Synthesis and Enzymatic Degradation of Aliphatic Polyesters Copolymerized with Trimesic Acid

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Abstract
Network copolyesters were made from adipic acid and ethylene glycol with 10–40 mol% trimesic acid (Y). Prepolymers prepared by melt polycondensation were cast from dimethylformamide solution and postpolymerized at 260°C for various times to form a network. The degree of reaction (D R), estimated from the infrared absorbance of hydroxyl and methylene groups, increased with increasing postpolymerization time and leveled out at about 90% after 4–6 hours. Heat distortion temperatures (T h) measured by thermomechanical analysis increased greatly from −83 to 48°C upon the incorporation of Y. Wide-angle x-ray diffraction patterns showed that the copolymer films are amorphous. Density, tensile strength, and Young's modulus decreased for the copolymers with 10–30 mol% Y, whereas they increased drastically for the copolymer with 40 mol% Y. The enzymatic degradation was estimated by the weight loss of the copolymer films in buffer solutions with a lipase at 37°C. The weight loss decreased remarkably with increasing Y and showed no weight loss for the copolymer with 40 mol% Y. On the other hand, the weight loss by alkali hydrolysis increased for the copolymers with 10 and 20 mol% Y, implying a difference in the degradation mechanism between enzymatic degradation and alkali hydrolysis.