Lipase-catalyzed synthesis and characterization of biodegradable polyester containing l -malic acid unit in solvent system

Lipase-catalyzed direct polycondensation of L-malic acid (L-MA), adipic acid, and 1,8-octanediol in organic media was achieved using Novozym 435 as the biocatalyst. ¹H-nuclear magnetic resonance spectroscopy indicated that the selectivity of Novozym 435 was unaffected by changes in the organic media. The molecular weight (M_w) of the copolymers was affected by the L-MA feed ratio in the diacids, hydrophobicity of the solvent, and solubility of the substrates in the solvents. The M_w reached a maximum of 17.4 kDa at 80°C in isooctane at a L-MA feed ratio in the diacids of 40 mol %. The M_w increased from 3.2 to 16.6 kDa when the reaction time was extended from 6 to 48 hr at 70°C, and remained relatively constant with further increases in reaction time from 48 to 72 hr. The hydrophilicity, thermal stability, and crystallizability of the copolymer were also investigated.