Synthesis and properties of photochromic liquid-crystalline copolymers containing both spironaphthoxazine and cholesteryl groups

Abstract

Photochromic liquid-crystalline copolymers consisting of a photochromic monomeric unit containing both a spironaphthoxazine group and an undecamethylene spacer, and a liquid-crystalline monomeric unit containing both a cholesteryl group and a decamethylene spacer were prepared to investigate the effect of the thermal properties of the photochromic monomeric unit on the mesomorphic order of the side chain of the related copolymers. The photochromic liquid-crystalline copolymers containing a photochromic liquid-crystalline monomeric unit showed only a smectic phase. On the other hand, the photochromic liquid-crystalline copolymers containing a photochromic non-liquid-crystalline monomeric unit showed a chiral nematic phase (cholesteric phase). The photochromic chiral nematic liquid-crystalline copolymer containing 14 mol % photochromic monomeric unit reflected visible light around 104 °C. To lower the temperature range of reflection of visible light, cholesteryl oleyl carbonate was used as a chiral nematic plasticizer for the photochromic chiral liquid-crystalline polymer systems. Photo-induced pitch change of the mixture by means of UV irradiation was investigated and it was concluded that the pitch change observed under UV irradiation was mainly induced by thermal effect in the case of our system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 887–894, 2000