Liquid crystalline gels. 3. Role of hydrogen bonding in the formation and stabilization of mesophase structures

Copolymers composed of various amounts of 4'-(11-acryloyloxyundecyloxy)biph enyl-4-carboxylic acid (11ABA) and acrylic acid (AA), poly(11ABA-co-AA)s, w ere synthesized, and their liquid crystalline structures were investigated both in dry and in water-swollen states. Wide- and small-angle X-ray studie s revealed that both dry and swollen poly(11ABA-co-AA)s show a liquid cryst alline structure, which transforms from smectic C with the bilayer (SmC2) t o smectic C with the monolayer (SmC1), when the 11ABA composition, F([11ABA ]/([11ABA] + [AA])), decreases from 0.72 to 0.44. The phase diagram of thes e copolymers was established by changing F and the temperature. It shows th at the samples can build up a liquid crystalline structure for F as low as 0.07 at the elevated temperature of 155 degreesC. The enhanced ordering of the liquid crystalline structure and the thermostability of the copalymers were explained in terms of hydrogen bonding formed between carboxyls of mes ogenic side chains and AA.