CA1078087A - Process for preparing substantially linear water-soluble interpolymeric interfacially spreading polyelectrolytes - Google Patents

Abstract

Abstract of the Disclosure A process for preparing substantially linear water-soluble interpolymeric interfacially spreading polyelectrolytes, comprising (1) a homogeneous polymeri-zation in an aqueous emulsion of a mixture of ethylenically unsaturated nonionic monomers wherein at least one of such monomers contains a reactive group and wherein the polymerization reaction forms an interpolymer containing nonionic functional groups, then (2) adding a coreactant compound to the aqueous emulsion in an amount sufficient to convert the interpolymer to a water-soluble polyelec-trolyte having a charge which is the same as the charge of the emulsion of (1) above.

Description

1~78087 It is known from U.S. Patent 3,917,574, issued November 4, 1975 to Gibbs et al., to make substantially linear water-soluble interpolymeric interfacially spreading polyelectrolytes of the type contemplated herein in a continuous monomer addition solution poly-merization process wherein at least one ionic hydro-philic monomer and at least one nonionic hydrophobic monomer in a polar mutual solvent are added to a polymerization reactor at a rate no greater than the rate of polymerization and in a ratio which is sub-stantially equal to that desired in the resulting polymer phase.
It is also known from U.S. Patent 3,965,032, issued June 22, 1976 to Gibbs et al, to make such sub-stantially linear interpolymeric interfacially spreading polyelectrolytes by polymerization of a functional nonionic monomeric mixture in a nonaqueous solvent, followed by isolation of the polymer and subsequent con~ersion to an ionic derivative.
It is often the case when copolymerizing ionic and nonionic monomers that the monomers are not present in the same phase during polymerization and more than one polymerization reaction is occurring. The reaction mixture forms two phases with the ionic monomers preferentially distributed in one phase and the nonionic monomers in the other. Polymerization can take place simultaneously in both phases, forming a complex mixture of highly charged water-soluble polymer and slightly charged essentially nonionic polymer.

18,075B-F -1-`-`` 1~7~87 Further, only a limited number of solvents are available which can compatibilize nonionic and ionic species and such solvents are usually expensive and difficult to separate from the polymer.
In addition, monomer removal is a problem in purifying these mixtures. For ecological and health reasons, even low levels of monomers are not permis-sible. Since solution reactions rarely go to high conversion, the unreacted monomer must be separated '-from the polymer. The simplest way is to strip off the monomers and solvent, then redissolve the polymer in water for subsequent use. But ionic monomers are nonvolatile. Therefore, they must be removed by fractional precipltation extraction or dialysis. And, since in mos,t cases any polymeric surfactant synthesized wil'l be soluble in the same solvents as the monomer, dialysis is the only practical approach.
Added to the above problems are the fact that ionic monomers are often difficult to prepare, purify and -store and very often undergo small amounts of homopoly-merization wherein the homopolymer cannot be removed from the monomer and ends up, as a contaminant in the final product.
The invention provides a process for preparing a substantially linear water-soluble interpolymeric inter-facially spreading polyelectrolyte composed of a mixture of nonionic hydrophobic units and ionic hydrophilic units wherein the nonionic hydrophobic units are copolymerized ethylenically unsaturated monomers which when in the form of an amorphous homopolymer is less than 0.1 percent 18,075B-F

1~78087 soluble in water and wherein the monomer has no sub-stituent extending more than 10 Angstrom units from the point of ethylenic unsaturation the units being randomly distributed in the backbone of the polyelectrolyte and wherein the ionic hydrophilic units are copolymerized ethylenically unsaturated monomers which when in the form of amorphous homopolymers are soluble in water and wherein the ionic hydrophilic units remain substantially ionized over a pH range of 0 to 14; and the polyelectrolyte when incorporated into a dispersion is adsorbed at the disperse phase of the dispersion in a substantially flat configu-ration and where the area occupied by each ionic hydro-philic unit of the polyelectrolyte at the disperse phase surface is from 60 to 100 square Angstrom units per ionic hydrophilic unit, and wherein the polyelectrolyte has an adsorption constant equal to or greater than 1 at the point where the disperse phase is saturated with the polyelectrolyte wherein the adsorption con~tant is deter-mined as the amount of polyelectrolyte in the disperse phase divided by the amount of polyelectrolyte in the continuous phase; characterized by the steps of (1) the homogeneous polymerization in an aqueous emulsion of a mixture of ethylenically unsaturated nonionic monomers wherein at least one of the monomers contains a reactive group to form an interpolymer containing nonionic functional groups, then (2) adding a coreactant compound to the aqueous emulsion in an amount sufficient to convert the interpolymer to a water-solu~le polyelectrolyte the poly-electrolyte having a charge which is the same as the charge of the emulsion of ~1) above.

