Synthesis,characterization, and hydrolytic degradation of copolyesters of 3‐(4‐hydroxyphenyl) propionic acid and p‐hydroxybenzoic acid,vanilic acid,or syringic acid

A series of copolyesters were prepared by a direct polycondensation of 3‐(4‐hydroxyphenyl) propionic acid and p‐hydroxybenzoic acid (HBA), vanilic acid (VA), or syringic acid (SGA) of different composition in pyridine using diphenyl chlorophosphate and lithium bromide as condensing agents. The effects of methoxy substitution in the benzene ring and copolymer composition on the synthesis and thermal properties as well as hydrolytic degradation were examined. The methoxy substitution increased a glass transition temperature and a solubility, while it decreased a crystallinity and a thermal stability. The HBA series copolyesters showed a homogenous nematic phase, while the VA and SGA series copolyestes neither revealed an anisotropic melt nor formed a mobile melt below around 350°C. The hydrolytic degradation of melt‐pressed films was performed in a 5% sodium hydroxide aqueous solution at 40°C to test a biodegradability of the copolyesters. HBA‐50 and HBA‐30 exhibited the much higher degradation rate than HBA‐70, showing that the aliphatic ester linkage was more degradable than aromatic one. The degradation rates of VA‐50 and SGA‐50 were remarkably slower than that of HBA‐50 due to the steric hindrance of the methoxy group in the ortho position. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2474–2481, 2000