SIDE-CHAIN LIQUID-CRYSTALLINE COPOLYMERS CONTAINING SPACERS OF DIFFERING LENGTHS

A series of side-chain liquid-crystalline copolymers, the poly[4-1-(4-methoxy-4'-oxyazobenzene)-8-octyl]oxystyrene]-co-poly[4-[alpha-(4-methoxy-4'-oxyazobenzene)-omega-alkyl]oxystyrene]s, has been prepared in which the second spacer is varied in length from 3 methylene units up to 12. The properties of the copolymers are compared with those of the homopolymers, the poly[4-[alpha-(4-methoxy-4'-oxyazobenzene)-omega-alkyl]-oxystyrene]s. All the polymers exhibit smectic behavior with the exception of the propyl homopolymer, for which no mesophase is observed. The transition temperatures of the copolymers are similar to the mean values of the homopolymers. The largest deviations from this behavior are observed for copolymers containing either propyl or butyl spacers. In contrast the transitional entropies exhibited by the copolymers show significant negative deviations with the exception of dodecyl-octyl copolymer, for which a small positive deviation is observed. We interpret these differences in terms of steric factors.