United States Patent
`
`I72]
`
`[21]
`[22]
`[45]
`[73]
`
`Inventor
`
`Michael Niall Desmond O'Connor
`Norwalk, Conn.
`Appl. No. 878,883
`Filed
`Nov. 21, I969
`Patented Nov. 23, 1971
`Assignee American Cyanamid Company
`Stamford, Conn.
`Continuation-impart of application Ser. No.
`664,247, Aug. 30, 1967, now abandoned.
`This application Nov. 21, 1969, Ser. No.
`878,883
`
`[54]
`
`[521
`
`[51]
`[50]
`
`POLYACRYLAMIDE GELS CONTAINING LATENT
`THERMAL DEGRADATION INHIBITOR
`11 Claims, No Drawings
`
`0.5. CI ...................................................... .. 260/29.6 N,
`260/459 R
`Int. Cl ....................................................... .. C08f 29/00
`Field of Search .......................................... ..
`260/29.6
`HN, 29.6 N, 45.9 R
`
`["1 3,622,533
`
`’
`
`260/296
`260/296
`260/897
`
`[56]
`
`References Cited
`UNITED STATES PATENTS
`3,065,193 I l/l962 Volk ........................... ..
`3,235,523
`2/1966 SChUIZ et al.
`3,278,506 10/1966 Chamot et al. ............. ..
`FOREIGN PATENTS
`6/ 1967 Great Britain .............. .. 260/296 HN
`1,072,693
`8/l96l Germany .................... ..
`260/296
`1,112,294
`Primary Examiner-William H. Short
`Assistant Examiner-E. Nielsen
`Attorney-Evans Kahn
`
`ABSTRACT: Cyanamide, guanidine, succinimide, and urea
`inhibit the cross-linking of polyacrylamide without inhibiting
`the reaction or reactions by which monomeric acrylamide is
`converted to nontoxic form when aqueous gels containing a
`?nal polymer predominately or wholly composed of acryla
`mide residues and containing a ?nal polymerization catalyst is
`heated at temperatures above 70° C. until apparently dry.
`
`SNF Exhibit 1026, Page 1 of 7
`
`

`
`1
`POLYACRYLAMIDE GELS CONTAINING LATENT
`THERMAL DEGRADATION INHIBITOR
`
`3,622,533
`
`5
`
`IS
`
`25
`
`2
`In the past, attempts have been made to detoxify the
`residual acrylamide by the use of amines and ammonia; cf.
`Jones U.S. Pat. No. 2,831,481. The procedure is slow and only
`partially effective, and does not meet present-day standards.
`The discovery has now been made that aqueous gels of
`water-soluble acrylamide polymers which are toxic because of
`a content of monomeric acrylamide become nontoxic when
`subject to normal drying, without formation of more than a
`negligible amount of insoluble polymeric material, and
`without more than negligible detriment to the flocculating
`properties of the polyacrylamide, when the gels have a dis
`solved content of cyanamide, guanidine, succinimide, or urea,
`or mixtures thereof. Evidently when present in the gel the
`materials mentioned act as selective latent inhibitors, i.e., they
`stabilize the acrylamide polymer against the cross-linking
`reaction that would otherwise occur during the drying step
`and permit the residual acrylamide to be detoxi?ed by the
`heating. When present in the starting polymerization mixture,
`the materials do not interfere to more than a negligible extent
`20
`with the polymerization of the acrylamide or the monomers
`copolymerizable therewith.
`From another point of view I have discovered that aqueous
`acrylamide polymer gels containing acrylamide in toxic
`amounts and a polymerization catalyst therefor can be
`rendered substantially dry by evaporation of water therefrom
`at temperatures above 70° C. without insolubilization of the
`polyacrylamide and with substantially complete polymeriza
`tion of the residual acrylamide when the gels have a uniformly
`dissolved small amount of one or more of the four agents men
`tioned.
`The selective action of the inhibitors named above is excep
`tional. Many other materials have been tried but have been
`found unsatisfactory. Some are unsatisfactory because they do
`not cause adequately complete detoxi?cation of the residual
`acrylamide. Others are unsatisfactory because they do not
`protect the polyacrylamide from degradation (cross-linking),
`or are physiologically undesirable, or have o?‘ensive odors.
