Introduction to the themed collection on synthetic methodologies for complex macromolecular structures in honour of Prof. Yusuf Yagci's 70^th birthday

In this themed collection of Polymer Chemistry, we celebrate Professor Yusuf Yagci's 70^th birthday, his impact on the development of synthetic methodologies for complex macromolecular architectures and his commitment to diversity, education, and the polymer chemistry community. For more than 4 decades, Yusuf has had a tremendous impact on the advancement of many fields, including polymer synthesis, macromolecular engineering and applied materials science. By following his own quote, “Do not follow others, create your own strategy”, Yusuf has published over 700 papers in peer-reviewed journals with a total of over 35 000 citations, and is a co-inventor on 10 patents.

Importantly, Yusuf has always stated that he is one of the luckiest academics because he has always had brilliant students and scientists in his team. Hence, his scientific creativity, as well as his contribution to the field of polymer science, has not only inspired many Turkish young scientists to follow his steps and enabled this field to become prosperous in Turkey, but has also had a profound effect on conducting creative global research.

Moreover, Yusuf is also recognized for his entertaining character at international conferences. He has not missed any opportunity to organise soccer tournaments and dance shows at conferences and has created long lasting memories for scientists from all around the world. His remarkable scientific achievements have received prestigious international recognition, including the Alexander von Humboldt Research Award (2018), the International Science Award by the Belgian Polymer Group Society (2018) and the Japan Photopolymer Society Awards (2017), amongst others. Beyond scientific research, he also served as an Editorial Board Member/Advisory Board Member of several international journals, including Macromolecular Rapid Communications, Polymer Chemistry and Macromolecules.

According to Yusuf, “Science is constructed by the combination of knowledge, work and imagination”, hence, as a reflection of this quote, the content of this themed collection is a collection of over 25 contributions from scientists, all of whom are enormously grateful for Yusuf's scientific contributions to the field of polymer chemistry. Indeed, many of the contributions are from long-term friends and collaborators who have had the pleasure and honour to work together with him during his outstanding career. You can find a range of reviews, perspectives, communications and full articles, which cover a broad range of polymer chemistry subjects, not only limited to the design and preparation of complex functional macromolecules.

For instance, the groups of Holger Frey and Axel H. E. Müller have utilized in situ near-infrared (NIR) spectroscopy to investigate the kinetics of the statistical anionic copolymerisation of a biobased monomer (e.g., β-myrcene) in the presence of commodity chemicals (10.1039/D1PY00791B). In particular, the influence of the polar modifiers (i.e., Lewis bases) tetrahydrofuran (THF) and 2,2-di(2-tetrahydrofuryl)propane (DTHFP) on the reactivity ratios has been elaborated.

On the one hand, Helmud Schlaad et al. have investigated the microwave-assisted cationic ring-opening polymerization of 2-oxazolines to prepare a series of gradient or random poly(2-oxazoline) copolymers carrying both catecholic and cationic units, which are further designed as a bioinspired adhesive copolymer mimicking the mussel adhesive protein (10.1039/D1PY00679G). On the other hand, Martina Stenzel and her colleagues have shown that anti-adhesive compounds (e.g. trehalose coated nanocellulose) prevent bacterial infection, hence, they are a potential alternative to antibiotic treatment (10.1039/D1PY01422F).

Paul D. Topham et al. have demonstrated the use of bromine-based chain transfer agents in polymerisation formulations by introducing a straightforward, inexpensive, sulfur- or metal-free method to create commercially-relevant block copolymers in aqueous media (10.1039/D1PY00672J).

The team of Jacques Lalevée designed low-cost, novel charge-transfer complexes involving imidazoles in combination with a highly stable iodonium salt that were successfully applied as outstanding dual photo/thermal initiators for the polymerization of acrylate formulations under 405 nm LED irradiation and mild conditions (10.1039/D1PY01079D).

