| abstract |
Two or more esters of a cellulose ether, each having the same ether and ester substituents but different weight average molecular weights are prepared in a process which comprises the steps of esterifying a cellulose ether with (i) an aliphatic monocarboxylic acid anhydride or (ii) a dicarboxylic acid anhydride or (iii) a combination of an aliphatic monocarboxylic acid anhydride and a dicarboxylic acid anhydride in the presence of an alkali metal carboxylate in two or more separate reactions, wherein in each reaction a different molar ratio [alkali metal carboxylate / anhydroglucose units of cellulose ether] is used to produce esters of the cellulose ether of different weight average molecular weights. |