Transformation of a monotropic mesophase into an enantiotropic mesophase by copolymerization of the parent polymers' monomer pair containing constitutional isomeric mesogenic side groups

Abstract

Abstract : The synthesis and the mesomorphic behavior of poly(methylsiloxane)s containing 4-methoxy-4'-hydroxy-trans-alpha-methylstilbene (4-n-PS) and 4-hydroxy-4'-methoxy-trans-alpha-methylstilbene (4'-n-PS) connected to the backbone by flexible spacers containing three, six and eleven (n = 3, 6, 11) methylene units, and of some copolymers based on these two constitutional isomeric mesogenic side groups (4,4' (A/B)-n-coPS) is described. The copolymers derived from structural units whose homopolymers displayed enantiotropic mesophases (4,4'(A/B)-3-coPS and 4,4' (A/B)-11-coPS) exhibited a depression of both mesomorphic and crystalline phase transition temperatures. However, the 4, 4' (50/50)-6-coPS copolymers, derived from structural units whose homopolymers (4-6-PS and 4'-6-PS) displayed nematic monotropic mesophases, exhibited an enantiotropic nematic mesophase. Liquid crystal polymers, Monotropic, Enantiotropic.