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Synthesis and thermal behavior of new poly(ethylene terephthalate‐imide)s

Copoly(ethylene terephthalate-imide)s (PETIs) were synthesized by the melt copolycondensation of bis(2-hydroxyethyl)terephthalate with a new imide monomer, N,N'-bis[p-(2-hydroxyethoxycarbonyl)phenyl]-biphenyl-3,3',4,4'-tetracarboxydi-imide (BHEI). The copolymers were characterized by intrinsic viscosity, Fourier transform infrared, 1 H NMR, differential scanning calorimetry, and thermogravimetric analysis techniques. Although their crystallinities decreased as the content of BHEI units increased, the glass-transition temperatures (T g ) increased significantly. When 5 or 10 mol % BHEI units were incorporated into poly(ethylene terephthalate), T g increased by 10 or 24 °C, respectively. The thermal stabilities of PETI copolymers were about the same as the thermal stability of PET, whereas the weight loss of PETIs decreased as the content of BHEI units increased.