`Broadly, the compositions of the present invention are
`aqueous gels of water-soluble polyacrylamides which contain
`a small but effective amount of cyanamide, guanidine, succini
`mide or urea (or mixtures thereof) as latent agents which in
`hibit the formation of insoluble polymeric material and the
`degradation of the acrylamide polymer as ?occulant which
`occur when the gel is dried at elevated temperature.
`In preferred or particularly useful embodiments the gels
`contain water, a water-soluble acrylamide polymer, monomer
`ic acrylamide in toxic amount and a polymerization catalyst
`for the monomeric acrylamide. The gels may also contain such
`other materials as are customarily present in gels of this type.
`Such other materials include methanol or some other lower al
`kanol as stabilizer and as viscosity depressant; sodium sulfate;
`acetone; a dye (for identi?cation or for other purposes), and a
`perfume to mask any undesired odor present.
`Vinyl residues (i.e., units) other than acrylamide which can
`be present in the acrylamide polymer may be nonionic (for ex
`ample,
`those
`derived
`for
`methyl
`methacrylate,
`methylenebisacrylamide, p-chlorostyrene, vinyl acetate and
`acrylonitrile), or anionic (for example, those derived from
`acrylic acid, methacrylic acid, allylsulfonic acid, vinyl
`benzenesulfonic acid, vinyl sulfonic acid), or cationic (for ex
`ample, those derived from vinylbenzyltrimethyl ammonium
`chloride, diethylaminoethyl acrylate, diallyldimethyl ammoni
`um chloride, and p-vinylphenyl ammonium chloride).
`The amount of inhibitor which is added in any instance de
`pends chie?y on the average cross section of the gel during
`drying, the length of time at which the gel is maintained at that
`temperature, and the speci?c effectiveness of the inhibitor
`selected. In the case of urea (which appears to be the most ef
`?cient inhibitor on a weight basis), the least amount is
`required when the gel is dried as a thin film (or as thin strands
`or particles) at about 70° C. with efficient air circulation, so
`that the gel is reduced to apparently dry state in a compara
`tively short time. Under these conditions comparatively few
`cross-linkages form and these are easily inhibited, as gel hav
`
`This is a continuation-in-part of my copending application
`Ser. No. 664,247 ?led on Aug. 30, 1967, and now abandoned.
`The present invention relates to aqueous acrylamide gels of
`acrylamide polymers which contain toxic quantities of
`monomeric acrylamide, and to the drying of said gels with
`simultaneous decrease in the amount of the acrylamide
`present to nontoxic levels and without formation of insoluble
`cross-linked polymer. The invention includes the manufacture
`of apparently dry acrylamide polymers which are substantially
`free from insoluble cross-linked material and from monomeric
`acrylamide by processes which comprise incorporating one or
`more nitrogenous monomers into the polymerization mixture
`or into the polymer-containing gel at any subsequent stage
`prior to the drying step and then drying the gel at or above a
`certain temperature. (Acrylamide polymers, as used herein,
`refer to the homopolymer of acrylamide and to water-soluble
`copolymers of acrylamide with at least one other vinyl organic
`compound which forms a linear polymer when copolymerized
`therewith. The acrylamide is present to the extent of at least
`10 mol percent in the polymer.)
`Water-soluble acrylamide polymers are prepared industri
`ally by forming an aqueous solution containing 5-15 percent
`by weight of acrylamide (and if desired a suitable water-solu
`ble vinyl compound copolymerizable therewith), adding a
`polymerization catalyst (or combination of catalysts), and al
`lowing the solution to stand at appropriate temperature. The
`product is an aqueous solution containing at least 50 percent
`water by weight and roughly 5-15 percent by weight of the
`polymer; because it is normally a viscous or rubbery mass it is
`hereinafter tenned a gel.
`'
`The polymerizing reaction generally does not go to comple
`tion. The gel product, consequently, contains unreacted
`acrylamide (typically 0.5-5 percent of the acrylamide taken,
`and correspondingly small amounts of any other monomers
`present in the starting mixture), together with an equivalent
`unconsumed amount of the catalyst.
