Preparation and thermal properties of semi-rigid homopoly(imide–carbonate)s composed of symmetric aromatic diimide units using diphenyl carbonate

New aromatic–aliphatic homopoly(imide–carbonate)s composed of symmetric aromatic diimide rings (3,4,3′,4′-biphenyltetracarboxdiimide, 3,4,3′,4′-benzophenonetetracarboxdiimide and 3,4,3″,4″-p-terphenyltetracarboxdiimide), aliphatic chains (tetra, penta and hexamethylene) next to the imide rings and carbonate linkage were prepared by melt polycondensation from dialcohols of the diimides and diphenyl carbonate in the presence of zinc acetate according to the ordinary procedure and the effect of the polymer structures on thermotropic liquid crystalline (LC) properties was discussed. Differential scanning calorimetry measurements, polarizing microscope observations and miscibility tests indicated that the homopolymers composed of the 3,4,3″,4″-p-terphenyltetracarboxdiimide and 3,4,3′,4′-biphenyltetracarboxdiimide units, and hexamethylene chain form thermotropic LC phase, but the others have no LC melts. It is suggested that the aliphatic chains next to the imide rings play an important role in the LC formation of the semi-rigid poly(imide–carbonate)s having the symmetric diimide rings.