Reversing Blocking Order of Trithiocarbonate-Mediated RAFT Polymerizations Using Photocatalysis

Many acrylic-methacrylic block copolymer sequences remain inaccessible due to synthetic limitations. Herein, photoinduced electron/energy transfer (PET) catalysis is leveraged to reverse blocking order limitations in trithiocarbonate (TTC)-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization. We synthesized poly(methyl acrylate-b-methyl methacrylate) by PET-RAFT using fac-Ir(ppy)₃, achieving predictable, linear increases in molecular weight with conversion. Kinetics studies showed that adding a tertiary amine (triethanolamine) introduced a reversible redox reaction to stabilize the TTC radical during chain extensions, leading to more uniform block copolymers (Р< 1.47) compared to block copolymers synthesized without amine (Р< 1.56). To highlight the utility of this method, triblock copolymers of poly(methyl acrylate) and poly(methyl methacrylate) blocks were investigated. The order of acrylic and methacrylic blocks impacted the physical properties of compositionally similar polymeric materials. For example, a high molecular weight triblock copolymer (P(MMA-b-MA-b-MMA), M_n = 564 kg mol^-1) thermoplastic elastomer showed exceptional strain (>1600%). Overall, we report (i) a new methodology to unlock synthetic access to acrylic-methacrylic block copolymers using TTCs and photocatalysis, (ii) insight into photocatalyst-mediated radical polymerization, and (iii) synthesis of new high-performance materials.