Metal Free Reversible-Deactivation Radical Polymerizations: Advances, Challenges, and Opportunities

Abstract

Abstract:A considerable amount of the worldwide industrial production of synthetic polymers is currently based on radical polymerization methods. The steadily increasing demand on high performance plastics and tailored polymers which serve specialized applications is driven by the development of new techniques to enable control of polymerization reactions on a molecular level. Contrary to conventional radical polymerization, reversible-deactivation radical polymerization (RDRP) techniques provide the possibility to prepare polymers with well-defined structures and functionalities. The review provides a comprehensive summary over the development of the three most important RDRP methods, which are nitroxide mediated radical polymerization, atom transfer radical polymerization and reversible addition fragmentation chain transfer polymerization. The focus thereby is set on the newest developments in transition metal free systems, which allow using these techniques for biological or biomedical applications. After each section selected examples from materials synthesis and application to biomedical materials are summarized.

Redox-Initiated Reversible Addition–Fragmentation Chain Transfer (RAFT) Polymerization

“…The majority of the transition metals employed to catalyze the above-mentioned RAFT systems are considered toxic, with the need to remove them from the polymer post-synthesisespecially for biological and biomedical applications. [42] Moreover, these catalyst complexes increase the cost of production since the techniques used to purify the polymers are usually quite expensive. [43] Recently, Maxiniano et al [43] have introduced a metal-free dissociative electron transfer (DET)-RAFT system at ambient temperature using sodium sulfite as the catalyst.…”

Precise Synthesis of Ultra‐High‐Molecular‐Weight Fluoropolymers Enabled by Chain‐Transfer‐Agent Differentiation under Visible‐Light Irradiation

“…Polymerizations in the presence of other organic PC (3,7‐bis(4‐butylphenyl)‐10‐biphenyl‐10 H ‐phenothiazine) showed that UHMWs could also be obtained under metal‐free conditions (Table S2, entry 1, and Figure S9), revealing the capability to provide UHMW fluoropolymers without metal‐contamination . In contrast, polymerization using heptadecafluorodecyl‐substituted PC only gave less than 10 % conversion within the same exposing time under light irradiation (Table S2, entry 2), supporting our hypothesis that the single‐electron transfer (SET) reaction between photo‐excited catalyst (PC*) and TTC unit took place in organic phase, rather than within the fluorous particles.…”

Molecular bionics – engineering biomaterials at the molecular level using biological principles

“…In a particular case, the so called polymerisation-induced self-assembly (or PISA) [169], supramolecular assemblies can be obtained directly during polymerisation in high concentrations (up to 25% w/v solids), thus compatibly with large-scale production [152][153][154][169][170][171][172][173][174][175][176][177][178]. Despite their popularity, supramolecular biomaterials obtained by polymers made via ATRP and RAFT suffer from a purification drawback, which might encumber their safety [141][142][143][144] and/or the patient compliance for therapeutic applications due to the exhibition of a certain colour or odour in the final product [145,146]. From this point of view, nitroxide-mediated polymerisation (NMP) deserves to be mentioned [149].…”