Facile synthesis of star-shaped copolymers via combination of RAFT and ring opening polymerization

Reversible addition fragmentation chain transfer (RAFT) polymerization and bifunctional sparteine/thiourea organocatalyst-mediated ring opening polymerization (ROP) were combined to produce poly(L-lactide) star polymers and poly(L-lactide-co-styrene) miktoarm star copolymers architecture following a facile experimental procedure, and without the need for specialist equipment. RAFT was used to copolymerize ethyl acrylate (EA) and hydroxyethyl acrylate (HEA) into poly(EA-co-HEA) co-oligomers of degree of polymerization 10 with 2, 3, and 4 units of HEA, which were in turn used as multifunctional initiators for the ROP of L-lactide, using a bifunctional thiourea organocatalytic system. Furthermore, taking advantage of the living nature of RAFT polymerization, the multifunctional initiators were chain extended with styrene (poly((EA-co-HEA)-b- styrene) copolymers), and used as initiators for the ROP of L-lactide, to yield miktoarm star copolymers. The ROP reactions were allowed to proceed to high conversions (>95%) with good control over molecular weights (ca. 28,000-230,000 g/mol) and polymer structures being observed, although the molecular weight distributions are generally broader (1.3-1.9) than those normally observed for ROP reactions. The orthogonality of both polymerization techniques, coupled with the ubiquity of HEA, which is used as a monomer for RAFT polymerization and as an initiator for ROP, offer a versatile approach to star-shaped copolymers. Furthermore, this approach offers a practical approach to the synthesis of polylactide star polymers without a glove box or stringent reaction conditions. The phase separation properties of the miktoarm star copolymers were demonstrated via thermal analyses.