Studies on photoreactive and biodegradable copolymers composed of poly(ɛ-caprolactone) and 4-hydroxycinnamic acid

Abstract

A novel group of photoreactive and biodegradable copolymers known as poly(ɛ-caprolactone)-co-poly(4-hydroxycinnamic acid) (PCL-co-P4HCA) was obtained by the thermal melt polycondensation of poly(ɛ-caprolactone) (PCL) with 4-hydroxycinnamic acid. The chemical structures of the PCL-co-P4HCA copolymers were analyzed by Fourier transform infrared spectroscopy and nuclear magnetic resonance. The melting points of the PCL-co-P4HCA copolymers were dependent on the PCL and 4HCA compositions, as observed by differential scanning calorimetry measurements. Wide-angle X-ray diffraction (WXRD) analysis showed highly crystalline structures of the P4HCA, PCL and PCL-co-P4HCA polymers. The PCL-co-P4HCA copolymers were fluorescent and had good photoreactivities. Crosslinking of the cinnamoyl groups in the copolymers via ultraviolet (UV) irradiation significantly affected the fluorescence, thermal stability, hydrophobicity and water absorption of the resultant copolymers. The PCL-co-P4HCA copolymers underwent degradation when placed in buffer solutions at pH 7.4 and pH 13.3, and UV irradiation was able to regulate the degradation process. The photoreactive and biodegradable copolymers with high thermal stability may be potentially applied in both the biomedical and environmental fields. Fluorescence emission spectra of PCL-co-P4HCA50 with UV irradiation at λ=302 nm for various times, and the inset shows the fluorescent intensity changes with UV irradiation time.