Thermotropic behavior of side-chain liquid-crystalline copolymers from maleic anhydride and mesogen-containing methacrylates

Side-chain liquid-crystalline copolymers (SCLCPs) were synthesized by copol ymerization of maleic anhydride (MA) and mesogenic methacrylates. For copol ymers with a hexyl spacer and methoxybiphenyl mesogens. smectic A1 and smec tic E1 mesophases are observed. Furthermore, it has been found that the iso tropization temperature increases and the width of the monotropic smectic A 1 mesophase decreases with increasing MA content. For methoxybiphenyl-conta ining copolymers with about 25 mol-% MA, the glass transition temperature d ecreases with increasing spacer length, whereas the isotropization temperat ure shows little dependence on spacer length, although a small odd-even eff ect is observed. For octyl or shorter spacers, these polymers exhibit a sme ctic E mesophase, whereas for longer spacers smectic B mesophases were obse rved. These mesophases are succeeded by a smectic Al mesophase for SCLCPs w ith heptyl or longer spacers. SCLCPs with cyanoazobenzene mesogens exhibit only a smectic Ad mesophase, whereas SCLCPs with cyanobiphenyl mesogens are not liquid crystalline.