312546.
13. M. Zeng, Y.-H. Lee, G. Strong, A. M. LaPointe, A. L. Kocen, Z. Qu, G. W. Coates, S. L. Scott and M. M. Abu-Omar, Chemical upcycling of polyethylene to value-added α,ω-divinyl-functionalized oligomers, ACS Sustainable Chem. Eng., 2021, 9, 13926–13936,  DOI:10.1021/acssuschemeng.1c05272.
14. K. V. Khopade, S. C. Chikkali and N. Barsu, Metal-catalyzed plastic depolymerization, Cell Rep. Physiol. Sci., 2023, 4, 101341,  DOI:10.1016/j.xcrp.2023.101341.
15. W.-T. Lee, A. V. Muyden, F. D. Bobbink, M. D. Mensi, J. R. Carullo and P. J. Dyson, Mechanistic classification and benchmarking of polyolefin depolymerization over silica-alumina-based catalysts, Nat. Commun., 2022, 13, 4850,  DOI:10.1038/s41467-022-32563-y , PubMed: 35977921.
16. S. Chen, A. Tennakoon, K.-E. You, A. L. Paterson, R. Yappert, S. Alayoglu, L. Fang, X. Wu, T. Y. Z. Zhao, M. P. Lapak, M. Saravanan, R. A. Hackler, Y.-Y. Wang, L. Qi, M. Delferro, T. Li, B. Lee, B. Peters, K. R. Poeppelmeier, S. C. Ammal, C. R. Bowers, F. A. Perras, A. Heyden, A. D. Sadow and W. Huang, Ultrasmall amorphous zirconia nanoparticles catalyse polyolefin hydrogenolysis, Nat. Catal., 2023, 6, 161–173,  DOI:10.1038/s41929-023-00910-x.
17. W. Zhang, S. Kim, L. Wahl, R. Khare, L. Hale, J. Hu, D. M. Camaioni, O. Y. Gutiérrez, Y. Liu and J. A. Lercher, Low-temperature upcycling of polyolefins into liquid alkanes via tandem cracking-alkylation, Science, 2023, 379, 807–811,  DOI:10.1126/science.ade7485 , PubMed: 36821681.
18. Z. Xu, N. E. Munyaneza, Q. Zhang, M. Sun, C. Posada, P. Venturo, N. A. Rorrer, J. Miscall, B. G. Sumpter and G. Liu, Chemical upcycling of polyethylene, polypropylene, and mixtures to high-value surfactants, Science, 2023, 381, 666–671,  DOI:10.1126/science.adh0993 , PubMed: 37561876.
19. H. Li, J. Wu, Z. Jiang, J. Ma, V. M. Zavala, C. R. Landis, M. Mavrikakis and G. W. Huber, Hydroformylation of pyrolysis oils to aldehydes and alcohols from polyolefin waste, Science, 2023, 381, 660–666,  DOI:10.1126/science.adh1853 , PubMed: 37561862.
20. S. Lüftl, P. M. Visakh and S. Chandran, Polyoxymethylene Handbook: Structure, Properties, Applications and Their Nanocomposites, Wiley-Scrivener, 2014.
21. https://en.kunststoffe.de/a/specialistarticle/polyoxymethylene-pom-245435 .
22. Z. O. G. Schyns and M. P. Shaver, Mechanical recycling of packaging plastics: A review, Macromol. Rapid Commun., 2021, 42, e2000415,  DOI:10.1002/marc.202000415 , PubMed: 33000883.
23. W. Zhang, L. Killian and A. Thevenon, Electrochemical recycling of polymeric materials, Chem. Sci., 2024, 15, 8606–8624,  10.1039/d4sc01754d , PubMed: 38873080.
24. Y. Zhou, J. Rodríguez-López and J. S. Moore, Heterogenous electromediated depolymerization of highly crystalline polyoxymethylene, Nat. Commun., 2023, 14, 4847,  DOI:10.1038/s41467-023-39362-z , PubMed: 37563151.
25. D. Kwon, D. Choi, H. Song, J. Lee, S. Jung and E. E. Kwon, Syngas production through CO₂-mediated pyrolysis of polyoxymethylene, Energy, 2024, 304, 132118,  DOI:10.1016/j.energy.2024.132118.
26. L. Lu, J. Luo, M. Montag, Y. Diskin-Posner and D. Milstein, Polyoxymethylene upcycling into methanol and methyl groups catalyzed by a manganese pincer complex, J. Am. Chem. Soc., 2024, 146, 22017–22026,  DOI:10.1021/jacs.4c07468 , PubMed: 39046806.
27. K. Beydoun and J. Klankermayer, Efficient plastic waste recycling to value-added products by integrated biomass processing, ChemSusChem, 2020, 13, 488–492,  DOI:10.1002/cssc.201902880 , PubMed: 31912617.
28. J. Li, X. Shi, M.-Q. Zhang, M. Wang and D. Ma, Co-upcycling of polyethylene terephthalate and polyoxymethylene into valuable chemicals, Chem. Catal., 2025, 5, 101232,  DOI:10.1016/j.checat.2024.101232.
