MICROPHASE SEPARATION BEHAVIOR IN A SERIES OF THERMOTROPIC LIQUID-CRYSTALLINE COPOLYETHERS

The phase transition and microphase separation behaviour have been stu died by means of differential scanning calorimetry, polarizing microsc opy, depolarizing transmittance and X-ray diffraction measurements for a series of thermotropic liquid crystalline random copolyethers. Thes e are composed of two similar aromatic azomethine ether units, derived from imethoxy-4,4'-diformyl-alpha,omega-diphenoxyhexane with 4,4'-dia minodiphenylmethane (system A) and with 4,4'-phenylenediamine (system B). These copolymers, with the exception of those containing a high co ntent of the A component, were found to transform from a crystalline t o a nematic liquid crystalline, and finally to an isotropic phase. For the specimens with 40, 50 and 60 mol% of the A component a microphase separation phenomenon was distinctly observed: segments of the A and B components along the polymer backbones may separately form their own crystalline domains, which melt in different temperature ranges. Afte r this, the A domains are transformed directly into the isotropic stat e, while the B segments can still form special mesomorphic domains. A phase diagram for these copolymers was also obtained: the melting poin ts of the crystalline domains formed by segments of the A component we re found to be only slightly changed with variation in the component c ontent, while the melting and the isotropization transition temperatur es of the B component domains were lowered significantly with decrease s in the B component content.