`When dried to a water content of less than about 15 percent
`by weight the gel becomes a friable solid which can be ground
`to be free-?owing water-soluble powder. When the drying is
`performed at low temperature, all of the product is soluble in
`water. However, when the gel is dried at temperatures above
`about 70° C., a proportion of the polymer chains cross-link, as
`a result of which at least a part of the acrylamide polymer is
`converted to water-insoluble form, and the effectiveness of
`the polymer as a flocculant decreases. Acrylamide polymers
`which contain even a trace of insoluble polymeric material are
`unsatisfactory for most purposes, and any substantial decrease
`in the efficiency of the ?occulant tends to render use of the
`?occulant uneconomic.
`_
`Most acrylamide polymers are nontoxic, but monomeric
`acrylamide is toxic. Water-soluble acrylamide polymers find
`use as ?occulants for suspended solids in water and as
`strengthening agents for paper. To ensure safety when these
`polymers are used for these purposes, the Public Health Ser
`vice has set 0.05 percent as the maximum permissible amount
`of acrylamide which may be present in any acrylamide
`polymer used for the clari?cation of drinking water. The limit
`for acrylamide in acrylamide polymers used in the manufac
`ture of paper is 0.2 percent, and a “Poison” label must be af
`fixed to containers of acrylamide polymers which contain
`monomeric acrylamide in excess of 0.5 percent by weight.
`To meet these standards, the polymerization of the acryla
`mide used for the preparation of these polymers must be
`driven to at least 99 percent of completion. Acrylamide
`polymers are heat-sensitive; they cross-link easily at tempera
`tures in excess of about 70° C. resulting in formation of insolu
`ble polymeric material. The rigorous standards imposed by the
`Public Health Service have handicapped manufacturers of
`acrylamide polymers because polymers which do not meet the
`aforesaid standards are not readily saleable, and polymers
`which do meet the standards are apt to require ?ltration to
`remove the insoluble material.
`
`70
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`75
`
`SNF Exhibit 1026, Page 2 of 7
`
`

`
`3,622,533
`
`20
`
`25
`
`35
`
`40
`
`4
`The inhibitors may be added in any form which will insure
`their rapid dissolution in the gel. The urea and succinimide are
`customarily added as such. The guanidine is most con
`veniently added as a water-soluble salt thereof. The cyana~
`mide may be added in its free fonn (as H,NCN) or may be
`added as a water-soluble salt thereof.
`‘
`The optimum amount of inhibitor which should be added in
`any instance depends upon the speci?c inhibitor (or combina
`tion of inhibitors) which are selected, and on the temperature
`and duration of the drying step. A suitable amount, however,
`can ‘be readily determined by laboratory trial, as is shown
`above and in the examples which follow. In the case of
`polymers at least 50 mol percent composed of acrylamide
`linkages, our data indicate that best results are obtained when
`the weight of the inhibitor is in the range of 0.5 percent to 1.5
`percent based on the dry weight of the polymer, peak results
`being generally obtained when the amount of inhibitor is in
`the middle part of this range, about 0.70 percent. Larger
`amounts either confer no advantage or are detrimental in that
`they cause detoxification of the residual acrylamide to
`proceed less rapidly than would otherwise be the case.
`The gels of the present invention, when containing
`preferred amounts of inhibitor, may be dehydrated to an ap
`parently dry state by evaporation of water therefrom at
`70°~l00° C.VThe drying may be performed by any of the
`present customary methods, preferably in an oven or continu
`ous tunnel hot air drier, the object being to evaporate suffi
`cient water to convert the gel into friable state without local
`overheating with formation of insoluble polymeric material.
`Preferably the gel has a high speci?c surface area during the
`drying. Thus the gel may be extruded as a ribbon and dried on
`a steam-heated drum, or it may be extruded in the form of
`spaghetti which may be dried in continuous tunnel. Such a
`method is claimed in copending application Ser. No. 41,807
`?led on June l, 1970 by M.L. Zonis, myself G. C. Shah, and
`Kenneth W. Saunders.
`The process of the present invention is capable of simul
`taneously drying the gel and detoxifying substantially all of the
`residual unpolymerized acrylamide without signi?cantly im
`pairing the solubility or flocculation e?iciency of the polymer.
`The invention is further described in the examples which
`follow. The examples are preferred embodiments of the inven
`tion, and the invention should not be regarded as limited
`thereto.
