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Patented June 4, 1946 2,401,445 UNITED STATES PATENT OFFICE 2,401,445 ' POLYMERIZATION OF VINYL ACETATE "Jesse Oris White, Arlington, N. J., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware 7 No Drawing. Application July 13, 1943, Serial No. 494,510 . 9 Claims. 1 This invention relates to the polymerization of vinyl acetate and, more particularly, to the poly merization of vinyl acetate while dispersed in an aqueous medium. _ The so-called “granular polymerization" of liq uid monomers, as described in Crawford et a1; U. S. Patent 2,108,044, comprises subjecting the monomer to polymerizing conditions while sus pended in the form of droplets in a non-solvent medium, commonly an aqueous medium. This process, when properly conducted, produces poly mer in the form of small globules. The mainte (Cl. 260-9) 2 Hydrogen peroxide is free from these objection able characteristics but it has been found to be a comparatively weak catalyst when used alone. Admixture, with hydrogen peroxide, of a small proportion ofbenzoyl peroxide has been shown by Marks U. S. Patent 2,109,595, to increase in surprising measure the activity of hydrogen per oxide as a catalyst of polymerization, but the complete exclusion of benzoyl peroxide is never theless desirable. ' An object of the present invention is to pro vide improvements in the polymerization of vinyl nance of the monomeric liquid in the form of ‘acetate in suspension in an aqueous vehicle by ‘droplets is accomplished by the combined in?u the general method of said U. S. Patent 2,108,044," ences of various agitation and a dispersing agent. 16 i. e., the method of so-called granular polymer Various dispersing agents have been proposed ization. More speci?cally, the invention relates for this purpose. For satisfactory service, a gran to improvements in the selection and manner of ulating agent must not merely be eifective as use of starch as a dispersing agent in this proc such, but also must be easy to prepare and in ess, and to the provision of a feasible technique troduce into the reaction batch, and either read 20 for the use of hydrogen peroxide as the sole added ily removed from the particles of polymer, on catalyst of polymerization. which it becomes adsorbed, or else unobjection A speci?c object of the invention is to make able if not removed from it. unnecessary the ancillary step’ of putting the The use of starch as a dispersing agent in a starch into solution in advance of adding it to process of this type has been suggested in the 25 the other ingredents Of the polymerization batch. above mentioned patent, but this patent, although Another object is the preparation of granular noting that the dispersing powers of a starch de polyvinyl acetate of desirable and uniform par pend on its past history, is silent with respect ticle size. Other objects will be apparent from to the basis for selection of a starch for optimum the description of the invention given herein performance. Furthermore, the method disclosed therein for the preparation and use of the starch presents certain practical di?iculties. In accordance with that patent a solution of the starch is prepared in advance of its use. This after, ‘ In accordance with the present invention, the above objects are accomplished by a process which comprises heating under agitation a mixture comprising monomeric vinyl acetate, water as necessarily adds to the process of polymerization vehicle, hydrogen peroxide as catalyst of poly an ancillary step. Furthermore, in actual prac merization, a water-soluble alkaline substance in tice the solution of starch cannot be made up in quantity to provide and maintain a pH between advance in large batches, because starch solutions 4.9 and 3.8 in the mixture during the process tend, upon standing, to be spoiled by action of and, as dispersing agent, a requisite quantity, molds or bacteria, and because it is not practi 40 between 0.05% and 0.25%, .by weight of the mon cable to use preservatives for the inhibition of _ omer, of a starch of viscosiy hereinafer speci such action since a preservative is likely to inter ?ed. In a preferred embodiment of the process, fere with the desired progress of polymerization the monomer is heated to about 50‘? C., to it are of the monomer. The necessity of limiting the added the starch, in dry comminuted form, and size of batches of starch solution to what can be drysodium ‘bicarbonate, or other water-soluble. used up before it spoils adds, of course, to the alkaline substance, 'then water at 75° C.