WO2020117736A1

WO2020117736A1 - Hydroxypropyl methylcellulose acetate succinates of very high molecular weight

Info

Publication number: WO2020117736A1
Application number: PCT/US2019/064134
Authority: WO
Inventors: Oliver O. Petermann
Original assignee: DDP Specialty Electronic Materials US, Inc.
Priority date: 2018-12-04
Filing date: 2019-12-03
Publication date: 2020-06-11

Abstract

A hydroxypropyl methylcellulose acetate succinate having a weight average molecular weight Mw of at least 800,000 Dalton is useful for preparing solid dispersions, coated dosage forms, capsule shells and hydrogels. The hydrogel is formed from the hydroxypropyl methylcellulose acetate succinate and water by heat treatment and syneresis, wherein the hydrogel, at a temperature of 21°C, has a water content of from 15 to 97 weight percent, based on the total weight of the hydrogel.

Description

HYDROXYPROPYL METHYLCELLULOSE ACETATE SUCCINATES OF VERY

HIGH MOLECULAR WEIGHT

FIELD

The present invention relates to novel hydroxypropyl methylcellulose acetate succinate (HPMCAS) polymers, solid dispersions of an active ingredient in such HPMCAS polymers as well as as liquid compositions, coated dosage forms, capsules and hydrogels comprising such HPMCAS polymers.

INTRODUCTION

Hydroxypropyl methylcellulose acetate succinate (HPMCAS) is known as enteric polymer for the production of hard capsules, tablet coatings or as a matrix polymer in tablets.

The solubility of HPMCAS in aqueous liquids is pH-dependent due to the presence of succinate groups, also called succinyl groups or succinoyl groups. In the acidic environment of the stomach HPMCAS is protonated and therefore insoluble. HPMCAS undergoes deprotonation and becomes soluble in the small intestine, which is an environment of higher pH. Tablets coated with HPMCAS protect the drug from inactivation or degradation in the acidic environment of the stomach or prevent irritation of the stomach by the drug but release the drug in the small intestine.

Moreover, HPMCAS is known for improving the solubility of poorly water-soluble drugs. The HPMCAS is aimed at reducing the crystallinity of the drug, thereby minimizing the activation energy necessary for the dissolution of the drug, as well as establishing hydrophilic conditions around the drug molecules, thereby improving the solubility of the drug itself to increase its bioavailability, i.e., its in vivo absorption by an individual upon ingestion.

European Patent Application EP-A- 0 219 426 discloses a method for preparing an enteric-soluble acidic dicarboxylic acid ester of a cellulose ether, such as HPMCAS, which is produced from a cellulose ether having hydroxypropoxyl groups and a viscosity of at least 5 cp, measured as a 2% by weight aqueous solution at 20 °C. EP-A- 0 219 426 shows that a HPMCAS produced from a HPMC of 6 cp viscosity had a higher molecular weight and a good resistance against a simulated gastric juice than a HPMCAS produced from a HPMC of 3 cp viscosity, which disintegrated in simulated gastric juice. EP-A- 0 219 426 discloses that the hydroxypropoxyl-containing cellulose ethers should have a viscosity not exceeding 70 centipoise because the esterification reaction of a cellulose ether having a higher viscosity requires a large volume of acetic acid as the reaction medium with a decrease in the % utilization of the esterifying reagent.

International Patent application No. WO 2014/137779 discloses HPMCAS polymers which have a high molecular weight but which can still be efficiently used in spray-drying and coating processes. Specifically, HPMCAS polymers are disclosed which have a viscosity of up to 100 mPa_*s, measured as a 10 wt% solution of the HPMCAS in acetone at 20 °C, and which have a weight average molecular weight M_w of from 310,000 to 500,000 Dalton. The HPMCAS polymers are produced by esterifying a cellulose ether that has a viscosity of from 2.3 to 5.0 mPa-s, measured as a 2.0 wt% solution in water at 20 °C.

International Patent application No. WO 2014/031447 discloses a process for produding esterified cellulose ethers, such as HPMCAS, in the presence of an aliphatic solvent as a reaction diluent. International Patent application No. WO 2014/031448 discloses a process for produding esterified cellulose ethers, such as HPMCAS, in the presence of an alkali metal carboxylate as a catalyst. The cellulose ethers used as a starting material for produding the esterified cellulose ethers have a viscosity of from 2.4 to 200 mPa-s, measured as a 2 weight-% aqueous solution at 20 °C according to ASTM D2363 - 79 (Reapproved 2006). WO 2014/031447 and WO 2014/031448 disclose that the weight average molecular weight M_w of the produced HPMCAS can be varied by varying the molar ratio of [aliphatic carboxylic acid / anhydroglucose units of cellulose ether ] and the molar ratio of [alkali metal carboxylate / anhydroglucose units of cellulose ether ], respectively. The examples in WO 2014/031447 relate to HPMCAS having an M_w in the range of 68,000 - 139,000. The examples in WO 2014/031448 relate to HPMCAS having an Mw in the range of 95,000 - 305,000. WO 2014/031447 and WO 2014/031448 both generally state that the produced esterified cellulose ethers can have an M_w of 40,000 to 700,000 Dalton.

In view of the great usefulness of HPMCAS in the pharmaceutical field, such as the use of enteric polymers for the production of hard capsules, tablet coatings or as a matrix polymer in tablets, it would be desirable to provide new HPMCAS polymers to enrich the art.

International patent applications WO2016/148976 and WO2016/148977 disclose HPMCAS polymers which are soluble in water at 2 °C or even at 20 °C although they have a low degree of neutralization. Aqueous solutions of many of these HPMCAS polymers gel at slightly elevated temperature, typically at 30 to 55 °C. This makes them very suitable for coating pharmaceutical dosage forms, such as tablets, or for producing capsule shells.

International patent application WO2017/099952 discloses that gels formed from aqueous solutions of HPMCAS display expulsion of water from the gels at further increased temperatures, for example above 60 °C, or more typically at 70 °C or more. This

phenomenon is known as“syneresis”. WO2017/099952 discloses that in applications where gel formation is desired at elevated temperature, such as the production of capsule shells wherein heated dipping pins are used, syneresis is undesired as it causes a breakdown of the gel structure. Adding a low viscosity cellulose ether, such as a low viscosity viscosity hydroxypropyl methylcellulose, to the aqueous solutions of HPMCAS is useful for reducing or preventing syneresis.

Although HPMCAS polymers are very useful and widely used as enteric polymers for the production of hard capsules, tablet coatings or as a matrix polymer in tablets, there is an urgent need to find new dosage forms for active ingredients. Some people have difficulties to swallow tablets or capsules, for example elderly people or children. The administration of tablets or capsules to pets or other animals is also difficult.

Therefore, chewable gels, also designated as gummies or pastilles, are also used as pharmaceutical or nutritional dosage forms. Chewable gels are particularly useful for administering nutritional supplements like vitamins or minerals or for applying

pharmaceuticals for the treatment of the oral cavity or throat, such as the treatment of sore throat or cough. Chewable gels are typically based on gelatin. Gelatin readily dissolves in hot water and sets to a gel on cooling. The most common materials for producing gelatin are pig skin, bovine hides or bones. Hence, there is great reluctance by many consumers to ingest such chewable capsules, e.g., for religious or other reasons, such as concerns about Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease.

