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Title:
RAPID HYDROLYSIS OF CROSS-LINKED MALEIC ANHYDRIDE/LOWER ALKYL VINYL ETHER COPOLYMERS
Document Type and Number:
WIPO Patent Application WO/1993/024540
Kind Code:
A1
Abstract:
A process for rapidly hydrolyzing a cross-linked maleic anhydride/lower alkyl vinyl ether copolymer to a clear gel comprises (a) suspending or dispersing fine granules of the cross-linked copolymer in deionized water, (b) agitating the resulting dispersion or suspension for a period of 15 to 130 minutes at a temperature of 60° to 90 °C and then (c) cooling the hydrolyzed mixture, and (d) introducing a basic neutralizing agent at a temperature of 15° to 85 °C the product is a clear, homogeneous, hydrolyzed gel having a Brookfield viscosity of from 5,000 to 250,000 cps.

Inventors:
KWAK YOON TAE
KOPOLOW STEPHEN L
Application Number:
PCT/US1993/004414
Publication Date:
December 09, 1993
Filing Date:
May 10, 1993
Export Citation:
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Assignee:
ISP INVESTMENTS INC (US)
International Classes:
A61K8/81; A61K47/32; A61Q19/00; C08F8/12; (IPC1-7): C08F8/12; A61K7/11; C08F8/32; C08F8/42
Foreign References:
US5032391A1991-07-16
US5024779A1991-06-18
US4874604A1989-10-17
US4952558A1990-08-28
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Description:
P'.PID HYDROLYSIS OF CROSSLINKED MALEIC ANHl-JR DE/LOWER ALKYL VINYL ETHER COPOLYMERS

This invention relates to a process for the production of clear gels from the rapid hydrolysis of crosslinked aleic anhydride/lower alkyl vinyl ether copolymers for use in the pharmaceutical and cosmetic industries.

Hydrolyzed crosslinked maleic acid methyl vinyl ether copolymers are much in demand as stabilizing agents for pharmaceutical and cosmetic formulations. One problem in the prior art preparation of a uniformly clear hydrolyzed maleic acid/alkyl vinyl ether cross-linked copolymer gel is that it involves time consuming procedures which requires treatment of a hydrolysis mixture up to 24 hours in order to achieve a clear gel form. The conventional hydrolysis processes involve introducing copolymer into an aqueous base solution containing about 0.2-5.0 weight % of an organic amine neutralizer. Another problem is that in many cases, the gels obtained have a hazy appearance and gel content is subject to variations in the extent of salt formation resulting from a secondary reaction between the maleic and amine components which causes a reduction in viscosity and which affects the clarity of the product.

To solve these problems, in this invention a hydrolysis process involves a critical sequence of steps in the production of a hydrolyzed, cross-linked maleic acid/^ to C 4 alkyl vinyl ether copolymer as a uniformly clear gel.

This process concerns the treatment of a finely particulate cross-linked maleic anhydride/alkyl vinyl ether copolymer having a monomer weight ratio of between about 1:1 and about 1:2, more often between about 1:1.05 and about 1:1.2, and having an average particle size of from about 1 micron to about 1500 microns, preferably 100 to about 800 microns or in the form of a fine powder.

The crosslinked copolymers of this invention are those of high molecular weights greater than 1,000,000 and Brookfield viscosities between about 45,000 and about 150,000 cps. A particularly preferred species is the crosslinked maleic anhydride/methyl vinyl ether copolymer. In certain cases, where the average particle size exceeds the above limit, the cross-linked copolymer can be subjected to micropulverization before use.

Various grades of the crosslinked copolymer are available, usually about 2-3.5% crosslinked. The copolymers of the invention can be crosslinked with any of the conventional crosslinking agents, including terminally unsaturated dienes, e.g., 1,9-decadiene, 1,7-octadiene, and the like.

The operation of the present invention is explained below.

(a) The particulate, crosslinked copolymer is introduced into deionized water with constant agitation to form a uniform dispersion or suspension of between about 0.1 and about 2.0 weight % solids as is achieved with a weight ratio of copolymer to water of from about 1:10 and about 1:10,000, more desirably, between about 1:100 and about 1:1,000, to provide a dispersion of about 0.2-0.6 weight % solids.