18,075B-F -3-1~781~7 It is a further embodiment of the present invention that a stabilizing amount of a polyelectrolyte, of the type as described herein, is used as the sur-factant in the preparation of the aqueous emulsion of step (1).
Utilization of the process of the present invention provides an aqueous solution of a polyelectrolyte which is free of undesirable contaminants and which is ready for use. The material is particularly adapted for use as a surfactant in the preparation of emulsions or dispersions of polymeric materials, such as styrene--butadiene latexes.
The preferred interpolymeric interfacially spreading polyelectrolytes (ISPE) as prescribed herein are copolymers of essentially random structure, narrow composition distribution and low molecular weight, i.e., having a number average molecular weight of less than 100,000 and are water soluble or at least spon-taneously dispersible in water to form colloidal solutions.
The number of different monomers combined in step (1) to form the reactive interpolymer is not critical to the process provided all are nonionic and at least one contains a reactive functional group. In practice, the number of monomers is normally limited to 4 or 5 with no more than two containing reactive functional groups since there is little advantage in polymer properties to be gained by using more complex mixtures. But this is not a limitation to the process since any number of monomers can be combined. In most cases, a single reactive functional monomer suffices to make an ISPE since its 18,075B-F -4-i(~78~87 primary purpose is to provide a site on the interpolymer for forming an ionic substituent. But in some cases, a combination is desirable as, for example, when small amounts of a very reactive functional group promotes the more rapid conversion of the other in step (2).
The combination of functional monomers must be selected to avoid interfering reactions, e.g. a combination of such monomers should not be selected wherein one monomer yields an anionic site and another monomer a cationic site on the resultant ISPE. Further-more, a nucleophilic monomer should not be combined with an alkylating monomer.
The polymerization is carried out with a mixture of nonionic monomers thus avoiding the incompatibility problem existing in a mixture containing an ionic com-ponent. When all components are compatible and copolymerize to form a water-insoluble polymer, the conditions of classical emulsion polymerization are realized. Poly-merization occurs in or on the polymer particles but not in the aqueous phase. Since the polymer particles are the principal loci of polymerization, there are no competing simultaneous polymerization reactions leading to mixtures of products. Instead, random interpolymers of narrow composition distribution can be formed.
If the reactivity ratios are favorable, the emulsion copolymexization can be carried out batch-wise to high conversion. In cases where the reactivity ratios are not favorable, composition drift would result at high conversion. To avoid this and obtain narrow composition 18,075B-F -5-distribution, the monomers can be metered into the reaction at the rate at which they are converted to polymer.
The essential ingredients in an emulsion poly-merization reaction are monomers which form water--insoluble polymers, emulsifiers and initiators. The choice of ingredients and their proportions in the recipe determine the characteristics of the reaction and the product.
It is important in the present process to carry out the polymerization at the highest possible rates to minimize contact of the reactive functional monomers with the hot aqueous environment. This can be accomplished by combining low organic/aqueous phase ratio, high surfactant level, high initiator level and high temperature. These conditions lead to a fluid latex and very high conversions with short run times.
The polymer formed is of low molecular weight and narrow composition distribution. Polymers of low molecular weight, e.g., 1000 to 40,000 and preferably <10,000 are especially useful because of their faster kinetics of adsorption. In many applications, such as in emulsion and suspension polymerization, this is very important.
The surfactants are critical to the process and may be either anionic or cationic depending on the type of ISPE desired. Cationic emulsion polymerization process is preferred for which combinations of a cationic ISPE with a conventional cationic surfactant and sometimes (optionally) nonionic surfactants, may be employed. The preferred combination is a relatively high level of ISPE