Moreover, gelatin does not have enteric properties.

Therefore, there is an urgent need to provide gelatin-free gels. There is another urgent need to provide gels that are based on polymers that are able to improve the solubility of poorly water-soluble drugs and/or display enteric properties. Unfortunately, HPMCAS polymers do not present themselves as an alternative to gelatin due to their gelling behavior. As discussed in WO2016/148976 and WO2016/148977, gelation of the disclosed aqueous solutions of HPMCAS is reversible. I.e., upon cooling of the gel to room temperature (20 °C) or less the gel transforms into a liquid aqueous solution. Gels that melt back to aqueous solutions when the gels cool down to room temperature or even refrigerator temperature are normally unsuitable as dosage forms for active ingredients, such as drugs. Producing, transporting and storing HPMCAS gels at temperatures of more than 30 °C to avoid their melt back and potentially even maintain the shape of the HPMCAS gels is energy consuming and inconvenient. Moreover, many active ingredients are heat sensitive and should not be stored at elevated temperatures. Some active ingredients should even be stored in a refrigerator. Therefore, the urgent need remains to provide gelatin-free gels, more specifically gelatin-free hydrogels that do not melt back at room temperature (21°C) or below.

SUMMARY

Surprisingly, the inventor of the present patent application has been able to provide novel HPMCAS polymers of very high molecular weight. The provision of such HPMCAS is highly desirable due to the known good resistance of high molecular weight HPMCAS against simulated gastric juice.

Moreover, the inventor of the present patent application has surprisingly found gelatin-free hydrogels or gummies or pastilles based on HPMCAS that do not melt back to aqueous solutions at room temperature (21 °C) or refrigerator temperature (4 °C). In preferred embodiments gelatin-free hydrogels or gummies or pastilles based on HPMCAS even maintain a substantially stable shape at room temperature or even at refrigerator temperature (4 °C).

Accordingly, one aspect of the present invention is a hydroxypropyl methylcellulose acetate succinate having a weight average molecular weight M_w of at least 800,000 Dalton.

Another aspect of the present invention is a solid dispersion which comprises at least one active ingredient and the above-mentioned hydroxypropyl methylcellulose acetate succinate.

Yet another aspect of the present invention is a coated dosage form wherein the coating comprises the above-mentioned hydroxypropyl methylcellulose acetate succinate.

Yet another aspect of the present invention is a capsule shell which comprises the above-mentioned hydroxypropyl methylcellulose acetate succinate.

Yet another aspect of the present invention is a composition which comprises a liquid diluent and the above-mentioned hydroxypropyl methylcellulose acetate succinate. Yet another aspect of the present invention is a hydrogel which is formed from the above-mentioned hydroxypropyl methylcellulose acetate succinate and water by heat treatment and syneresis, wherein the hydrogel, at a temperature of 21 °C, has a water content of from 15 to 97 weight percent, based on the total weight of the hydrogel.

Yet another aspect of the present invention is a process for producing a hydrogel from the above-mentioned hydroxypropyl methylcellulose acetate succinate and water, which comprises the steps of a) preparing an aqueous solution of at least 0.5 wt.-% of the above- mentioned hydroxypropyl methylcellulose acetate succinate, b) heating the aqueous solution of step a) to form a hydrogel from the aqueous solution, c) maintaining the formed hydrogel at least at a temperature at which the hydrogel has been formed in step b) for a sufficient time period such that i) the remaining water content in the formed hydrogel is from 15 to 97 weight percent, based on the total weight of the hydrogel, and ii) at least 30 weight percent of water are liberated from the hydrogel, based on the water weight in the aqueous solution in step a), and d) separating liberated water from the hydrogel and cooling the hydrogel to a temperature of 25 °C or less simultaneously or in any sequence.

BRIEF DESCRIPTION OF DRAWINGS

Figures 1 - 10 are photographical representations of hydrogels of the present invention.

DESCRIPTION OF EMBODIMENTS

The HPMCAS of the present invention has a weight average molecular weight M_w of at least 800,000 Dalton, preferably at least 850,000 Dalton, more preferably at least 900,000 Dalton, and most preferably at least 950,000 Dalton. The HPMCAS of the present invention generally has an M_w of up to 1,500,000 Dalton, preferably of up to 1,300,000 Dalton, more preferably of up to 1,150,000 Dalton, and most preferably of 1,050,000 Dalton.

The HPMCAS of the present invention generally has a number average molecular weight Mn of from 350,000 to 1,250,000 Dalton, preferably from 500,000 to 1,100,000 Dalton, more preferably from 700,000 to 1,000,000 Dalton, and most preferably from 800,000 to 900,000 Dalton.

The HPMCAS of the present invention generally has a Polydispersity M_w/M_n of from 1.05 to 2.5, preferably from 1.1 to 2.0, more preferably from 1.1 to 1.5, and most preferably from 1.1 to 1.3. The Polydispersity M_w/M_n is calculated based on the determination of the weight average molecular weight M_w and the number average molecular weight M_n.

The HPMCAS of the present invention generally has a z-average molecular weight, Mz_, of from 800,000 to 2,000,000 Dalton, more preferably from 1,000,000 to 1,8000,000 Dalton, and most preferably from 1,200,000 to 1,500,000 Dalton.

Mw, Mnand M_z are measured according to Journal of Pharmaceutical and Biomedical Analysis 56 (2011) 743 using a mixture of 40 parts by volume of acetonitrile and 60 parts by volume of aqueous buffer containing 50 mM NaThPC^ and 0.1 M NaNCb as mobile phase. The mobile phase is adjusted to a pH of 8.0. The measurement of M_w, M_nand M_zis described in more details in the Examples.

The HPMCAS of the present invention has a cellulose backbone having b-1,4 glycosidically bound D-glucopyranose repeating units, designated as anhydroglucose units in the context of this invention. At least a part of the hydroxyl groups of the anhydroglucose units are substituted by a combination of methoxyl and hydroxypropoxyl groups.

The degree of the substitution of hydroxyl groups of the anhydroglucose units by hydroxypropoxyl groups is expressed by the molar substitution of hydroxypropoxyl groups, the MS(hydroxypropoxyl). The MS(hydroxypropoxyl) is the average number of moles of hydroxypropoxyl groups per anhydroglucose unit in the HPMCAS. It is to be understood that during the hydroxypropylation reaction the hydroxyl group of a hydroxypropoxyl group bound to the cellulose backbone can be further etherified by a methylation agent, and/or a hydroxypropylation agent. Multiple subsequent hydroxypropylation etherification reactions with respect to the same carbon atom position of an anhydroglucose unit yields a side chain, wherein multiple hydroxypropoxyl groups are covalently bound to each other by ether bonds, each side chain as a whole forming a hydroxypropoxyl substituent to the cellulose backbone.

