CA1056542A - Process for forming acrylic elastomer containing interpolymer particles by emulsion polymerization - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Elastomer-containing interpolymers are prepared by the suspension polymerization of vinyl chloride in the presence of an aqueous emulsion of particles comprising a crosslinked acrylic elastomer having a glass transition temperature (Tg) of less than about 25°C., said emulsion containing from 0.2% to 5.0% by weight of a sulfonate salt of an ethoxylated alkyl phenol anionic emulsifier to insure smooth and clean running of both the emulsion and suspension steps. From about 0.1% to 0.5% of a salt of a polyvalent metallic cation or quaternary ammonium salt can also be added to the suspension batch as a coagulating agent after the suspension reaction has been completed to completely pre-cipitate the latex in the second step and give a clean process effluent. The interpolymers may be used as modifiers for the reinforcement of a large variety of rigid plastics whereby excellent impact strength is imparted without harming any other physical properties of the rigid plastics so treated.

Description

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Descr ption of the Invention Processes for the suspension polymeriaation of vinyl chloride or a mixture of vinyl chloride with a minor proportion of one or more comonomers, in the presence of an aqueou~ emulsion of crosslinked, acrylic elastomer particles are known. These processes yield particles of what may be termed "suspension~
emulsion interpolymer" (SEI) particles. The particles formed by this process are an admixture of the suspension polymerized vinyl monomer and the cross-linked acrylic elastomers. The particles have a particle size which is substantially greater than that of the original elastomer emulsion particles utilized in their preparation. As a result, these SEI particles are far .. ~

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easier to dry and to handle than the emulsion elastomer particles.
Moreover, they provide superior results as high impact plastics and as modifiers for the reinforcement of a large variety of rigid plastics wherein they impart excellent impact strength without substantially detracting from any other physical properties.
Examples of typical 5EI processes are described in U. S~ Patent Nos. 3,~57,172 to Gallagher and Hwa and 3,660,529 to Groch, and in U.S. Patent 3,969,431 ~n the name of Ruth E. Galla~her.

The SEI processes of the prior art utilized surfactants or emulsifiers in the emulsion containing the acrylic elastomer which often produced either agglomeration or plate-out of the latex in the emulsion step or additional plate-out which causes poor temperature control in the suspension step, or both of these undesired results, due to interference between the suspending agent and the residual emulsifier. Although many emulsifiers can be employed in the emulsion step without undesireable plate-out occurring, they cause the aforementioned problems in the second suspension step. Sodium lauryl sulfate, an anionic emulsi-fier, iB an example of one such emulsifier which causes plate-out in the suspension step. The sulfosuccinate emulsifiers have also been tried without success. The prior art processes normally allow no more than two batches to be run before the reactor must be solvent cleaned. The cleaning operation requires 4-5 hours of kettle time, plus the costs of solvents and labor. With the present invention, as described in greater detail below, a larger number of batches can be run between cleanin~ operations thereby leading to a more economical operation and avoidance of the ~OS654Z

aforementioned agglomeration and temperature control problems.
Prior art suspension emulsion interpolymer processes also often gave a process effluent which is quite hazy due to the presence of latex particles dispersed in the aqueous medium. According to a preferred embodiment of the present invention, an ef~luent is produced which is subst~ntially less hazy than those o~ the prior art.
The present in~ention entails the use o a sulfonate salt of an ethoxylated alkyl phenol anionic emulsifier in the preparation of the cross-linked acrylic elastomer and, in a preferred embodiment, the use of a coagulant containing either a polyvalent metallic cation or a quaternary ammonium cation in the later suspension batch. The use of the above described emulsifier solves the problems of agglomeration, plate-out and poor temperature control and the use of the coagulant eliminates a hazy effluent in a SEI process. The use of the above described anionic emulsifier results in a suspension step which runs smoothly with excellent temperature control and minimum wall fouling and produces a product having good impact properties. The use of the above described type of coagulant in the suspension step insures the complete precipitation of the latex, thereby facilitating a smooth running for that step and the production of an effluent which is substantially less hazy than the effluents resulting from prior art processes.