18,07SB-F 6-1~78087 surfactant, i.e., up to 12 parts or more based on monomer with from 0 to 3% of a conventional surfactant. Both species can be selected to have the same cationic structure as desired in the product ISPE. If this is done, the ISPE can be utilized in whatever amount desired because after reaction, it becomes indistinguishable from the product. The conventional surfactants include the classes of salts of aliphatic amines, especially the fatty amines, quaternary ammonium salts and hydrates, fatty amides derived from disubstituted diamines, fatty chain deriva-tives of pyridinium compounds, ethylene oxide condensation products of fatty amines, sulfonium compounds, isothio-uronium compounds and phosphonium compounds.
Free radical forming initiators suitable for the preparation of cationic ISPE's include those which form either nonionic or cationic end groups on the polymer chains. The nonionic types such as hydroperoxides and azo compounds are preferred, especially hydrogen peroxide, t-butylhydroperoxide (TBHP) and azobisiso-butyronitrile. They are employed at high levels, e.g., from 0.5-5 weight percent and can be added in one shot or introduced continuously into the reaction depending on the reactivity of the initiator. Redox systéms which can function in a cationic emulsion polymerization, such as TBHP and hydroxylamine, may also be utilized.
Molecular weight is a complex function of many variables but in this process, it can be contro}}ed by choice of temperature, initiator }eve} and chain transfer agent. Polymerization can be carried out using temperatures of from 25-100C but temperatures of 18,075B-F -7-1C~78~87 from 70-90C are preferred for most monomers. This results in run times of less than 12 and usually less than 5 hours with conversions exceeding 95~. The selection of chain transfer agent is also important.
Most conventional chain transfer agents can be used, with alkyl polyhalides and mercaptans being preferred.
Combinations of H202 with CBr4 or mercapto ethanol are especially preferred.
An advantage of the present process is that particle size control is not necessary save only that the latex remain fluid enough to stir. It is also preferred to operate at relatively low solids, e.g., less than 30% solids and preferably from 20-25 percent solids.
Small particle size, e.g., <2000A is preferred since this allows for faster conversion in step 2, however, any particle size or particle size distribution is acceptable.
Even small amounts of coagulum can be tolerated since in step 2, all species are ultimately converted to water--soluble products.
The process of this invention unexpectedly leads to narrow molecular weight distribution at low molecular weights. In fact, the distributions are virtually identical to those obtained in a solution process using the same monomers. ~y choice of initiator, chain trans-fer agent, and polymerization conditions, the number average molecular weight can be varied from 103 to 105 with w in the range of 1.5 to 3.
n In step 2, the aqueous emulsion of step 1 is converted to an aqueous solution of polyelectrolyte.
Any reaction between an added low molecular weight 18,075B-F -8-component and the functional groups on the polymer chain that takes place in aqueous media to yield a pH
independent site on the polymer chain, can be employed.
Exemplary are the class of nucleophilic displacement reactions between an nonionic nucleophile and nonionic alkylating agent to yield an organic cation as illustrated below:
RA + Z -> RZ A
where Z is a nucleophile, RA is the alkylating agent and A is a leaving group. RZ+ is the derived onium cation and A its anion formed from the leaving group.
Either reactant can be a substituent on the polymer chain and its counterpart coreactant is selected so as to yield a cationic polymeric product. It is, therefore, possible to make the same cationic product from these two different routes.
Nonionic monomers which form interpolymers with nucleophilic sites include the general classes of tertiary amines, phosphines and sulfides containing at least one polymerizable double bond as a substituent.
Examples include vinyl pyridines, vinylbenzyl dialkyl amines, dialkyl amino alkyl acrylates and methacrylates and alkyl thio alkyl acrylates and methacrylates.
Mix~ures of interpolymer latexes with the desired alkylating agent are allowed to react at from ambient temperature to 100C, or higher if under pressure, to convert the nucleophilic sites to attached onium ions. As the reaction proceeds, the polymer par-ticles become increasingly hydrophilic and eventually dissolve to form an a~ueous solution of the ISPE. After 18~075B-F -9-~a7808'7 reaction, the reaction product can be used as is or given other treatments such as stripping to remove unreacted alkylating agents.
The alkylating agents are selected to be highly reactive and volatile and must be at least slightly soluble, e.g., >0.001% in order to diffuse through the aqueous phase to the latex particles. Preferred alky-lating agents include alkyl bromides of 1-4 carbons, allyl and methallyl chlorides, benzyl chlorides, and di-methyl sulfate.
Preferentially, the alkylating site may be placed on the polymer chain by using an active halogen containing comonomer of the classes: vinyl aralkyl halides, haloalkyl butadienes, bromoalkyl acrylate and methacrylates and vinyl bromide. Preferred are vinyl-benzyl chloride, chloromethylbutadiene and the bromoalkyl esters. Latexes containing these species in copolymerized form are reacted with carbon-containing nucleophiles which are stable in and can diffuse through aqueous media having a hetero atom as the center of nucleophilicity wherein each covalent bond of said hetero atom is to a carbon atom.
The nucleophilic compounds which are used advantageously in the practice of this invention are repre ented by the following classes of compounds, sometimes called Lewis bases:
(a) monobasic aromatic nitrogen compounds;
(b) tetra (lower alkyl)thioureas;
(c) Rl-S-R2 wherein Rl and R2 individually are lower alkyl, hydroxy lower alkyl or 18,075B-F -10-i~78~87 wherein Rl and R2 are combined as one alkylene radical having 3 to 5 carbon atoms;
(d) Rl-N-R2 wherein R2 and R3 individually are lower alkyl or hydroxy lower alkyl, or are com-bined as one alkylene radical having-3 to 5 carbon atoms and Rl is lower alkyl, aralkyl or aryl except when R2 and R3 together are an alkylene radical then Rl is lower alkyl or hydroxy lower alkyl; and (e) Rl-P-R3 wherein Rl, R2 and R3 individually are lower alkyl, hydroxy lower alkyl or aryl.
In this specification the term lower alkyl means an alkyl having from 1 to 4 carbon atoms. Use of the nucleophilic component as the reactant i5 the preferred route because the monomer containing alkylating sites are less likely to interfere with emulsion polymeri-zation and the coreactant nucleophiles are more water soluble and blend more readily into the latex. They are also easier to remove in a post reaction cleanup and are less toxic than coreactant alkylating agents.
Another general class of reactions suitable for the present process are the reactions of epoxides with nucleophiles and acids as shown below:
/ ~ OH
R-CH-CH2 + KA + æ ~ RCH--CH2-Z A .