The term“hydroxypropoxyl groups” thus has to be interpreted in the context of the MS(hydroxypropoxyl) as referring to the hydroxypropoxyl groups as the constituting units of hydroxypropoxyl substituents, which either comprise a single hydroxypropoxyl group or a side chain as outlined above, wherein two or more hydroxypropoxyl units are covalently bound to each other by ether bonding. Within this definition it is not important whether the terminal hydroxyl group of a hydroxypropoxyl substituent is further methylated, or not; both methylated and non-methylated hydroxypropoxyl substituents are included for the determination of MS(hydroxypropoxyl). The HPMCAS generally has a molar substitution of hydroxypropoxyl groups in the range of 0.05 to 1.00, preferably 0.08 to 0.90, more preferably 0.12 to 0.70, most preferably 0.15 to 0.60, and particularly 0.20 to 0.50.

The average number of hydroxyl groups substituted by methoxyl groups, per anhydroglucose unit, is designated as the degree of substitution of methoxyl groups, DS(methoxyl). In the above-given definition of DS, the term“hydroxyl groups substituted by methoxyl groups” is to be construed within the present invention to include not only methylated hydroxyl groups directly bound to the carbon atoms of the cellulose backbone, but also methylated hydroxyl groups of hydroxypropoxyl substituents bound to the cellulose backbone. The HPMCAS generally has a DS(methoxyl) in the range of 1.0 to 2.5, preferably from 1.2 to 2.2, more preferably from 1.6 to 2.05, and most preferably from 1.7 to 2.05.

The HPMCAS generally has a degree of substitution of acetyl groups, DSA_c, of 0.05 to 1.50, preferably of 0.10 to 1.25, and more preferably of 0.20 to 1.00. The HPMCAS generally has a degree of substitution of succinoyl groups, DSs, of 0.05 to 1.6, preferably of 0.05 to 1.30, more preferably of 0.05 to 1.00, and most preferably of 0.10 to 0.70 or even 0.10 to 0.60.

The total degree of substitution of acetyl and succinoyl groups, DSA_c+ DSs, is generally from 0.10 to 2.0, preferably from 0.10 to 1.4, more preferably from 0.20 to 1.15, most preferably from 0.30 to 1.10 and particularly from 0.40 to 1.00.

It has been found that HPMCAS having a total degree of substitution of acetyl and succinoyl groups, DSA_c + DSs, of 0.10 to 0.70 is particulary useful for producing the hydrogel of the present invention. Accordingly, in one embodiment of the invention the total degree of substitution of acetyl and succinoyl groups, DSA_C + DSs, is from 0.10 to 0.70, preferably from 0.10 to 0.67, more preferably from 0.15 to 0.65, even more preferably from 0.15 to 0.60, most preferably from 0.20 to 0.55, and particularly from 0.25 to 0.55. In this embodiment of the invention the HPMCAS has a degree of substitution of acetyl groups of generally at least 0.05, preferably at least 0.10, more preferably at least 0.15, most preferably at least 0.20, and particularly at least 0.25 or at least 0.30. In this embodiment of the invention the HPMCAS generally has a degree of substitution of acetyl groups of up to 0.69, preferably up to 0.60, more preferably up to 0.55, most preferably up to 0.50, and particularly up to 0.45 or even only up to 0.40. In this embodiment of the invention the HPMCAS has a degree of substitution of succinoyl groups of generally at least 0.01, preferably at least 0.02, more preferably at least 0.05, and most preferably at least 0.10, and generally up to 0.65, preferably up to 0.60, more preferably up to 0.55, and most preferably up to 0.50 or up to 0.45. Moreover, in one embodiment of the invention the sum of i) the degree of substitution of acetyl groups and ii) the degree of substitution of succinoyl groups and iii) the degree of substitution of methoxyl groups, DS(methoxyl), generally is from 1.7 to 2.6, preferably from 1.9 to 2.55, more preferably from 2.0 to 2.5, and most preferably from 2.1 to 2.45. A HPMCAS having such sum of degrees of substitution generally forms clear solutions in water at a concentration of 2 wt.-% at 2 °C.

The content of the acetate and succinate ester groups is determined according to “Hypromellose Acetate Succinate, United States Pharmacopeia and National Formulary, NF 29, pp. 1548-1550”. Reported values are corrected for volatiles (determined as described in section“loss on drying” in the above HPMCAS monograph).

The content of the ether groups, i.e., the methoxyl and hydroxypropoxyl groups, in the HPMCAS is determined in the same manner as described for“Hypromellose”, United States Pharmacopeia and National Formulary, USP 35, pp 3467-3469.

The contents of ether and ester groups obtained by the above analyses are converted to DS and MS values of individual substituents according to the formulas below.

% cellulose backbone

M(OCH₃) - M(OH)\

= 100 - %MeO *

M(OCH₃)

%MeO %HPO

M(OCH₃) M(HPO)

DS(Me) = MS(HP) =

%cellulose backbone %cellulose backbone

M(AGU) M(AGU)

%Acetyl %Succinoyl

M (Acetyl) M(Succinoyl)

DS (Acetyl) = DS(Succinoyl) =

%cellulose backbone %cellulose backbone

M(AGU) M(AGU)

M(MeO) = M(OCH₃) = 31.03 Da M(HPO) = M(OCH₂CH(OH)CH₃) = 75.09 Da M (Acetyl) = M(COCH₃) = 43.04 Da M(Succinoyl) = M(C0C₂H₄C00H) = 101.08 Da M(AGU) = 162.14 Da M(OH) = 17.008 Da M(H) = 1.008 Da By convention, the weight percent is an average weight percentage based on the total weight of the cellulose repeat unit, including all substituents. The content of the methoxyl group is reported based on the mass of the methoxyl group (i.e., -OCH3). The content of the hydroxypropoxyl group is reported based on the mass of the hydroxypropoxyl group (i.e., -0-CH2CH(CH3)-0H). The content of the acetyl groups is reported based on the mass of acetyl (-C(0)-CH₃). The content of the succinoyl group is reported based on the mass of succinoyl groups (i.e., - C(O) - CH2 - CH2 - COOH).

The HPMCAS generally has a degree of neutralization of the succinoyl groups of not more than 0.4, preferably not more than 0.3, more preferably not more than 0.2, most preferably not more than 0.1, and particularly not more than 0.05 or even not more than 0.01. The degree of neutralization can even be essentially zero or only slightly above it, e.g. up to 10 ³ or even only up to 10 ⁴.

The term“degree of neutralization” as used herein defines the ratio of deprotonated succinoyl groups over the sum of deprotonated and protonated succinoyl groups, i.e., degree of neutralization =

[ -C(O) - CH_{2 -} CH_{2 -} COCT ] / [ -C(O) - CH_{2 -} CH_{2 -} COCT + -C(0) - CH_{2 -} CH_{2 -} C00H]. If the succinoyl groups are partially neutralized, the cation preferably is an ammonium cation, such as NHC or an alkali metal ion, such as the sodium or potassium ion, more preferably the sodium ion.

