Synthesis of soluble LC‐polyesters

Soluble LC polymers were synthesized with the aim to approach molecular reinforcement. Chemical modification results in a decrease of the crystallinity and an increase of the solubility. Substitution of the amide hydrogen in poly(4‐aminobenzoic acid) by a methyl group reduces the stiffness of the polymer very much, and as a result no lyotropic solutions are obtained. Poly(p‐phenylene terephthalate) with substituents on the hydroquinone or on both monomer units were synthesized. With one phenylalkyl group in the repeating unit the polyesters are crystalline with melting points > 300°C. With two substituents the polymers form in many cases amorphous anisotropic glasses at room temperature. 2‐Biphenyl is the most effective substituent with regard to increase of solubility. These polyesters form isotropic solutions in chloroform. Isotropic films obtained from these solutions become anisotropic on heating above the glass transition temperature. Films of polyester/polycarbonate blends show additivity of E‐modulus with respect to both compounds.