18,075B-F -11-As described earlier, either the epoxide or the nucleo-phile may be attached to the polymer chain. Epoxide groups can be incorporated into the copolymer by co-polymerization of an unsaturated epoxide such as glycidyl acrylate or methacrylate. Alternatively, the nucleophilic polymers described earlier can be reacted with a lower epoxide such as ethylene oxide, propylene oxide, glycidyl ethers and the like. Suitable acids for either case include HCl, H2SO4, and lower carboxylic acids, and are selected on the basis of the anion desired.
In the preparation of anionic ISPE's anionic emulsion polymerization is required. For such process, anionic ISPE's can be used with conventional anionic soaps known in the art and initiators which yield nonionic o~ anionic end groups. Any reaction can be used in step 2 which converts a functional copolymer in aqueous emulsion to a water-soluble anionic polyelectrolyte.
For example, an anionic latex of a vinyl benzyl chloride copolymer can be formed and then post reacted with sulfite ion to yield a vinyl benzyl sulfonate anionic polyelectrolyte.
The following examples, wherein all parts and percentages are by weight, illustrate the present invention:
Example 1 A series of functional nomers were copoly-merized in emulsion. The reaction ingredients and conditions are set forth on the following Table I. The continuous addition polymerization reaction of step 1 was conducted by metering the designated monomers along with an aqueous stream containing cationic polymeric 18,075B-F -12-~078087 surfactant, H2O2 and FeC13-6H2O into a polymerization reactor over a one-hour period, followed by heating the admixture for an additional one hour at the desig-nated temperature. The ren~aining reactions were conducted using a batch polymerization technique. In each instance a water-soluble, essentially contaminant--free ISPE of indicated composition was obtained using the ingredients and conditions as specifically set forth in step 2 of Table I.

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~ _ _ _ lB, 075B--F --15--1~78~87 Example 2 A series of emulsion polymerization reactions were carried out by batch polymerization as per Runs 2 through 4 of Example 1, using a mixture of 60 mole per-cent methylmethacrylate, 40 mole percent vinyl benzyl chloride, varying amount of the polymerization initiator H2O2, varying amounts and types of chain transfer agents, about 7 weight percent of a preformed cationic ISPE
(as per USP 3,965,032) composed of 3 moles of methyl methacrylate and 2 moles of vinyl benzyl dimethyl sulfonium chloride, and about 0.5 weight percent of the conventional soap dodecylbenzyl dimethyl sulfonium chloride. The following Table II sets forth the compositions used as well as the molecular weight of the products formed.

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18, 075B-F --17--1~780B7 Example 3 Multicomponent interpolymers were prepared in a batch process as in Example 2 using same ISPE as sur-factant.

