TITLE AQUEOUS SOLUTIONS OF HYDROLYZEL) MΛLEIC ANHYDRIDE COPOLYMERS

FIELD OF THE INVENTION The present invention relates to a process for the preparation of aqueous solutions of hydrolyzed ethylenically unsaturated aromatic/maleic anhydride polymers.

BACKGROUND OF THE INVENTION For some time ethylenically unsaturated aromatic/maleic anhydride copolymers have been treated with alkaline materials, such as ammonium hydroxide or alkali metal hydroxides, to produce aqueous solutions of ethylenically unsaturated aromatic/maleic acid salt copolymers, by hydrolysis. Fitzgerald et al., in U.S. Patent Application Serial No. 07/502819, filed 2 April 1990, disclosed the usefulness of aqueous solutions of aromatic/maleic anhydride ^" copolymers in the treatment of textiles to render them resistant to

# staining. The preferred precursor of Fitzgerald et al. is a styrene/ aleic anhydride copolymer.

The styrene/maleic anhydride copolymers currently available commercially can be obtained in either of two solid forms, powder and flake. The powder form, which is inherently more expensive because it is produced by grinding the flake, is more readily soluble than the flake, probably due to its larger surface area. The powder, however, is difficult to charge safely to a reactor because it presents a dust explosion hazard and has a tendency to contaminate the operating area, thereby generating environmental concerns. The Jake, on the other hand, reacts more slowly than the powder when treated under the same conditions. It also tends to form lumps due to the

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lengthy processing time resulting from the time/- temperature restrictions recommended in the trade literature to preserve product color (See "general bulletin' ⁷ 3/88 U/C MTH on SMA Resins and the "product bulletin" on SMA Resins dated 8/1/85 both by the Sartomer Company, the former supplier of the SMA Resins) . Those Bulletins suggest that solubilization is best carried out by dispersing the resin well in a stoichiometric excess of an alkaline material and then heating to temperatures in the range of about 49 to 77*C. They caution that excessive time at higher temperatures (24 hours at 80*C) may lead to darkening of the product solution.

Recently, Hansen et al., in U.S. Patent No. 4,623,692, described a new process for solubilizing maleic anhydride-containing copolymers. It consisted of treating the maleic anhydride copolymer with metal complexes which contain fugitive ligands, such as zinc or zirconium ammonium carbonates. That method suffers from the disadvantage that environmentally undesirable heavy metals are introduced into the product solution. A method of affording a more rapid reaction of flake forms to produce lightly colored hydrolyzed aromatic/maleic anhydride copolymer solutions free of heavy metals, would be desirable. It would be additionally advantageous if special effort to obtain a homogeneous slurry before heating could be avoided.

BRIEF SUMMARY OF THE INVENTION The present invention relates to a process for the hydrolysis of ethylenically unsaturated aromatic/maleic anhydride copolymers to form lightly colored solutions of ethylenically unsaturated aromatic/maleic acid salt copolymers, the improvement comprising carrying out the reaction at temperatures above about 100*C at elevated pressure.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for the reaction of aromatic/maleic anhydride copolymers with aqueous alkaline materials to form clear lightly-colored solutions of aromatic/maleic anhydride copolymers, the improvement comprising carrying out the reaction at temperatures above about 100°C and a pressure above atmospheric in equipment suitable for pressure operation. The clarity and light color of the product aromatic/maleic anhydride copolymer solutions are surprising in view of the recommendations to use temperatures of about 77"C or below and the warning about the deleterious effect of higher temperatures on product color, contained in the trade literature. _

The aromatic/maleic anhydride polymers suitable as starting materials for this invention contain between about one and three polymer units derived from one or more ethylenically unsaturated aromatic monomers per polymer unit derived from maleic anhydride. A variety of ethylenically unsaturated aromatic compounds can be used for the purpose of preparing these unhydrolyzed polymers. They can be represented by the formula

wherein

R2 I- R is R1-CH=C- or CH2=CH-CH ₂ --7 R ¹ is H-, CH ₃ or C ₆ H5-;

R ² is II- or CH ₃ -;

R ³ is II- or CH ₃ O-;

O R4 is II-, CH ₃ -, or CH ₃ C H-0-, and

R ³ plus R ⁴ is -O-CH2-O-.

