TRANSESTERIFICATION IN BLENDS OF WHOLLY AROMATIC THERMOTROPIC COPOLYESTERS

The X-ray diffraction data for the copolyesters prepared from p-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) give nonperiodic layer lines that indicate a completely random monomer sequence distribution and also provide analytical information on the monomer proportions. Hence, these data provide a unique method to study transesterification between copolyesters with different monomer ratios. Immediately after melt blending, mixtures of the 30/70 and 75/25 copolymers exhibit a single solid-nematic transition at a temperature well below either the transitions of the starting copolymers or those of intermediate compositions. However, the meridional maxima for both starting copolymers can be resolved in the fiber diffraction patterns, which indicates the formation of a compatible blend. Compression molding of the melt-blended samples at 315-degrees-C results in transesterification, leading to a random copolymer of intermediate composition after 1 h. The progress of this reaction is followed by monitoring the shift in position of the first meridional maxima as a function of time, until they merge to give a single maximum at the d-spacing characteristic of the random copolymer of intermediate composition. During this process, the temperature of the solid-nematic transition slowly rises until it reaches the value for the intermediate composition.