Preparation and characterization of novel biodegradable optically active network polyesters from malic acid

Novel optically active biodegradable network polyesters were prepared from L- and D-malic acid (Ym(L) and Ym(D)) and glycols of different number of me thylene groups (HO(CH2)(n)OH, nG, n = 2-6, 8-10. and 12). Prepolymers were prepared by a melt polycondensation, and the prepolymer films cast from dim ethylformamide solution were postpolymerized at 220 degrees C for various p eriods of time to form network films. The resultant films were transparent, flexible, and insoluble in organic solvents. The network polyesters obtain ed were characterized by C-13 nuclear magnetic resonance, gel permeation ch romatography, infrared absorption spectra, wide-angle X-ray diffraction ana lysis, density measurement, differential scanning calorimetry, thermomechan ical analysis, and scanning electron micrographs. The biodegradation experi ments for the network polyester films were carried out in enzymatic solutio n with Rhizopus delemar lipase and in an activated sludge. The degree and r ate of biodegradation were estimated by the weight loss of the films. After the incubation for 10 days at 37 degrees C in Rh. delemar lipase buffer so lution, the weight loss significantly depended on the number of methylene g roups in the glycol component and showed the maximum weight loss of 52 g/m( 2) for 4GYm(L) (6.8 g/m(2) in the absence of Rh. delemar lipase). In the ex posure to activated sludge, the network polyester films showed a similar de pendence of weight loss on the number of methylene groups as in the case of the enzymatic degradation, while the rate of biodegradation was much slowe r than that of the enzymatic degradation. The effect of stereochemistry of network polyesters prepared from L-/D-malic acid on the biodegradability wa s also investigated: the rate of the biodegradation for the network polyest ers with L-isomers was slightly higher than that for those with D-isomers.