-85° C. cost of the dispersing agent used per pound of and ?nally hydrogen perioxide; the tempera polymer produced. ture of the mixture is raised by heat applied and The polymerization of liquid monomers by the by the heat developed in the resulting polymer- general method just described involves regularly a9 ization of the vinyl acetate, until it reaches about the use of a catalyst, in an amount so selected as to promote the polymerization at an eco nomical rate and at the same time to exercise some control upon the size of the macromolecules _ developed by the polymerization. The most usual catalyst is benzoyl peroxide but it is-not alto gether a satisfactory one since not only is it ex— 92° C. To be acceptable for use as granulating agent in this process, the starch must exert an ~ade quate granulating or dispersing e?ect to supple ment the dispersing effect of the agitation in opposition to the tendency of the suspended ma terial to coalesce in the course of‘ its polymeriza pensive and somewhat hazardous, but also, it is a tion. At the beginning of the process, when the source of discoloration in the resulting polymer. 60 vinyl, acetate exists still as a mobile liquid, and 2,401,445 again at'the end of the process, when it has been converted practically completely into polymer, the suspension can be adequately maintained by means of agitation alone, at least in any reason ably well designed equipment operated at suit able speed. But during the intermediate stages of the polymerization the partially polymerized vinyl acetate is relatively adhesive and the glob ules of it tend to coalesce and to adhere to the equipment. It is during this stage that the dispersing in?uence of a granulating agent must be provided to supplement the agitation in pre venting such coalescence and adherence. In the course of the rise in temperature during the proc ess, which accompanies the progressive polymeri 15 4 cup is heated to 161.5° F. (:1° F.) and main tained at that temperature by suitable adiust- ment of a voltage-regulator in the line supply ing current to the heater. An accurately weighed sample'of the starch (2.02 grams, dry basis) "is slurried in exactly 20 grams of water at 28° C. in a 400 cc. beaker, and to this suspension there is added rapidly, with a minimum of agitation, 180 grams of water at 80° C. The cover of the viscosimeter isremoved, and the mixture of starch and water is poured into the inner cup, up to the second graduation on the plunger. Immediately the cover is replaced, the platform is set into rotation at 42 R. P. M. and a stopwatch is started. zation, a temperature, or range of temperature, The temperature of the liquid is now about is reached at which the tendency of the globules 69° C. It is maintained at 69° C.:0.5° Cxthrough to coalesce is at its strongest. This temperature, the determination by maintaining the tempera or range of temperature, is designated herein, for ture of the water in the outer cup at this tem convenience of reference, the "temperature of 20 perature. maximum adhesiveness”; for vinyl acetate it has The viscosity of the liquid at any time is read a characteristic and fairly de?nite value of 67° in “degrees M” on the graduated disc. Previous C-'l0° C. ' calibration of the instrument with liquids of ac According to the present invention, the cri terion of acceptability of a starch for use as gran 25 curately known viscosities makes it possible to convert "degrees M" to millipoises (mp). ulating agent is that, under specific conditions In testing a starch for suitability for use in of test, presently to be described, a solution of this invention, a reading of viscosity is made at not more than one per cent of it in water ex hibits a viscosity of not less than 10 millipoises after having been heated for 15 minutes at the temperature of maximum adhesiveness of mono meric vinyl acetate, and also after having been heated for 120 minutes at this temperature. 15 minutes after the start. If the viscosity is too low at this time, the determination may be discontinued and the starch rejected as un suitable. If the viscosity at 15 minutes is above the required minimum, then the test is continued. If at the end of 105 minutes additional (120 In characterizing the starches which are op minutes total) the reading is still above the re erative in the present invention, the term "vis 35 quired minimum, the starch is acceptable. If cosity" is used herein, as a matter of convenience before that time the reading falls. below the in language, to designate a property of solutions required minimum, the test may be stopped, and of starch in which viscosity in the strict sense of the starch rejected. the word is complicated by at least one other If, on the other hand, the one per cent solu factor. Starches are not homogeneous in struc 40 tion of a starch, made up as described, is too “vis ture or behavior, in that each granule is made cous” or jellylike to be handled satisfactorily by up of a