Hydrolytic degradation of cellulose-graft-poly(l-lactide) copolymers

A series of cellulose-g-poly(l-lactide) (cellulose-g-PLLA) copolymers with 30.65–85.21 % PLLA weight content and the molar substitution of PLLA (MSPLLA) from 0.99 to 12.73 were synthesized via the homogeneous graft-from reaction in 1-allyl-3-methylimidazolium chloride (AmimCl) with 4-dimethylaminopyridine (DMAP) acting as the catalyst. In common organic solvents, the solubility of obtained graft copolymers was better than cellulose and strongly depended on the MSPLLA. The hydrolytic degradation of cellulose-g-PLLA copolymers was investigated in phosphate buffered solution (PBS, pH 7.4) at 37 °C. Interestingly, it was found that, when the MSPLLA was below 8.83, the hydrolytic degradation rate of cellulose-g-PLLA copolymers was obviously faster than that of both pristine cellulose and PLLA. Moreover, as the MSPLLA decreased, the cellulose-g-PLLA copolymers showed a more rapid weight loss, due to its higher hydrophilicity. Both XPS and 1H NMR analyses demonstrated the degradation occurred mainly at PLLA segments. The morphological observations indicated that, during the hydrolytic degradation, the graft copolymers firstly experienced a surface erosion process, and then the bulk erosion happened.