Steric hindrance effect on thermo-responsive behaviors of well-defined water-soluble semi-rigid polymers

Abstract

Three series of water-soluble semi-rigid thermo-responsive polymers with well-defined molecular weights based on mesogen-jacketed liquid crystal polymers, poly[bis(N-(2-hydroxypropyl) pyrrolidone) 2-vinylterephthalate] [P(2-HPPVTA)], poly[bis(N-(1-methyl-2-hydroxyethyl) pyrrolidone) 2-vinylterephthalate] [P(1-M-2-HEPVTA)] and poly[bis(N-hydroxypropyl pyrrolidone) 2-vinylterephthalate] (PHPPVTA) have been synthesized via reversible addition-fragmentation chain transfer polymerization. The steric hindrance effects on liquid crystalline property and thermo-responsive behaviors of semi-rigid water-soluble polymers (P(2-HPPVTA), P(1-M-2-HEPVTA), and PHPPVTA) were carefully investigated. From molecular structure, the steric hindrance of P(1-M-2-HEPVTA) is stronger than that of P(2-HPPVTA). Polarized light microscope and one-dimensional wide-angle X-ray diffraction revealed that both the P(2-HPPVTA) and P(1-M-2-HEPVTA) display a columnar nematic phase, indicating that the steric hindrance effect do not affect liquid crystalline behavior of the polymers. The dynamic light scattering results demonstrated that P(1-M-2-HEPVTA) exhibited lower cloud point compared with that of P(2-HPPVTA) at the same mass concentration and the same molecular weight. The more significant molecular weight and concentration dependence on cloud point have been observed in P(2-HPPVTA) solution than in P(1-M-2-HEPVTA) solution. We also discovered that the cloud points of both P(2-HPPVTA) and P(1-M-2-HEPVTA) solution are lower in D2O than in H2O. It is noted that the cloud point of PM-2 is 9.9 °C lower in D2O than in H2O, much less pronounced than the cloud point difference of PH-2. The differences of thermo-responsive behaviors between P(2-HPPVTA) and P(1-M-2-HEPVTA) were resulted from the steric hindrance effect existed in their side groups. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3429–3438