Thermally stable optically anisotropic polymer networks obtained from mesogenic LC cellulose derivatives

Abstract

The birefringence of anisotropic polymer composites obtained by photopolymerisation of lyotropic liquid crystalline systems composed of (hydroxypropyl)cellulose derivatives (R-PC) and photopolymerisable organic acids that are also lyotropic solvents is studied. The orientation of the systems before photopolymerisation was induced by shearing. The mechanically oriented lyotropic solutions after cessation of shearing form a band texture visible under crossed polarisers. This band texture shows relaxation phenomena and the grain texture observed before shearing recovers with time. The decay time of the relaxation of the band texture at room temperature is much longer than the time of band texture formation after cessation of shearing. The photopolymerisation of acrylic acid (or methacrylic acid) in the oriented R-PC/acid lyotropic solutions leads to birefringent polymer composites. These composites show reversible anisotropic optical properties as examined by thermo-optical analysis (In contrast with the samples before photopolymerisation); therefore they can be classified as reversible anisotropic polymer networks. It is demonstrated that the thermal stability of the birefringence of the R-PC/poly(acid) composites is mainly determined by the molecular mobility of the poly(acid) connected with its glass transition temperature.