relatively insoluble capsule (amylopectin) the test apparatus, then a less concentrated solu and its relatively soluble contents (amylose) . At "; tion may be used instead and, if this latter passes the temperatures of use of starch in this inven test at both points of time, the starch is obvi tion, the material of the interior of the granule 45' the ously acceptable as being of well over minimum is readily soluble in water and, once it is released acceptable viscosity and behavior. upon the swelling and bursting of the capsules, The failure of a starch to pass this test may this material goes smoothly into solution. The be due to de?ciency in one or both of the factors material of the capsule, however, is merely swoll en and gelled, and persists as fragments suspend ed in the solution. In a viscosimeter these frag ments in suspension contribute to the reading of what is designated as viscosity. And because these fragments are fragile and become subdi vided by agitation of the solution, the magnitude which contribute viscosity, 1. e. to de?ciency in the inherent viscosity of the relatively easily solu ble amylose, to failure of the amylopectin to be effectively gelatinized at the temperature of the test, to excessive fragility of the gelatinized amylopectin, or to a combination of these de of their in?uence upon the‘ viscosity depends in 55 ?ciencies. Thus a starch of which the amylopec tln fails to gel adequately at 69° C. is not satis part upon the manner in which the solution has facory, even though it may become well gela been prepared. ' tinized at a somewhat higher temperature, for it Accordingly, it is necessary that the viscosity is at or near this temperature of maximum ad of a starch, for the purposes of describing the hesiveness of vinyl acetate that its granulating invention, be de?ned in terms of the apparent effect is required. And failure of a‘ starch to hold viscosity of a solution of it prepared in a speci?c its viscosity above the set minimum in the two manner and measured in a speci?c manner in a hours of gentle agitation in the test apparatus is speci?c viscosimeter. ' ' evidence that the gelatinized amylopectin is too A starch for use in the present invention is 65 fragile to maintain the viscosity of the starch tested as follows: under the more vigorous agitation encountered The instrument used is the Mac Michael vis cosimeter, as described in bulletin No. 560 of in the commercial reaction of polymerization. Elmer and Amend, New York city. As has been pointed out in the aforementioned Into the outer cup of this instrument is placed U. S. Patent 2,108,044, the amount of dispersing 120 cc. of water, and the inner cup (No. 32,788c) 70 agent should be, on the one hand, adequate to is inserted. The cylindrical plunger of 1 cm. di supplement the dispersing effect of the agitation ameter (No. 32,788!) is suspended by the wire of provided, so as to prevent coalescence of the dis gauge No. 34 B. and 8., the instrument is lev persed globules during the polymerization, but elled, the pointer is adjusted to zero, and the also should be, on the other hand, not so great cover is put into place. The water in the outer 5 2,401,445 6 as to make the dispersed globules obiectionably small. Other factors being constant, the amount used of a given dispersing agent serves to con trol the size of the particles of the polymer pro duced. The amount to be used of a given starch of some acidity by hydrolysis of vinyl acetate. and a further addition of alkaline substance will ‘ The following examples, wherein all propor tions are given by weight unless otherwise stated, illustrate speci?c embodiments of the invention. Example I The following ingredients are used: will be selected on that basis and will ordinarily be not more than about 0.25 per cent of the weight of the monomer nor less than 0.05 per cent. More frequently, when the starch is of. really su perior type, the amount will be of the order of 0.08 to 0.2 per cent of the weight of the monomer, preferably between 0.10 and 0.15 per cent. The selection of the precise optimum amount must be based upon accumulated experience and spe ci?c trials, since various factors must be taken into account. In general, the more effective the agitation of the mixture of monomer and aqueous vehicle, the less will be the amount of starch needed to sup plement the agitation itself in maintaining the monomer suspended in droplets of desired size in the vehicle. Thus the design of the reaction kettle and its agitator, and the speed of the lat ter, will in?uence the amount of starch to be used. The greater the ratio of aqueous vehicle to suspended monomer, the less is the amount of starch required to supplement the effect of agita tion in keeping the monomer in suspension. The type of polymer being made is also a factor, in that when polymer of low viscosity is being made .the globules of monomer in the course of being converted into granules of polymer remain longer in a soft and sticky condition, which promotes their coalescence, than is the case in the manu facture of polymer of higher viscosity. Finally, of course, the amount of starch required depends inversely upon the viscosity of the starch selected for use. The viscosity characteristics of a starch con not be needed. 