A series of thermotropic side-chain liquid-crystalline ionomers (LCIs) containing 4-(4-alkoxybenzyloxy)-4'-allyloxybiphenyl (M) as mesogenic units and allyl triethylammonium bromide (ATAB) as nonmesogenic units were synthesized by graft copolymerization upon polymethylhydrosiloxane. The chemical structures of the polymers were confirmed by IR spectroscopy. DSC was used to measure the thermal properties of these polymers. The mesogenic properties were characterized by polarizing optical microscopy, DSC, and X-ray diffraction. Homopolymers without ionic groups exhibit smectic and nematic mesophases. The nematic mesophases of the ionomers disappear and the mesomorphic temperature ranges decrease with increasing concentration of ionic units. The influence of the alkoxy chain length on clearing temperature (T-c) values of ionomers clearly shows an odd-even effect, similar to that of other side-chain liquid-crystalline polymers. The mesomorphic temperature ranges increase with increasing alkoxy chain length when the number of alkoxy carbon is over 3. (C) 2003 Wiley Periodicals, Inc.