Esterified cellulose ethers which have i) as ester groups aliphatic monovalent acyl groups or a combination of aliphatic monovalent acyl groups and groups of the formula C(O) R COOA wherein R is a divalent aliphatic or aromatic hydrocarbon group and A is hydrogen or a cation ii) a weight average molecular weight M of from 80 000 Dalton to 220 000 Dalton iii) a Polydispersity M/M of from 1.3 to 4.0 and iv) an M/M of not more than 18.5 when the weight average molecular weight M the number average molecular weight Mn and the z average molecular weight M are measured by SEC MALLS using as mobile phase a mixture produced from 40 parts by volume of acetonitrile and 60 parts by volume of aqueous buffer containing 50 mM NaHPO and 0.1 M NaNO. are useful as enteric polymers for pharmaceutical dosage forms.
