Thermotropic liquid‐crystalline aromatic‐aliphatic polyimides, 1. Novel poly(imide‐carbonate)s containing pyromellitimide ring

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Abstract
Semi‐rigid poly(imide‐carbonate)s with high inherent viscosities were synthesized in high yields by melt polycondensation of the monomer, N,N′‐bis(6‐hydroxyhexyl)pyromellitdiimide and/or 6,6′‐(4,4′‐biphenylylenedioxy)dihexanol with alkylene bis(phenyl carbonate)s (m = 6, 8, 10 and 12). The monomer was prepared by deacetylation of an intermediate diacetylated compound derived from the condensation of pyromellitic dianhydride with 6‐aminohexanol followed by cyclization with acetic anhydride. The resulting polymers were characterized by FTIR and 13C NMR measurements and elemental analyses. The thermal and mesomorphic properties were evaluated by polarizing microscope observation, DSC measurements and powder X‐ray analyses. The polymers showed very good solubilities in organic solvents such as chloroform and 1,4‐dioxane. Flexible and tough films were cast from the chloroform solutions. All the polymers have low glass transition temperatures below room temperature which decreased with increase of the aliphatic spacer lengths. Most of the polymers display no thermotropic liquid‐crystalline properties, but only the biphenyl unit‐rich copolymer exhibits a nematic melt. It is suggested that the mesogenic character of the pyromellitimide ring is very low.