Interchain exchange and interdiffusion in blends of poly(ethylene terephthalate) and poly(ethylene naphthalate)

The interchain exchange and interdiffusion in blends of poly(ethylene terephthalate) and poly(ethylene naphthalene-2,6-dicarboxylate) are investigated with reprecipitated commercial samples (M _η ～ 10⁴) and samples containing no polycondensation catalyst (M _η ～ 10³) synthesized in the course of this study. The kinetics of multiblock copolymer formation and gradual reduction of the mean block length in quasi-homogeneous blends were shown to fit a simple theoretical model of a second-order reaction. The increase of the reaction-rate constants on the transition from commercial samples to synthesized ones revealed a significant role of chain ends in interchain exchange. The detected activation energy of the interchange in the absence of catalysts (97 kJ/mol) was noticeably less than that previously reported for the polymer pair under study (120–170 kJ/mol). The obtained data were applied for analysing the interdiffusion between melts of the same polymers accompanied by the interchain exchange. By means of the microinterference method, the interdiffusion in the synthesized samples was shown to be much faster than that in the reprecipitated commercial samples, a result that may be due to the better compatibility of the initial polyesters as their molecular mass decreased. In later stages of the process in both systems, the interpenetration of components was slower than that predicted by Fick’s law, owing to formation of copolymer species that diminished the thermodynamical factor of mixing.