Nitroxide-mediated controlled statistical copolymerizations of N-isopropylacrylamide with N-tert-butylacrylamide

The copolymerization of N-isopropylacrylamide (NIPAM) and N-tert-butyl-acrylamide (TBAM) via conventional radical polymerization and nitroxide-mediated polymerization (NMP) with N-tert-butyl-N-[1-diethylphosphono- (2,2-dimethylpropyl)]-nitroxide (SG1) was investigated. The monomer reactivity ratios were determined to be 0.58 and 1.00 for NIPAM and TBAM, respectively. The reactivities were approximately the same at 120 and 60°C in N,N-dimethylformamide (DMF) and toluene, respectively, for the conventional copolymerizations and in DMF at 120°C for NMP. Controlled/living characteristics for NMP were achieved with a 2,2′-azobisisobutyronitrile/ SG1 bimolecular system and a unimolecular polystyrene [poly(STY)]-SG1 macroinitiator in the presence of excess free SG1. Block copolymers of poly(N-isopropylacrylamide-stat-N-tert-butylacrylamide) [poly(NIPAM-stat-TBAM)] with styrene {poly(N-isopropylacaylamide-stat-N-tert-butylacrylamide)-block- polystyrene [poly(NIPAM-stat-TBAM)-block-poly(STY)]} were obtained by chain extension of either poly(NIPAM-siat-TBAM)-SG1 with styrene or poly(STY)-SG1 with NIPAM/TBAM. A comparison of the number-average molecular weight calculated from the end-group content with the number-average molecular weight measured by gel permeation chromatography for poly(NIPAM-stat-TBAM)-block-poly(STY)-SG1 indicated that nearly all poly(NIPAM-stat-TBAM) chains were capped by SG1 and were thus living.