Synthesis and enzymatic degradation of regular network aliphatic polyesters

Regular network aliphatic polyesters were prepared from glycerol (Yg) and a series of various length aliphatic dicarboxylic acids (HOOC-(CH2)_n−2-COOOH, n = 4–10, 12 and 14). Prepolymers prepared by melt polycondensation were cast from dimethylformamide solution and post-polymerized at 230°C for various times to form a network. The resultant films were transparent, flexible and insoluble in organic solvents. The degree of reaction (D_R) estimated from the infrared absorbance of -OH and >CH₂ or >CH groups increased with increasing post-polymerization time and length of methylene chain. The heat distortion temperature also increased with increasing post-polymerization time and was 55, 28, 15, 6, 0, −1, −5, 4 and 32°C for Yg4, Yg5, Yg6, Yg7, Yg8, Yg9, Yg10, Yg12 and Yg14 post-polymerized for 4 h, respectively. Wide angle X-ray scattering patterns showed a distinct single diffraction peak, suggesting some ordered structure due to the establishment of a regular network. Density, water absorption and weight loss by alkali hydrolysis decreased with increasing methylene chain length. The enzymatic degradation was estimated by weight loss of the network films in a buffer solution of lipase at 37°C. The films of Yg4, Yg5, Yg6 and Yg7 showed no weight loss, but the weight loss increased greatly for Yg8, Yg9 and Yg10, and then decreased abruptly for Yg12 and Yg14. This suggests that the enzymatic degradation is affected by network structure, which allows the lipase to penetrate, and by the concentration of the enzymatically degradable ester linkage.