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) pyrrolidoneand 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 onedimensional 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 D 2 O than in H 2 O. It is noted that the cloud point of PM-2 is 9.9 C lower in D 2 O than in H 2 O, 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.
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