Tailoring the morphology of branched poly(N-isopropylacrylamide)via self-condensing atom-transfer radical copolymerization and its unique self-assembly behavior in alcohol

Abstract

Highly branched poly(N-isopropylacrylamide) (PNIPAM) was first synthesized by self-condensing atom transfer radical copolymerization (SCATRCP) catalyzed by CuBr/tris[2-(dimethylamino)ethyl]amine (Me₆TREN) complex in isopropanol at room temperature. This method showed good control over chain morphology and lower critical solution temperature (LCST) type phase transition behavior of PNIPAM by varying reaction time and monomer/inimer feed ratios. On the basis of GPC, FTIR, ¹HNMR and DSC results, four stages were discerned during the polymerization procedure, at which chain architectures experienced “linear – comblike – slightly branched – highly branched” transformations. Additionally, the synthesized highly branched PNIPAM chains were found to be able to self-assemble into hollow spheres in alcohols such as methanol and ethanol, which arise from the presence of large amounts of hydrophobic branched points inside polymer chains.