29. M. J. Cullen, M. G. Davidson, M. D. Jones and J. A. Stewart, Valorization of polyoxymethylene (POM) waste as a C1 Synthon for industrially relevant dialkoxymethanes and cyclic aminals, RSC Sustainability, 2025, 3, 1114–1121,  10.1039/D4SU00547C.
30. J. F. Noboa, S. Yamaguchi, T. Mitsudome and T. Mizugaki, Polyoxymethylene upcycling into cyclic acetals catalyzed by proton-exchanged montmorillonite. The 134th Catalysis Society of Japan Meeting, 2E04 (Nagoya, Japan, 2024).
31. M. Chen, K. Wang, Z. Sun, W. Guo, C. Chen, J. Fei, T. Yang, H. He, Y. Liu and Y. Cao, Upcycling Polyoxymethylene via H₂O₂-Mediated Selective Oxidation, ChemSusChem, 2025, 18, e202500179,  DOI:10.1002/cssc.202500179.
32. F. Medina, C. Besnard and J. Lacour, One-step synthesis of nitrogen-containing medium-sized rings via α-imino diazo intermediates, Org. Lett., 2014, 16, 3232–3235,  DOI:10.1021/ol5012532 , PubMed: 24885761.
33. Y. Liu, H. Zou, Z. Huang, Q. Wen, J. Lai, Y. Zhang, J. Li, K. Ding, J. Wang, Y.-Q. Lana and Q. Zheng, In situ polymerization of 1,3-dioxane as a highly compatible polymer electrolyte to enable the stable operation of 4.5 V Li-metal batteries, Energy Environ. Sci., 2023, 16, 6110–6119,  10.1039/D3EE02797J.
34. Y. Zhang, H. Xu, G. Bhattacharjee and P. Linga, Methane storage in simulated seawater enabled by 1,3-dioxane as an environmentally benign promoter, Energy Fuels, 2023, 37, 8272–8283,  DOI:10.1021/acs.energyfuels.3c01036.
35. H. Hu, H. Ota, H. Baek, K. Shinohara, T. Mase, Y. Uozumi and Y. M. A. Yamada, Second-generation meta-phenolsulfonic acid–formaldehyde resin as a catalyst for continuous-flow esterification, Org. Lett., 2020, 22, 160–163,  DOI:10.1021/acs.orglett.9b04084 , PubMed: 31841008.
36. E. Soliman, H. Baek, N. Mase and Y. M. A. Yamada, Continuous-flow Ritter reaction for sustainable amide synthesis using a recyclable m-Phenolsulfonic Acid-Formaldehyde resin catalyst, J. Org. Chem., 2025, 90, 1447–1454,  DOI:10.1021/acs.joc.4c02384 , PubMed: 39801057.
37. A. Sen, V. Bukhanko, H. Baek, A. Ohno, A. Muranaka and Y. M. A. Yamada, Overcoming the low reactivity of aryl chlorides: Amination via reusable polymeric nickel−iridium dual catalysis under microwave and visible light, ACS Catal., 2023, 13, 12665–12672,  DOI:10.1021/acscatal.3c02171.
38. H. Baek, K. Kashimura, T. Fujii, S. Fujikawa, S. Tsubaki, Y. Wada, Y. Uozumi and Y. M. A. Yamada, Production of Bio Hydrofined Diesel, Jet Fuel, and Carbon Monoxide from Fatty Acids Using a Silicon nanowire array-supported rhodium nanoparticle catalyst under microwave conditions, ACS Catal., 2020, 10, 2148–2156,  DOI:10.1021/acscatal.9b04784.
39. Y. Wada, Microwave chemistry as a candidate of electrification technology toward carbon neutrality—Microwave magnesium smelting as an example, IEICE Trans. Electron., 2024, E107.C, 288–291,  DOI:10.1587/transele.2024MMI0005.
40. N. L. Strutt, R. S. Forgan, J. M. Spruell, Y. Y. Botros and J. F. Stoddart, Monofunctionalized Pillar[5]arene as a host for Alkanediamines, J. Am. Chem. Soc., 2011, 133, 5668–5671,  DOI:10.1021/ja111418j , PubMed: 21443238.
41. C. Yunta, J. M. F. Ooi, F. Oladepo, S. Grafanaki, S. A. Pergantis, D. Tsakireli, H. M. Ismail and M. J. I. Paine, Chlorfenapyr metabolism by mosquito P450s associated with pyrethroid resistance identifies potential activation markers, Sci. Rep., 2023, 13, 14124,  DOI:10.1038/s41598-023-41364-2 , PubMed: 37644079.
42. K. Tao, G. Shuang, Z. Li-Xia, Z. Yue;, Y. Fei and F. Ying, Design, Synthesis, and SAR of Novel 1,3-Disubstituted Imidazolidine or Hexahydropyrimidine Derivatives as Herbicide Safeners, J. Agric. Food Chem., 2021, 69, 45–54,  DOI:10.1021/acs.jafc.0c04436.

---