Design, Synthesis And Phase Behavior Of Semi-rigid Water-soluble Thermo-responsive Polymer

Thermo-responsive polymer systems might recognize a change of environment temperature as a signal, judge the magnitude of this signal, and then change their chain conformation in direct response. Combines the molecular designs of the thermo-responsive polymers and mesogen-jacketed liquid crystal polymers (MJLCP), we have designed and synthesized a series of water-soluble semi-rigid thermo-responsive (co)polymers with well-defined molecular weights based on the MJLCP. The relationship between molecular structure and properties, and the influence factors on thermo-responsive behaviors were investigated. Our results will shed light on the molecular design of new thermo-responsive polymers with semi-rigid backbones and provide new opportunities in the field of thermo-responsive materials. Research progress and the highlights are as follows:1. a series of pyrrolidone-based monomers were successfully synthesized, i.e., bis(N-hydroxyethyl pyrrolidone)2-vinylterephthalate (HEPVTA), bis(N-hydroxy-propyl pyrrolidone)2-vinylterephthalate (HPPVTA), bis(N-(2-hydroxypropyl) pyrrolidone)2-vinylterephthalate ((2-HPP)VTA), bis(N-(1-methyl-2-hydroxyethyl) pyrrolidone)2-vinylterephthalate ((1-M-2-HEP)VTA) and bis(N-(1-ethyl-2-hydroxy-ethyl) pyrrolidone)2-vinylterephthalate ((1-E-2-HEP)VTA). The chemical structures of these monomers were confirmed by1H NMR,13C NMR, MS and elemental analysis. The cloud point of monomer increased with increasing of its hydrophobic properties, i.e., CPHEPVTA＞CP(2-HPP)VTA＞CPHPPVTA＞CP(1-M-2-HEP)VTA＞CP(1-E-2-HEP)VTA.2. The corresponding semi-rigid thermo-responsive polymers with various pendant group structures were prepared by conventional radical polymerization. The thermo-responsive property of semi-rigid polymer is influenced by hydrophilic/hydrophobic ratio and steric hindrance effect around hydrophilic group. The thermo-responsive behavior of the polymer is consistent with the monomer results. That is, CPP(2-HPP)VTA＞CPPHPPVTA＞CPP(1-M-2-HEP)VTA＞CPP(1-E-2-HEP)VTA.3. A series of water-soluble semi-rigid thermo-responsive polymers (P(2-HPP)VTA) with well-defined molecular weights were synthesized via reversible addition-fragmentation chain transfer (RAFT). The cloud point of polymer increased with increasing of its molecular weight, which showed the opposite trend comparing with other thermo-responsive polymers with flexible backbones.4. Three series of water-soluble semi-rigid thermo-responsive polymers with well-defined molecular weights based on mesogen-jacketed liquid crystal polymers, PHPPVTA, P(2-HPPVTA) and P(1-M-2-HEPVTA) have been synthesized via reversible addition-fragmentation chain transfer polymerization. The steric hindrance effect on bulk and solution properties was studied. The experiment results revealed that the PHPPVTA, P(2-HPPVTA) and P(1-M-2-HEPVTA) display a hexatic columnar nematic phase, indicating that the steric hindrance effect don’t affect liquid crystalline behavior of the polymers. However, the most significant solvent isotopic effect, molecular weight and concentration dependence on cloud point have been observed in (P(2-HPP)VTA) solution, indicating that the enhanced steric hindrance suppresses the solvent isotopic, molecular weight and concentration effect on thermo-responsive phase transition behaviors.5. Four series of water-soluble semi-rigid thermo-responsive copolymers based on MJLCPs were synthesized via conventional radical copolymerization. The thermo-responsive behavior of semi-rigid polymer is related to the flexibility on polymer molecular chain. For instance, poly[(N-isopropylacrylamide-co-bis(N-(2-hydroxypropyl) pyrrolidone)2-vinylterephthalate], the cloud point of the copolymers showed unexpected trend (i.e., parabolicaly other than linearly or exponentially) with the increasing of semi-rigid segment content. That is, with an increase of semi-rigid segment molar content, the cloud point of copolymer decreases at first and then increases, it was obviously different from that of copolymer with flexible backbones. The copolymer poly[(N-vinylpyrrolidone-co-bis(N-(2-hydroxypropyl) pyrrolidone)2-vinylterephthalate] also exhibit a similar thermo-responsive phase separate behavior. That is, the cloud point of copolymer decreases at first and then increases during the progress of the change comonomer content. The thermo-responsive phase separate behavior the copolymers poly[(bis(N-hydroxypropyl pyrrolidone)2-vinyltereph-thalate-co-bis(N-(2-hydroxypropyl) pyrrolidone)2-vinylterephthalate] and poly[(styrene-co-bis(N-(2-hydroxypropyl) pyrrolidone)2-vinylterephthalate] aqueous solution was consistent with that of conventional thermo-responsive copolymers based on flexible chain, the cloud point of copolymer aqueous solutions monotone increased/decreased with increasing of its comonomer content.6. Thermo-responsive rod-coil diblock copolymers poly[(N-isopropylacrylamide- block-bis(N-(2-hydroxypropyl) pyrrolidone)(N43bHm and N151bHm) have been synthesized via RAFT polymerization, where the rod part consists of MJLCP. The characterization of the block copolymers was performed with1H NMR, GPC and TGA. Differential scanning calorimetry, polorized light microscopy, one-dimensional and two-dimensional wide angle X-ray diffraction were used to study the phase structure of these rod-coil block copolymers. The experiment results demonstrated phase structure of PNIPAm-b-P P(2-HPP)VTA) is a hexatic columnar nematic phase when N43bHm and N151bHm with m≥95and146, respectively. Moreover, the polymerization degrees (PD) of semi-rigid block have slight effect on the thermo-responsive behavior of rod-coil diblock copolymer with high flexible block PD. However, the cloud point of diblock copolymer with small flexible block PD quickly increased with increasing of semi-rigid block molecular weight.