Synthesis of ultra-high molecular weight ABA triblock copolymers via aqueous RAFT-mediated gel polymerisation, end group modification and chain coupling†
The synthesis of ultra-high molecular weight (UHMW) polymers using reversible deactivation radical polymerisation techniques remains a challenge and has been the centre of attention only in a limited number of studies. Although UHMW polymers were synthesised in these research studies, the complexity in architecture has mainly been limited to linear homopolymers and AB diblock copolymers. We hereby report a new pathway to synthesise UHMW ABA triblock copolymers using a combination of reversible addition–fragmentation chain transfer (RAFT) polymerisation, end-group modification by aminolysis and chain coupling. A simple aqueous RAFT-mediated gel polymerisation technique was initially employed to synthesise high molecular weight AB diblock copolymers with low dispersities (Đ < 1.50). The use of the said gel polymerisation method in combination with a redox initiation system allowed for the rapid chain propagation of water-soluble monomers at a low reaction temperature of 20 °C. These polymers were subsequently treated by aminolysis to convert the chain end into a thiol functionality, which spontaneously coupled under oxidative conditions to form a disulfide bridge between the AB diblock copolymers to produce the final UHMW ABA triblock copolymers (Mn,SEC > 1000k; Đ < 1.70).