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The elastomer particles which are utilized in preparing the SEI particles of this invention are made by means of conventional aqueous emulsion procedures w~ll known to those skilled in the art of using emulsifiers and water soluble catalysts and are described in a number of U.S.
patents including the above mentioned U.S. Patent Nos.
3,657,172 and 3,660,523 and U.S. Patent 3,929,933.
Thus in accordance with the present teachings, an improvement is provided in the method of making acrylic elastomer containing interpolymer particles by the emulsion polymerization of an acrylate monomer charge containing a monomer having at least two ethylenically unsaturated bonds as a cross-linking agent to form an aqueous emulsion which contains cross-linked acrylic elastomer particles and by thereafter suspension polymerizing a monomer charge comprising vinyl chloride in the presence of acrylic elastomer particles.
The improvement in such process comprises using a sulfonate salt of ethoxylated alkyl phenol in the range of from 0.2%
- to 5% by weight of the monomer charge containing the acrylate compound.
In conducting the aqueous emulsion polymerization step leading to the preparation of these elastomer particle~, there is first prepared a monomer charge comprising an aqueous emulsion containing about 10 to 50%, by weight, of one or more monomers the identify of which will be described in detail hereinbelow.

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~ (~ C-1~150 ~15~S42 From about 0.05 to 2. ~, by weight of the monomer mixtureJ of a water-soluble catalyst suchJ for exampleJ as ammoniumJ sodium or potassium persulfate, hydrogen peroxide, or a redox system, such as a mixture of a persulfate wi~h an alkali metal bisulfite, thiosulfate or hydrosulfiteJ is introduced and the mixture is then heated at a tempsrature o~ from about 40 to 95C. ~or a period of about 0.5 to 8 hours~
In order to obtain the benefits of this invention, the emulsion must contain from about 0.2 to 5.0~ by weight of the total monomer charge, of a sulfonate salt of an ethoxylated alkyl phenol anionic emulsifier. Such emulsifiers are a known class of surfactants and have been described in a number of prior art publications and patents although they have not been advocated for use in the type of SEI process described herein.
McCutcheon's Detergents and Emulsifiers, 1969 A~naal, p. ~l et seq.,German Offenlegungsschrift ~o. l,9~8,193~ and Chemical Abstracts, 72: 79,900m (1970). Suitable emulsifiers which fall into this class are available under the following trade name designations: Cellopal*40 and lO0 (Tanate~ Chemical Corp.).
2C Sinnozon P~*50 and PEA ~0 (Sinn~va rFrance~ ); and Triton X-200 and X-202 (Rohm & Haas Co., Inc.~. The preferred emulsi~er or surfactant is "Triton X-200"s a liquid, 28 wt~
solids, sodium sulfonate salt of an ethoxylated alkyi phenol anionic emulsifier~ which has a specific gravity of about l.064 at 25C/25C and a PH of 7 to 9( ~ by wt. solids solution at 25C~

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-~ C-~150 ~0S~;S42 The polymerization of the SEI interpolymers is greatly facilitated by ntroducing the monomer charge to the system in several portions over a period of from about 1 to 3 hours.
Thus, where this is not done and the total monomer charge is introduced in one portion, the resulting exothermic polymeriza-tion reaction often becomes virtually uncontrollable leading to overheating which, in turn, may set up, i.e. coagulate, the resulting polymer latex. However, by dividing the monomer charge and introducing it in several portions, the resulting polymerization reaction remains controllable, and overheating and coagulation can be prevented.
The acrylic elastomer particles used in preparing the SEI particles of this invention can comprise any crosslinked acrylic polymer or copolymer having a Tg, i.e. a glass transi-tion temperature, of less than about 25C. and having the ability to be polymerized by means of free radical initiated emulsion techniques. These acrylic elastomer particles should be crosslinked so that they can retain their size and shapa during subsequent poLymer processing steps. ~his crosslinking can be achieved during the polymerization of the acrylic elastomer if a monomer containing more than one ethylenically unsaturated bond is included in the polymerization re~ipe. As used in this disclosure, the term "crosslinked" denotes a polymer which at ambient temperatures is su~stantially insoluble in such organic ~05~;~i4~
solvents as tetrahydrofuran or cyclohexanone Examples of acrylic elastomers that can be used include the polymers of the aromatic and the C2-C8 alkyl acrylates such as poly-(benzyl acrylate) and poly-(n-butyl acrylate), poly-(ethyl acrylate)J poly(n-octyl acrylate) and poly-(2-ethyl-hexyl acrylate) and copolymers thereof which are crosslinked with small quantities o a monomer containing more than one ethylenic~lly unsaturated bond such as, for example, allyl methacrylate~ divinyl benzene, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, trimethylolpropane trimeth-acrylate, methylene-bis-acrylamide, diethylene glycol diacrylate, ethylene glycol diacrylate, divinyl ether, diallyl fumarate, diallyl phthalate, divinyl sulfone, divinyl car~itol, triethylene glycol dimethacrylate, trimethylene glycol diacrylate, butylene glycol diacrylate, pentamsthylene glycol diacrylatel glyceryl triacrylate, octylene glycol diacrylate, trimethy~1 propane triacrylate, the tetraacrylate ester of pentaerythritol and various diallyl phosphonates.Preferred for use is a copolymer of n-butyl acrylate and 2-ethylhexyl acrylate in a 30:70 to 70:30 weight ratio. The preferred cross-linking agent is buty-lene glycol diacrylate.
Also useful are copolymers of the aromatic and C2-C8 alkyl acrylates with minor proportions, i.e., less than about 1 ~ by weight~ of one or more of such vinyl monomers as styrene, acrylonitrile, vinyl acetate3 and met~yl methacrylate, ethylsn-` ` C-1~150 :~L0565~;Z

