Synthesis And Properties Of Side-chain Cholesteric Liquid Crystalline Elastomers

Cholesteric liquid crystalline polymers (LCPs) combine the basic features of orientational-order and positional-order of cholestericLC molecules with physical properties of polymers. Cholesteric liquid crystalline Elastomers (LCEs) combine unique optical properties of cholesteric LC with good mechanical property, thermal and chemical stabilities of polymer networks, which have been an important research project in the field of LCPs. Therefore, study on cholesteric LCEs holds not only important theoretical purpose, but also potential applications in numerous areas, especially in the fields of piezoelectric materials and nonlinear optics etc. However, to the best of our knowledge, little research on cholesteric LCEs has been reported. Therefore, it is necessary and interesting to study cholesteric LCEs, which is not only affluent in the content of LCPs, but also provides theoretical basis and novel thought to synthesize cholesteric LCEs with special optical properties. Moreover, they provide necessary experimental data and technology to explore their application in piezoelectric and anti-fogery areas on cholesteric LCEs.In this dissertation, ten monomers (M1～M10) and five series of cholesteric LCPs and LCEs (P1～P5 series) were synthesized, which include 4-allyloxybiphenyl-4'-cholesteryloxycarbonylvalerate (M1),4-allyloxybenzoyloxyphenyl-4'-cholesteryloxycarbonyl valerate (M2),4-allyloxybenzoyloxybiphenyl-4'-cholesteryloxycarbonylvalerate (M3), 4-allyloxybiphenyl-4'-cholesteryloxycarbonylvaleryloxybenzoate (M4),4-allyloxybenzoyloxy phenyl-4'-cholesteryloxycarbonylvaleryloxybenzoate (M5),4-allyloxybenzoyloxybiphenyl-4'-menthyloxyacetyloxybenzoate (M6),4-allyloxybenzoyloxyphenyl-4'-menthyloxy acetyloxy benzoate (M7),2-(10-undecylen-1-yloxy)-5-[(4-ethoxybenzoyloxy)biphenyl-4'-oxycarbonyl] valerate (M8), phenyl 4,4'-bis(10-undecylenate) (M9), phenyl 4,4'-bis(10-undecylen-1-yloxy benzoate) (M10). Moreover, the obtained monomers, except M10, and all the polymers are novel. The structures and properties of the obtained LC monomers, crosslinking agent, LCEs were investigated by FT-IR spectroscopy, 1H-NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), and polarizing optical microscopy (POM). Their structure-property relationships were discussed in detail.The LC monomers M1～M8 displayed enantiotropic cholesteric phase, and exhibited oily-streak texture and finger print texture on heating process and focal-conic texture on cooling cycle, which can transforms to oily-streak texture by shearing. For these cholesteric monomers, the melting temperatures (Tm) and clearing or isoropic temperatures (Ti) increased with increasing the rigidity of mesogenic core. M9 did not show any texture and mesomorphic properties. M10 revealed enantiotropic nematic phase and monotropic smectic phase, and exhibited neamtic thread texture on heating process, and nematic droplet texture and smectic fan-shaped texture on heating and cooling cycles. All the elastomers obtained had good thermal stability and thermal decomposition temperature (Td) was greater than 270℃.For cholesteric LCEs P2～P5 series, the effect of the content of crosslinking agent on phase behavior and thermal properties was discussed. They all exhibited cholesteric Grandjean texture. With increasing the concent of non-mesogenic crosslinking agent, Tg of P2 series and P3 series decreased firstly, and then increased; their Ti all decreased. With increasing the concent of mesogenic crosslinking agent, Tg of P4 series and P5 series decreased firstly, and then increased; their Ti firstly decreased and then increased.The research achievement had not only important theoretical purpose, but also provided technological support to study their application in piezoelectric areas.