Enantiomer-selective radical cyclopolymerization of rac-2.4-pentanediyl dimethacrylate using a ruthenium-mediated chiral atom transfer radical polymerization initiating system

摘要

The enantiomer-selective radical polymerization of rac-2,4-pentanediyl dimethacrylate, an equimolar mixture of (2S,4S)-2,4-pentanediyl dimethaerylate (SS-1) and (2R,4R)-2,4-pentanediyl dimethacrylate (RR-1), was carried out with a chiral atom transfer radical polymerization initiating system consisting of methyl 2-bromoisobutyrate (3), dichlorotris(triphenylphosphine)ruthenium [RuCl2(PPh3)(3)], and a chiral additive in anisole at 60 degreesC. When (S)-1,1'-bi-2-naphthol (a-3) was used as the chiral additive, the recovered monomer was enriched in SS-1, and the enantiomeric excess was 16.9% at a 22.6% monomer conversion. The specific rotation ([alpha](435), c 0.3, CHCl3) of the resulting polymer was +40.3degrees at a 22.6% monomer conversion. For the copolymerization of SS-1 and RR-1 with 3/RuCl2(PPh3)(3)/a-3 in anisole at 60 degreesC, the monomer reactivity ratio for RR-1 (r(R)) was determined to be 4.94, and that for SS-1 (r(S)) was 0.27. For the homopolymerizations of SS-1 and RR-1 with 3/RuCl2(PPh3)(3)/a-3 in anisole at 60 degreesC, the polymerization rate of RR-1 was considerably faster than that of SS-1, and the rate constants for the homopolymerizations were determined to be k(SS) = 2.0 x 10(-3) h(-1) and k(RR) = 8.2 x 10(-3) h(-1), respectively. With the values of k(SS), k(RR), r(R), and r(S), the relative ratio k(SS)/k(RR)/k(SR)/k(RS) was determined to be 1.2:4.9:4.5:1, which indicated that both the growing end of SS-1 and that of RR-1 preferentially reacted with RR-1. (C) 2004 Wiley Periodicals, Inc.