(b) The dispersion or suspension is then heated to a temperature of from about 60° to about 90°C, preferably from about 60° to about 80°C, with constant agitation over a period of from about 15 to about 130 minutes or for a period sufficient to insure completion of the hydrolysis reaction, as may be indicated by the formation of a translucent liquid. Temperatures significantly lower than 60°C, e.g. 40°C. are not used because the required hydrolysis reaction time is

inordinately increased, thus removing one of the advantages of the present process. Generally, it is recommended that with larger particles of crosslinked copolymer, e.g. above about 850 microns, hydrolysis temperatures within the upper portion of the above range, e.g. above 65°C, be employed to shorten the reaction time. When premixing of copolymer and water is not employed, the crosslinked copolymer can be directly introduced into the deionized water maintained at the desired reaction temperature with constant agitation to form the translucent hydrolyzed, acidic liquid product. It is critical that no basic neutralizer be present during this hydrolysis step.

(c) After the hydrolysis is completed, the liquid mixture is allowed to cool, or is cooled to below the hydrolysis temperature, preferably to at leart 5° below the hydrolysis temperature, by the addition of cool water. Typically cooling to a temperature of between about 15° and about 80°C. , preferably between about 25° and about 65°C, is recommended.

(d) At this point, a basic neutralizer is added and thoroughly mixed into the hydrolyzed liquid over a period of from about 1 to 12 minutes to provide the uniform, clear gel having a Brookfield viscosity within the range of from about 5,000 to about 250,000, more desirably between about 40,000 and 130,000 cps and containing substantially no salt contaminant.

Alternatively, the hydrolysis and cooling process can be carried out by using only a portion, e.g. a half-portion, of the water requirement for hydrolyzing the dispersed or suspended particles and the remaining portion for cooling the reaction mixture before introduction of the neutralizing agent.

Any basic neutralizer can be employed in this invention, species of which include organic and inorganic bases. For example, sodium, potassium and ammonium hydroxides can be employed as well as organic amines, alcohols and glycinate esters such as mono-, di- or tri- ethanol amines, aminomethyl propanol, aminomethyl propanediol, tris(hydroxymethyl)amino methane, tetrahydroxypropyl ethylenediamine, sodium hydroxymethyl glycinate, polyethylene glycol cocamine, triethylamine, triamylamine, etc. The base component employed is added in an amount of from about 0.4 to about 5 parts per part of hydrolyzed, crosslinked copolymer depending on the basic component used. Generally, the amount of ammonium, sodium or potassium hydroxides is used in an amount of at least 1.5 parts per part of polymer, as opposed to organic bases which are generally employed in lower amounts. The neutralizer stabilizes the hydrolyzed mixture to provide a clear gel having a pH of between about 5 and about 8 which contains substantially no salt contaminant. The neutralizing agent is usually added as a 95 to 50 weight % aqueous solution.

The clear hydrolyzed crosslinked copolymer is formed immediately upon contact with'the neutralizer so that laborious hours of mixing and digesting formerly required are eliminated. Additionally, by the present process, the formation of organic salt monomer is avoided so that the product is achieved in a high state of purity. Finally, the prehydrolysis step allows for increased solids content in the gel product obtained such that a 2 to about 7% solids in the gel can be recovered as the clear gel product of the process.

Now the manufacturing method of this invention and the meritorious advantages thereof will be explained by reference to the following working examples.

EXAMPLE 1

One gram of the copolymor* was added to 197 g. of deionized water at 80°C. with constant stirring and agitation continued for about 20 minutes. A translucent liquid developed which indicates that the dispersed, crosslinked copolymer (pH 2.5) was hydrolyzed.

The dispersion was cooled to 60°C. and then a 50% aqueous solution of 2.0 g. of triethanolamine was added. A homogeneous clear gel of the hydrolyzed, crosslinked copolymer was obtained within 1 minute.

