FUNCTIONAL POLYMERS AND SEQUENTIAL COPOLYMERS BY PHASE-TRANSFER CATALYSIS .25. TRANSFORMATION OF A MONOTROPIC MESOPHASE INTO AN ENANTIOTROPIC ONE BY INCREASING THE MOLECULAR-WEIGHT OF THE POLYMER AND BY COPOLYMERIZATION

The influence of molecular weight on thermal transitions and on the thermodynamic parameters was studied for two polymers based on 4,4 prime - dihydroxy- alpha - methylstilbene with either 1,9-dibromononane (HMS-C9 polyethers) or 1,11-dibromoundecane (HMS-C11 polyethers). HMS-C9 polyethers present an enantiotropic nematic mesophase over the entire range of molecular weights and a monotropic smectic mesophase for polymers of number average molecular weights higher than 17,000. The low molecular weight HMS-C11 polyethers are only crystalline. On increasing their molecular weight, the polymers become monotropic nematics, and at higher molecular weights, enantiotropic nematics. The thermodynamic parameters of isotropization for both polyethers and copolyethers are compared and suggest that copolymerization does not significantly decrease the degree of order of the mesogenic units in the mesomorphic phase.