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~¢ -- _ 18, 075B--F --20--1~78087 Each of the above reaction products were easily converted to water-soluble, essentially contaminant free, ISPE's by reaction as set forth in step 2 of Table I, Example 1.
S Further, the products of the emulsion reaction, as set forth in Table II above, were found to have essentially equivalent molecular weight values às materials produced by a solution polymerization technique. More particularly, such solution polymerization comprised preparing a mixture containing methyl ethyl ketone and a monomer mixture comprising 60 mole percent methyl methacrylate and 40 mole percent vinyl benzyl chloride, along with 1.7 mole percent (based on monomer) of the polymerization initiator azobisbutyronitrile and from 0.36 to 3.64 mole percent (based on monomer) of carbon tetrabromide as a chain transfer agent. The mixture was then metered, over a period of one hour, into a reaator containing additional methyl ethyl ketone.
The final mixture was then refluxed for a period of five hours.
It was unexpected that materials having sufficiently low molecular weight to be useful as sur-factants could be prepared by an emulsion polymerization process. Further, it was unexpected that such a process would provide a means of obtaining products having a narrow molecular weight distribution, such as is normally obtained only by using solution polymerization techni~ues.
More particularly, molecular weights obtained by emulsion polymerization are affected by the same variables as in any free radical process. For example, increases in 18,075B-F -21-1~78087 initiator concentration and temperature as well as the use of chain transfer agents normally decrease the mole-cular weight of the reaction product. However, such result is often accompanied by a broadening of the molecular weight distribution due to the generation of a fraction of low molecular weight material resulting from primary termination reactions. In contrast to these expectations, the process of the present invention provides polymers having molecular weights as low as can be obtained by solution polymerization and with comparable molecular weight distribution.

18,075B-F -22-

Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for preparing a substantially linear water-soluble interpolymeric interfacially spreading polyelectrolyte composed of a mixture of nonionic hydro-phobic units and ionic hydrophilic units wherein the nonionic hydrophobic units are copolymerized ethylenically unsaturated monomers which when in the form of an amorphous homopolymer is less than 0.1 percent soluble in water and wherein the monomer has no substituent extending more than 10 Angstrom units from the point of ethylenic unsatu-ration the units being randomly distributed in the backbone of the polyelectrolyte and wherein the ionic hydrophilic units are copolymerized ethylenically unsaturated monomers which when in the form of amorphous homopolymers are soluble in water and wherein the ionic hydrophilic units remain substantially ionized over a pH range of 0 to 14;
and the polyelectrolyte when incorporated into a dispersion is adsorbed at the disperse phase of the dispersion in a substantially flat configuration and where the area occupied by each ionic hydrophilic unit of the polyelectrolyte at the disperse phase surface is from 60 to 100 square Angstrom units per ionic hydrophilic unit, and wherein the polyelectrolyte has an adsorption constant equal to or greater than 1 at the point where the disperse phase is saturated with the polyelectrolyte wherein the adsorption constant is determined as the amount of poly-electrolyte in the disperse phase divided by the amount of polyelectrolyte in the continuous phase; characterized by the steps of (1) the homogeneous polymerization in an aqueous emulsion of a mixture of ethylenically unsaturated nonionic monomers wherein at least one of the monomers contains a reactive group to form an interpolymer con-taining nonionic functional groups, then (2) adding a coreactant compound to the aqueous emulsion in an amount sufficient to convert the interpolymer to a water-soluble polyelectrolyte the polyelectrolyte having a charge which is the same as the charge of the emulsion of (1) above.

2. Process of Claim 1 characterized in that the interpolymeric interfacially spreading polyelectrolyte is a water-soluble cationic compound.

3. Process of Claim 2 characterized in that a stabilizing amount of the cationic interfacially spreading polyelectrolyte is used as the surfactant for the prepara-tion of the aqueous emulsion.

4. Process of Claim 2 characterized in that the polyelectrolyte is the reaction product of methyl meth-acrylate, vinylbenzyl chloride and dimethyl sulfide.

5. Process of Claim 2 characterized in that the polyelectrolyte is the reaction product of methyl meth-acrylate, glycidyl methacrylate, dimethyl sulfide and acetic acid.

6. Process of Claim 2 characterized in that the polyelectrolyte is the reaction product of methyl meth-acrylate, bromoethyl methacrylate and trimethyl amine.

7. Process of Claim 2 characterized in that the polyelectrolyte is the reaction product of methyl meth-acrylate, chloromethyl butadiene and dimethyl sulfide.

8. Process of Claim 2 characterized in that the polyelectrolyte is the reaction product of methyl meth-acrylate, 4-vinyl pyridine and methyl bromide.

9. Process of Claim 2 characterized in that the polyelectrolyte is the reaction product of styrene, acrylonitrile, vinyl benzyl chloride and N,N-dimethyl-ethanolamine.