Homopolymerization and Block Copolymerization of <i>N</i>-Vinylpyrrolidone by ATRP and RAFT with Haloxanthate Inifers

Difunctional haloxanthate inifers were used for successive reversible addition−fragmentation transfer (RAFT) polymerization of <i>N</i>-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, <i>S</i>-[1-methyl-4-(6-chloropropionate)ethyl acetate] <i>O</i>-ethyl dithiocarbonate (<b>CPX</b>) and <i>S</i>-[1-methyl-4-(6-chloroisobutyrate)ethyl acetate] <i>O</i>-ethyl dithiocarbonate (<b>CiBX</b>), were synthesized. These two difunctional chloroxanthate inifers were used to prepare PNVP-<i>b</i>-PSt, PNVP-<i>b</i>-PMMA, and PNVP-<i>b</i>-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-<i>b</i>-PSt (<i>M</i>_n,GPC = 15,000 g/mol and <i>M</i>_w/<i>M</i>_n < 1.4) and PNVP-<i>b</i>-PMMA (<i>M</i>_n,GPC = 50,600 g/mol and <i>M</i>_w/<i>M</i>_n < 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-<i>b</i>-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 <b>CiBX</b> initiator (<i>M</i>_n = 13,000 and <i>M</i>_w/<i>M</i>_n < 1.3). Significant reshuffling reactions between the xanthate moiety and styryl/acrylate propagating radicals were observed with the <b>CPX</b> 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-<i>b</i>-PSt and PNVP-<i>b</i>-PMMA, but not to PNVP-<i>b</i>-PMA block copolymers.