Characterization and thermal-oxidative degradation behavior of poly(ethylene terephthalate-co-4,4'-bibenzoate) prepared via direct esterification technique

A series of poly(ethylene terephthalate-co-4,4'-bibenzoate)s (PETBBs) were prepared via direct esterification from the monomers of terephthalic acid (TPA), 4,4'-biphenyl dicarboxylic acid (BPDA), and ethylene glycol (EG) with different molar ratios. The chemical compositions of the obtained PETBBs, investigated by H1-NMR, were identical with the feed ratio, and the high molecular weights of PETBBs were confirmed by GPC analysis. The glass transition, crystallization, and melting behavior of them were measured by DSC; the results indicated that, in the range of 525 mol% of BPDA addition, the glass transition temperature (Tg) increased almost linearly and the melting temperature (Tm) decreased with increasing content of BPDA unit. As expected, the crystallization of PETBB became difficult with increasing introduction of BPDA, explained by higher crystallization temperature and smaller crystallization enthalpy from the glassy state. This decrease of crystallization rate may be beneficial to film processing. Moreover, owing to the introduction of rigid-rod BPDA unit, the initial and maximum thermal-oxidative decomposition temperatures were enhanced. The kinetic analysis of the thermal-oxidative degradation indicated that the apparent activation energies of degradation for these PETBBs became higher than that of PET. POLYM. ENG. SCI., 2012. (C) 2012 Society of Plastics Engineers