Agitation was continued for an additional ten minutes to insure uniform distribution of the amine.

The resulting clear gel product had a pH of 7.1 and a Brookfield viscosity of 117,000 cps.

EXAMPLE 2

Example 1 was repeated, except that aminomethyl propanediol was substituted for triethanolamine. The results of this experiment in the formation of a clear gel within one minute of contact with the diol, simulated that in Example 1. The pH of this gel product was 6.88 and the Brookfield viscosity was 99,000 cps.

* maleic anhydride/methyl vinyl ether (1:1) copolymer 2.5% crosslinked with 1,9-decadiene and having a Brookfield viscosity (TE Spindle, 10 rpm) of 70,000- 90,000 cps.

EXAMPLE 3

Example 1 was repeated, except that tris(hydroxymethyl) amino ethane was substituted for triethanolamine. The results of this experiment in the formation of a clear gel within one minute of contact with the present base, simulated that in Example 1. The pH of this gel product was 6.82 and the Brookfield viscosity was 100,000 cps.

EXAMPLE 4

Example 1 was repeated, except that tetrahydroxy propyl ethylenediamine was substituted for triethanol amine. The results of this experiment in the formation of a clear gel within one minute of contact with the present base simultated that in Example 1. The pH of this gel product was 6.83 and the Brookfield viscosity was 111,000 cps.

EXAMPLE 5

Example 1 was repeated, except that diethanolamine was substituted for triethanolamine. The results of this experiment in the formation of a clear gel within one minute of contact with the present base simulated that in Example 1. The pH of this product was 6.92 and the Brookfield viscosity was 103,000 cps.

COMPARATIVE EXAMPLE 6

One gram of the polymer was added to 170 g. of deionized water containing 1 g. of triethanolamine at 80°C. with constant stirring, and agitation was continued for about 35 minutes. Since the dispersion remained milky, the mixture was agitated for an additional 5.5 hours, after which a hazy gel was obtained as the final product.

COMPARATIVE EXAMPLES 7-10

Repetitions of Example 6 were carried out with the substitution of each of the bases: aminomethylpropanediol, tris(hydroxymethyl) aminomethane, tetrahydroxypropyl ethylenediamine and diethanolamine. These experiments resulted in the same hazy gel product after 6-8 hours of agitation at about 80 β C. as was obtained in Example 6.

EXAMPLE 11

In a glass beaker, 1 g. of the polymer was agitated with 99 g. of deionized water at 80°C. for 40 minutes, after which the resulting hydrolyzed translucent product solution was cooled to 60°C. by the addition of 97.0 g. cool water. Then 2.0 g. of triethanolamine (50% aqueous solution) was added with agitation. A clear gel was obtained within one minute of contact with the base. The gel product had a pH of 6.70 and a Brookfield viscosity of 98,500 cps.

EXAMPLE 12

Example 1 was repeated except that 4.0 g. KOH in 10% aqueous solution was substituted for triethanol amine. A clear gel was formed within one minute of contact with KOH solution. The gel product had a pH of 6.53 and a Brookfield viscosity of 108,000 cps. Similar results were obtained with 10% NaOH.

EXAMPLE 13

Example 1 was repeated except that 2.0 g. NH 4 OH 30% aqueous solution was substituted for triethanolamine. A clear gel formed within one minute of contact with NH 4 OH solution. The gel product had a pH of 6.53 and a Brookfield viscosity of 107,000 cps.

EXAMPLE 14

Example 1 was repeated except that Suttocide A (sodium hydroxymethyl glycinate) was substituted for triethanolamine and a copolymer hydrolysis solution of 0.5% solids was employed. A clear gel was formed within one minute of contact with this base. The gel product had a pH of 6.50 and a Brookfield viscosity of 103,000 cps.

Since the present invention is constituted as explained above, these structural differences in the process produce the meritorious effect of providing very rapid hydrolysis of the subject copolymers with resultant clear gel formation and without variations in the extent of salt formation.

It should be readily apparent to those skilled in the art that various modifications and alterations of the present invention are readily available without departing from the spirit and scope of the present invention.