ically unsaturated carboxylic acids such asJ ~or example, acrylic,methacrylic, itaconic and maleic acids; isoprene;
chloroprene; 1, 3-butadiene; vinylidene chloride; propylene;
ethylene; and, other common vinyl monomers. Optimum results 1 are obtained by the use of a crosslinked copolymer containing from about 90 to 99.8~, by weight, o an n-butyl acrylate/2-ethylhexyl acrylate copolymer cross-linked with about 0.2~ to lo~, by weight, of 1, 3-butylene glycol diacrylate, said percentages being based on the combined weight of cross linking agent and the weight of acrylate copolymer.
The next step in the process of preparing these SEI
particles involves the suspension polymerization of a monomer charge comprising vinyl chloride in the presence of the aqueous emulsion of elastomer particles whose preparation has been described hereinabove. Applicable vinyl chloride polymers for preparation of the SEI particles incluae homopolymers and copolymers of vinyl chloride together with a minor proportion of one or more of such vinyl monomers as the alpha-olefins such as ethylene, propylene and butylene; vinyl esters o~ car-boxylic acids such as vinyl acetate, vinyl benzoate, vinyl butyrate, and vinyl stearate; vinylidene halides such as vinyli-dene chloride; the Cl-c2o alkyl esters of acrylic and meth-acrylic acid such as methyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate and lauryl C-l~150 ~OS654Z

acrylate; aryl, halo- and nitro- substituted benzyl esters of acrylic and methacrylic acid such as benzyl acrylate and 2-chlorobenzyl acrylate; ethylenically unsaturated monocarboxylic acids such as acrylic and methacrylic acids; ethylenically unsaturated dicarboxylic acids, their anhydrides and their C1--C20 mono- and dialkyl esters such as aconitic acid, fumaric acid, maleic acid, itaconic acid, citraconic acid, maleic anhydride, dibutyl fumarate and monoethyl maleate; amides oE
ethylenically unsaturated carboxylic acids such as acrylamide and methacrylamide; vinyl aryl compounds such as styrene and alphamethyl styrene; nitriles of ethylenically unsaturated carboxylic acids such as acrylonitrile and m~sthacrylonitrile, vinyl pyrrolidones such as ~-vinyl-2-pyrrolidone; C1-C20 alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and stearyl vinyl ether; dienes such as isoprene and ~utadiene; and, any other vinyl monomers copolymerizable with vinyl chloride.
From this group, the use of vinyl esters such as vinyl acetate is preferred for selection as constituting a minor proportion of the vinyl chloride-containing charge. The resulting products are found to have improved physical properties as evidenced by their superior impact strength which is achieved without any substantial reduction in their tensile strength. It is, however, preferred to employ vinyl chloride as the sole monomer during this suspension polymerization step.

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If a clean process effluent is desired from about 0.1 wt.~ to o.5 wt.~, based on the weight of the suspension batch, of a coagulating agent can be added to the suspension batch containing the vinyl monomer either prior to, during, or after the suspension polymeri7ation is run to facilitate the complete precipitation of the elastomer latex particles contained in the suspension batch.
The types of coagulating agent which are used contain either a polyvalent metallic cation or are quaternary ammonium lo compounds. Included within this description are such salts of polyvalent metallic cations as, calcium chloride, the preferred coagulant, ferric chloride, barium chloride, magnesium chloride aluminum c~lo~lde, aluminum chlori~e hexahydrate, aluminum sulfate, calcium sulfate, and, such quaternary ammonium compounds as, polyvinylpyridinum butyl chloride.
Such compounds, for example, the salts of the poly-valent metallic cations are described, e.g., in U.S. Patent No~. ~,669,914, 3,661,867 and ~,442,g79, in French Demande No.