`'
`
`3
`ing this small cross section need remain at cross-linking tem
`perature for not more than a few minutes. More inhibitor is
`needed if drying is prolonged, i.e., when the gel is in the form
`of large (e.g. l inch) cubes. In such instances complete drying
`of the cubes takes l-2 hours at cross-linking temperatures. In
`general, no more than 2 percent (based on the weight of the
`acrylamide polymer) of inhibitor need be used, and industri
`ally 0.5 percent of urea has given substantially complete pro
`tection.
`The polymerization catalyst present in the gel may be any of
`the catalysts customarily used for the polymerization of
`acrylamide. Such catalysts include peroxides, (e.g., hydrogen
`peroxide, sodium peroxide, and t-butyl hydroperoxide) and
`redox pairs, (e.g. nitrilotrispropionamide-ammonium (or
`potassium) persulfate, ammonium persulfate-sodium bisul?te,
`and potassium persulfate-sodium sul?te combinations. The
`catalyst may be an excess catalyst from the amount initially
`used for formation of the polymer gel. The catalyst may be
`added after completion of the polymerization reaction, if for
`any reason an unduly large amount of the starting catalyst
`should have been unactivated or volatilized during the
`polymerization operation.
`The compositions of the present invention are gels which
`may be either viscous liquids or rubbery solids, depending on
`the concentration and the molecular weight of the polymer
`therein. Since the concentration of monomeric material to be
`polymerized in starting polymerization mixtures is generally
`between about 5 percent and 15 percent by weight, the gels of
`the present invention generally contain approximately 95 per
`cent to 85 percent of water, but may contain up to 50 percent
`of water by weight. The precise amount of water, in any in
`stance, however, is not a characterizing feature of the gels of
`the present invention and may be greater or less than the
`amount stated.
`The thermal degradation inhibitor may be incorporated at
`any stage in the polymerization process, or the inhibitor may
`be incorporated into the gel after the polymerization reaction
`has gone to substantial completion and before the gel has been
`dried. In the latter instance the gel may be cut into small
`pieces which may be sprayed with an aqueous solution of the
`inhibitor; in the course of a few hours the inhibitor di?‘uses
`uniformly through the gel and dissolves therein. However, it
`will generally be found more convenient to dissolve the inhibi
`tor into the initial reaction mixture, before or during the
`polymerization process, prior to the stage where the reaction
`mixture becomes a gel. It is an important feature of the
`present invention that the inhibitor does not signi?cantly af
`fect the action of the polymerization catalyst and does not
`enter into the polymerization reaction.
`-
`The inhibitor is added in sufficient amount to inhibit ther
`mal degradation of the polymer to the desired extent. The
`term “degradation" in this speci?cation for convenience is
`used to designate the formation of insoluble polymeric materi
`al which occurs as the polymer is maintained above about 70°
`C. and is also used to designate the decrease in the ?occulat
`ing efficiency which the heating also causes.
`Formation of small amounts of insoluble polymeric material
`can be readily detected by stirring a small amount of the
`polymer in neutral water at room temperature and stirring the
`mixture gently for 3 hours. Any insoluble material present can
`be detected as gelatinous particles which are termed “?sh
`eyes" in the art, and generally these must be removed (by ?l
`tration) before solutions of the polymer can be used.
`Deterioration of the ?occulating ef?ciency of the polymer
`can be determined by forming a substantially self-sustaining
`suspension of silica, cellulose fines or sewage particles, adding
`sufficient of the polymer to cause the suspended particles to
`flocculate and noting the time required for the particles to set
`tle a predetermined distance. Any material increase in the
`time required for suspensions treated in this manner to settle
`to this extent (undried polymer being used as the control) in
`dicates that the ?occulating efficiency of the polymer has
`decreased.
`
`75
`
`45
`
`50
`
`55
`
`60
`
`65
`
`EXAMPLE l
`The following illustrates the comparative effectiveness of
`cyanamide, urea, guanidine, and succinimide as agents which
`inhibit the formation of cross-linkages when an acrylamide
`polymer gel containing monomeric acrylamide in toxic
`amount is heated above 70° C. to dry the same and to detoxify
`the monomeric acrylamide therein. In these runs, the inhibi
`tors are added to the gel before the gel is dried.
