Investigation of the cyclodehydration of a poly-o-oxyamide based on 3,3′-dioxy-4,4′-diaminodiphenylmethane and isophthalic acid dichloride☆

Abstract A method has been developed whereby the degree of cyclization of a polybenzoxazole based on 3,3′-dioxy-4,4′-diaminodiphenylmethane and isophthalic acid dichloride has been estimated on the basis of an analysis of the IR spectra of model compounds and polymeric ones containing o -oxyamide and benzoxazole fragments. The method in question based on IR analysis along with gas chromatographic and gravimetric investigation of the amount of water evolved has been used to shed light on the cyclodehydration of poly- o -oxyamide to polybenzoxazole. It was found that the cyclodehydration process takes place at a noticeable rate even at 200–250°, while an 80–90% degree of cyclization is attained in only one hour at 300–325°. Less than 25% noncyclized units has little effect on the thermo-oxidative stability of the polymer.