EP0495000A4 - Stable emulsion polymers and methods of preparing same - Google Patents

Stable emulsion polymers and methods of preparing same

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Publication number
EP0495000A4
EP0495000A4 EP19900916634 EP90916634A EP0495000A4 EP 0495000 A4 EP0495000 A4 EP 0495000A4 EP 19900916634 EP19900916634 EP 19900916634 EP 90916634 A EP90916634 A EP 90916634A EP 0495000 A4 EP0495000 A4 EP 0495000A4
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EP
European Patent Office
Prior art keywords
stage
polymer
monomer
styrene
process according
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19900916634
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English (en)
French (fr)
Other versions
EP0495000A1 (de
Inventor
Richard A. Kiehlbauch
Vince S. Volk
Lee W. Morgan
Richard J. Esser
Dennis P. Jensen
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SC Johnson and Son Inc
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SC Johnson and Son Inc
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Publication date
Application filed by SC Johnson and Son Inc filed Critical SC Johnson and Son Inc
Publication of EP0495000A1 publication Critical patent/EP0495000A1/de
Publication of EP0495000A4 publication Critical patent/EP0495000A4/en
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F291/00—Macromolecular compounds obtained by polymerising monomers on to macromolecular compounds according to more than one of the groups C08F251/00 - C08F289/00

Definitions

  • This invention relates to stable, aqueous latexes and t methods for their preparation.
  • Aqueous dispersions of polymers which are referred to as "latexes" in the art, are generally known to be useful, both alone and in a variety of formulations, as, for example, coatings and impregnants.
  • latexes of various homopolymeric and copolymeric compositions (such as styrene-butadiene copoly ers, acrylic homopolymers and copolymers, vinylidene chloride homopolymers and copolymers, etc.) have been developed having specific chemical and/or mechanical properties for particular end-use applications.
  • aqueous interpolymer latexes resulting from the emulsion-polymerization of: certain monovinyl aromatic monomers such as styrene; certain diolefins such as butadiene; and certain monoethylenically-unsaturated carboxylic acids such as acrylic acid, are known to be particularly useful as film-forming binders for pigments in various paper-coating applications. See, for example, U.S.
  • Blank et al. point out that one problem associated with emulsion polymerization-produced polymers that are employed for coatings is the presence of certain surfactants. That is, certain surfactants, while employed to stabilize emulsions, tend to adversely affect the water-resistance and/or corrosion-resistance of the resulting film as well as the adhesion of the coating especially to metal surfaces.
  • the Blank et al. emulsion polymers are prepared in a so-called "two-stage" process. The process includes a first stage and a second stage.
  • a conventional carboxyl group-containing polymer is prepared either by a conventional solution-polymerization technique or by a bulk-polymerization technique, and thereafter is water-dispersed or solubilized by partial or full neutralization with an organic amine or base and application of high shear agitation.
  • a mixture of polymerizable monomers and polymerization catalyst is added to the first-stage emulsion at an elevated temperature to effect polymerization of the second-stage monomers, resulting in the formation of an emulsion coating composition.
  • Such a coating composition is thus said to be "surfactant-free".
  • U.S. Pat. No. 4,179,417 to Sunada et al. discloses a composition for water-based paints, such composition containing a water-soluble resin and a water-dispersible polymer.
  • the water-soluble resin contains 50-99.5 percent by weight of either an alpha, beta monoethylenically-unsaturated acid alkyl ester or an alkenyl benzene; 0.5-20 percent by weight of an alpha, beta monoethylenically-unsaturated acid; and 0-30 percent by weight of a hydroxyalkyl ester of an alpha, beta monoethylenically-unsaturated acid.
  • These monomers are polymerized in the presence of at least one unsaturated compound selected from the group consisting of an alkyd resin containing a polymerizable unsaturated group, an epoxy ester containing a polymerizable unsaturated group, a drying oil, a fatty acid of a drying oil, and a diene polymer.
  • the resulting polymers are water-solubilized by the addition of ammonia or an amine.
  • the water-dispersible polymer contains not only hydroxy and/or carboxyl functional groups but also an alpha, beta monoethylenically-unsaturated acid monomer and/or a hydroxy alkyl ester of such a monomer as well as certain other ethylenically-unsaturated monomers.
  • compositions disclosed in U.S. Pat. No. 4,179,417 are employed in waterbased paints and can optionally contain a cross-linking agent.
  • Canadian Pat. No. 814,528 to Kaminski discloses low molecular weight alkali-soluble resin, resin solutions and methods for their preparation and purification. The disclosed resins are said to be especially useful as emulsifiers, leveling agents, and film-formers. Kaminski discloses that the number-average molecular weight of such a resin ranges from 700-5000 and that such a resin can have an acid number which ranges between 140-300.
