Abstract: Poly(N-phenyl urethanes) and methods of preparing same by heating poly(N-phenyl iminocarbonates) to a temperature above 250.degree. C. so that the backbone of the polyiminocarbonate rearranges to form the poly(N-phenyl urethane). Poly(N-substituted iminocarbonates and methods of preparing same by suspending a dialkaline diphenol in an aprotic solvent at a basic pH and adding to the suspension an N-substituted iminophosgene. Methods for making heat-stable articles by forming an article from a poly(N-phenyl iminocarbonate) while heating the article to a temperature above about 250.degree. C. so that the poly(N-phenyl iminocarbonate) rearranges to form a poly(N-phenyl urethane).