POLY(URETHANE-IMIDE)S FROM BLOCKED POLYURETHANE PREPOLYMER AND PYROMELLITIC DIANHYDRIDE: EFFECT OF ALKALI METAL ALKOXIDES AND PHENOXIDES AND SUBSTITUENTS ON THE BLOCKING AGENT IN THE POLYMERIZATION REACTION

Abstract

Poly(urethane-imide)s were prepared using a series of N-methylaniline-blocked polyurethane (PU) prepolymers. The PU prepolymer was prepared using polypropylene glycol of molecular weight 2000 and tolylenediisocyanate, and masked with N-methyl aniline, N-methyl-p-anisidine and N-methyl-p-nitroaniline. The blocked PU prepolymer was reacted with pyromellitic dianhydride (PMDA) to yield poly(urethane-imide). The effect of alkali metal alkoxides (sodium methoxide and potassium methoxide) and alkali metal phenoxides (sodium phenoxide, potassium phenoxide, potassium p-methoxyphenoxide and potassium p-nitrophenoxide) as catalysts was studied for the polymerization reaction between blocked prepolymer and PMDA. Phenoxides were found to have effective catalytic activity for the polymerization. Electron withdrawing substituents tend to enhance the catalytic activity of phenoxides while electron donating substituents tend to reduce. The polymerization was faster with N-methyl-p-anisidine blocked PU prepolymer and slower with N-methyl-p-nitroaniline blocked PU prepolymer as compared to the polymerization with unsubstituted N-methylaniline blocked PU prepolymer. The poly(urethane-imide)s were characterized by FTIR, GPC, TGA, and DSC analyses. The thermal stability of the PU was found to increase by the introduction of imide component.