2,005,174, in Chemical Abstracts, 73: 122,447 h (1970); and in British Patent No. 2,20~,110, as coagulants in a variety of polymerization procedures but hitherto it was not realized that they could be used with the type of anionic emulsifier used in the process of this invention to give a smooth running and clean SEI process.
In conducting the suspension polymerization, the vinyl -lo-~ C-4150 iLOS6542 chloride or the mixture of vinyl chloride with one or more comonomers and, preferably~ the coagulant, e.g. calcium chloride, is added to the previously prepared aqueous emulsion of the rubber polymer particles in a concentration of about 20 to 90~0J by weight, of the latter rubber particles Also required to be admixed with the aqueous emulsion of the rubber polymer particles i5 a concentration of from about 0,05~ to 1.0~, as based on the total weight of the vinyl chloride monomer or monomer mixture, of a suspending agent such, for example, as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellu-lose, carboxymethyl cellulose, talc, clay, polyvinyl alcoholJ
gelatine and the like. Pref~rrad for this purpose is hydroxy-propyl methyl cellulose which should, preferably, have a viscosity of at least about 3,000 cps, most preferably, about 15,000 cps. as determined, at 20C.~ with a 2%, by weight, aqueous solution of the polymer in a Ubbelohde viscometer ac-cording to ASTM Procedures D-1347-64 and D-2363-65T.
In addition~ a monomer-soluble catalyst or initiator such~ for example, as azobisisobutyronitrile, lauroyl peroxide, benzoyl peroxide or isopropylperoxy dicarbonate is present in a concentration of from about 0.02 to 1.0~, by weight, of the vinyl chloride monomer or monomer mixture. It has also been found that adjusting the pH to a level within the range of from about 7-9 has the effect of improving its mechanical stability and also serves to aid in the production of a clean U

lOS654Z
reaction during the suspe.nsion polymerization step. This pH adjustment may be readily accomplished by the addition o~
the requisite quantity of a basic solution such, for example, as an aqueous solution of sodium carbonate, bicarbonate, or hydroxide.
Polymerization may then be initiated by heating the a~ove descri~ed recipe at a temperature in the range o~ from about 45 to 75C. for a period of from about 2 to 12 hours with a~itation being applied throughout the course of the reaction. The resulting product is an aqueous suspension of SEI particles wherein the supernatant fluid is completely de-void of any of the original rubber polymer emulsion. The total SEI particle solids content of these suspensions will be in the range of from about 20~ to 50~, by weight. Each of these SEI particles comprise, in effect, a particle of an elastomer polymer prepared by means of an emulsion polymerization pro-cedure having a vinyl chloride suspension polymer which has been polymerized onto the elastomer polymer particle by means of a suspension polymerization step so that it surrounds and/or is homogeneously dispersed throughout the mass of the crosslinked acrylic elastomer emulsion polymer particle. The extent to which this vinyl chloride suspension polymer will surround and/or be dispersed within the mass of the crosslinked acrylate elastomer emulsion polymer particle will, of course, be de-termined by the particular monomers which are utilized in the C-1~ 150 ~S~;4Z

suspension polymerization step as well as by the particular polymer which comprises th~ crosslin~ed acrylic elastomer polymer fraction.
Thus, in these SEI particles, the crosslinked acrylic elastomer polymer may be present in a concentration of from 20 to 80%, by weight, said elastomer particles having the suspension pol~ner surrounding and/or homogeneously dispersed therein, the latter proportions being based on the total weight o the SEI interpolymer particles. Preferred products should contain from about 30-55~, by weightJ of the crosslinked acrylic elastomer emulsion polymer and about 45-70~, by weight, of the vinyl chloride suspension polymer surrounding and/or homogeneously dispersed throughout the mass of said elastomer emulsion polymer.
Examples of rigid plastics that can be reinforced with the SEI particles resulting from the improved process described herein are described in U.S. Patent ~o. 3,660,529.
The SEI particles may be dispersed in the rigid plastics by means of any convenient procedure which will result in an intimate admixture of the SEI particles within the mass of the substrate polymer. This may be accomplished with the substrate while both are in the form of solid powders, aqueous dispersions or slurries. With respect to the proportionsl the resulting blends should contain a sufficient concentration of the SEI particles so that from about 0.5 to 30%, by weight, of elastomer pol~mer derived from the SEI particles is present therein.