Specific examples of ethylenically unsaturated aromatic compounds suitable as monomers in the preparation of the copolymers used as starting materials in the process of this invention include styrene , alpha-methylstyrene, 4-methylstyrene, stilbene, 4-acetoxystilbene (used to prepare a hydrolyzed polymer from maleic anhydride and 4-hydroxystilbene) , eugenol acetate, isoeugenol acetate, 4-allylphenyl acetate, safrole, mixtures of the same, and the like. The copolymerization of any of the above ethylenically unsaturated aromatic monomers with maleic anhydride should be carried out in any of the ways, known to the art, to produce copolymers with a relatively low molecular weight(number average) . The copolymers, used as starting materials for this invention should have a number average molecular weight in the range between about 500 and 4000, preferably between about 800 and 2000. Preferably the copolymer is a styrene/maleic anhydride copolymer having a number average molecular weight in the range between about 500

I and 4000, and most preferably a copolymer containing styrene and maleic anhydride at a molar ratio of about 1: 1 and having a number average molecular weight in the range between about 800 and 2000. In addϋion to the aromatic/maleic anhydride copolymers, a wide variety of other materials, soluble in water and stable under the conditions of the process of our invention, can be incorporated into the reaction mass when the present invention is carried out. This can be done when solutions containing one or more components in addition to the aromatic/maleic anhydride copolymers are desired. This allows one-step preparation of more complex compositions. Surfactants,

antimicrobials, other stabilizers and the like, are non-limiting examples of components that could be added to the initial charging. When it is desired to prepare the stain-resist compositions described by Fitzgerald et al. in U.S. Patent No. 4,883,839, it is convenient to charge the aromatic/maleic anhydride copolymer, the polymeric sulfonated phenol-formaldehyde condensation product and the aqueous alkaline material to the reactor before carrying out the heating cycle of this invention. Clear dark amber solutions are obtained. Since phenol-formaldehyde solutions are generally darker than aromatic/maleic anhydride copolymer solutions, it is not surprising that solutions containing both of these components are darker than those containing only aromatic/maleic anhydride copolymers.

The alkaline materials useful in this invention include alkali metal oxides, hydroxides or salts. Magnesium oxide, hydroxide and alkaline salts of magnesium also lead to clear lightly colored solutions when used in this invention. Calcium derivatives do not. They result in slurries, the calcium salts of the hydrolyzed copolymers evidently being less soluble than the magnesium salts, if soluble at all. Typical examples of alkaline materials that afford clear solutions of the hydrolyzed copolymers of this invention are sodium hydroxide, preferred because of price and ease of availability, potassium hydroxide, magnesium hydroxide, magnesium oxide, sodium carbonate, potassium carbonate, disodium phosphate and trisodium phosphate. The ratio of alkaline material to anhydride units in the polymer"can vary over a considerable range in the application of this invention. It is not necessary to use stoichiometric equivalents of alkali to anhydride units in the polymer to obtain complete solution. As little as 25% of the stoichiometric

quantity of alkali required to completely neutralize the carboxylic acid groups formed by the hydrolysis of the anhydride, can yield complete solution of the hydrolyzed polymer. The product obtained by the use of less than stoichiometric quantities of alkaline material therefore contains a mixture of maleic acid salt moieties and free maleic acid moieties.

While it is convenient to operate the present invention by incorporating the alkaline material into the reaction mixture of aromatic/maleic anhydride copolymer and water, before subjecting it to the higher temperatures, the present invention can also be carried out by simply mixing water and the aromatic/maleic anhydride copolymer and heating at the higher temperatures of this invention. An intermediate product mixture is obtained in the form of a slurry which remains quite fluid on cooling to 65-80'C. The solid component of the slurry is the hydrolysed aromatic/maleic anhydride copolymer, the anhydride polymer units now converted to dicarboxylic acid units. The addition of an alkaline material to the slurry results in easy solution as the pll is raised.