10 . Parts Vinyl acetate monomer _______________ __ 100 Water _ ' 131 Aqueous hydrogen peroxide (27.56% by weight) ___________________________ __, 0.23 15 Sodium bicarbonate ____________ __'______ 0.13 Potato starch _______________________ _.., 0.35 In the viscosity test described above, an 0.34% solution of this starch gives a reading of 15.5 M. P. at 15 minutes and a reading of 21.5 M. P. at 120 20 minutes. A one per cent solution would, of course, give still higher readings. The vinyl acetate is introduced into a stain less-steel kettle provided with an agitator, re flux condenser, and jacket for heating by steam 25 or hot water. The vinyl acetate is heated to about 50° C. and then the starch and sodium bicar bonate are added, dry, and stirred with it to a slurry. To this slurry is now added the water, which has been preheated to about 80° C. Then 30 the hydrogen peroxide is added. With agitation continuing, the mixture is heated until re?ux ing-begins, at about 66° C. When the tempera ture of the charge reaches about 92° C., after about 52 minutes, the reaction is considered to be complete. The pH 'of the aqueous vehicle is slightly below 4.85 at the start of the reaction, ' and falls not below 3.8 at its conclusion. The liquid monomeric vinyl acetate, suspended in droplets in the aqueous vehicle by action of stitute the only criterion of its suitability, other 40 the agitation and the dispersing agent, has been than that it be free;.from objectionable con converted into solid globules of polyvinyl acetate, taminants. The source of the starch is imma of substantially uniform size. ' terial. For example, cornstarch; tapioca starch, The polyvinyl acetate thus made carries ad potato starch, and others have been used with - scrbed starch, which is removed or not according success, as has also methyl starch. As will be to the purpose for which the-polyvinyl acetate seen, the process of the invention serves to gelat is to be used. If the polyvinyl acetate is to be inize and dissolve the raw starch. converted into a polyvinyl acetal resin, the starch The water-soluble alkaline substance, serves will be destroyed in the natural course of the re two purposes, namely, (1) to promote the solu actions involved in this conversion, and there is bilization of the starch, and thus to render it ef 50 - therefore no need to remove it from the granules fective as a granulating agent, and (2) to pro-‘ of polyvinyl acetate. However, if the starch is vide a pH which is favorable to the polymeriza not to be removed, it is advisable to add a lubri tion under the catalytic in?uence of the hydro cant before the isolation of the resin from the gen peroxide. The amount of alkaline substance to be used is such as to develop and maintain in 55 aqueous slurry, as shown in Example IV. If, on the other hand, the polyvinyl acetate is to be the aqueous vehicle a pH between about 3.8 and used as such, and if the slight haziness contrib ' 4.9. Sodium bicarbonate, sodium phosphate, and uted by the starch will be found objectionable. sodium hydroxide are convenient substances to then the granules of polyvinyl acetate are freed use for this purpose but obviously other alkaline from starch by a treatment with a suitable deter substances can be employed. 60 gent, such-as a fatty alcohol sulfate. beforebe In the absence of the added alkaline substance, ing washed and dried. the system would be more strongly acid than this, by reason of hydrolysis of the vinyl acetate both Example II before and during polymerization. ‘This acidity The following ingredients are handled in the I must be reduced in order to promote the poly 66 same manner as were those of Example I. merization, because hydrogen peroxide does not Parts function effectively as a catalyst at a pH below Vinyl acetate __ ____ 100 about 3.8. On the other hand, the pH should Water ____ ___ 100 be kept below about 4.9 in order to avoid excessive Hydrogen peroxide (aqueous solution , hydrolysis of the vinyl acetate. 70 27.56% by weight) _________________ __ 0.4 If the amount of alkaline substance added is Potato starch ____ 1 0.4 sufficient to bring the pH at the start into the Sodium bicarbonate ___________________ _.. 