Homopolymerization and Block Copolymerization of N-Vinylpyrrolidone by ATRP and RAFT with Haloxanthate Inifers

Abstract

Difunctional haloxanthate inifers were used for successive reversible addition-fragmentation transfer (RAFT) polymerization of N-vinylprrolidone (NVP) and atom transfer radical polymerization (ATRP) of styrene (St), methyl actylate (MA), and methyl methacrylate (MMA). Since a quantitative dimerization of NVP in the presence of bromoxanthate inifer occurred, two chloroxanthate mifers, S-[1-methyl-4-(6-chloropropionate)ethyl acetate] O-ethyl dithrocarbonate (CPX) and S-[1-methyl-4-(6-chloroisobutyrate)ethyl accetate] O-ethyl dithiocarbonate (CiBX), were synthesized. These two difunctional chloroxanthate imfers were used to prepare PNVP-b-PSi, PNVP-b-PMMA, AND PNVP-b-PMA block copolymers, where each block was synthesized by different polymerization procedures (either RAFT or ATRP). In the RAFT-first approach, well-controlled polymerization of NVP was observed. Well-defined PNVP-b-PSt (M(n, GPC) = 15,000 G/MOL AND M(w)/M(n) < 1.4 and PNVP-b-PMMA (M(n, GPC) = 50,600 g/mol and M(w)/M(n) < 1.3) were successfully synthesized through a subsequent chain extension by ATRP. A reshuffling reaction between propagating acrylate radicals in poor control of the MA chain extenstion. In the ATRP-first approach a well-controlled polymerization was observed only for the ATRP of MMA with the CiBX initrator (M(n) = 13,000 and M(w)/M(n) < 1.3). Significant reshuffling reactions between the xanthate moiety and styryl/acrylate propagating radicals were observed with the CPX initrator. This resulted in poor control and broad molecular weight distribution for the subsequent RAFT chain extension of NVP. Thus, teh chloroxanthate inifers provide synthetic access to well-defined PNVP-b-PSt and PNVP-b-PMMA, but not to PNVP-b-PMA block copolymers.