Synthesis and thermal properties of polyesters from cyclotriphosphazene

Polyesters containing cyclotriphosphazene units have been prepared by phase transfer catalyzed two-phase polycondensation and direct polycondensation. The polycondensation of the acid chloride of (trans-2,4-dicarboxyphenoxy-2,4,6,6-tetraphenoxy)cyclotriphosphazene (trans-CPP) and bisphenol A (BA) in the presence of benzyltriethylammonium chloride (BTEAC) as phase transfer reagent gave a polyester with a molecular weight of 22,000, whereas only oligomer was obtained by the polycondensation of the cis-isomer with BA. The result indicates that the trans-isomer is favorable to effective growth of the polyester. The direct polycondensation using SOCl2/pyridine and TsCl/DMF, however, resulted in the formation of low molecular weight polyesters even though trans-CPP was used. In the copolycondensation of BA with acid chlorides of trans-CPP and terephthalic acid, copolymers with molecular weights of 24,000-13,000 were obtained. The homopolyester prepared from trans-CPP and BA exhibited a significantly low glass transition temperature of 65 degrees C, and the copolymers had glass transition temperatures in the range 220-91 degrees C, depending on the contents of trans-CPP units. Thermogravimetric analysis showed that the homopolyester was stable up to 390 degrees C in a nitrogen atmosphere, and the char yield of copolyester with 5.5 mol.% of trans-CPP unit was 36% at 600 degrees C, which was seven times higher than that of the polyester without cyclotriphosphazene units. The presence of cis-CPP units in the polyesters lowered the initial decomposition temperatures, but not char yields. Copyright (C) 1996 Elsevier Science Ltd