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

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Difunctional haloxanthate inifers were used for successive reversible addition−fragmentation transfer (RAFT) polymerization of N-vinylpyrrolidone (NVP) and atom transfer radical polymerization (ATRP) of styrene (St), methyl acrylate (MA), and methyl methacrylate (MMA). Since a quantitative dimerization of NVP in the presence of bromoxanthate inifers occurred, two chloroxanthate inifers, S-[1-methyl-4-(6-chloropropionate)ethyl acetate] O-ethyl dithiocarbonate (CPX) and S-[1-methyl-4-(6-chloroisobutyrate)ethyl acetate] O-ethyl dithiocarbonate (CiBX), were synthesized. These two difunctional chloroxanthate inifers were used to prepare PNVP-b-PSt, 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 (Mn,GPC = 15,000 g/mol and Mw/Mn < 1.4) and PNVP-b-PMMA (Mn,GPC = 50,600 g/mol and Mw/Mn < 1.3) were successfully synthesized through a subsequent chain extension by ATRP. A reshuffling reaction between propagating acrylate radicals and the xanthate moiety next to the NVP unit occurred for the preparation of PNVP-b-PMA, resulting in poor control of the MA chain extension. In the ATRP-first approach, a well-controlled polymerization was observed only for the ATRP of MMA with the CiBX initiator (Mn = 13,000 and Mw/Mn < 1.3). Significant reshuffling reactions between the xanthate moiety and styryl/acrylate propagating radicals were observed with the CPX initiator. This resulted in poor control and broad molecular weight distribution for the subsequent RAFT chain extension of NVP. Thus, the chloroxanthate inifers provide synthetic access to well-defined PNVP-b-PSt and PNVP-b-PMMA, but not to PNVP-b-PMA block copolymers.