  • the resins are further disclosed as being useful as emulsifiers in the preparation of emulsion polymers, resulting in emulsion polymers that are said to be stable and substantially free from coagulum.
  • the resin are said to require a number-average molecular weight of between 1,000 and 2,000 and preferably between 1,000 and 1,500.
  • Resins having a number-average molecular weight greater than 2,000 are said to lead to unstable and coagulated emulsion polymers when used as the emulsifier in conventional emulsion-polymerization reaction.
  • Two-stage latex polymers are known to exist in many morphological forms, which are determined by many factors including the relative hydrophilicity, miscibility and molecular weights of the first-stage and second-stage polymers.
  • core-shell latexes are formed when such a second-stage polymer forms a "shell” (or coating) around a discrete "core” (or domain) of the first-stage polymer.
  • core-shell latexes are disclosed in U.S. Pat.c.No. 4,515,914 to Tsurumi et al., where, an exemplary composition containing a first-stage styrene/butadiene polymeric core is encapsulated by a second-stage monovinyl polymeric shell.
  • inverted core-shell latexes So-called “inverted core-shell” latexes are also known. Lee and Ishikawa, in an article entitled “The Formation of 'Inverted' Core-Shell Latexes,” and appearing in J. Poly. Sci., 21, 147-154 (1983), shows that such "inverted” latexes are those where the second-stage polymer becomes the "core” domain and is encapsulated by the first-stage polymeric shell. These inverted latex compositions can be formed when the first-stage polymer is more hydrophilic than the second- stage polymer.
  • the shell was composed of the more hydrophilic poly (MA/MAA) molecules which were relatively high in MAA content and (2) that the core was composed of both poly (MA/MAA) and poly (EA/MAA) molecules, with the thus-investigated copolymeric particles being relatively uniform from surface to center with respect to distribution of all other components (i.e., except for MAA) .
  • the monomer content of MAA was found to increase in the direction of the shell surface.
  • Muroi et al. studied five compositions, including one where the first-stage feed was MA/MAA (90/10) and the second-stage feed was EA/MAA (90/10) . These investigators discovered that as the pH of the resulting latex was increased, as a result of the addition o NaOH, the optical density decreased, indicating complete dissolution of all the latex particles. In view of the above, it is desirable to provide a stable latex emulsion that is capable of employing a relatively broad spectrum of hard and soft monomers wherein such monomers possess "acidic" as well as "basic" functiona1ity.
  • the present invention is directed to a stabilized latex emulsion and the process for preparing it.
  • the process comprises the steps of: a) reacting latex-forming monomers under predetermine emulsion-polymerization reaction conditions to form a hydrophilic first-stage polymer; and b) contacting the first-stage polymer with an effective amount of at least one hydrophobic latex- forming monomer under predetermined emulsion- polymerization reaction conditions to form a hydrophobi second-stage polymer, wherein the second-stage hydrophobic polymer partitions into the first-stage hydrophobic polymer thereby producing an inverted core- shell emulsion polymer, wherein the improvement comprises the additional step of adjusting the pH of the inverted core-shell emulsion polymer by an amount effective to dissolve the first-stage hydrophilic polymer, the first-stage hydrophilic polymer being dissolvable and the second- stage hydrophobic polymer being insoluble upon adjustment of pH, for thereby producing a stabilized latex emul
  • the latexes of this invention exhibit excellent mechanical properties as a result of the stabilization of the second-stage polymer. Many latexes of this invention exhibit superior coating properties for those applications known in the art. Such applications include uses in floor polish, varnishes, including water-borne graphic arts varnishes, paints, inks, adhesives, and the like. Best Mode For Carrying Out The Invention
  • the polymer particles of this invention are broadly characterized as latex particles comprising a hydrophilic first-stage polymer dissolved in a continuous aqueous phase containing discrete domains of a hydrophobic second-stage polymer.
  • hydrophilic means that the polymer is capable of being dissolved in an aqueous medium upon adjustment of the pH.
  • First-stage polymers containing acid-functional groups i.e., possessing "acidic” functionality
  • first-stage polymers containing basic functional groups will be solubilized upon addition of alkali; first-stage polymers containing basic functional groups
  • hydrophobic as used herein includes a polymer which will not be dissolved in any aqueous medium by adjusting the pH.
  • inverse core- shell latex means a latex formed in a two-stage polymerization process wherein the second-stage polymer tends to form a "core” domain in the first-stage polymer.
  • the first-stage polymer may either encapsulate the second-stage polymer, or may form a "shell” around the second-stage polymer "core”, or may incorporate the second-stage polymer into its swollen matrix.
  • Emssion polymerization is a process that requires a polymerizable monomer or severa polymerizable co-monomers, an initiator, and water as the continuous phase.
  • This invention may also optionally utiliz such commonly-employed emulsion-polymerization ingredients a chain-transfer agents to regulate the molecular weight of th resulting first-stage polymer and/or second-stage polymer, a well as conventional free-radical polymerization catalysts and/or conventional cross-linking agents, if desired.
