STRUCTURE OF A MESOMORPHIC POLYMER - POLY(HEXAMETHYLENE 4,4'-BIPHENYLDICARBOXYLATE) .2. THE POLYMER

The title polymer, P6BP, was studied by X-ray fiber diffraction and differential scanning calorimetry. Three solid crystalline forms (alpha, beta, and gamma) and the mesophase S-A were observed. The transformation temperatures are alpha- to beta-form (200-208 degrees C), beta- to gamma-form (210-216 degrees C), gamma-form to S-A (216 degrees C), and S-A to isotropic liquid (227 degrees C). The three crystalline forms belong to the monoclinic system. The unit-cell dimensions are a = 10.98 Angstrom, b = 11.47 Angstrom, c = 19.62 Angstrom, and beta = 89.7 degrees (alpha-form); a = 13.39 Angstrom, b = 12.84 Angstrom, c = 39.19 Angstrom, and beta = 84.7 degrees (beta-form); a = 9.70 Angstrom, b = 9.20 Angstrom, c = 19.39 Angstrom, and beta = 83.0 degrees (gamma-form). The structures of the alpha- and gamma-forms were established using the model-compounds' structural information which was obtained in the first part of this work. The polymer chains in the alpha- and gamma-forms are composed of the aliphatic sequences in the all-trans conformation, but the dihedral; angles formed between the aromatic rings of the biphenyl groups are 40 and 19 degrees, respectively. The unit cell of the alpha-form contains six chains which are packed in the ''face-to-face'' pattern with respect to the aromatic groups. The four chains in the unit cell of the gamma-form pack in the herringbone pattern. The chain arrangements in the beta-form and in the S-A mesophase are also proposed. An abnormal phenomenon in the diffraction pattern, preferred tilt of the c-axis related to fiber, was found in the gamma- and alpha-forms, which was described quantitatively and explained.