0.1 upper part of the range 3.8-4.9, the pH will or dinarily remain within the range throughout the This starch is the same as that used ln'Ex reaction of polymerization despite the. release 75 ample I. v ‘ 9,401,445 7 The pH is within the same stated range throughout the reaction of polymerization. Example III 8 maintained at a temperature of 45' C.-55° C. in the reaction‘ vessel and the mixture is thoroughly _ stirred to distribute the starch in suspension. There is then added, with stirring, the amount of The followinglingredients are handled in the 5 water at 75° C.-80° C.. required to constitute the aqueous vehicle; the amount of water can be same manner as were those of Example I. varied widely but normally is at least equal in weight to the monomer. An alkalizing agent .Vinyl acetate ______________ __.. ______ __ 100 Water _____________________________ _.. 200 Hydrogen peroxide (aqueous solution 27.56% by weight) _________________ -_ Sodium bicarbonate __________________ .._ . 0.13 Sando tapioca‘ starch _________________ __ 0.5 such as sodium bicarbonate is introduced either 10 with the starch or with the water, and the cata lyst is introduced ‘in any convenient manner. The starch becomes‘ converted into‘ a water-solu- . ble product which serves as the dispersing agent ' and this, together with continuous ‘active agita In the viscosity test, a 0.88% solution of this tion, keeps the liquid monomer suspended in starch gives readings of 14.8 and 17.5 M. P. at 15 15 droplets in the aqueous vehicle. The joint action and 120 minutes, respectively. Example IV of heat and catalyst gradually effect the poly merization whereby the droplets of vliquid mono mer are converted into globules of polymer. The A glass lined reaction vessel equipped with an reaction vessel is provided with a reflux. con 20 e?icient stirrer is charged with 120 parts of mono denser to prevent loss of monomer by volatiliza meric vinyl acetate. While this material is tion. Alternatively, the starch may be intro gently agitated, 0.12 part of sodium bicarbonate duced into the water instead of into the monomer followed by 0.3 part of starch are added. These but the water should not be hot enough to cause ingredients are allowed to admix for five minutes gellation of the starch which would result in its after which 135.5 parts of water followed by 0.3 25 becoming lumpy. Slurrying the starch with the part of hydrogen peroxide"(2'l.56% aqueous solu monomer, as in the preferred procedure, provides tion) are introduced into the reaction mixture. a uniform distribution of it and guards against The entire mixture is then heated to re?ux by its lumping when it becomes gelled after contact the circulation of steam in an external heating with the hot water. 30 jacket. Gentle re?uxing is allowed to continue Obviously, it is preferred to use hydrogen per for 45 minutes by supplying external heating as ' oxide as the polymerization catalyst since one of necessary. As the reaction mixture continues to the advantages of this invention is that it per re?ux, the temperature gradually rises from about mits hydrogen peroxide to be used effectively. 60° C. to a peak temperature of about 96° C. However, other polymerization catalysts such as When the temperature of the reaction mixture 35 benzoyl peroxide and the like may be used if de is at 80° C., 0.24 part of sorbitan monopalmitate sired. The proportion of, catalyst isnot critical are admixed with reaction mixture. After the although the amount of hydrogen peroxide will mixture is re?uxed for the 45 minutes, the tem usually be between 0.04% and 4.0%, by weight perature is adjusted to 90° C. and maintained of the monomer. at this value for 10 minutes. The mixture is then 40 An advantage of the present invention is that cooled to 20° C. and the polymeric vinyl acetate it provides an improved method for using starch is isolated as satisfactory granules of substan as the dispersing agent in the granular polymeri tially uniform size by centrifuging the slurry. zation of vinyl acetate. Further, it provides a In the indicated viscosity test, a 0.34% solution means for the selection of a satisfactory starch in water of the starch used in this example pos for the purpose and a procedure which makes un sessed a viscosity of 12.5 M. P. and 17.0 M. P. at 15 necessary the heretofore necessary and undesir minutes and 120 minutes respectively. able step of preparing the solution of starch in The sorbitan monopalmitate employed in this advance. Further, the invention provides a pro example serves to lubricate the particles to poly 60 cedure for effectively using hydrogen peroxide as meric vinyl acetate during the steps of isolating the polymerization catalyst;‘- while hydrogen per the resin from the aqueous slurry. Other mate oxide has heretofore been recognized as desir rials may be employed for this purpose. The