Study Of Structural Designs Of Liguid Crystal Molecules And Their Applications In Materials

In this study, several novel types of liquid crystal molecules such as liquid crystal dimers, liquid crystal dendrimers and hyperbranched liquid crystal polymers were synthesized. The structure-property relationships of these novel liquid crystal molecules were discussed. Novel techniques of transformation of these molecules into constructural materials were proposed.Twelve symmetrical liquid crystal dimers (Ml-n, M2-n, M3-n) with different spacers and different mesogenic units were synthesized. All of the dimers displayed Smectic mesophase. Phase transition temperatures and smectic layer spacing both obeyed odd-even effect. Mesogeic units with larger draw ratio would enhance the stability of mesophases. Liquid crystal dimers were used to prepare thermoset materials with high crosslinking density according to hydrosilylation method. These materials possessed "hard and strong" properties.Four Schiff-base typed liquid crystal dendrimers (M1-DAB, M2-DAB, Ml-PAMAM, M2-PAMAM) with different dendritic cores and different mesogenic units were synthesized. All of the dendrimers displayed SmA mesophase except Ml-PAMAM. The rigidity of the dendritic core would hinder the formation of mesophase. Liquid cyrstal dendrimers from mesogenic unit with high draw ratio showed a more stable mesophase.Two vinyl-terminated liquid crystal dendrimers (G1-(MU)4and G2-(MU)8) with dendritic polyols as the core were synthesized. Both of the dendrimers exhibited SmA mesophase. This phenomenon indicated that dendrimers without "promoting groups" could also show a mesophase. Thermoset elastomers G1-TDS and G2-TDS were prepared via hydrosilylation reaction beween vinyl-terminated liquid crystal dendrimers (G1-(MU)4and G2-(MU)8) and siloxane crosslinker. These two elastomers were confirmed of excellent elasticity and strength. The layer packing of the previous liquid crystal dendrimers were reserved in the crosslinking network of the elastomers.Mesogenic functionalization of CNT was performed by grafting of hyperbranched polyglycerol (HPG) and mesogenic units successively to afford CNT-HPG-LC. Then in-situ crosslinked liquid crystal dendrimer/CNT nanocomposites were prepared by using G2-(MU)8as the matrix and CNT-HPG-LC as the additive. It was concluded that this nanocomposite exhibited much higher modulus than that of pure elastomer. Moreover, large layer spacing was observed in the in-situ crosslinking network.Two novel types of liquid crystal epoxy resins, liquid crystal dimeric epoxy resin (Dimer-EP-1and Dimer-EP-2) and hyperbranched liquid crystal epoxy resin (HPG-LCER) were synthesized. Both of the two dimeric epoxy resins exhibited SmC mesophase. Dimer-EP-2with large draw ratio possessed extremely wide mesogenic temperature range. Non-isothermal curing kinetics of Dimer-EP/DDM systems indicated the high reactivity between liquid crystal dimeric epoxy resins and diamine. Hyperbranched epoxy resin HPG-LCER displayed nematic mesophase. Moreover, HPG-LCER was demonstrated to be a self-curing hyperbranched liquid crystal epoxy resin.