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

Side-chain liquid-crystalline copolymers (SCLCPs) were synthesized by copolymerization of maleic anhydride (MA) and mesogenic methacrylates. For copolymers with a hexyl spacer and methoxybiphenyl mesogens, smectic A1 and smectic E1 mesophases are observed. Furthermore, it has been found that the isotropization temperature increases and the width of the monotropic smectic A1 mesophase decreases with increasing MA content. For methoxybiphenyl-containing copolymers with about 25 mol-% MA, the glass transition temperature decreases with increasing spacer length, whereas the isotropization temperature shows little dependence on spacer length, although a small odd-even effect is observed. For octyl or shorter spacers, these polymers exhibit a smectic B mesophase, whereas for longer spacers smectic B mesophases were observed. These mesophases are succeeded by a smectic A1 mesophase for SCLCPs with heptyl or longer spacers. SCLCPs with cyanoazobenzene mesogens exhibit only a smectic Ad mesophase, whereas SCLCPs with cyanobiphenyl mesogens are not liquid crystalline