Oxidized cellulose esters: I. Preparation and characterization of oxidized cellulose acetates--a new class of biodegradable polymers.
Oxidized cellulose acetates (OCA), with a degree of substitution (DS) value ranging between 1.1 and 2.3 and a free carboxylic acid group content of 20% (w/w), have been prepared by reacting oxidized cellulose (OC, COOH content 20% w/w) with a mixture of acetic acid and acetic anhydride in the presence of sulfuric acid as a catalyst. The DS of OCA, in general, increased with increasing reaction temperature, reaction time, and concentration of acetic anhydride in the reaction mixture. The yield of OCA, in contrast, increased with increasing concentration of acetic anhydride and decreased with increasing reaction time and temperature. The intrinsic viscosity of OCA varied between 0.100 and 0.275, depending on the reaction conditions used during its preparation. In general, an increase in reaction temperature and the use of a prolonged reaction time decreased the intrinsic viscosity of OCA. No correlation was found between DS and intrinsic viscosity of OCA. The apparent pKa of OCA is 3.7-3.9. The new OCA polymers are practically insoluble in water and slowly dissolve in pH 7.4 phosphate buffer solution. They are, however, soluble in a range of organic solvents (e.g. ethyl acetate, acetone, acetone/water, chloroform/methylene chloride, dimethylsulfoxide, dimethylformamide, and/or chloroform/methanol).