A HPMCAS that has a total degree of substitution of acetyl and succinoyl groups, DSA_C + DSs, of 0.10 to 0.70 generally has a solubility in water of at least 2.0 weight percent at 2 °C, i.e., the HPMCAS can be dissolved as an at least 2.0 weight percent solution, preferably at least 3.0 weight percent solution, more preferably at least 5.0 weight percent solution or even at least 10.0 weight solution in water at 2 °C. Generally a HPMCAS having a DSA_C + DSs of 0.10 to 0.70 can be dissolved as up to 20 weight percent solution or in the most preferred embodiments even as up to 30 weight percent solution in water at a temperature of 2 °C. The term“an x weight percent solution in water at 2 °C” as used herein means that x g of the HPMCAS is soluble in (100 - x) g of water at 2 °C.

The hydroxypropyl methylcellulose (HPMC), also designated as hypromellose, that is used as a starting material for producing the HPMCAS of the present invention has an MS(hydroxypropoxyl) and a DS(methoxyl) as stated further above. The hydroxypropyl methylcellulose generally has a viscosity of at least 20,000 mPa-s, preferably at least 50,000 mPa-s, more preferably at least 75,000 mPa-s, and most preferably at least 100,000 mPa-s, determined as a 2 weight-% solution in water at 20 °C. The hydroxypropyl methylcellulose generally has a viscosity of up to 200,000 mPa-s, preferably up to 180,000 mPa-s, more preferably up to 150,000 mPa-s, and most preferably up to 130,000 mPa-s, determined as a 2 weight-% solution in water at 20 °C. The viscosity is determined as a 2 weight-% solution in water at 20 °C as described in the United States Pharmacopeia (USP 35, “Hypromellose”, pages 423 - 424 and 3467 - 3469) using a Brookfield viscometer.

Descriptions on preparing the 2 wt. % HPMC solution and Brookfield viscosity

measurement conditions are described in USP 35.

The HPMC is reacted with acetic anhydride and succinic anhydride simultaneously or in sequence in one reaction device. Suitable reaction devices, such as batch reactors or reaction vessels, are known in the art. Preferred are reactors equipped with a stirring device or kneaders.

The amount of each anhydride to be introduced into the reaction device is determined depending on the desired degree of esterification to be obtained in the final product, usually being 1 to 10 times the stoichiometric amounts of the desired molar degree of substitution of the anhydroglucose units by esterification.

The molar ratio between the acetic anhydride and the anhydroglucose units of the HPMC generally is 0.1 / 1 or more, preferably 0.3 / 1 or more, more preferably 0.5 / 1 or more, most preferably 1 / 1 or more, and particularly 1.5 / 1 or more. The molar ratio between the acetic anhydride and the anhydroglucose units of the HPMC generally is 17 / 1 or less, preferably 10 / 1 or less, more preferably 8 / 1 or less, most preferably 6 / 1 or less, and particularly 4 / 1 or less. The molar ratio between the succinic anhydride and the anhydroglucose units of the HPMC preferably is 0.01 / 1 or more, more preferably 0.04 / 1 or more, and most preferably 0.2 / 1 or more. The molar ratio between the succinic anhydride and the anhydroglucose units of the HPMC preferably is 2.5 / 1 or less, more preferably 1.5 / 1 or less, and most preferably 1 / 1 or less.

When a HPMCAS is produced that has a total degree of substitution of acetyl and succinoyl groups, DSA_c+ DSs, of from 0.10 to 0.70 as described above, the molar ratio between the acetic anhydride and the anhydroglucose units of the HPMC generally is from 0.1 / 1 to 7 / 1, preferably from 0.3 / 1 to 3.5 / 1, and more preferably from 0.5 / 1 to 2.5 / 1. For producing a HPMCAS having a DSA_c+ DSs of from 0.10 to 0.70, the molar ratio between the succinic anhydride and the anhydroglucose units of the HPMC preferably is from 0.01 / 1 to 2.2 / 1, more preferably from from 0.04 / 1 to 1.2 / 1, most preferably from 0.2 to 1.2 / 1, and most preferably from 0.3 / 1 to 0.8 / 1.

The molar number of anhydroglucose units of the cellulose ether utilized in the process of the present invention can be determined from the weight of the HPMC used as a starting material, by calculating the average molecular weight of the substituted

anhydroglucose units from the DS(methoxyl) and MS(hydroxypropoxyl).

The esterification of the HPMC is typically conducted in a diluent, preferably in an aliphatic carboxylic acid as a reaction medium, such as acetic acid, propionic acid, or butyric acid. Acetic acid is preferred. The reaction medium can comprise minor amounts of other solvents or diluents which are liquid at room temperature and do not react with the cellulose ether, such as aromatic or aliphatic solvents like benzene, toluene, 1,4-dioxane, or tetrahydrofurane; or halogenated C1-C3 derivatives, like dichloro methane or dichloro methyl ether, but the amount of the aliphatic carboxylic acid should generally be more than 50 percent, preferably at least 75 percent, and more preferably at least 90 percent, based on the total weight of the reaction medium. Most preferably the reaction medium consists of an aliphatic carboxylic acid. The esterification reaction is generally conducted in the presence of at least 1500 parts, preferably at least 2000 parts, more preferably at least 2500 parts, and most preferably at least 2800 parts by weight of the reaction medium, such as acetic acid, per 100 weight parts of HPMC. The esterification reaction is generally conducted in the presence of up to 5000 parts, preferably up to 4000 parts, more preferably up to 3500 parts and most preferably up to 3200 parts by weight of the reaction medium, such as acetic acid, per 100 weight parts of HPMC.

The esterification reaction is generally conducted in the presence of an esterification catalyst, preferably in the presence of an alkali metal carboxylate, such as sodium acetate or potassium acetate. The amount of the alkali metal carboxylate is generally 20 to 200 parts by weight, preferably 30 to 100 parts by weight, and more preferably 40 to 60 parts by weight of the alkali metal carboxylate per 100 parts by weight of the cellulose ether.

The reaction mixture is generally heated at 60 °C to 110 °C, preferably at 70 to 100 °C, for a period of time sufficient to complete the reaction, that is, typically from 2 to 25 hours, more typically from 2 to 8 hours.

After completion of the esterification reaction, the reaction product can be precipitated from the reaction mixture in a known manner, for example by contacting with a large volume of water, such as described in U.S. Patent No. 4,226,981, International Patent Application WO 2005/115330 or European Patent Application EP 0 219 426. In a preferred embodiment of the invention the reaction product is precipitated from the reaction mixture as described in International Patent Application PCT/US13/030394, published as

WO2013/148154, to produce the HPMCAS in the form of a powder.

Another aspect of the present invention is a composition comprising a liquid diluent and an above described HPMCAS. The term“liquid diluent” as used herein means a diluent that is liquid at 25 °C and atmospheric pressure. The diluent can be water or an organic liquid diluent or a mixture of water and an organic liquid diluent. Preferably the amount of the liquid diluent is sufficient to provide sufficient fluidity and processability to the composition for the desired usage, such as spray-drying, coating purposes or for producing hydrogels.

