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

Abstract

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 (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 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 (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 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.

Synthesis and applications of polystyrene-block-poly(N-vinyl-2-pyrrolidone) copolymers

“…Normally, very narrow Ɖ values (M w /M n ≤ 1.2) are obtained at low monomer conversion rates and/or by using solvent in the polymerization [25,37,38] . In the present work, we conducted the PS polymerization in bulk resulting Ɖ values slightly above very narrow Ɖ values (M w /M n ≤ 1.2) but still in the range of CRP Ɖ values (M w /M n ≤ 1.5).Thus, this work is in agreement with literature reported Ɖ values [4,6,[20][21][22]25,35] . DSC heating curves of the PS-b-PVP copolymers is shown in Figure 3.…”

“…Amphiphilic copolymers of polystyrene-block-poly(N-vinyl-2-pyrrolidone) (PS-b-PVP) have been reported employing the following radical polymerizations: pseudo-living [18] , atom transfer radical polymerization (ATRP) [9,19] , ATRP followed by reversible addition−fragmentation chain-transfer polymerization (RAFT) [20] , RAFT [21] , RAFT followed by ATRP [22] , nitroxide-mediated polymerization (NMP) [23,24] , organostibine-mediated [25] and organogermanium-mediated polymerizations [26] . Although PS-b-PVP copolymers have been synthesized by several methods, some did not provide suitable PS-b-PVP amphiphilic copolymers due to the presence of homopolymers as impurities and high Ɖ values (i.e.…”

Living Radical Polymerization by the RAFT Process – A Third Update

“…[205] Further examples of the synthesis of polymers by a combination of ATRP and RAFT have been reported. [185,525,618] This can involve preparing one block comprising a MAM by ATRP and then a second block comprising a LAM by RAFT.…”

“…[525] Bromoisobutyrate derivatives (e.g. 241, successful with VAc) could not be used as RAFT agents in this context because of dimerization of NVP which was catalyzed by trace amounts of HBr.…”

“…241, successful with VAc) could not be used as RAFT agents in this context because of dimerization of NVP which was catalyzed by trace amounts of HBr. [525] This problem was overcome with the use of the corresponding chloroisobutyrate (242).…”