Microphase separation behaviour in a series of thermotropic liquid crystalline copolyethers

Abstract The phase transition and microphase separation behaviour have been studied by means of differential scanning calorimetry, polarizing microscopy, depolarizing transmittance and X-ray diffraction measurements for a series of thermotropic liquid crystalline random copolyethers. These are composed of two similar aromatic azomethine ether units, derived from 3,3′-dimethoxy-4,4′-diformyl-α,ω-diphenoxyhexane with 4,4′-diaminodiphenylmethane (system A) and with 4,4′-phenylenediamine (system B). These copolymers, with the exception of those containing a high content of the A component, were found to transform from a crystalline to 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. After this, the A domains are transformed directly into the isotropic state, while the B segments can still form special mesomorphic domains. A phase diagram for these copolymers was also obtained: the melting points of the crystalline domains formed by segments of the A component were found to be only slightly changed with variation in the component content, while the melting and the isotropization transition temperatures of the B component domains were lowered significantly with decreases in the B component content.