Modification of Side-Chain Liquid-Crystalline Poly(maleic anhydride-alt-1-alkene)s with Mesogen-Containing Alcohols

Side-chain liquid-crystalline copolymers from maleic anhydride and 1-alkenes carrying biphenyl mesogens have been modified by reaction of the anhydride moieties with different mesogenic alcohols to give maleic acid monoesters. FTIR and 1H NMR showed high degrees of modification. Grafting methoxybiphenyl-containing alcohols having different spacer lengths onto methoxybiphenyl-containing polymers yielded polymers exhibiting smectic A mesophases with a variable degree of interdigitation. The glass transition temperature decreased with spacer length, whereas the isotropization temperature remained almost constant. Grafting azobenzene-containing alcohols onto methoxybiphenyl-containing copolymers yielded side-chain liquid-crystalline polymers exhibiting nematic mesophases. The effect of the 4‘-azobenzene terminal group on the temperature window of the mesophase was CN > OMe > F > H. Grafting a cyanostilbene-containing alcohol onto a methoxybiphenyl-containing copolymer resulted in a polymer that exhibited a smectic E mesophase with complete interdigitation of side chains. Introducing methoxybiphenyl mesogens into cyanobiphenyl-containing copolymers or vice versa resulted in polymers with smectic A mesophases. Furthermore, an increase in isotropization temperatures was observed in comparison with polymers carrying only one type of mesogen. This indicates specific favorable interactions between unlike mesogens.