Direct Synthesis of New Soluble and Thermally Stable Poly(urethane-imide)s from an Imide Ring-Containing Dicarboxylic Acid Using Diphenylphosphoryl Azide Hossein Behniafar Department of Chemistry, Damghan University of Basic Sciences, 3671616549, Damghan, Iran Received 3 May 2005; accepted 16 October 2005 DOI 10.1002/app.23483 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The direct preparation of various aromatic poly(urethane-imide)s from 4-p-biphenyl-2,6-bis(4-trimelliti- midophenyl)pyridine (1) using diphenylphosphoryl azide (DPPA) was investigated. The polymers were mainly ob- tained by the conversion of imide ring-containing diacid 1 to corresponding di(carbonyl azide) 2 with DPPA and then to diisocyanate 3 through the Curtius rearrangement of com- pound 2 followed by polyaddition of 3 in different amounts with aromatic dihydroxy compounds. The molecular weights of the resulting poly(urethane-imide)s were evalu- ated viscometrically. All of the resulted polymers were thor- oughly characterized by spectroscopic methods and elemen- tal analyses. The poly(urethane-imide)s exhibited an excel- lent solubility in a variety of polar solvents. Crystallinity nature of the polymers was estimated by means of WXRD. The glass-transition temperatures of the polymers deter- mined by DSC method were in the range of 191–202°C. The 10% weight loss temperatures of the poly(urethane-imide)s from their thermal gravimetric analysis curves were found to be in the range of 392– 416°C in nitrogen. The films of the resulting polymers were also prepared by casting the solu- tion. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 869 – 877, 2006 Key words: direct polycondensation; poly(urethane-imide)s; inherent viscosity; diphenylphosphoryl azide INTRODUCTION Diisocyanates are widely used as initial monomers for the preparation of various kinds of polymers. 1–4 The commercial use of the most diisocyanates is often limited because of their poor stability, and in fact, these compounds are very susceptible to deterioration during storage. 5 In the field of polymeric materials, one approach to solving this problem is to employ di(carbonyl azide) precursors as starting monomers in stead of diisocyanates for direct synthesis of them. In 1983, Ghatge and Jadhav reported the synthesis of m- and p-hydroxyethoxy benzoyl azides, and the direct polymerization of these monomers to homo- and ran- dom copolyurethanes. Because it was difficult to iso- late monomers with reactive groups, these workers generated isocyanate groups in situ of the polymer- ization stage. 6 Thereafter, in 1991, various kinds of polyurethanes were prepared by Nishi et al. through the reaction of a hydroxyl group with the isocyanate group that was formed by Curtius rearrangement of the carbonyl azide precursor. 7 In general, the most carbonyl azides are readily converted to correspond- ing isocyanates, which react in situ with hydroxylic compounds to form urethanes. 8,9 Moreover, it is mentionable that a major drawback of polyurethanes is their poor resistance toward me- chanical strains and high temperatures. Generally, their acceptable mechanical properties vanish above 80°C and thermal degradation takes place above 200°C. 10 Various attempts have been made to incor- porate imide heterocyclic units into polyurethane backbone. 11–17 On the other hand, the most heat resis- tant homopolyimides have almost poor processability because of their insolubility in common organic sol- vents. However, it is found that the synthesis of co- polyimides by the introduction of other functional groups into the polymer backbone remarkably en- hance their positive properties. 18 –21 Therefore, the presence of urethane linkages by the side of imide groups into a copolymer chain is useful both for poly- urethane and polyimide. This putting together in- creases thermal stability and processability of polyure- thane and polyimide, respectively. In our previous studies, we successfully prepared a series of wholly aromatic poly(amide-imide)s, poly(es- ter-imide)s, and poly(urethane-imide)s from a number of new imide-containing dicarboxylic acids. 22–27 Among them, a dicarboxylic acid bearing two imide rings 4-p- biphenyl-2,6-bis(4-trimellitimidophenyl)pyridine, 1, was used for some polymerization purposes. The results Correspondence to: H. Behniafar (h_behniafar@dubs.ac.ir). Contract grant sponsor: Research Council of Damghan University of Basic Sciences. Journal of Applied Polymer Science, Vol. 101, 869 – 877 (2006) © 2006 Wiley Periodicals, Inc.