Synthesis of polyarylates and aliphatic polyesters by divalent acyl-1,2,4-triazole: a route to metal-free synthesis at low temperature

Aromatic, semiaromatic, and aliphatic polyesters were synthesized at moderate temperatures (25–80 °C) by the polymerization of divalent acyl-1,2,4-triazoles using 4-(dimethylamino)pyridine as a catalyst. The monomers were prepared from divalent acyl chloride in high yields, although some of them required that toluene and pyridine be used as solvents due to their high crystallinity. Melt polymerization in diphenyl ether was effective in affording semiaromatic and aliphatic polyesters. However, this method was not suitable for aromatic polyesters, as the reaction system became heterogeneous at 80 °C. Nevertheless, solution and interfacial polymerization reactions were effective in obtaining aromatic polyesters. The novel monomers provided polyester synthesis at moderate temperature without the use of any metal catalyst or halide monomers. The polymerization of divalent acyl-1,2,4-triazoles and diols/bisphenols afforded a series of aromatic, semiaromatic, and aliphatic polyesters. Compared with polymerization by transesterification, this polymerization proceeded irreversibly at relatively low temperature (<100 °C) without a metal catalyst. The reactivities of acyl-1,2,4-triazoles were thus comparable to acyl chlorides. On the other hand, higher crystallinity and lager masses of acyl-1,2,4-triazole caused technical problems, particularly for the synthesis of polyarylates. Nevertheless, solution polymerization was effective to prepare polyacrylates, particularly which could not be synthesized by interfacial polymerization.