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A series of novel thermotropic side-chain liquid crystalline polymers(P 0 -P 12 ) were synthesized by grafting copolymerization of mesogenic monomer cholesteryl undecylenate (M1) and photochromic monomer 4-allyoxy-4Ј-nitroazobenzene (M2) on polymethylhydrosiloxane. The chemical structures of polymers were characterized by infrared (IR) and ultraviolet (UV) spectroscopy. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to measure the thermal properties of those polymers, and the mesogenic properties were characterized by polarized optical micrograph, DSC, wide-angle X-ray diffraction and small-angle X-ray scattering. The glass transition temperatures (T g s) of the polymers increased from P 0 to P 4 and decreased from P 5 to P 12 . The clearing point temperatures (T i s) of the polymers P 1 -P 12 were lower than that of P 0 , but increased from P 1 to P 4 and decreased from P 5 to P 12 . They showed thermotropic liquid crystalline properties in a broad mesogenic region at temperatures Ͼ100°C. The polymers P 0 -P 8 exhibited a cholesteric mesophase with oily streaks and lined texture, and polymers P 9 -P 12 showed a chiral smectic mesogenic phase with a layered texture. All of the polymers were thermally stable to ϳ 320°C. The UV-induced trans-cis photoisomerization was investigated for the azo monomer and polymers P 8 and P 12 . The solution of the azo monomer and liquid crystalline polymers P 8 and P 12 can undergo photoisomerization, and the environments of the azo group were responsible for the aforementioned photochemical process.

A series of ionic liquid-crystalline (LC) elastomers were synthesized by using chemical crosslinking agents containing sulfonic acid groups, which were siloxane-based materials. A ionic divinyl monomer 2,2′-(1,2-ethenediyl)bis [5-[(4-undecenoyloxy)phenyl]azo]benzenesulfonic acid was used as chemical cross-linking agent. Cholest-5-en-3-ol(3 )-10-undecenoate was synthesized as a liquid-crystalline monomer. The effective cross-link density of the ionic elastomers was determined by swelling experiments in organic/buffer mixtures. Their liquid-crystalline properties were characterized by DSC, POM, and SAXS. A proposed multilayer buildup containing LC segment structure and ionic cross-linking lamellar structure separated by siloxane chains was given. The ion aggregated in domains forces the siloxane chains to fold and form an irregular lamellar structure. The ionic cluster lamellae may be tangled with the rigid mesogenic groups of LC segments to form multiple blocks. Liquid-crystal mesophase region of the polymers become narrow with increasing ionic cross-linking content.

ABSTRACT:A new series of network liquid crystal polymers were synthesized by graft copolymerization of the difunctional mesogenic monomer 4-allyloxy-benzoyloxy-4Ј-allyloxybiphenyl (M) upon polymethylhydrosiloxane (PMHS). Monomer M acted not only as a mesogenic unit but also as a crosslinker for the network polymers. The chemical structures of the polymers were confirmed by IR spectroscopy. DSC, TGA, and X-ray scattering were used to measure their thermal properties and mesogenic properties. The glass transition temperature (T g ) of these network liquid crystal polymers was increased when the monomer was increased, and T d (temperature of 5% weight loss ) at first went up and reached a maximum at P 1 , then went down. The slightly crosslinked polymers (P 0 , P 1 ) show rubber-like elasticity, so it was called liquid-crystal elastomer. Network polymers will lose elasticity property with a highly crosslinked degree, and turn into thermosetting polymers (P 4 , P 5 ). All polymers exhibited a smectic texture by X-ray scattering.

Liquid-crystalline monomer cholesteryl 4-allyloxybenzoate (M 1 ), new ionic mesogenic monomer cholesteryl 4-allyloxy-3-(potassium sulfonate)benzoate (M 2 ), and corresponding polymer P 1 and ionomer P 2 were synthesized. The chemical structures of the monomers and homopolymer were confirmed with Fourier transform infrared and 1 H-NMR spectroscopy. The mesogenic properties were studied with differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction measurements. The effect of the ionic units on the phase behavior was examined. M 1 showed a cholesteric phase, and M 2 revealed a smectic A phase. P 1 and P 2 displayed smectic A phases. The experimental results demonstrated that the addition of ionic units to the mesogenic molecule not only affected the phase-transition temperature but also changed the mesogenic phase type.