The term“organic liquid diluent” as used herein means an organic solvent or a mixture of two or more organic solvents. Preferred organic liquid diluents are polar organic solvents having one or more heteroatoms, such as oxygen, nitrogen or halogen like chlorine. More preferred organic liquid diluents are alcohols, for example multifunctional alcohols, such as glycerol, or preferably monofunctional alcohols, such as methanol, ethanol, isopropanol or n-propanol; ethers, such as tetrahydrofuran, ketones, such as acetone, methyl ethyl ketone, or methyl isobutyl ketone; acetates, such as ethyl acetate; halogenated hydrocarbons, such as methylene chloride; or nitriles, such as acetonitrile.

In one embodiment the composition of the present invention comprises as liquid diluent an organic diluent alone or mixed with a minor amount of water. In this embodiment the composition of the present invention preferably comprises more than 50, more preferably at least 65, and most preferably at least 75 weight percent of an organic liquid diluent and preferably less than 50, more preferably up to 35, and most preferably up to 25 weight percent of water, based on the total weight of the organic liquid diluent and water. This embodiment of the invention is particularly useful if the present invention comprises an active ingredient of poor water solubility. This embodiment of the invention is also preferred if the HPMCAS has a total degree of substitution of acetyl and succinoyl groups, DSA_C + DSs, of more than 0.7 and the degree of neutralization of the succinoyl groups is not more than 0.4.

In another embodiment the composition of the present invention comprises as liquid diluent water alone or mixed with a minor amount of an organic liquid diluent as described above. In this embodiment the composition of the present invention preferably comprises at least 50, more preferably at least 65, and most preferably at least 75 weight percent of water and preferably up to 50, more preferably up to 35, and most preferably up to 25 weight percent of an organic liquid diluent, based on the total weight of the organic liquid diluent and water. This embodiment of the invention is particularly useful for providing coatings, capsules or hydrogels from aqueous compositions comprising the HPMCAS of the present invention. When preparing an aqueous solution, it is preferred that i) the HPMCAS has a total degree of substitution of acetyl and succinoyl groups, DSA_C + DSs, of not more than 0.7, preferably from 0.1 to 0.7, and/or ii) the degree of neutralization of the succinoyl groups in the HPMCAS is more than 0.4, preferably more than 0.6.

The composition of the present invention comprising a liquid diluent and an above described HPMCAS is useful as an excipient system for active ingredients and particularly useful as an intermediate for preparing an excipient system for active ingredients, such as fertilizers, herbicides or pesticides, or biologically active ingredients, such as vitamins, herbals and mineral supplements and drugs. Accordingly, the composition of the present invention preferably comprises one or more active ingredients, most preferably one or more drugs. The term "drug" is conventional, denoting a compound having beneficial

prophylactic and/or therapeutic properties when administered to an animal, especially humans. Preferably, the drug is a "low-solubility drug", meaning that the drug has an aqueous solubility at physiologically relevant pH (e.g., pH 1-8) of about 0.5 mg/mL or less. The compositions of the present invention are preferred for low-solubility drugs having an aqueous solubility of less than 0.1 mg/mL or less than 0.05 mg/mL or less than 0.02 mg/mL, or even less than 0.01 mg/mL where the aqueous solubility (mg/mL) is the minimum value observed in any physiologically relevant aqueous solution (e.g., those with pH values between 1 and 8) including USP simulated gastric and intestinal buffers. Useful low-solubility drugs are listed in the International Patent Application WO 2005/115330, pages 17 - 22.

In one aspect of the invention the composition comprising a HPMCAS as described above, one or more active ingredients and optionally one or more adjuvants can be used in liquid form, for example in the form of a suspension, a slurry, a sprayable composition, or a syrup. The liquid composition is useful, e.g., for oral, ocular, topical, rectal or nasal applications. The liquid diluent should generally be pharmaceutically acceptable, such as ethanol or glycerol, optionally mixed with water as described above. In another aspect of the invention the liquid composition of the present invention is used for producing a solid dispersion comprising at least one active ingredient, such as a drug described further above, a HPMCAS as described above and optionally one or more adjuvants. The solid dispersion is produced by removing the liquid diluent from the composition. One method of removing the liquid diluent from the liquid composition is by casting the liquid composition into a film or a capsule or by applying the liquid composition onto a solid carrier that in turn may comprise an active ingredient.

A useful method of producing a solid dispersion is by spray-drying. The term "spray drying" refers to processes involving breaking up liquid mixtures into small droplets (atomization) and rapidly removing solvent from the mixture in a spray-drying apparatus where there is a strong driving force for evaporation of solvent from the droplets. Spray drying processes and spray-drying equipment are described generally in Perry's Chemical Engineers' Handbook, pages 20-54 to 20-57 (Sixth Edition 1984). More details on spray drying processes and equipment are reviewed by Marshall, "Atomization and Spray- Drying," 50 Chem. Eng. Prog. Monogr. Series 2 (1954), and Masters, Spray Drying

Handbook (Fourth Edition 1985). A useful spray-drying process is described in the

International Patent Application WO 2005/115330, page 34, line 7 - page 35, line 25.

Alternatively, the solid dispersion of the present invention may be prepared by i) blending a) at least HPMCAS defined above, b) one or more active ingredients and c) one or more optional additives, and ii) subjecting the blend to extrusion. The term“extrusion” as used herein includes processes known as injection molding, melt casting and compression molding. Techniques for extruding, preferably melt-extruding compositions comprising an active ingredient such as a drug are known and described by Joerg Breitenbach, Melt extrusion: from process to drug delivery technology, European Journal of Pharmaceutics and Biopharmaceutics 54 (2002) 107-117 or in European Patent Application EP 0 872 233.

In another aspect of the invention the composition of the present invention comprising a liquid diluent and an above described HPMCAS may be used for coating dosage forms, such as tablets, granules, pellets, caplets, lozenges, suppositories, pessaries or implantable dosage forms, to form a coated composition. If the composition of the present invention comprises an active ingredient, such as a drug, drug layering can be achieved, i.e., the dosage form and the coating may comprise different active ingredients for different end- uses and/or having different release kinetics. In yet another aspect of the invention the composition of the present invention comprising a liquid diluent and the above described HPMCAS may be used for the manufacture of capsule shells and capsules in a process which comprises the step of contacting the liquid composition with dipping pins.

In yet another aspect the present invention relates to a hydrogel formed from the above described HPMCAS and water by heat treatment and syneresis, wherein the hydrogel, at a temperature of 21 °C, has a water content of from 15 to 97 weight percent, based on the total weight of the hydrogel. The inventor of the present patent application has surprisingly found gelatin-free hydrogels or gummies or pastilles based on the above described HPMCAS that do not melt back to aqueous solutions at room temperature (21 °C) or refrigerator temperature (4 °C).

According to the general understanding in the art "gel" refers to a soft, solid, or solid like materia! which comprises at least two components, one of which is a liquid present in abundance (Almdal, Dyre, J., Hvidt, S., Kramer, O.; Towards a phenomologicai definition of the term 'gel'. Polymer and Gel Networks 1993, 1, 5-17). A hydrogel is a gel wherein water is the main liquid component.