long able because of its absence of bad effect on color chain fatty acid partial esters of hexitol anhy of the resulting monomer, it has seldom been drides and the polyoxyalkene derivatives of hex 55 used because of its weakness as a catalyst. A itol anhydride have been found especially useful further and important speci?c advantage of the for this purpose. invention, resulting from its effective use of It will be understood that the above examples starch as a granulating agent, is the unusual uni are merely illustrative and that in its broad phase formity of the size and shape of the granules of the invention comprises heating under agitation no the polymerized product. Such uniformity is of a mixture of vinyl acetate monomer, water as a great value in commercial operations such as cen vehicle, a polymerization catalyst, a, water-solu trifuging, drying, and dissolving the polymer. ble alkaline substance in quantity to provide and As many apparently widely different embodi maintain throughout the reaction a pH between ments of this invention may be made without de 4.9 and 3.8 in the mixture, and, as a dispersing 65 parting- from the spirit and scope thereof, it is agent a starch having viscosity characteristics to be understood that the invention is not limited such that a solution of 1%. by weight, of the . to the speci?c embodiments thereof except as de- ' starch in water has a viscosity of notless than ?ned in the appended claims. , 10 millipoises after having been heated for- 15 'I claim: minutes at approximately 67° C.-'70° C. and also 1. Process of polymerizing vinyl acetate which after having been heated for 120 minutes at that comprises heating under agitation a mixture of temperature. vinyl acetate monomer, water as a vehicle, a per In carrying out the invention in its preferred oxide polymerization catalyst, a water-soluble al form both the liquid monomer and the water are kaline substance in quantity to provide and main pre-heated. The starch, in finely divided-form, is added in dry condition to the liquid monomer " tain a pH between 4.9 and 3.8 in the mixture and, 2,601,445 10 as a dispersing agent, a starch having viscosity ‘characteristics such that a solution of 1%. by weight. of said starch in water has a viscosity oi‘ not less than 10 millipoises after having been heated for 15 minutes at approximately 69° C. and also after having been heated for 120 min‘ utes at that temperature. 2. Process of polymerizing vinyl acetate which comprises heating under agitation a mixture of resulting mixture under active agitation until polymerization of said vinyl acetate is substan tially complete, the water-soluble alkaline sub‘ stance being so apportioned-that the pH of the water phase of the reaction mixture is main tained between 4.9 and 3.8 throughout the pe riod oi.’ heating. vinyl acetate monomer, water as a vehicle, a per 6. Process of polymerizing vinyl acetate which comprises heating vinyl acetate monomer to 45° ‘0.45’ (2., adding thereto with stirring between oxide polymerization catalyst, a water soluble al kaline substance in quantity to provide and main 0.05% and 0.25%, by weight thereof, of a dry comminuted starch having viscosity characteris tain a pH between 4.9 and 3.8 in the mixture and, tics such that a solution of 1%, by weight, of said as a dispersing agent,-between 0.05% and 0.25%. starch in water has a viscosity of not less than by weight of said monomer. of a starch having 15 10. millipoises‘aafter having been heated for 15 viscosity characteristics such that a solution, of minutes at approximately 69° .C. and also after‘ 1%, by weight, of said starch in water has a vis having been heated for 120 minutes at that tem cosity of not less than 10 millipoises after having perature, and dry comminuted sodium bicar been heated for 15 minutes at approximately 69° bonate, then adding thereto water at 75° C.-85° C. and also after having been heated for 120 min 20 C. in an amount at least equal to the weight of utes at that temperature. said monomer, and finally hydrogen peroxide in 3. Process of polymerizing vinyl acetate which catalytic amounts, and heating the resulting mix- . comprises ‘heating under agitationa mixture of ture under active agitation until polymerization vinyl acetate monomer, ‘water as a vehicle, hy of said vinyl acetate is substantially complete. drogen peroxide as a polymerization catalyst, a 25 the sodium bicarbonate being so apportioned that water-soluble alkaline substance in quantity to the pH of the water phase of the reaction mix provide and maintain a pH between 4.9 and 3.8 in ture is maintained between 4.9 and 3.8 through the mixture and, as a dispersing agent, between out the period of heating. 