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

Three series of poly(pyromellitimide-urethanes)s were synthesized from vari ous N,N'-bis (omega-hydroxyalkyl)pyromellitimides (HAPMIs) and various dica rbooxyloxyl diazides namely terephthaloyl diazide (TPDA), 4,4'-diphenyldiac id azide (BPDAA) and 4,4'-azobenzenediacid azide by solution polycondensati on in DMSO at 75 degrees C in the presence of di-n-butyltin dilaurate as ca talyst. The polymers were characterized by elemental analysis, IR,H-1 and C -13-NMR and X-ray diffraction analysis. Thermal stability and phase transit ion behavior were studied by TGA, DSC, and hot-stage optical polarized micr oscopy (HOPM). T-g values decrease linearly as the number of methylene spac er increases while T-m shows odd-even effect. In a given series, polymers w ith even number of methylene spacers possess higher T-m values than the nei ghboring polymers with odd number of methylene spacers and thermal stabilit y decreases with increase in number of methylene spacers. Thermal stability is also influenced by the aromatic segment present in the polymer backbone , order being : phenyl > biphenyl > azobenzene.