Patented Mar. 7, 1950 2499,924 UNITED STATES PATENT office 2,499,924 HIGH VIscosiTY PoLYVINYL Alcohol Edward Lavin, Springfield, Mass, assigner to Shawinigan Resins Corporation, Springfield, Mass, a corporation of Massachusetts No Drawing. Appliention November 20, 1946, Serial No. 711,207 4 Claims. (CL 260-91s), 2 This invention relates to a process for pre The process employed in preparing the prod paring polyvinyl alcohols having high viscosities. lucts set forth in the examples in Tables A and B Hydrolyzed polyvinyl acetates are useful for comprises dissolving the polyvinyl acetate in the many purposes. However, for some uses e. g., toluene and then adding the methanol containing as thickening agents, protective colloids and the the sulfuric acid (98% HaSO4) dissolved therein. like, it is desirable that such materials possess The charge is prepared in a suitable apparatus materially higher viscosities. provided with an agitator and a water-cooled It is an object of this invention to provide a return condenser. The hydrolysis is carried out process for preparing partially hydrolyzed poly by heating the charge at its reflux temperature vinyl acetates having an unusually high viscosity. O and continuing the heating under these condi A particular object of this invention is to pro tions until the desired degree of hydrolysis is vide a process for preparing high viscosity poly effected. The reaction mixture is then cooled vinyl alcohols having an acetate content of 15-40 and the hydrolyzed product which is in the form per cent by weight, calculated as polyvinyl of...a precipitate is allowed to settle. Thereafter acetate. s the supernatant liquid is decanted and the pre These and other objects are accomplished ac cipitate washed with methyl acetate to further cording to this invention by hydrolyzing poly remove solvent, thereby hardening the granular vinyl acetate in a solvent mixture comprising product. The product is then washed several methanol and a hydrocarbon from the group con times with a mixture of methyl acetate and sisting of benzene, xylene, and toluene, the meth 20 methyl alcohol and neutralized by a treatment anol content of such solvent mixture being in the . with a N/10 aqueous solution of sodium hydroxide range 3-25 per cent by weight. Surprisingly, it while slurried with a mixture of methyl acetate is discovered that when polyvinyl acetate is hy and methyl alcohol, until the liquid in contact drolyzed under such conditions until the acetate. therewith is neutral to brom-thymol blue. The content calculated as polyvinyl acetate is in the 25 product is separated from the liquor, washed range 15-40 per cent on a weight basis, aqueous. again with methyl acetate and dried at 50-60° C. solutions of the hydrolyzed product possesses vis In the tables the designation W60 indicates that cosities far in excess of those normally encoun the polyvinyl acetate is polymerized to such a tered. degree that a 1 molar benzene solution thereof The following examples are illustrative of the has a viscosity of 60 centipoises at 20° C. The process of this invention. Where parts are men designation W15 indicates a viscosity of 15 centi tioned, they are parts by weight. poises under the same-conditions. Table at

Example------3 : T of PolyvinylAcetate------W0------f Methanol in Toluene-Methanol Sol- 0.0------weat. ... • FrcentPercent SulfuricPo yAcetate Acid (98%H80) S. in -Charge. a ------10.0------10...... 10.0- Parcent Acetate in ydrolysis Product Cact. 25.3------29.6------Wiscositylated as of E.Solution Acetate; of Product , in Wateris 250,000 cp- incompletely 630 cp. - at 20O. soluble. -