`The acrylamide polymer used is a tough, rubbery gel con
`taining 1.7 percent (based on the weight of polyacrylamide
`therein) of residual (monomeric) acrylamide. The gel is
`prepared by forming (under a blanket of nitrogen) a reaction
`mixture of 9,000 lb. of deionized and deoxygenated water,
`1,000lb. of acrylamide (monomeric, inhibitor-free), 0.04 per
`cent of ammonium persulfate, and 0.16 percent of 3,3',3"
`nitrilotrispropionamide (based on the weight of the acryla
`mide) as redox catalyst, as shown in Kolodny U. 5. Pat. No.
`3,002,960, and maintaining the mixture at 20° C. under
`nitrogen for 8 hours. Polymerization proceeds spontaneously.
`The gel contains about 90 percent of water by weight, l.7 per
`cent of unreacted acrylamide (based on the dry weight of
`solids), and sufficient unreacted catalyst to polymerize the
`residual acrylamide. The gel is completely soluble in water at
`room temperature.
`‘
`into a l,0O0-g. portion of the gel in a heavy-bladed (sigma)
`mixer is blended one of the materials shown in the table
`below. The material is added in powder state and appears to
`
`SNF Exhibit 1026, Page 3 of 7
`
`

`
`3,622,533
`
`5
`i 6
`dissolve rapidly in the gel. The gel is cut into slabs one-fourth
`of methanol, and sufficient phosphoric acid to adjust the pH to
`inch thick which are placed in a forced draft oven having an
`3. The solution is then aerated vigorously for 15 minutes at 20°
`air temperature of 85° C. After 2 hours the slabs contain 6 per
`C. and heated to 50° C. To the solution is then added with stir
`cent water by weight and are hard and brittle sheets which are
`ring 200 p.p.m. (based on the weight of the acrylamide) of
`apparently dry. The dry material is ground in a laboratory 5 potassium persulfate and 80 p.p.m. of potassium mctabisul?te
`grinder equipped with a —40 mesh screen. The -—40 mesh
`as redox polymerization catalyst. Stirring is then halted, and
`product is an apparently dry, free-?owing powder. The
`the solution is then allowed to polymerize at 50° C. The solu
`powder is analyzed for its content of unpolymerized
`tion is analyzed for its content of monomeric acrylamide and
`(monomeric) acrylamide and insoluble matter, and the ef?- l 0 its ?occulation efficiency is determined by standard laborato
`ciency of the polymer as a flocculant is determined. The
`ry test, in the same mannerasin example i.
`procedure is repeated with the other agents. Results are as fol-
`Run B. The procedure of run A is repeated, except that the
`lows:
`amount of urea is decreased to 0.55 g. to determine the com
`
`Pereent monomeric
`Acrylamide in gel 1
`
`Inhibitor
`
`Number
`
`Before
`drying
`
`After percent
`drying
`deer. N time
`
`Percent
`added 1
`
`Floeo. Insolubles
`elite,
`t.
`seconds 5
`percent a
`
`1 70
`1.70
`
`54. 0
`........................ _.
`(Not dried)
`0.0
`100.0 None _____________________________ __
`
`0, 0
`21
`
`76. 4 Ureu ________ ..
`0. 405
`1. 70
`36.0 __-..do6.___....
`1.08
`1.70
`53. 5 Guanidine l___
`0.65
`1. 70
`36.6 ___..do ______ ..
`1.08
`1.70
`83. 5 Sueeinimide- _
`0. 28
`1. 70
`83.6 Cyanamide 0..
`0.28
`1. 70
`1 Based on dry weight of polymer in gel.
`1 Seconds to settle standard laboratory silica suspension (see text above). In absence of
`polymer, settles in approx. 600 seconds.
`3 After three hours of vigorous
`agitation with water at room temperature.
`4 Added as 7.79 g. of guanidine nitrate.
`5 Added as 11.48 g. of guanidino carbonate.
`0 Added as free cyanamide (IIzHCN).
`
`0. 0
`0.0
`0. 0
`0.0
`0. 0
`0. 0
`
`0. e2
`3.73
`3. 0
`6.0
`G 35
`1 30
`
`03. 7
`58.3
`70.0
`(10.7
`58. 2
`65. 5
`
`The results show that the inhibitors substantially completely
`stabilize polyacrylamide against degradation of its flocculating'
`cf?ciency and against insolubilization, while permitting a very
`large amount of polymerization of the residual acrylamide
`present to occur.
