Esterified cellulose ethers of high molecular weight and homogeneity

1. An esterified cellulose ether having

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 Mw of from 80,000 Dalton to 220,000 Dalton,

iii) a Polydispersity Mw/Mn of from 1.3 to 4.0, and

iv) an Mz/Mn of not more than 18.5,

when the weight average molecular weight Mw, the number average molecular weight Mn and the z-average molecular weight Mz 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 NaH 2 PO 4 and 0.1 M NaNO 3 .

2. The esterified cellulose ether of claim 1 wherein the aliphatic monovalent acyl groups are acetyl, propionyl or butyryl groups and the groups of the formula —C(O)—R—COOA are —C(O)—CH2-CH2-COOA,

—C(O)—CH═CH—COOA, or —C(O)—C6H4-COOA.

3. The esterified cellulose ether of claim 1 being hydroxypropyl methyl cellulose acetate succinate.

4. The esterified cellulose ether of claim 1 having a weight average molecular weight Mw of from 90,000 to 185,000 Dalton.

5. The esterified cellulose ether of claim 1 having an Mw/Mn of from 1.5 to 3.5 or an Mz/Mn of from 3.0 to 17.0, or a combination thereof.

6. A composition comprising a liquid diluent and at least one esterified cellulose ether of claim 1 .

7. The composition of claim 6 additionally comprising at least one active ingredient and optionally one or more adjuvants.

8. A solid dispersion comprising at least one active ingredient in at least one esterified cellulose ether of claim 1 .

9. The solid dispersion of claim 8 in the form of strands, pellets, granules, pills, tablets, caplets, microparticles, fillings of capsules or injection molded capsules or in the form of a powder, film, paste, cream, suspension or slurry.

10. A process for producing the solid dispersion of claim 8 comprising the steps of blending a) at least one esterified cellulose ether of claim 1 , b) one or more active ingredients and c) one or more optional additives, and subjecting the blend to extrusion.

11. A process for producing the solid dispersion of claim 8 comprising the steps of blending

a) at least one esterified cellulose ether having 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 Mw of from 80,000 Dalton to 220,000 Dalton, iii) a Polydispersity Mw/Mn of from 1.3 to 4.0, and iv) an Mz/Mn of not more than 18.5, when the weight average molecular weight Mw, the number average molecular weight Mn and the z-average molecular weight Mz 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 NaH 2 PO 4 and 0.1 M NaNO 3 ,

b) one or more active ingredients,

c) one or more optional additives, and

d) a liquid diluent to prepare a liquid composition, and removing said liquid diluent.

12. A dosage form being coated with the esterified cellulose ether of claim 1 .

13. A capsule shell comprising the esterified cellulose ether of claim 1 .

14. A process for producing an esterified cellulose ether of claim 1 comprising the steps of

(A) dissolving or dispersing a cellulose ether and a first amount of alkali metal carboxylate in a reaction diluent,

(B) heating the obtained mixture to a temperature of 60° C. to 110° C. before, during or after adding (i) an aliphatic monocarboxylic acid anhydride or (ii) a combination of an aliphatic monocarboxylic acid anhydride and a dicarboxylic acid anhydride to the mixture obtained in step (A), and allowing the esterification reaction to proceed, and

(C) before the esterification reaction in step (B) is completed, adding a second amount of alkali metal carboxylate and allowing the esterification reaction to further proceed,

wherein the esterified cellulose ether product has

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 Mw of from 80,000 Dalton to 220,000 Dalton,

iii) a Polydispersity Mw/Mn of from 1.3 to 4.0, and

iv) an Mz/Mn of not more than 18.5,

when the weight average molecular weight Mw, the number average molecular weight Mn and the z-average molecular weight Mz 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 NaH 2 PO 4 and 0.1 M NaNO 3 .

15. The process of claim 14 wherein the first amount of alkali metal carboxylate added in step (A) is 15 to 35 percent and the second amount of alkali metal carboxylate added in step (B) is 65 to 85 percent, based on the total amount of added alkali metal carboxylate in the process.

16. The esterified cellulose ether of claim 3 having a weight average molecular weight Mw of from 90,000 to 185,000 Dalton.

17. The esterified cellulose ether of claim 16 having an Mw/Mn of from 1.5 to 3.5 or an Mz/Mn of from 3.0 to 17.0, or a combination thereof.