Unusual effect of molecular weight and concentration on thermoresponsive behaviors of well-defined water-soluble semirigid polymers

A series of water-soluble semirigid thermoresponsive polymers with well-defined molecular weights based on mesogen-jacketed liquid crystal polymers (MJLCPs), poly[bis(N-hydroxyisopropyl pyrrolidone) 2-vinylterephthalate] (PHIPPVTA) have been synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization. Dynamic light scattering (DLS) revealed that the novel monomer and polymers have thermoresponsive properties with cloud point in the range between 10 and 90 degrees C. The cloud point was increased by 56.2 degrees C when the polymer molecular weight increased from 0.47 X 104 g mol-1 to 3.69 X 104 g mol-1. In addition, the cloud point of PHIPPVTA was decreased by 18.8 degrees C with the increase of polymer concentration from 5 to 10 mg mL-1. A slight increase (0.13.5 degrees C) of cloud point has been observed after knocking off the end-groups of PHIPPVTA. Moreover, the cloud point of polymer increased with increasing of its molecular weight with or without the trithiocarbonate end-groups, which showed the opposite trend comparing with other thermoresponsive polymers with flexible backbones. These polymers show a dramatic solvent isotopic effect that the cloud point in D2O was lower than in H2O. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012