STUDIES ON ODD-EVEN EFFECT OF METHYLENE SPACERS IN POLY(PYROMELLITIMIDE-URETHANE)S

Abstract

Three series of poly(pyromellitimide-urethanes)s were synthesized from various N,N′ -bis(ω-hydroxyalkyl)pyromellitimides (HAPMIs) and various dicarbooxyloxyl diazides namely terephthaloyl diazide (TPDA), 4,4′ -diphenyldiacid azide (BPDAA) and 4,4′ -azobenzenediacid azide by solution polycondensation in DMSO at 75°C in the presence of di-n-butyltin dilaurate as catalyst. The polymers were characterized by elemental analysis,IR, ¹H and ¹³C-NMR and X-ray diffraction analysis. Thermalstability and phase transition behavior were studied by TGA, DSC, and hot-stage optical polarized microscopy (HOPM). T_g values decrease linearly as the number of methylene spacer increases while T_m shows odd-even effect. In a given series, polymers with even number of methylene spacers possess higher T_m values than the neighboring polymers with odd number of methylene spacers and thermal stability 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.

Keywords:

• Poly(pyromellitimide-urethanes)s
• Odd-Even Effect
• Methylene Spacers
• Thermal Stability

Acknowledgments