able 3

Examps.------was -w- weor - an a was as ww. 4. 7 Typefit of PolyvinyiNilsen...... Acetate------. V15..... W6.------V15.----- W15. PSMethanol Polyvinyl solvent. Acetate. . . . in 150-----200...... Percentharge. sulfuric Acid (90%.- 10....--,0. PercantBSO) Acetatein Charge. in Hydrolysis- - vinylAcetate.Product Qalculated as oys. Viscosity of 68lution of Prod 2,72020 cp-cp-aco tly -. uctin beat 20 O. . " see,084 - S 4. In contrast to the results obtained according to The ratio of the solvent mixture to the poly this invention as exemplified by the examples in vinyl acetate in the hydrolysis charge may be sub Tables A and B, if corresponding polyvinyl ace stantially varied but usually it is preferred that tates are hydrolyzed in the usual manner, for the charge have a solids content of 5-40 per cent example, under acid or alkaline conditions in 6, by Weight. the presence of an alkano such as methanol or It is to be understood that the amount of ethanol, the products have viscosities in the range solvent should be so correlated with the propor 20-30 centipoises when measured under the same tion of methanol in the solvent that sufficient conditions as set forth in Tables A and B. . methanol is present to produce the desired de . In place of toluene-methanol mixtures, ben O gree of hydrolysis. Eene-methanol mixtures may be used as shown Usually, a sulfuric acid content of at least 0.1% by the following example: based on the total charge is desirable but, for cample 8 most purposes, a sulfuric acid content of over Parts 3% is not advantageous. - s It has further been discovered that the stability Polyvinyl acetate (V60).------100 of the polyvinyl alcohols made according to the Benene ------80 invention may be enhanced by alkali treatment. Methanol------90 Thus, the tendency of these polyvinyl alcohols Sulfuric acid (98% HaSO4).------0.0 to discolor and become insoluble on heating the The hydrolysis is carried out as in Examples 20 dry product and to undergo a sharp reduction in 1-7 except that benzene is substituted for toluene. viscosity on heating aqueous solutions thereof, The product is worked up in the same manner. is vastly reduced by such treatment. The effect The product has an acetate content calculated of such treatment is illustrated by the examples in as polyvinyl acetate of 24.8% and a 4% aqueous Table Cin which the effect of treating the product solution has a viscosity of 1275 centipoises at in Example 4 with varying amounts of potassium 20°C. acetate is shown. Xylene-methanol mixtures may also be used as The procedure followed is to add 10 gram sam the hydrolyzing medium to produce polyvinyl al ples of the polyvinyl alcohol to 100 cc. of a meth cohols having usually high viscosities although the anol solution of potassium acetate containing the products are not characterized by the exception 30 specified amount of potassium acetate and then ally high viscosities obtained with toluene. stir the resulting mixture at room-temperature Numerous variations may be introduced into for one hour. The product is separated from the the process of the invention as exemplified by the alkaline liquor, washed with methanol and dried foregoing examples. Thus, the methanol content at a moderately elevated temperature, e. g., of the solvent mixture may be varied from about 35 50-60C. y able C ?

Eample.------. 4. 4A 4D 4. Mols of Potassium Acetate per 1000 none.------0.01------0.075------0.1----0-2.------0.5 cc. of Methano Solution. 'Alkali Titer' of Product. 0.15------1-0------o 180------45.0. Wiscosity of 4%. 8olution of Product 2,720.------6,00------6,50------3,750.-3, 480------slightly insolu in Water at 20° C. - ble. C : After Heating at 150 Deep brown--- Deep Brown. Light Tan--Tan. Light Brown-- Deep Brown. ... for IHOT. -

