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

The copolymerization of N‐isopropylacrylamide (NIPAM) and N‐tert‐butylacrylamide (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‐isopropylacrylamide‐stat‐N‐tert‐butylacrylamide)‐block‐polystyrene [poly(NIPAM‐stat‐TBAM)‐block‐poly(STY)]} were obtained by chain extension of either poly(NIPAM‐stat‐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.