The process of this invention is conveniently operated by charging the aromatic/maleic anhydride copolymer, preferably in flake form, an alkali or alkaline salt and water to a reactor capable of withstanding moderate pressures and heating the mixture to temperatures above about 100*C at a pressure in excess of atmospheric, preferably autogenous pressure, until solution is complete. Temperatures between 120 to 140 ^* C are preferred because this range affords complete solution in a reasonable length of time. For example, heating a mixture of 3/1 styrene/maleic anhydride copolymer at 125'C in aqueous caustic soda leads to a lightly colored solution in the course of about two hours. Temperatures in the range of 100 to 120 ^* C require longer times for complete reaction.

Temperatures higher than 140 ^* C can be used, but they result in correspondingly higher pressures which require more substantial equipment to contain them.

The process of this invention is usually run at concentrations of copolymer plus alkaline material of about 10 to 40 weight percent in water, i.e. about 60 to 90% by weight water. Lower concentrations are uneconomical and higher ones lead to products with increasingly high viscosities which become difficult to handle. The product's pll also has an effect on its viscosity. The lower the pH, the higher is the viscosity. The relationships between concentration, pH and viscosity for aqueous sodium salt solutions of hydrolyzed 1/1 styrene/maleic anhydride copolymer are demonstrated in Table 1.

Table 1 Viscosity in Centipoises at 22*C

8 120 43 20 6.5 3230 390 70

*active ingredient

The following examples are given in further illustration of the invention but not by way of limitation.

EXAMPLE 1

Th€vre were added to a 100 ml stainless steel bomb 24 g of flaked 1/1 styrene/maleic anhydride copolymer with a number average molecular weight of about 1600 and an acid number of about 480 (SMA 1000 from Λtochem Company) , 24 g of 30 weight percent aqueous sodium hydroxide and 32 g of water. The bomb

was sealed and heated at 130 ^* C for two hours with shaking. After cooling, the contents of the bomb were a cϊear amber solution with no trace- of undissolved starting material.

EXAMPLE 2

To a 2,000 gal reactor were charged 9,000 lb of v/ater. The agitator was started and the free space in the reactor was blanketed with nitrogen. There were then charged 3,960 lb of flaked SMA 1000 from Λtochem

Company and 2,640 lb, 1.0 mol per anhydride unit in the copolymer, of aqueous 30%, by weight, sodium hydroxide.

The reactor was sealed and the mass was heated to 120 to 125*C where it was held for 3 hours. The charge was cooled to yield a clear pale yellow solution.

EXAMPLE 3 To a 400 ml stainless steel bomb were charged 246.3 g of water, 39.6 g of 30%, by weight, aqueous sodium hydroxide, 10.4 g of a polymeric sulfonated phenol-formaldehyde condensation product (MesitolTM NBS from Mobay Chemical Corporation) and 59.4 g of SMA 1000 flakes. The bomb was sealed and heated at 120-5'C for 3 hrs. with shaking. On cooling a clear dark amber solution, free of undissolved starting material, was obtained.

EXAMPLE 4 SMA 1000 flakes, 40 g, and 360 g of water were reacted according to the method described in

Example 3, except that no base was used. The product was a milky white_slurry. The solids showed no anhydride linkages by infra-red analysis and dissolved in aqueous sodium hydroxide at ambient temperature.

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EXAMPLE 5 A 3/1 styrene/maleic anhydride copolymer with a number average molecular weight of 1900 and an acid number of about 280, (SMA 3000 suplied by Atochem ₅ Company) 82.1 g, 53.3 g of 30%, by weight, of aqueous sodium hydroxide and 193 g of water were reacted according to the method descibed in Example 3. The product was a clear light yellow solution.

10 EXAMPLE 6

SMA looo, 112.5 g, 250.3 g of water and 11.1 g of magnesium oxide were reacted according to the method described in Example 3. The product was a clear straw colored moderately viscous liquid. 15

EXAMPLE 7 SMA 1000 flakes, 75 g, and 190 g of water were sealed in a 300 ml bomb and heated at 120-125*C for 4 hrs. with shaking, and the bomb was then cooled 20 to 65'C. The resultant milky white slurry was partially neutralized with 35 g of 20% ammonium hydroxide at 65 ' C to yield a clear light amber solution.

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