Development of photoreactive degradable branched polyesters with high thermal and mechanical properties.

Branched polyesters composed of poly(L-lactide)s (PLLAs) and 3,4-dihydroxycinnamic acid (DHCA) were obtained by the thermal melt-polycondensation of 3,4-diacetoxycinnamic acid (DACA)-terminally conjugated PLLAs (DACA-PLLAs). The chemical structures of the DHCA/PLLA polyesters were confirmed by FT-IR and (1)H NMR measurements. All of the polyesters showed high photoreactivities independent of LLA content. Furthermore, the polyesters had high solubility even after UV irradiation. Interestingly, the thermal stability and mechanical properties of PLLA were improved depending on the incorporation ratio of the DHCA moiety into the backbone. The hydrolysis speed of the DHCA/PLLA polyesters decreased upon increasing the composition of LLA, but the pure PLLA presented the highest hydrolysis speed. Furthermore, all of the polyesters showed faster hydrolysis after UV irradiation as compared to the uncross-linked samples. These novel branched DHCA/PLLA polyesters with high thermal stabilities, mechanical properties and photocontrollable degradability may be useful as functional degradable polyester for the environmental and biomedical fields.