Biodegradability of copolyesteramides from hexamethylene adipate and hexamethyleneadipamide

Abstract

A series of copolyesteramides (E66/A66) were prepared by a melt polycondensation from hexamethylene glycol (E6), hexamethylenediamine (A6), and adipic acid (6). Spacing measured by WAXS showed the discontinuous change at the copolymer composition of A66 = 20 mol. %. Melting temperature ( T m) of A66 decreased continuously with increasing E66 component, while T m of E66 increased by the copolymerization of A66 component, suggesting the partial isomorphism. Degree of crystallinity estimated by WAXS and the heat of fusion estimated by DSC decreased by the copolymerization and showed a minimum at the copolymer composition of A66 = 20 mol.%. Solubility in various solvents decreased and thermal stability estimated by thermogravimetry increased with increasing A66 component. The biodegradability of E66 increased very rapidly by the copolymerization up to 20 mol.% of A66 component and then decreased very rapidly with increasing A66 component. The weight loss in aqueous solution of a lipase at 37° for 18 hr is 5.0 and 56.5 g/m 2 for E66 homopolymer and E66/A66(80/20) copolymer, respectively. This much higher biodegradability of copolymer could be explained by the large decrease of crystallinity. The weight loss by alkali hydrolysis increased up to 60 mol.% of A66 component and then decreased with increasing A66 component.