Partial substitution of cellulose by ring-opening esterification of cyclic esters in a homogeneous system

Partially substituted cellulose derivatives were prepared by the regioselective derivatization of cellulose with cyclic esters (CEs), L-lactide (LA), and s-caprolactone (CL), in a lithium chloride (LiCl)/N,N-dimethylacetamide solvent. They were characterized by spectroscopic analyses, calorimetry, solvent solubility inspection, and an enzymatic degradability test. Fourier transform Raman spectra of the cellulose derivatives confirmed that the CE moieties were covalently introduced into cellulose molecules at their hydroxyl groups via ring-opening esterification through the catalysis by LiCl. The C-13-NMR analysis indicated that the ring-opened CEs were regioselectively combined with cellulose C6-OH. The CE portions were partially grafted on the cellulose backbone; the degree of substitution was ca. 0.5-0.7 and the degree of polymerization of grafted CEs was less than 3. Both cellulose derivatives were highly soluble in dimethylsulfoxide, which allows material fabrication. Some of the cellulose-LA was soluble or swollen in water, while cellulose-CL had poor affinity for water. Enzymatic degradation of cellulose-CEs occurred immediately on cellulase treatment, even under mild conditions which are not able to hydrolyze commercial cellulose diacetate at all. Some cellulose derivatives displayed endothermic changes. The cellulose derivatives prepared in this study are expected to be used as cellulose-based biomaterials with environmentally friendly features. (c) 2006 Wiley Periodicals, Inc.