Synthesis and properties of main-chain oligomeric benzoxazine precursor containing cyclotriphosphazene units

A linear oligobenzoxazine precursor with cyclotriphosphazene ring was prepared through the Schiff base route. The resulting polymers showed higher molecular weight and better thermal stability than those from the traditional Mannich polycondensation method. The oligomeric benzoxazine precursor can form a high-quality transparent yellow film; however, it was fragile after being cured. In order to identify the effect of end groups on the cured polymer, an aniline-capped polymer was prepared by the same Schiff base method and then was changed into a benzoxazine end group. The results indicated that the uncapped polymer exhibited higher stability than the capped polymer. This can be ascribed to different chemical structures resulting from different end groups.