THERMALLY STABLE OPTICALLY ANISOTROPIC POLYMER NETWORKS OBTAINED FROMMESOGENIC LC CELLULOSE DERIVATIVES

The birefringence of anisotropic polymer composites obtained by photop olymerisation of lyotropic liquid crystalline systems composed of (hyd roxypropyl)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 m echanically oriented lyotropic solutions after cessation of shearing f orm a band texture visible under crossed polarisers. This band texture shows relaxation phenomena and the grain texture observed before shea ring recovers with time. The decay time of the relaxation of the band texture at room temperature is much longer than the time of band textu re formation after cessation of shearing. The photopolymerisation of a crylic acid (or methacrylic acid) in the oriented R-PC/acid lyotropic solutions leads to birefringent polymer composites. These composites s how reversible anisotropic optical properties as examined by thermo-op tical analysis (in contrast with the samples before photopolymerisatio n); therefore they can be classified as reversible anisotropic polymer networks. It is demonstrated that the thermal stability of the birefr ingence of the R-PC/poly(acid) composites is mainly determined by the molecular mobility of the poly(acid) connected with its glass transiti on temperature.