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The following examples will further illustrate the em-bodiment of this invention. In these examples, all parts given are by weight unless otherwise noted. In addition, it ls to be pointed out that the glass transition temperature of all of the rubber polymers described in these Examples is less than 25C.
EXAMPLE I
This example shows the use of the sodium ~alt of an alkyl aryl polyether sulfonate as the emulsiier and calcium lo chloride as the coagulant in an SEI process.
The following materials were chargea into a lo gal.re- -act,r: 41.5 lbs. oi deionized water, 429 g of an aqueous solu-tion of the sodium salt of an alkyl aryl polyether sulfonate eidulsifier (i.e.~ Triton X-200), 7.0g NaHCO3, o.lg FeSO4, 9.5g potassium persulfate, and a blend of 6.19 lbs. of n-butyl acrylate, 2.65 lb. of 2-ethylhexyl acrylate and 80~8g of butylene glycol diacrylate. The oxygen was removed from the reactor by applying vacuum and breaklng it three times with nitrogen. The mixture was agitated and was warrned to 50C. Twelve grams of sodium bisulfite was added in four increments. The acrylate polymerization proceeded until the reaction was essentially 100 complet-e and the latex was cooled to 30C. It contained 18 polymeric solids.
In the same reactor, 25 grams of dissolved Methocel*
~9OHG;15,000cps) were added to the latex wit~ agitation. Tne agi-tator ~as stopped, and 4~6 grams o~ azobisisobutyronitrile *Trademark ' .

c-)~150 ~05~;5~ .

(Vazo 64~ initiator were charged. Oxygen was removed by applying vacuum and breaking with vinyl chloride two times.
After adding 8.53 lb. of vinyl chloride, the batch was agitated and 55.4 gm calcium chloride were added. The reaction tempera-ture was then maintained at 60C until the vapor pressure of vinyl chloride dropped to 80 psig lower than start-up pressures. ~hen 4.8 grams of Ionol*antioxidant (Shel~) and 6.o grams of de~oa~er were added and the excess vinyl chloride -~ was vaporized from the batch. After centrifuging of the water and drying, the resin was white, free flowing granules, and contained 54.5~ acrylic rubber. Wall coating inside the reactor was minimal.
EX~MP~E 2 The above procedure was used to màke a batch which dif ered from the batch prepared in Example 1 by the substitu-tion of sodium lauryl sulfate for the Triton X-200 used in Example 1:
1st Step Butyl acrylate 5 o3 lb.
2-ethylhexyl acrylate 2.16 lb.
Butylene glycol diacrylate 65.7 gm.
Deionized water 41.5 lb.
Sodium lauryl sulfate 100 grams (dry) Potassium persulfate 12.9 grams Soaium bisulfite 8 grams *Trademark -15 ~S~;S42 _d Ste~

Vinyl Chloride 7.25 lb.
Deionized water 10 lbs.
Methocel (9OHG;15000 cp) 15 grams Calcium Chloride 33-8 grams Vazo 64 4.0 grams Ionol 4.8 grams The above formulation encountered severe thickening in the second polymerization step, with wall coating and loss of heat transfer from the reactor.

Claims (10)

What is Claimed:

1. In a method of making acrylic elastomer containing-interpolymer particles by the emulsion polymerization of an acrylate monomer charge containing a monomer having at least two ethylenically unsaturated bonds as a cross-linking agent to form an agueous emulsion which contains cross-linked acrylic elastomer particles and by thereafter suspension polymerizing a monomer charge comprising vinyl chloride in the presence of the acrylic elastomer particles, wherein the improvement comprises using a sulfonate salt of an ethoxylated alkyl phenol in the range of from 0.2% to 5% by weight of the monomer charge containing the acrylate compound.

2. A method as claimed in Claim 1 wherein the emulsifier is a sodium sulfonate salt of an ethoxylated alkyl phenol anionic emulsifier.

3. A method as claimed in Claim 1 wherein the sodium sulfonate salt emulsifier has about a 28 wt% solids content, a specific gravity of about 1.o64 at 25°C/25°C and a pH of 7 to 9 when in a 5% solids solution at 25°C

4. A method as claimed in Claim 1 which further comprises use of a coagulant selected from the group consisting of the salts of polyvalent metallic cations and quaternary ammonium compounds in the suspension batch to precipitate elastomer particles.

5. A method as claimed in Claim 4 wherein the coagulant is selected from the group consisting of calcium chloride, barium chloride, magnesium chloride, aluminum chloride hexa-hydrate, aluminum sulfate, ferric chloride, calcium sulfate and polyvinylpyridinium butyl chloride.

6. A method as claimed in Claim 4 wherein the coagulant is calcium chloride,

7. A method as claimed in Claim 4 wherein the amount of coagulant which is used ranges between o.1% and o.5% by weight of the suspension charge.

8. A method as claimed in Claim 4 wherein the coagulant is added to the batch prior to running the suspension polymeriza-tion.

9. A method as claimed in Claim 4 wherein the coagulant is added to the batch while the suspension polymerization is being run.

10. A method as claimed in Claim 4 wherein the coagulant is added to the batch after the suspension polymerization is being run.