Synthesis of PEVE b P(CTFE alt EVE) block copolymers by sequential cationic and radical RAFT polymerization
Block copolymers containing chlorotrifluoroethylene (CTFE) are relatively rare. This article presents the synthesis of unprecedented CTFE containing block copolymers (PEVE b P(CTFE alt EVE) where EVE stands for ethyl vinyl ether, via sequential cationic and radical Reversible Addition Fragmentation chain Transfer (RAFT) polymerizations. Two synthetic pathways were followed and compared: (1) synthesis of a PEVE block by cationic RAFT polymerization from a P(CTFE alt EVE) macromolecular Chain Transfer Agent (macroCTA) prepared by radical RAFT copolymerization, and (2) synthesis of a P(CTFE alt EVE) block by radical RAFT copolymerization from a PEVE macroCTA prepared by cationic RAFT polymerization. Careful chain end analysis using 1H and 19F NMR spectroscopies revealed that irreversible transfer reactions severely affected the chain end fidelity of the P(CTFE alt EVE) macroCTA. In addition, the penultimate CTFE unit of these macroCTAs seemed to adversely alter the reactivity of the CH2 CH(OEt) XA end group under cationic RAFT conditions. The chain extension of these macroCTAs by cationic RAFT polymerization thus led to poorly defined block copolymers. Nevertheless, both xanthate and dithiocarbamate RAFT agents were shown to provide efficient control over the radical RAFT copolymerization of CTFE and EVE. In contrast, the cationic RAFT polymerization of EVE afforded PEVE macroCTAs with high chain end fidelity and chain extension reactions resulting in well defined PEVE b P(CTFE alt EVE) block copolymers with low dispersities (D 1.35)