resin"Alkali using tilter'bron-phenol - Number blue of indicator cubic centimeters of NIOOBO) required to neutralise 10 grams of a 4% aqueous solution of the 3 to 25 per cent. Usually more than five per 50 From the results in Table C, it is readily seen cent is to be preferred when soluble products are that treatment with potassium acetate markedly desired and for extremely high viscosities the improves the resistance to discoloration on heat methanol content is preferably not over 15 per ing, particularly in view of the fact that the prod cent. Thus, for most purposes a methanol con uct of Example 4 is light tan initially and after tent of about 5-15 per cent is very desirable. treatment as in Example 4B, retains its initial The polyvinyl acetate employed may be widely o color even after heating at 150 C. for 1 hour. varied as to its method of preparation. Thus, In addition, heating 4% aqueous solutions of polyvinyl acetates prepared by polymerization in the product of Example 4 as compared with the mass, in solution in such a solvent as benzene or product treated as in Example 4B shows the toluene or while suspended or emulsified in an greatly improved stability of the alkali treated aqueous medium may be used. The polyvinyl product. These results are given below. acetates used in the examples are prepared by polymerizing vinyl acetate in solution in benzene using acetyl peroxide as the catalyst. As shown by the examples, polyvinyl acetate of widely vary rample------4. 4B ing viscosities may be used, for example, 1-molar Initial Wiscosity------re-ra -----a - a -a------2,%io benzene solutions thereof may possess viscosi Wiscosity after 2 hours at 70 C- 3252,876 ties of from 2-500 or more centipoises at 20° C. The temperature at which the hydrolysis is car Wiscosity after 4 hours at 70° C. 1802,505 ried out may be substantially varied. However, in O order to expedite the reaction, temperatures above Thus, it is to be noted that the product in Ex room temperature are usually preferred and by ample 4 shows a progressive decrease in viscosity operating in a closed system, temperatures above whereas the product in Example 4B even after the boiling point of the reaction mixture may be 4 hours heating is substantially that of the prod used O. g., up to 150 C. or higher. . . 75 uct in Example 4 before heating. 2,499,924 5 Eacample 9 products and the higher concentrations very fine Following the procedure used in Examples 1-7, grains. a high viscosity polyvinyl alcohol is made from In the preparation of emulsions, the products the following charge: of the invention are found to act as thickening Parts agents. Thus, 1-5% of a polyvinyl alcohol of Polyvinyl acetate (V60).------150 the invention such as that illustrated by Example Toluene ------1200 1 serves to increase greatly the viscosity of poly Methanol ------135 vinyl acetate emulsions. Sulfuric acid (98%. HaSO4).------15 The foregoing description is given in illustra O tion and not in limitation of the invention as set The hydrolysis is continued until the acetate forth in the appended claims. content of the product calculated as polyvinyl What is claimed is: acetate is reduced to 23.2%. The product, after 1. A process for preparing high viscosity poly Washing, neutralizing, and drying as in the pre vinyl alcohol which comprises hydrolyzing poly vious examples, is found to require 0.5 cc. of NA100 ls vinyl acetate by treatment with a catalytic HCl to neutralize 10 grams of a 4% aqueous solu amount of sulfuric acid while dissolved in a mix tion to brom-phenol blue. ture of methanol and a hydrocarbon selected A 2% aqueous solution of the product has a from the group consisting of benzene, toluene, viscosity of 38 centipoises at 20° C. After heating and Xylene, said mixture containing 3-25% meth the dry product for 1 hour at 150° C., it is found anol by weight, and the balance being the hydro to be insoluble in Water and to be brown in color. carbon, and continuing the hydrolysis until the In contrast to these characteristics, after treat acetate content of the polyvinyl acetate is re ment of 10 grams of the product with 100 cc. of duced to 15-40% by weight calculated as poly a 0.04 molar solution of potassium acetate in vinyl acetate. m methanol for 1 hour at room temperature, 3.6 cc. 2. A process as defined in claim 1 in which the of N/100 HCl are required to neutralize 10 grams polyvinyl acetate content of the charge is in the of a 4% aqueous Solution to bron-phenol blue range 5-40%, by weight, the methanol content of and a 2% aqueous solution has a viscosity of 44 the solvent mixture is in the range 5-15%, by centipoises at 20° C. After heating the product weight, and the balance being the hydrocarbon, for 1 hour at 150° C., a 2% aqueous Solution there and the sulfuric acid content of the charge is in of has a viscosity of 45 centipoises at 20° C. and the range of 0.1-2%, by Weight. substantially all of the product is white in color. 3. A process for preparing high viscosity poly in place of potassium acetate, other alkaline vinyl alcohol which comprises hydrolyzing poly materials may be used Such as potassium hy vinyl acetate by treatment with a catalytic droxide, potassium carbonate, the corresponding amount of sulfuric acid while dissolved in a mix Sodium compounds, quaternary ammonium bases ture of methanol and toluene, said mixture con such as tetraethyl ammonium hydroxide, alkyio taining 3-25% methanol and 97-75% toluene by amines, e. g., triethanolamine, tetraethanol weight and continuing the hydrolysis until the amine, etc. Usually, Sufficient alkali is used to acetate content of the polyvinyl acetate is re produce at least a 0.02 molar solution and a 0.02 duced to 15-40% by weight calculated as poly 0.2 molar Solution results in maximum color vinyl acetate. stability. 4. A process as defined in claim 3 in which the In place of methanol, other nonsolvent liquid polyvinyl acetate content of the charge is 5-40% compounds containing hydroxyl groups may be by weight, the methanol content of the solvent used in stabilizing the polyvinyl alcohols of the 45 is in the range 5-15% by weight and the balance invention. For example, lower aliphatic alcohols, being the hydrocarbon, and the sulfuric acid such as ethanol, propanol, butanol, pentanol, etc. content of the charge is in the range 0.1-2%, by and mixtures of tWO or more of Such compounds weight. may be used. Water may also be present, pro EDWARD AWN. vided insufficient is used to cause the polyvinyl 50 alcohol to dissolve. REFERENCES Cob The polyvinyl alcohols of the invention are found to be useful as suspending agents in the The following references are of record in the aqueous suspension polymerization of vinyl con fle of this patent: pounds. Thus, granular products are obtained sis by polymerizing vinyl acetate in aqueous suspen UNEO STATES PATENTS sion using the product of Example 1 as the sus Number Name Date pending agent, Concentrations of the polyvinyl 2,226,075 Rowe ------Dec. 24, 1940 alcohol (based on the water) of 0.01-0.15% are 2,227,997 Berg ------Jan., 1941 found to be suitable for this purpose, the lower 60 2,266,996 Scott et al. ------Dec. 23, 1941 concentrations yielding rather coarse-grained 2,356,282 Stamatoff------Aug. 22, 1944