0.05% and 0.25%, by weight of said monomer, 7. Process of polymerizing vinyl acetate which‘ of a starch having viscosity characteristics such 30 comprises heating under agitation a mixture of that a solution of 1%, by weight, of said starch in vinyl acetate monomer, water as a vehicle, a water has a viscosity of not less than 10 milli-‘ peroxide polymerization catalyst, a water-soluble poises after having been heated for 15 minutes alkaline substance in quantity to provide ‘and at approximately 69° C. and also after having maintain a pH between 4.9 and 3.8 in the mix been heated for 120 minutes at that tempera 35 ture, a long chain fatty acid partial ester of a ture. hexitol anhydride as a lubricant, and, as a dis 4. Process of polymerizing vinyl acetate which persing agent, a starch having viscosity char comprises heating vinyl acetate monomer, add acteristics such that a solution of 1%, by weight, ing thereto with stirring between 0.05% and of said starch in water has a viscosity of not less 0.25 %, by weight thereof, of a dry comminuted 40 than 10 millipoises after having been heated for starch having viscosity characteristics such that 15 minutes at apprordmately 69° C. and also after a solution of 1%, by weight, of said starch in having been heated for ‘120 minutes at that tem water has a viscosity of not less than 10 milli perature, . poises after having been heated for 15 minutes 8. Process of. polymerizing vinyl acetate which at approximately 69° C. and also after having been 45 comprises heating under agitation a mixture of heated for 120 minutes at that temperature, and vinyl acetate monomer, water as a vehicle, a a dry comminuted water-soluble alkaline sub peroxide polymerization catalyst, a water-soluble stance, then adding thereto water at elevated alkaline substance in quantity to provide and temperature in an amount at least equal to the maintain a pH between 4.9 and 3.8 in the mixture. weight of said monomer, and ?nally hydrogen 60 sorbitan monopalmitate as a lubricant, and, as a peroxide in catalytic amounts, and heating the dispersing agent, a starch having viscosity char resulting mixture under active agitation until acteristics such that a solution of 1%, by weight, polymerization of said vinyl acetate is substan of said starch in water has a viscosity of not less tially complete, the water-soluble alkaline sub than 10 millipoises after having been heated for stance being so apportioned that the pH of the 65 15 minutes at approximately 69° C. and also after ‘ water phase of the reaction mixture is main having been heated for 120 minutes at that tem tained between 4.9 and 3.8 throughout the period perature. of heating. 9. Process of polymerizing vinyl acetate which 5. Process of polymerizing vinyl acetate which comprises heating under agitation a mixture of comprises heating vinyl acetate monomer to 60 vinyl acetate monomer, water as a vehicle, hy 45° C.-55° (2., adding thereto with stirring be drogen peroxide as a polymerization catalyst, a tween 0.05% and 0.25%, by weight thereof, of a water-soluble alkaline substance in quantity to dry comminuted starch having viscosity char provide and maintain a pH between 4.9 and 3.8 acteristics such that a solution of 1%, by weight, in the mixture, 9. long chain fatty acid partial of said starch in water has a viscosity of not less 65 ester of a hexitol anhydride as a lubricant, and, than 10 millipoises after having been heated for as a dispersing agent, a starch having viscosity 15 minutes at approximately 69° C. and also after characteristics such that a solution of 1%, by having been heated for 120 minutes at that tem weight, of said starch in water has a viscosity of perature, and a dry comminuted water-soluble not less than 10 millipoises after having been alkaline substance, then adding thereto water at 70 heated for 15 minutes at approximately 60° C. 75° C.-85° C. in an amount at least equal to the and also after having been heated for 120 mim weight of said monomer, and ?nally hydrogen utes at that temperature. - peroxide in catalytic amounts, and heating the JESSE CRIS WHITE. Certificiteof ‘Correction ‘ June 4, 1946;?- I‘ ‘Patent No. 2,401,445. ‘ ' ‘JESSE’. oms WHITE‘ - . It is hereby certi?ed that errors appear in the printed speci?cation of the above . numbered patent requiring'correotion as‘ follows: Column 1, line 15, for “various” read vigorous; column 2, line 41, for “vi'scosiy? read viscosity; line 48, same column for ‘l‘perioxide” read peroxide; c01u1m147, line 49; after the word “particles” strike out “to” and insert instead of; end that the said‘ Letters Patent should be read with glese coéréotions therein that the same may conform to the record of the case in the atent ce. 1 ‘ ' ‘ ' Signed and sealed this'13th day of August, Af ‘D. 1946. [w] LESLIE FRAZER, First Assistant Oommz'asioner of Pqtenta. .