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Reversible addition–fragmentation chain-transfer (RAFT) polymerizations are one of the most versatile and powerful polymerization techniques for the synthesis of complex macromolecular architectures. While RAFT polymerizations often give polymers with narrow molecular weight distributions (MWDs), commodity plastics often have broad MWDs to give targeted properties and processability. Thus, new methods to precisely control both MWD breadth and shape are essential for fine-tuning polymer properties for next generation materials. Herein, we report a simple method for controlling polymer MWD features in thermally activated radical RAFT and redox activated cationic RAFT polymerizations by means of metered additions of chain transfer agents. 

Recent developments in photocontrolled polymerizations have facilitated the development of previously inaccessible materials. While photocontrolled radical polymerizations have been extensively studied, related processes involving cationic polymerizations are underexplored and limited to RAFT processes. In this study, we disclose a visible light, temporally controlled cationic polymerization of vinyl ethers utilizing thioacetals and a photoredox catalyst. We demonstrate a broad scope of thioacetal initiators that achieve a well-controlled polymerization by recapping propagating chains via photocatalyst turnover in combination with a degenerate chain transfer process through sulfonium intermediates. Furthermore, we show that a photocatalyst with a more reducing ground state reduction potential allows for enhanced control and excellent temporal regulation of polymerization. 

Plastic production continually increases its share of global oil consumption. Thermoplastic elastomers (TPEs) are a necessary component of many industries, from automotive and construction to healthcare and medical devices. To reduce the environmental burden of TPE production on the world, we developed two new ABA triblock copolymers synthesized through cationic reversable addition–fragmentation chain transfer (RAFT) polymerization from renewable monomers. Using poly(isobutyl vinyl ether) (PIBVE) as the soft block and either poly( p -methoxystyrene) (PMOS) or poly(2,3-dihydrofuran) (PDHF) as the hard blocks, we produced triblock copolymers with varying volume fractions and characterized their material properties. PDHF-PIBVE-PDHF is sourced almost entirely from simple alcohols and exhibits mechanical properties comparable to those of commercial TPEs. This effort demonstrates the utility of cationic RAFT for the production of sustainable TPEs.