SIDE-CHAIN LIQUID-CRYSTALLINE COPOLYMERS .2. POLYSTYRENE-BASED SIDE-CHAIN POLYMERS CONTAINING NITROAZOBENZENE

Two new series of side-chain liquid-crystalline copolymers, the poly[4-[1-(4-nitro-4'-oxy-azobenzene)-8-octyl]oxystyrene]-co-poly[4-[alpha-(4-nitro-4'-oxyazobenzene)-o mega-alkyl]oxystyrene]s and the poly[4-[1-(4-nitro-4'-oxyazobenzene)-9-nonyl]oxystyrenel-co-poly[4-[alpha-nit ro-4'-oxyazobenzene)-omega-alkyl]oxystyrene]s, have been prepared in which the second spacer is varied in length from 3 to 12 methylene units. All the copolymers exhibit a smectic phase identified using polarizing microscopy. The thermal behavior of the copolymers has been investigated and is compared with that of the analogous homopolymers. To make such comparisons, we scale the transition temperatures of the copolymers with respect to the mean temperatures of the respective homopolymers. The deviations from ideal behavior in all cases are very small. By comparison, the entropy changes associated with the smectic-isotropic transition for the copolymers are more sensitive to changes in the molecular structure. We discuss these results in terms of the interaction parameters between the mesogenic cores and the formation of antiparallel dimers which serve to minimize the dipolar energy.