Synthesis and properties of photochromic cholesteric liquid crystalline polysiloxane containing chiral mesogens and azobenzene photochromic groups

摘要

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-4'-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-8 to P-12. They showed thermotropic liquid crystalline properties in a broad mesogenic region at temperatures >100 degreesC. 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 similar to320 degreesC. 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. (C) 2002 Wiley Periodicals, Inc. [References: 19]