`When tested in the same manner:
`Acetamide
`Ammonium sulfamate
`Biuret
`Dicyandiamide
`methyl phosphite
`Ethylene glycm
`Formaldehyde
`
`parative e?'ect of this smaller amount.
`The resulting polymer gels are completely water-soluble.
`The gels are then kneaded in a sigma mixer for a few
`minutes to ensure uniformity, and the gels are cut into small
`35 cubes. The cubes are tray-dried in a forced draft oven having
`an air temperature of 85° C. for the time shown in the table.
`The products have water contents of respectively 10.2 percent
`and 9.2 percent and are hard, granular, and apparently dry.
`The products are then ground to I00 percent —40 mesh.
`The insolubles in the product are determined as well as their
`?occulation efficiency.
`The monomeric acrylamide contents of the two products
`and the efficiency of the products as ?occulants are then
`redetermined. Results are as follow.
`
`. 40
`I
`
`l’oreont 'uerylumldo
`mouoinoringoll
`
`Flocculntion olll~
`eioney, soc."
`
`ltuu
`
`lioforo
`llrs.
`dryed drying
`
`iii-mt
`Alter Percent
`drying
`door. added 1
`
`lioforo
`drying
`
`After
`drying
`
`l’ert-vnt
`insol.2
`
`.. .. . ......._.__.._.._.._._. .. ,. . _
`
`. pal-cm“ . ___.._ ____.__. .
`
`2. 07
`2. 0
`2. 7s
`2. a
`1 Based on weight of polymer.
`2 For test 50o Example 1.
`
`0. 0:13
`0. 076
`
`98. It
`07. :t
`
`1. 0
`0. 6
`
`on. o
`71. o
`
`70. a
`74. 5
`
`0. 0
`ll. 0
`
`Fm'mmf‘ide
`Hydl'almfl
`Hydmqumonc
`Hydroxylamine hydrochloride
`Mcrcaptosuccinic acid
`Sodium bicarbonate
`Sodium isopropyl xanthate
`Sodium nitrite
`are substantially ineffective. in each instance the polyacryla
`mide undergoes substantial thermal degradation on drying,
`losing in the process a substantial part of its water-solubility orl
`its flocculating power, or both.
`‘
`
`EXAMPLE 2
`The following illustrates a procedure similar to the forego-.
`ing, but wherein the inhibitor is added to the startingv
`polymerization mixture.
`,
`Run A. To a solution of 1 l2 g. of acrylamide in 626 g. of;
`water are addcd L! g. of urea as cross-linking inhibitor, 48 g.
`
`The results show that the urea does not interfere signi?
`cantly with the polymerization of the acrylamide and permits
`substantially all of the residual acrylamide to be converted
`while the gel is being dried, yet has no detrimental effect on
`the efliciency ofthe polyacrylamide as a flocculant.
`
`EXAMPLE 3
`
`60
`
`65
`
`The polymerization procedure of example 2 is repeated ex
`cept that amount of urea added is varied as shown in the table
`below, addition of the urea is deferred until the p0lymeriza~
`tion reaction is completed, and the drying time is extended to
`3 2.35 hours at 85°C. The urea is incorporated by the method of
`example l. Control (I) is the polyacrylamide gel which has
`not been treated with inhibitor and which has not been dried.
`(.‘ontrol (2) is the same gel which has been dried.
`
`SNF Exhibit 1026, Page 4 of 7
`
`

`
`3,622,533
`
`Run
`
`Control (1) ..... . _
`Control (2) _____ _.
`1
`
`Acrylamide content l
`———— Percent
`Percent
`urea
`decr.
`added 1
`
`After
`drying
`
`Before
`drying
`
`Flocc.
`eff.
`seconds 4
`
`Percent
`insol 4
`
`1. 42 ______________________ _ _
`1. 42
`None __________ ._
`1. 42
`0. 013
`09.
`1. 42
`0. 013
`99. 5
`1. 42
`0. 00
`100. 0
`1. 42
`0. 05
`07. 5
`
`None
`None
`0. 28
`8 0. 63
`0. 08
`2. 1
`
`52.7 __________ . .
