The substitution of poly@-phenylene terephthalate) and poly@-phenylene terephthalamide) with phenyl and biphenylyl substituents (Cbiphenylyl and 2-biphenylyl) in the terephthalic acid unit lowers the melting temperatures and crystallization tendency and increases the solubility. The melting temperatures of the polyesters are in the range of 285 -350 "C. Melting of the polyamides occurs between 440-490 "C. The polyamides begin to decompose in the same temperature range. In polyesters as well as in polyamides the 2-biphenylyl substituent was found to be more effective in decreasing the crystallinity, lowering the melt transition temperatures and increasing the solubility.
The synthesis of aromatic liquid-crystalline polyesters soluble in common organic solvents is described. The polyesters carry methyl, tert-butyl, phenyl and 4-biphenyl substituents. The polyesters with biphenyl substituents have an isotropization temperature below 300 "C. Blends of these polyesters with polycarbonate show one glass transition temperature in differential scanning calorimetry whereas transmission electron microscopy indicates a homogeneous dispersion of the polyester in the polycarbonate, but not on a molecular level. The moduli of the components of the blends are additive.
Properties of pure polyestersPolyesters 1-3 (Scheme 1) were synthesized by a melt polycondensation using the acyl chlorides of the corresponding terephthalic acids and a substituted hydroquinone. a) Present address: Zentrale Polymerforschung,
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