Franck D'Agosto and colleagues report a robust and straightforward synthesis of surfactant-free poly(vinylidene fluoride) (PVDF) latexes in order to address the constraints related to the use of fluorinated and low molar surfactants (10.1039/D1PY00728A).

Christopher Barner-Kowollik and his team have critically expanded the synthetic capabilities towards multi-segmented polymers of various architectures by developing an environmentally friendly and scalable technique via a combination of step-growth (based on Diels–Alder chemistry) and reversible addition–fragmentation chain transfer (RAFT) polymerization (10.1039/D1PY01163D).

Michael R. Buchmeiser et al. have shed light on the stereospecific ring-opening metathesis polymerization (ROMP) of endo,exo-2,3-dimethoxymethylnorborn-5-ene (DMMNBE) to deliver cis-syndiotactic polymers by the action of non-chelating cationic tungsten imido alkylidene N-heterocyclic carbene (NHC) complexes as initiators (10.1039/D1PY01158H).

A long-term friend of Yusuf, Nikos Hadjichristidis, has reported a novel approach that provides an alternative resolution to a long-standing challenge related to the synthesis of cyclic polymers (10.1039/D1PY01337H). Accordingly, a traditional Williamson etherification-based efficient cyclization was employed to prepare cyclic PS and PEG homopolymers with moderate dilution and up to a gram scale.

Takeshi Endo and colleagues pave the way towards the synthesis of a well-defined novel sulfur-rich polymer decorated with a bulky tertiary amine moiety via the controlled cationic ring opening polymerization of a new cyclic dithiocarbonate monomer (10.1039/D1PY01230D). In order to expand the toolbox of sulfur-rich polymeric architectures, Judit E. Puskas and her team have explored the utilization of reversible radical recombination polymerization (R3P) as an aqueous based “green” method for the synthesis of sulfur-rich polymer macrocycles at the 10–100 g scale. The respective macrocycles revealed unexpected properties which are identical to biodegradable elastomers (10.1039/D1PY01426A).

Robert Liska and his team report a disulfide-based linker series synthesized from cheap and readily available starting materials, which extends the scope of photolabile functional groups for the light-controlled formation/degradation of hydrogels (10.1039/D1PY00914A). Particularly, it was shown that the degradation also works in the two-photon irradiation regime, permitting 3D-micropatterning of such hydrogels.

Brigitte Voit et al. have explored the design and synthesis of tailor-made supramolecular redox-sensitive double cross-linked hydrogels with fine-tunable viscoelastic properties (10.1039/D1PY01211H). The possibility to control the properties of hydrogels with the β-cyclodextrin/ferrocene complex as a reversible cross-linking point provides an opportunity for future applications, e.g. in microfluidics and diagnostics.

Tsutomu Yokozawa and colleagues have demonstrated in an elegant way the precision synthesis of a fluorene–thiophene alternating conducting copolymer by means of Suzuki–Miyaura catalyst-transfer condensation polymerization (10.1039/D1PY01184G). Most importantly, their findings reveal that the steric hindrance around the propagating end (as a result of the bulky alkyl substituent) is effective for the suppression of the undesired disproportionation reaction.

To expand the toolbox of functional conducting polymers, a novel thioacetate functionalised poly(3,4-ethylenedioxythiophene) (PEDOT) sensor was designed and synthesized by the team of Jadranka Travas-Sejdic for the re-usable and repeatable electrochemical detection of biological thiols, such as glutathione (10.1039/D1PY01394G).

In summary, during the process of putting together this themed collection, we received an overwhelming enthusiasm from many researchers in the community of polymer synthesis chemistry, in recognition of Yusuf's tremendous contribution to the field and/or in appreciation of his mentorship. Thus, we, as guest editors, are grateful to all authors for sharing their research and insights in this exciting themed collection. Finally, we would like to conclude with a poem (written by Yusuf himself while he was staying in Toyohashi, Japan in 2002) to express our lofty respect for Yusuf and wish him all of the best for his 70^th birthday this year.

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