`(5)
`0. 0
`50. ‘.l
`1. 9
`65. 0
`0.0
`56. 3
`0.0
`59. 8
`0. 0
`
`1 Based on dry weight of solids.
`I
`1 Based on starting acrylamide.
`_ 3 )1. sample withdrawn after 2% hours of drying contained 0.00% of acrylamide and 0.6%
`
`mso u cs.
`4 For method used, see Example 1.
`5 Not; tested becausecontengol i_nsolubles is in excess of commercial standard_._v ’ W __
`
`-
`
`Comparison of these results with the results of example. l in- l
`dicates that the urea may be added before or after the
`polymerization step with closely similar results.
`‘
`
`EXAMPLE4
`
`EXAMPLE 6
`The following shows the comparative effect of too much in
`hibitor on conversion of residual monomeric acrylamide and
`on the amount of insoluble matter in the products after drying,
`together with the comparative efficiencies of the products as
`~?occulants.
`'20
`The gel used as starting material is prepared by mixing 920
`I
`g. of acrylamide (AM). 80.0 g. of sodium sulfate as
`The following illustrates the large scale manufacture of
`polymerization accelerator. l00 g. of methanol as viscosity
`polyacrylamide with the inhibitor added prior to the
`depressant. and water to make up to 10 kg. at 32° C. The solu
`polymerization step.
`i
`5 tion is deoxygenated by sparging with nitrogen for 2 hours. ad
`To 7,250 lb. of water at 20° C. in a 1.000-gal. closed reactor i 2
`justed to pH 6.5 by addition of saturated aqueous sodium
`is added with stirring 1,090 lb. of acrylamide (monomeric, in- '
`bicarbonate solution after which 200 p.p.m. (based on the
`hibitor-free) and l0.9 lb. of urea. The resulting solution isv
`acrylamide), each of (NH.),S,O.. and NaBrO3. and 20 p.p.m.
`heated under nitrogen to 50° C. To this is added with stirring
`of Na,SO, are added. The mixture is allowed to stand over
`4.9 lb. of a 1 percent aqueous solution of K,S,O, (potassium'
`30 night. Polymerization is then complete; the product is a stiff.
`rubbery gel containing 3.74 percent of monomeric acrylamide
`metabisultite). 43.6 lb. of a 1 percent aqueous solution of1
`K,S,O.. (potassium persulfate), and 80 lb. of methanol; stirring
`based on the polyacrylamide present.
`is stopped as soon as the initiators are dispersed. Polymeriza
`tion is essentially complete in the usual time of 6 hours. The
`resulting rubbery gel is removed from the reactor by a‘screw
`type pump under a positive pressure of nitrogen. and is ex
`truded through 54inch ori?ces upon a moving belt passing
`through a circulating hot-air drier at 85° C. The rods which
`emerge from the drier are apparently dry. They are then
`ground to a powder. The product is free-?owing and ap
`0.1 percent by weight of '40 Run B. A second 1 kg. portion of the gel is treated in the
`parently dry. it contains less than
`same way except that the amount of urea added is doubled
`monomeric acrylamide, and dissolves completely when gently
`(2.04 percent).
`stirred for 3 hours in water at 20° C.
`Control. A third 1 kg. portion is taken and is reserved as
`in the absence of the added urea the product before drying
`5 control. To this nothing is added.
`would contain l-5 percent residual monomeric acrylamide
`The gels are chopped into ‘la-inch cubes which are placed
`based on the weightof polyacrylamide therein, and after dry
`for 2.5 hours is a laboratory oven at 85° C.. at which time they
`ing would contain about 20 percent by weight of insoluble
`have a water content of 9.5 percent. The properties of the
`polymer.
`products are as follow:
`
`A
`35 Run A. Upon l kg. of the gel in a sigma kneader is sprinkled
`0.935 g. of powdered urea (1.02 percent on the weight of
`polyacrylamide present). The mixture is kneaded for l0
`minutes.
`
`EXAMPLE 5 ‘
`
`The following illustrates the large-scale manufactuire of an
`anionic acrylamide copolymer with addition of the stabilizing
`agent to the mixture of monomers to be copolymerized.
