Preparation And Phase Behaviors Of The Main-chain/Side-chain Liquid Crystalline Supramolecular Polymers With A Mesogen-jacketed Polymer Backbone

Liquid crystalline polymers(LCPs) have received much attention because of their potential applications on photoelectricity, catalysis, nano-template, etc.Main-chain/side-chain liquid crystalline polymers(MCSCLCP), a complex structure which combine the chemical features of main-chain liquid crystalline polymer(MCLCP) and side-chain liquid crystalline polymer(SCLCP), may have more complicated behaviors compared to conventional MCLCPs and SCLCPs. Generally,in a traditional MCSCLCP, the main chain is a rigid rod or an alternative structure of rod-like mesogenic groups connected by flexible spacers, while the side chain is usually contains a rod-like group linked to the main-chain repeating unit through a flexible spacer. The conventional method to obtain this kind of MCSCLCP is condensation polymerization, thus the molecular weight(MW) and the polydispersity index(PDI) are not controllable. It brings difficulties in studying the structure-property relationships of the MCSCLCPs. In this work, we designed and prepared new MCSCLCPs based on a mesogen-jacketed liquid crystalline polymer(MJLCP) backbone via hydrogen bonding, which is simpler and may be more useful.The main chain, which was used as the hydrogen-bonding donor, was a mesogen-jacketed polyelectrolyte(MJPE) containing the carboxylic acid group(-COOH) in the side chain, which was used to link hydrogen-bond acceptors. The competition and cooperation between the main-chain and side-chain mesogens were investigated. The details are as follows:1. The MJPE with a phenyl-based rigid core poly(vinyl terephthalic acid)(PVTA)was designed and synthesized as the hydrogen-bonding dornor and prepared from its precursor, poly(di-tert-butyl-vinylterephthalate)(PTBVT), which was polymerized by atom transfer radical polymerization(ATRP). The chemical structures of the monomers and polymers were confirmed through 1H NMR, mass spectroscopy(MS),gel permeation chromatography(GPC), and IR. The liquid crystalline(LC) property of PVTA was invested by differential scanning calorimetry(DSC) and one-dimensional wide-angle X-ray diffraction(1D WAXD). The results show thatPVTA is not liquid crystalline.2. Two pyridine derivatives containing a biphenyl rod-like LC mesogen were designed and synthesized as hydrogen-bonding acceptors. The formation of the hydrogen-bonding complexes were confirmed by DSC and IR. LC behaviors of the complexes were investigated by DSC, polarized light microscopy(PLM), small-angle X-ray scattering(SAXS), and two-dimensional(2D) WAXD. The results show that the molar ratio and the length of the spacer have important influences on the LC behaviors of the complexes. PVTA(BBOC6)0.5 exhibits a smectic(Sm X) phase, and the LC behavior is not affected by temperature. PVTA(BBOC6)1 forms a double-layered smectic C(Sm C) phase at ambient temperature; when the temperature is high enough, PVTA(BBOC6)1 transforms to a smectic A(Sm A) phase because of the isotropization of biphenyl moieties in the side chains. Both PVTA(BBOC12)0.5 and PVTA(BBOC12)1 form Sm C structures with the increase in the length of the spacer.3. Two pyridine derivatives containing the triphenylene(Tp) disc-like LC mesogen were designed and synthesized as hydrogen-bonding acceptors. The formation of the hydrogen-bonding complexes were confirmed by DSC and IR. LC behaviors of the complexes were also investigated by DSC, PLM, SAXS, and 2D WAXD. The results show that the molar ratio and the length of spacer are also important factors that influence the LC behaviors of these complexes.PVTA(PHTC6)0.5 exhibits a columnar nematic(Coln) phase, and its LC behavior is not affected by temperature. PVTA(PHTC6)1 forms a hierarchical nanostructure, where the Tp moieties can pack orderly to form a discotic nematic(ND) phase among with the hexagonal columnar(Colh) phase formed by the complex as a whole at ambient temperature. And PVTA(PHTC6)1 transforms to the Coln phase when the temperature is high enough due to the isotropization of Tp moieties in the side chains. Both PVTA(PHTC12)0.5 and PVTA(PHTC12)1 form a hierarchical structure with a ND phase and a Coln phase formed by the complexes as a whole with increasing length of the spacer.