Preparation and properties of poly(urethane-imide)s derived from amine-blocked-polyurethane prepolymer and pyromellitic dianhydride

Poly(urethane-imide)s were prepared using amine-blocked-polyurethane (PU) prepolymer and pyromellitic dianhydride. The PU prepolymers were prepared by the reaction of different diols (polypropyleneoxy glycol, polytetramethyleneoxy glycol, polycaprolactonediol and hydroxyl terminated polybutadiene) and different diisocyanates (2,4-tolylene diisocyanate, 1,4-phenelene diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate and 4,4^′-methylenebis(cyclohexyl)isocyanate) and end capped with N-methylaniline. The polymerization was faster with aromatic isocyanates than with aliphatic isocyanates. The effect of imide content on the thermal and mechanical properties was studied. The poly(urethane-imide)s were characterized by FTIR, GPC, TGA and for dynamic and static mechanical properties. Weight average molecular weight (M_w) of the polymers did not vary significantly with change in -NCO/-OH ratio where as number average molecular weight (M_n) increased with increasing -NCO/-OH ratio, correspondingly, the dispersity (PD) decreased. Polymers with higher hard segment content exhibited higher glass transition temperature. The thermal stability of the PU was found to increase significantly by the introduction of imide component.