ANALYSIS OF SMECTIC STRUCTURE FORMATION IN LIQUID-CRYSTALLINE THERMOSETS

Smectic network formation using a twin liquid crystalline epoxy monome r (4-(oxiranylmethoxy)benzoic acid 1,8-octanediylbis(oxy-4,1-phenylene ) ester) cross-linked with sulfanilamide was examined in real time by polarizing optical microscopy, X-ray diffraction, dynamic viscometry a nd differential scanning calorimetry. The initial curing reaction of t he twin epoxy monomer and sulfanilamide was found to be diffusion cont rolled because of the heterogeneity of the system. An acceleration of the curing rate was observed a critical time after the start of the re action. It was found that the adduct of the twin epoxy monomer and sul fanilamide produced a smectic phase even though the twin epoxy monomer itself only displayed a nematic phase. The strong interaction of the sulfonamide function may contribute to the formation of smectic order. A change in curing behaviour took place when the curing reaction was carried out above similar to 170 degrees C. Above this transition regi on, a smectic phase forms directly from an isotropic melt. On the othe r hand, below this transition, the smectic phase forms via a transient nematic phase. Cross-linking causes fine disclination lines in the op tical texture as well as a decrease of the smectic layer spacing. (C) 1997 Elsevier Science Ltd.