STUDY OF THE CONFORMATIONAL DISORDER IN POLYESTERS GIVING LIQUID-CRYSTALLINE PHASES

Conformational and packing energy analyses have been performed by mole cular mechanics calculations on the polyester derived from the condens ation of 2-(4-hydroxyphenyl)-6-hydroxybenzoxazole with terephthalic ac id, which presents a high degree of crystallinity in spite of the head -to-tail constitutional disorder. The line repetition groups in accord ance with the experimental value of the c axis have been taken into ac count. Possible conformations of chains having constitutional and conf ormational disorder in the crystalline phase have been proposed. Packi ng energy calculations performed on pairs of chains give the close pac king distances and indicate the best symmetry elements. The results ar e in agreement with the unit cell obtained by X-ray data, the thermody namical properties of the polymer and the existence of liquid-crystal phases.