Influence Of The Structure Of The Side Chain And Molecular Weight On The Re-entrant Behaviors Of Mesogen-jacketed Liquid Crystalline Polymers

This dissertation is focused on the investigation of the phase behavior and phase structures of mesogen-jacketed liquid crystalline polymers(MJLCPs). Series of MJLCPs have been synthesized via changing the length of spacer and the volume of side group. Meantime, a series of MJLCPs with different molecular weights have been prepared by ATRP polymerization. Throngh studing the relationship between the chemical structure and molecular weight to the reentrant behavior of the MJLCPs, the influence rule of “coupling effect” and “side-chain effect” on the phase behavior of MJLCPs was be summarized. It provides the theoretical direction for preparing the temperature response intelligent liquid-crystal polymer materials. The main contents of this paper are as follows:1. A series of mesogen-jacketed liquid-crystalline polymers containing two triphenylmethyl(Tr) units in the side chains, named poly {2,5-bis[(triphenylmethoxy-alkyl)oxycarbonyl]-styrenes}(denoted as Pv- m-Tr, m =2, 4, 6, 8, 10, 12, which is the number of the methylene units between the terephthalate core and Tr moieties in the side chains), were designed and successfully synthesized via free radical polymerization. The chemical structures of the monomers were confirmed by 1H NMR and Mass Spectrometry. The molecular characterizations of the polymers were performed with 1H NMR, GPC and TG analysis. The phase structures and transitions of the polymers were investigated by the combination of techniques including DSC, POM and 1D/2D WAXD. The experimental results revealed that all the polymers exhibited excellent thermal stabilities and the liquid crystalline(LC) phase structures and behaviors of the polymers were found to be strongly dependent on the spacer length(m). W ith the increasing of m, Tg of Pv- m-Tr decreased from 116.7 oC to 11.5 oC because of the alkyl plasticization. When m =2, 4, 6, 8, 10, the Pv- m-Tr formed a stable columnar nematic(ΦN) phase above Tg. When m =12, the Pv-12-Tr presented a re-entrant isotropic phase above Tg and a LC phase at higher temperature.2. Two series of mesogen-jacketed liquid-crystalline polymers containing different terminal groups(phenmethyl and diphenylmethyl) in the side chains, named poly {2,5-bis[(phenmethyl-alkyl)oxycarbonyl]-styrenes} Pv-m- Bn and poly {2,5-bis[(diphenylmethoxy-alkyl)oxycarbonyl]-styrenes} Pv- m-DPM(m =2, 4, 6, 8, 10, 12, which is the number of the methylene units between the terephthalate core and terminal groups in the side chains), were designed and successfully synthesized via free radical polymerization. The molecular characterizations of the polymers were performed with 1H NMR, GPC and TG analysis. The phase structures and transitions of the polymers were investigated by the combination of techniques including DSC, POM and 1D/2D WAXD. We combined the results of the polymers Pv-m-Bn and Pv- m-DPM with the results of the polymers Pv- m-Tr. The experimental results revealed that all the polymers exhibited excellent thermal stabilities and the re-entrant behaviors of MJLCPs were found to be strongly dependent on the structure of the side chain and molecular weight. The spacer length for the re-entrant behaviors of the polymers is increased with the increasing volume of the side chain.3. A series of mesogen-jacketed liquid-crystalline polymers poly {2,5-bis[(diphenylmethoxy-ethyl)oxycarbonyl]-styrenes}(Pv-2-DPMs) with different molecular weights(MW) and narrow MW distributions have been successfully synthesized via atom transfer radical polymerization. The molecular characterizations of the polymers were performed with GPC and TG analysis. The phase structures and transitions of the polymers were investigated by the combination of techniques including DSC, POM and 1D/2D WAXD. The experimental results showed the samples with Mn below 1.73 × 104 g/mol, only isotropic phase can be observed. When Mn between 3.40 × 104 g/mol and 8.48 × 104 g/mol, a re-entrant isotropic phase in low temperature and columnar nematic phase in high temperature formed. Further increasing the Mn to exceed 9.71 × 104 g/mol a stable columnar nematic phase could develop. It was the first time that MJLCPs formed isotropic phase→reentrant isotropic phase→ columnar phases with the increase of MW.