Studies on the odd-even effect of methylene spacers in poly(pyromellitimide-ester)s

Three series of poly(pyromellitimide-ester)s were synthesized from various N,N'-bis(w-hydroxyalkyl)pyromellitimides (HAPMIs) by melt condensation with dicarboxylic acids, including terephthalic acid (TPA), 4,4'-biphenyldicarb oxylic acid (BPDA), and 4,4'-azobenzenedicarboxylic acid (ABDA). Polymers w ere characterized by elemental analysis, solubility, inherent viscosity, sp ectra (IR, IH-NMR, C-13-NMR), and X-ray diffraction (XRD). Thermal stabilit y and phase transition behaviour were evaluated by thermogravimetric analys is (TGA), differential scanning calorimetry (DSC), and hot-stage optical po larized microscopy (HOPM). The d-spacings, calculated from XRD data, showed an odd-even effect with varying numbers of methylene spacers. Crystallinit y of polymers decreased in the following order: azobenzene > biphenyl > phe nyl polymers. Similarly, DSC-obtained melting temperatures (T-m's) showed a n odd-even effect, and glass transition temperatures (T-g's) decreased with increasing numbers of methylene spacers. Thermal stability decreased as me thylene chain length increased. Thermal stability of polymers occurred in t he following order: phenyl > biphenyl > azobenzene polymers. (C) 1999 John Wiley & Sons, Inc.