The HPMCAS used for preparing a hydrogel by heat treatment and syneresis has a weight average molecular weight M_w of at least 800,000 Dalton and preferably a total degree of substitution of acetyl and succinoyl groups, DSA_c + DSs, of from 0.10 to 0.70. Prreferred ranges for the weight average molecular weight M_w, the number average molecular weight M_n, the Polydispersity M_w/M_n, and the z-average molecular weight M_z of the HPMCAS are described further above. Preferred ranges for the molar substitution of hydroxypropoxyl groups, the MS(hydroxypropoxyl), the degree of substitution of methoxyl groups, DS(methoxyl), the degree of substitution of acetyl groups, DSA_c, and the degree of substitution of succinoyl groups, DSs, and the total degree of substitution of acetyl and succinoyl groups, DSA_c + DSs, are also described further above. HPMCAS polymers having a DSA_C + DSs of from 0.10 to 0.70 are soluble in water at 2 °C or even at 20 °C although they have a low degree of neutralization. The degree of neutralization of the succinoyl groups is preferably not more than 0.4. Preferred degrees of neutralization are described further above.

In the hydrogel formed from the above described HPMCAS and water by heat treatment and syneresis, the water content of the hydrogel is up to 97 wt.-%, preferably up to 96 wt.-%, more preferably up to 95 (wt.-%, and most preferably up to 94 weight percent, based on the total weight of the hydrogel. The water content of the hydrogel is preferably at least 30 wt.-%, more preferably at least 50 wt.-%, even more preferably at least 70 wt.-%, and most preferably at least 80 weight percent, based on the total weight of the hydrogel. In some embodiments of the invention the water content of the hydrogel is even at least 85 wt.-%, based on the total weight of the hydrogel.

The term“formed by heat treatment and syneresis” as used herein means that heat treatment is sufficient to liberate at least 30 weight percent of water from the hydrogel, based on the weight of water used to form the hydrogel. The term“formed by heat treatment and syneresis” preferably means that heat treatment is sufficient to liberate at least 50 wt.-%, more preferably at least 60 wt.-%, most preferably even at least 70 weight percent of water and in some embodiments even at least 75 wt.-% or even at least 80 wt.-% of water from the hydrogel, based on the weight of water used to form the hydrogel. In the hydrogel formed from the above described HPMCAS and water by heat treatment and syneresis preferably up to 95 wt.-% water has been liberated from the hydrogel, based on the weight of water used to form the hydrogel. Ways to conduct the heat treatment are described further below.

The hydrogel of the present invention may comprise a minor amount of one or more organic liquids which are preferably physiologically acceptable, such as ethanol or one or more animal or vegetable oils, but the total amount of organic liquids is preferably not more than 10 percent, more preferably not more than 5 percent, even more preferably not more than 2 percent, based on the total weight of water and organic liquid in the hydrogel at a temperature of 21 °C. Most preferably, the hydrogel does not comprise an organic liquid.

The hydrogel of the present invention is formed from an above-described HPMCAS and water. This means that no other gelling agents than the above described HPMCAS are needed for gel formation at room temperature (21 °C) or lower. Generally the hydrogel of the present invention is gelatin-free. Other than the HPMCAS described above, the hydrogel preferably does not comprise a significant amount of ingredients, such as thickeners or gelling agents, that are able to increase the gel strength of the hydrogel at room temperature (21 °C) or at a lower temperature. The sum of the HPMCAS and water is generally at least 70 percent, preferably at least 80 percent, more preferably at least 90 percent, and most preferably at least 95 percent, based on the total weight of the hydrogel.

The hydrogel of the present invention is formed in an novel and inventive process as described below. In step a) of the process of the present invention an aqueous solution comprising at least 0.5 wt.-%, more preferably at least 0.7 wt.-%, and most preferably at least 0.9 wt.-% of the above-described HPMCAS is prepared, based on the total weight of the aqueous solution. Generally an aqueous solution comprising up to 5 wt.-%, typically up to 4 wt.-%, and more typically up to 3 wt.-%, of the above-described HPMCAS is prepared, based on the total weight of the aqueous solution. The above described HPMCAS is typically utilized in ground and dried form. The HPMCAS is generally mixed with water while cooling the aqueous mixture to a temperature of not higher than 10 °C, preferably not higher than 8 °C, more preferably not higher than 6.5 °C, even more preferably not higher than 5 °C, and particularly from 0.5 to 2 °C. Water or the aqueous solution of the HPMCAS may be mixed with a minor amount of one or more organic liquids which are preferably physiologically acceptable, such as ethanol or one or more animal or vegetable oils, but the total amount of organic liquids is preferably not more than 10 percent, more preferably not more than 5 percent, even more preferably not more than 2 percent, based on the total weight of water and organic liquid. Most preferably, the aqueous liquid is not mixed with an organic liquid.

The aqueous solution prepared in step a) may comprise one or more active

ingredients, such as fertilizers, herbicides or pesticides, or biologically active ingredients, such as vitamins, herbals and mineral supplements or drugs.

In step b) of the process of the present invention, the aqueous solution of step a) is heated to form a hydrogel. For practical reasons the aqueous solution of step a) is generally heated to a temperature of at least 55 °C, preferably at least 65 °C, more preferably at least 75 °C, and most preferably at least 80 °C to form a hydrogel from the aqueous solution. Generally the aqueous solution is heated to a temperature of up to 95 °C, typically up to 90 °C, and more typically up to 87 °C.

In step c) of the process of the present invention, the formed hydrogel is maintained at least at a temperature at which the hydrogel has been formed in step b) for a sufficient time period to liberate at least 30 weight percent of water from the hydrogel, based on the weight of water in the aqueous solution in step a). Preferably at least 50 wt.-%, more preferably at least 60 wt.-%, most preferably at least 70 wt.-%, and in some embodiments of the process at least 75 wt.-%, or even at least 80 wt.-% of water is liberated from the hydrogel.

Generally up to 95 wt.-% of water is liberated from the hydrogel, based on the weight of water in the aqueous solution in step a). In any event a sufficient amount of water is liberated from the hydrogel provided that the remaining water content in the hydrogel is as described further above.

For practical reasons the formed hydrogel is generally maintained at a temperature of at least 55 °C, preferably at least 65 °C, more preferably at least 75 °C, and most preferably at least 80 °C. Generally the temperature in step c) is up to 95 °C, typically up to 90 °C, and more typically up to 87 °C. Generally maintaining the formed hydrogel at an above- mentioned temperature for at least 1 hour, preferably at least 2 hours, more preferably for at least 3 hours, and most preferably at least 4 hours is sufficient for expelling or liberating an amount of water as described above. During the heating of the hydrogel for an extended time period as described above, syneresis takes place and water is expelled or liberated from the hydrogel. Water is typically liberated from the hydrogel in its liquid state, however a portion of the expelled or liberated water can evaporate. In some embodiments of the invention even most or all of the expelled or liberated water can directly evaporate, e.g., by placing the formed hydrogel on a sieve or in or on another device that facilitates water evaporation. The preferred time periods to liberate an amount of water and to achieve a remaining water content as described above depends on the temperature and on the concentration of the HPMCAS in the aqueous solution. The higher the chosen temperature and the concentration of the HPMCAS, the less time period is generally needed to expel the desired amount of water. Generally the formed hydrogel is maintained at an above- mentioned temperature for a time period of up to 12 hours, typically up to 10 hours, more typically up to 8 hours and in preferred embodiments up to 6 hours.