`The general procedure of example 4_ is followed. To 7,250
`lb. of deoxygenated and deionized water at 20° C. is added
`with stirring 218 lb. of anhydrous sodium sulfate, l7.4 lb. of
`acrylic acid (stabilized with 2.000 p.p.m. of eugenol), 854.6
`lb. of acrylamide (monomeric, inhibitor-free), and 8.72 lb. of 60
`urea. The resulting solution is heated at 50° C. and then 3.9 lb.
`of a 1 percent solution of K,S,O_-, and 41.9 lb. of 1 percent.
`solution of K,S=O.. are added. Agitation is stopped as soon as
`the initiators are dispersed. Thereafter the procedure of exam
`ple 2 is followed.
`The dry, ground product corresponds to a 96:4 molar ratio
`acrylamidezacrylic acid copolymer, and rapidly and complete
`ly dissolves in cold water. It contains less than 0.2 percent by
`weight of unsaturation (monomeric acrylamide-l-monomeric ‘
`.70
`acrylic acid) calculated as acrylamide.
`‘
`Had the urea been omitted, the product before drying .
`would have contained l-5 percent residual (acryla
`mide+acrylic acid), based on the weight of polymer present, l
`and after drying would have contained about 20 percent of in- ‘
`575
`solubles.
`‘
`l
`
`Percent -
`urea
`added 1
`
`Percent acrylamide
`-—-————-——
`Before
`After Percent Percent
`drying drying
`deer.
`insol.l
`
`Product
`
`3. 74 __________________ _ _
`3. 74
`0. 0075
`99. 8
`3. 74
`0. 0850
`97. 8
`
`15
`0. 15
`0. 00
`
`Floc.
`cilic.
`sees.2
`
`78
`55
`57
`
`5 5
`
`‘
`
`1 Based on weight of polymer.
`._’.§BQ_EXBIIIPIQ.1.:
`
`65
`
`Comparison of Run A with Run B shows that while each
`amount of urea was about equally as effective as the other.
`there was a great difference between the two in terms of the
`amount of monomeric acrylamide detoxi?ed, 1.02 percent of
`urea causing the detoxification of about ll times as much
`acrylamide during the drying as 2.04 percent of urea.
`I claim:
`1. An aqueous gel consisting essentially of ( l) at least 50
`percent by weight of water, (2) at least 5 percent by weight of
`a water-soluble acrylamide polymer at least 10 mol percent
`composed of acrylamide units, (3) monomeric acrylamide in
`toxic amount, (4) a polymerization catalyst for said monomer
`ic acrylamide, and (5) a small but effective amount, less than
`about 2 percent of the weight of said polyacrylamide. of a
`material selected from the group consisting of cyanamide,
`guanidine. succinimide. urea, and mixtures thereof. as agents
`
`SNF Exhibit 1026, Page 5 of 7
`
`

`
`3,622,533
`9
`inhibiting the formation of insoluble polymeric material when‘
`said gel is heated at a temperature in excess of 70°
`C. to dry
`the same and to detoxify said monomeric acrylamide.
`2. A gel according to claim 1 wherein the inhibitor is urea.
`3. A gel according to claim 1 wherein the inhibitor is
`guanidine.
`4. A gel according to claim 1 having a pH between 3 and 6.
`5. A gel according to claim 1 wherein the acrylamide
`polymer is at least 50 mol percent composed of acrylamide
`units, and the weight of the inhibiting agent is between 0.5
`percent and 1 percent of the weight of said polymer.
`6. In the manufacture of
`an apparently dry water-soluble;
`acrylamide polymer by :a process wherein an aqueous gel of a
`water-soluble acrylamide polymer at least 10 mol percent
`composed of acrylamide units, said gel containing more than
`50 percent water by weight, monomeric acrylamide in toxic
`amount, and polymerization catalyst for said acrylamide, is
`heated above about 70° C., thereby drying said gel to a water
`content of less than about 10 percent by weight and detoxify
`ing said acrylamide: the improvement which consisting essen
`tially in dissolving in said gel a small but effective amount, less
`than 2 percent based on the weight of said polyacrylamide, of
`a material selected from the group consisting of cyanamide,
`guanidine, succinimide, urea, and mixtures thereof as agents
`inhibiting the formation of insoluble polymeric material while 25
`said gel is heated to
`dry the