Controlled one-pot synthesis of polystyrene-block-polycaprolactone copolymers by simultaneous RAFT and ROP

摘要

A convenient one-pot method for the controlled synthesis of polystyrene-block-polycaprolactone (PS-b-PCL) copolymers by simultaneous reversible addition-fragmentation chain transfer (RAFT) and ring-opening polymerization (ROP) processes is reported. The strategy involves the use of 2-(benzylsulfanylthiocarbonylsulfanyl)ethanol (1) for the dual roles of chain transfer agent (CTA) in the RAFT polymerization of styrene and co-initiator in the ROP of ε-caprolactone. One-pot polymerizations using the electrochemically stable ROP catalyst diphenyl phosphate (DPP) yield well-defined PS-b-PCL in a relatively short reaction time (≈4 h; M34;n= 9600-43 600 g mol-1; Ma-34;w/Ma-34;n = 1.21-1.57). Because the hydroxyl group is strategically located on the Z substituent of the CTA, segments of these diblock copolymers are connected through a trithiocarbonate group, thus offering an easy way for subsequent growth of a third segment between PS and PCL. In contrast, an oxidatively unstable Sn(Oct)_2 ROP catalyst reacts with (1) leading to multimodal distributions of polymer chains with variable composition. Well-defined polystyrene-block-polycaprolactone (PS-b-PCL) diblock copolymers are prepared in a one-pot synthesis comprising simultaneous RAFT and ROP controlled processes. The blocks are connected through a trithiocarbonate group, thus allowing for subsequent growth of a third middle segment between PS and PCL.