In step d) liberated water is separated from the hydrogel and the hydrogel is cooled to a temperature of 25 °C or less or to 23 °C or less or to 21 °C or less simultaneously or in any sequence. Typically the hydrogel is cooled to a temperature of 0 °C or more, more typically of 4 °C or more. Preferably liberated water is separated from the hydrogel before, while or shortly after the hydrogel is cooled to a temperature of 25 °C or less. It is preferred to separate liberated water from the hydrogel within 24 hours, preferably within 12 hours, and more preferably within 3 hours upon completion of step c). Generally at least 80 percent, preferably at least more 85 percent, more preferably at least 90 percent, most preferably at least 95 percent, and particularly at least 98 percent of the liberated water is separated from the hydrogel, for example by draining or contacting the hydrogel with a cloth or another article that is able to remove liberated water from the hydrogel. If desired, in step d) the hydrogel can even be cooled to a temperature of 0 °C or less, e.g., to a temperature of 0 °C to - 20 °C, more typically of 0 °C to - 10 °C. It is advisable to separate liberated water from the hydrogel before cooling the hydrogel to such a low temperature. For practical reasons the hydrogel is preferably cooled to a temperature of 23 °C to 4 °C.

Surprisingly, it has been found that the produced hydrogel does not display any melt back, remains a gel and keeps its shape even when it is stored for hours or days at a temperature of 25 °C or less, such as 23 °C to 4 °C.

The liquid composition, the solid dispersion, the coated dosage form, the capsule shell and the hydrogel of the present invention may comprise one or more active ingredients, such as fertilizers, herbicides or pesticides, or biologically active ingredients, such as vitamins, herbals and mineral supplements or drugs. The liquid composition, the solid dispersion, the coated dosage form, the capsule shell and the hydrogel of the present invention may comprise optional additives, such as coloring agents, pigments, opacifiers, flavor and taste improvers, antioxidants, preservatives, salts, and any combination thereof. Optional additives are preferably pharmaceutically acceptable. Useful amounts and types of one or more optional adjuvants are generally known in the art and depend on the intended end-use.

Some embodiments of the invention will now be described in detail in the following Examples.

EXAMPLES

Unless otherwise mentioned, all parts and percentages are by weight. In the

Examples the following test procedures are used.

Content of ether and ester groups

The content of methoxyl and hydroxypropoxyl groups in the hydroxypropoxyl methylcellulose (HPMC) and hydroxypropoxyl methylcellulose acetate succinate

(HPMCAS) is determined as described for“Hypromellose”, United States Pharmacopeia and National Formulary, USP 35, pp 3467-3469.

The ester substitutions with acetyl groups (-CO-CFE) and with succinoyl groups (-CO-CH2-CH2-COOH) are determined according to Hypromellose Acetate Succinate, United States Pharmacopeia and National Formulary, NF 29, pp. 1548-1550. Reported values for ester substitution are corrected for volatiles (determined as described in section “loss on drying” in the above HPMCAS monograph).

Determination of M_w and Mn

Mw and M_n are measured according to Journal of Pharmaceutical and Biomedical Analysis 56 (2011) 743 unless stated otherwise. The mobile phase is a mixture of 40 parts by volume of acetonitrile and 60 parts by volume of aqueous buffer containing 50 mM NaThPCri and 0.1 M NaNCb. The mobile phase is adjusted to a pH of 8.0. Solutions of the HPMCAS were filtered into a HPLC vial through a syringe filter of 0.45 pm pore size. The exact details of measuring M_w, M_nand M_z are disclosed in the International Patent

Application No. WO 2014/137777 in the section“Examples” under the title“Determination of Mw, Mnand Mz”. The recovery rate was at least 97 %.

Hydrogel Example

A Production of hydroxypropyl methylcellulose (HPMC)

257.6 g of cotton linter pulp grade 1067, commercially available from Southers Cellulose Products were reacted with 569.7 g of 50 wt.-% aqueous NaOH (4.7 mol NaOH/mol anhydroglucose unit (AGU) of cellulose) at 40 °C for 15 minutes to produce alkali cellulose. 86.4 g of dimethyl ether (1.25 mol/mol AGU) were added and the mixture was stirred for 10 min. 431.8 g of methyl chloride (5.7 mol/mol AGU) were added and stirred for 15 min. Then 152.5 g of propylene oxide (1.75 mol/mol AGU) were added and the reaction mixture was heated to 60 °C within 20 min. Afterwards the reaction mixture was heated to 80 °C within 50 min. and etherification was conducted at 80 °C for 30 min. The mixture was then neutralized with 80 wt.-% formic acid and the produced was washed repeatedly with water having a temperature of 95 °C. The washed HPMC was dried in a circulating air oven at 55 °C and subsequently milled using an Alpina mill at 15,000 rpm. The resulting HPMC had a methoxyl substitution (DSM) of 1.91, a hydroxypropoxyl substitution (MSHP) of 0.23 and a viscosity of 120,000 mPa-s. The viscosity was determined as a 2 weight-% solution in water at 20 °C as described in the United States Pharmacopeia (USP 35,“Hypromellose”, pages 423 - 424 and 3467 - 3469) using a Brookfield viscometer. Descriptions on preparing the 2 wt. % HPMC solution and Brookfield viscosity measurement conditions are described in USP 35. B. Production of hydroxypropyl methylcellulose acetate succinate (HPMCAS)

1500 g of glacial acetic acid, 90 g of acetic anhydride, 20 g of succinic anhydride, 50 g of the HPMC (water free) described in paragraph A. above and 25 g of of sodium acetate were introduced into a reaction vessel under stirring.

The mixture was heated to about 85 °C and under stirring and the reaction mixture was allowed to react at this temperature for 3.5 hours. Then the crude product was precipitated by adding 2L of water having a temperature of 95 °C. Subsequently the precipitated product was separated from the mixture by filtration and washed several times with water having a temperature of 95 °C. Then the product was isolated by filtration and dried at 55°C overnight. The dried mass was ground in a kitchen grinder.

The produced HPMCAS had the following properties: 26.9 wt.-% methoxyl groups, 7.7 wt.-% hydroxypropoxyl groups, 4.2 wt.-% acetyl groups and 4.2 wt.-% succinoyl groups. This corresponds to a DS(methoxyl), i.e., a degree of substitution with methoxyl groups, DSM, of 1.91; a MS(hydroxypropoxyl), i.e., a molar substitution with

hydroxypropoxyl groups, MSHP, of 0.23; a degree of substitution of acetyl groups, DSA_c, of 0.21, and a degree of substitution of succinoyl groups, DS_s, of 0.09.

