Synthesis of block and graft copolymers of styrene by raft polymerization, using dodecyl-based trithiocarbonates as initiators and chain transfer agents

摘要

A series of dodecyl-based monofunctional trithiocarbonate chain transfer agents (CTAs) were successfully synthesized, toward the reversible addition-fragmentations chain transfer (RAFT) polymerization of styrene. The CTAs were used as initiators for RAFT polymerization, in the absence of the conventional free radical initiator, at higher temperature. Polystyrene (PS) of narrow polydispersity index (PDI) is synthesized. Subsequently, poly(styrene-b-benzyl methacrylate) diblock and poly(styrene-b-benzyl methacrylate-b-2-vinyl pyridine) triblock copolymers were synthesized from the PS macro-RAFT agent by simply heating with the second and third monomer, respectively. These experiments suggest that it should be possible to control the RAFT polymerization initiated by a CTA through the adjustment of the temperature of polymerization in such manner that initiation is tailored to proceed at faster rate (at higher temperature) in comparison to propagation (lower temperature). For the specific CTAs studied in this work, the polymerization rate of styrene was high in the case of the reinitiating cyano (CN)-substituted group (R group) compared to the other groups studied. The results further show that 4-cyano pentanoic acid group is superior to the other R groups used for the RAFT polymerization of styrene, especially based on the polydispersity at a given conversion as well as the variation in the expected and experimental number-average-molecular weights.