KINETICS OF MESOPHASE TRANSITIONS IN THERMOTROPIC COPOLYESTERS .4. PENDANT SIDE-GROUP EFFECT

A series of five poly(phenyl-p-phenylene terephthalate)-co-(1-phenylethyl-p-phenylene terephthalate) copolyesters having different compositions of p-benzenedicarboxylic acid (TPA), phenylhydroquinone (PHQ), and (1-phenylethyl)hydroquinone (PEHQ) have been studied via wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). A systematic analysis of the crystal unit-cell parameters indicates that they change continuously with composition. Nonisothermal DSC experiments lead to a complete phase diagram of both solidus and liquidus lines as a function of PHQ (or PEHQ) composition in the copolyesters. The phase diagram indicates solid solution behavior of the isodimorphic type in this series of copolyesters. Isothermal crystallization kinetics reveals two transition processes when the experiments were conducted below the solidus line: a fast transition process occurs during quenching; and a slow transition process takes place during subsequent annealing. The influence of the composition, and, therefore, the pendant side-group effect, on the transition kinetics can be observed.