Melt-processable poly(oxyphenylalkanoate): Synthesis, properties, andin vitro degradation of poly(4-oxyphenylacetate)

Abstract

The homopolyester of 4-hydroxyphenylacetic acid (HPAA) was synthesized by one-pot, slurry-melt, and acidolysis melt polymerization techniques and was characterized by its inherent viscosity and IR and NMR spectra. Differential scanning calorimetry (DSC), polarizing light microscopy (PLM), and wide-angle X-ray diffraction (WAXD) studies of the homopolymer were carried out for its thermal and phase behavior. The results indicated that the yield and molecular weight of the polymer depended on the method of preparation; moreover, the acidolysis melt polymerization of the pure acetoxy derivative of HPAA was the best method for the preparation of high molecular weight poly(4-oxyphenylacetate) (polyHPAA) without side reactions. DSC and PLM studies also showed that the thermal and optical properties depended largely on the polymerization conditions and inherent viscosity values. PolyHPAA did not show a clear texture typical of liquid-crystalline polymers, whereas after cooling from the melt, structures similar to spherulitic crystals were observed. WAXD patterns showed a crystalline nature. The in vitro degradability of the polymer was also studied via the water absorption in buffer solutions of pH 7 and 10 at 30 and 60 °C; this was followed by Fourier transform infrared, inherent viscosity, DSC, thermogravimetric analysis, WAXD, and scanning electron microscopy techniques. Unlike Vectra®, which showed no degradation, polyHPAA showed an increase in hydrolytic degradation from 5.0 and 6.0% at 30 °C to 12.5 and 15.0% at 60 °C after 350 h in buffer solutions of pH 7 and 10, respectively. The results indicated a possible biomedical prosthetic application of poly(oxyphenylalkanoate)s such as polyHPAA with better crystallinity coupled with degradability as a substitute for poly(hydroxyalkanoates). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2430–2443, 2001