M_n: 850,000 Dalton;

M_w: 998,000 Dalton;

Mw/Mn: 1.17; and

M_z: 1,334,000 Dalton.

C) Preparation of a Hydrogel

A HPMCAS was used that had been produced as described above and that had the properties as described above.

In all experiments 30.0 g of an aqueous solution of the HPMCAS was prepared in a glass container by stirring in an ice bath for 6 hours and storage overnight in a refrigerator. After 1-2 hours 3 drops of Foamstar SI 2210 are added. Foamstar SI 2210 is a modified polydimethylsiloxane-based defoamer that is commercially available from BASF. Then the solution was centrifuged (Sorvall Lynx 4000 centrifuge at 4000 rpm at 4°C) for 10 min.

The HPMCAS concentration, based on the total weight of the aqueous solution, is as listed in Table 1 below. Each aqueous solution was then heated to 85 °C and kept at 85 °C for a time period as listed in Tables 1 below. The temperature of 85 °C was held by placing the glass container in an oven maintained at 85 °C. Alternatively, the glass container can be placed in a water bath of corresponding temperature.

All aqueous solutions gelled at 85 °C. During the heat treatments they underwent syneresis to a very large degree wherein the entire amount of HPMCAS remained in the hydrogels and the major portion of the water originally present in the aqueous solutions were expelled from the hydrogels. The hydrogels were removed from the liberated water, mechanically dried with a tissue and weighed while the gel is still hot. The % liberated water after the heat treatment is calculated according to the formula:

[1 - (g gel - g HPMCAS in aq. sol.) / (g aq. solution - g HPMCAS in aq. solution)] x 100. The remaining water content of the produced hydrogel after heating is calculated from the weight of the hydrogel and the HPMCAS weight of the starting aqueous solution, which corresponds to the HPMCAS weight in the hydrogel.

The produced hydrogels were placed on a glass plate without delay and allowed to cool to room temperature. The texture of each hydrogel was assessed immediately after heat treatment, removal of expelled water and cooling to room temperature, but before storage.

In each Example a stable gel was formed.

The produced hydrogels were then placed in separate bags and stored at 4 °C in a refrigerator over night. Additional amounts of water were expelled from some of the hydrogels, but these amounts were small.

Table 1 below lists the HPMAS concentrations in the aqueous solutions used for the production of the hydrogels, the time period during which the aqueous solutions were kept at 85 °C, the measured weights of the gels while still hot after heat treatment, the calculated percentages of liberated water by the heat treatment, the calculated water concentration in the hot gels after the heat treatment and the weights of the gels after they had been stored at 4 °C in a refrigerator over night.

Figures 1 - 10 are photographical representations of the hydrogels listed in Table 1 below, i.e. of Examples 1-i, 2-i, 3-i, 4-i, 5-i, 6-i, 7-i, 8-i, 9-i and 2-ii, respectively, after the hydrogels had been stored at 4 °C in a refrigerator over night. Fig. 1 is a photographical representation of the hydrogel of Example 1-i, Fig. 2 is a photographical representation of the hydrogel of Example 2-i, and so on, Fig. 9 is a photographical representation of the hydrogel of Example 9-i, and Fig. 10 is a photographical representation of the hydrogel of Example 2-ii.

The hydrogel of Example 1-i, illustrated by Fig. 1, had the highest water content and was the least dimensionally stable hydrogel of all hydrogels in Table 1.

The hydrogel of Example 3-i, illustrated by Fig. 3, was also quite soft in view of its water content that was higher than in 2-i, 4-i, 5-i, 6-i, 7-i, 8-i, 9-i and 2-ii.

Table 1

Claims

1. A hydroxypropyl methylcellulose acetate succinate having a weight average molecular weight M_w of at least 800,000 Dalton.

2. The hydroxypropyl methylcellulose acetate succinate of claim 1 having a weight average molecular weight M_w of up to 1,500,000 Dalton.

3. The hydroxypropyl methylcellulose acetate succinate of claim 1 or 2 having a number average molecular weight M_nof from 350,000 to 1,250,000 Dalton.

4. The hydroxypropyl methylcellulose acetate succinate of any one of claims 1 to 3 having a total degree of substitution of acetyl and succinoyl groups, DSA_c+ DSs, of from 0.10 to 2.0.

5. The hydroxypropyl methylcellulose acetate succinate of claim 4 having a total degree of substitution of acetyl and succinoyl groups, DSA_C + DSs, of from 0.10 to 0.70.

6. The hydroxypropyl methylcellulose acetate succinate of any one of claims 1 to 5 wherein the degree of neutralization of the succinoyl groups is not more than 0.4.

7. A solid dispersion comprising at least one active ingredient and the hydroxypropyl methylcellulose acetate succinate of any one of claims 1 to 6.

8. A coated dosage form wherein the coating comprises the hydroxypropyl methylcellulose acetate succinate of any one of claims 1 to 6.

9. A capsule shell comprising the hydroxypropyl methylcellulose acetate succinate of any one of claims 1 to 6.

10. A composition comprising a liquid diluent and the hydroxypropyl methylcellulose acetate succinate of any one of claims 1 to 6.

11. A hydrogel formed from the hydroxypropyl methylcellulose acetate succinate of any one of claims 1 to 6 and water by heat treatment and syneresis, wherein the hydrogel, at a temperature of 21 °C, has a water content of from 15 to 97 weight percent, based on the total weight of the hydrogel.

12. The hydrogel of claim 11 wherein the hydroxypropyl methylcellulose acetate succinate has a total degree of substitution of acetyl and succinoyl groups, DSA_C + DSs, of from 0.10 to 0.70 and the degree of neutralization of the succinoyl groups is not more than 0.4.

13. A process for producing a hydrogel from the hydroxypropyl methylcellulose acetate succinate of any one of claims 1 to 6 and water, comprising the steps of

a) preparing an aqueous solution of at least 0.5 wt.-% of the hydroxypropyl methylcellulose acetate succinate of any one of claims 1 to 6,

b) heating the aqueous solution of step a) to form a hydrogel from the aqueous solution,

c) maintaining the formed hydrogel at least at a temperature at which the hydrogel has been formed in step b) for a sufficient time period such that i) the remaining water content in the formed hydrogel is from 15 to 97 weight percent, based on the total weight of the hydrogel, and ii) at least 30 weight percent of water are liberated from the hydrogel, based on the water weight in the aqueous solution in step a), and

d) separating liberated water from the hydrogel and cooling the hydrogel to a temperature of 25 °C or less simultaneously or in any sequence.

14. The process of claim 13 wherein the hydroxypropyl methylcellulose acetate succinate has a total degree of substitution of acetyl and succinoyl groups, DSA_C + DSs, of from 0.10 to 0.70 and a degree of neutralization of the succinoyl groups of not more than 0.4.

15. The process of claim 13 or 14, wherein in step b) the aqueous solution is heated to a temperature of at least 55 °C and in step c) the formed hydrogel is maintained for a time period of at least 1 hour at a temperature of at least 55 °C.