  • the first step in the emulsion polymerization process o this invention is selecting the monomers which will produce the hydrophilic first-stage polymer.
  • the monomers should be selected so that there is at least one monomer from each of the two monomer groups, namely (i) specified monomers that are at least partially water-insoluble and (ii) specified "acidic" or "basic" functional group-containing monomers.
  • water insoluble monomers is intended to include those monomers that form polymers which, upon pH adjustment, do not become appreciably water- soluble.
  • the term "functional group- containing monomers” includes those monomers that form polymers whose solubility characteristics become appreciably changed upon pH adjustment.
  • Typical monomers that are at least partially water- insoluble, for purposes of the present invention are certai open-chain conjugated dienes as well as certain vinyl monomers such as monovinyl aromatic monomers.
  • a suitable monomer that is at least partially water-insoluble is selected from the group consisting of styrene, methyl styrene, alpha-methyl styrene, ethyl styrene, isopropyl styrene, tertiary-butyl styrene, ⁇ ethyl methacrylate, methyl methacrylate, butyl aerylate, butyl methacrylate, 2-ethyl hexylacrylate, ethyl acrylate, vinyl acetate, methyl aerylate, open-chain conjugated dienes, 2-hydroxyethyl methacrylate, 2-hydroxyethyl aerylate, methylol acrylamide, glycidyl aerylate, glycidyl methacrylate, and combinations thereof.
  • the hydrophilic first-stage polymer is produced from a onoalkenyl aromatic monomer such as methyl styrene, alpha-methyl styrene, tertiary-butyl styrene or, most preferably, styrene.
  • a onoalkenyl aromatic monomer such as methyl styrene, alpha-methyl styrene, tertiary-butyl styrene or, most preferably, styrene.
  • a suitable monomer that is at least partially water-insoluble is selected from the group consisting of styrene, methyl styrene, alpha-methyl styrene, ethyl styrene, isopropyl styrene, tertiary butyl styrene, ethyl methacrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethyl hexylacrylate, ethyl acrylate, vinyl acetate, methyl acrylate, open-chain conjugated dienes, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, methylol acrylamide, glycidyl acrylate, glycidyl methacrylate, an aromatic or an acrylate or a methacrylate having a functionality of at least 2, and combinations thereof.
  • Suitable aromatic monomer having a functionality of at least two is divinyl benzene.
  • Suitable acrylate monomers having a functionality of at least two or greater include: 1,3-butane diol diacrylate; 1,4-butane diol diacrylate; ethylene glycol diacrylate; diethylene glycol diacrylate; triethylene glycol diacrylate; tetraethylene glycol diacrylate; 1,6-hexane diol diacrylate; pentaerythritol tetraacrylate; and trimethylol propane triacrylate.
  • Suitable methacrylate monomers having a functionality of at least 2, for example, include: 1,3- butane diol dimethacrylate; 1,4-butane diol dimethacrylate; ethylene glycol dimethacrylate; diethylene glycol dimethacrylate; triethylene glycol dimethacrylate; tetraethylene glycol dimethacrylate; 1,6-hexane diol dimethacrylate; pentaerythritol tetramethacrylate; and trimethylol propane trimethacrylate.
  • monovinyl aromatic monomer includes those monomers wherein a radical of the formula R
  • Suitable monovinyl aromatic monomers are styrene; alpha-methyl styrene; ortho-, meta- and para-methyl styrene; ortho-.
  • meta- and para-ethyl styrene O-methyl-para-isopropvl styrene; para-chloro styrene; para-bromo styrene; ortho, para-dichloro styrene; ortho. para-dibromo styrene; vinyl naphthalene; diverse vinyl(alky1-naphthalenes) and vinyl(halonaphthalenes) , and co-monomeric mixtures thereof.
  • open-chain conjugated diene is meant to include, for example, 1,3-butadiene, 2-methyl-l,3-butadiene, 2,3-dimethyl-l,3-butadiene, pentadiene, 2-neopentyl-l,3- butadiene and other hydrogen analogs of 1,3-butadiene and, i addition, the substituted 1,3-butadienes, such as 2-chloro- 1,3-butadiene, 2-cyano-1,3-butadiene, the substituted straight-chain conjugated pentadienes, the straight-chain an branched-chain conjugated hexadienes, other straight and branched-chain conjugated dienes typically having from 4 to about 9 carbon atoms, and co-monomeric mixtures thereof.
  • the functional group-containing monomers of the present invention can have basic or acidic functionalities such as amino or carboxy functionality.
  • Typical functional group-containing monomers include "acidic" group-containing monomers such as acrylic acid, methacrylic acid, other unsaturated acid monomers, and combinations of these, and "basic” group-containing monomers such as vinyl pyridines, amino acrylates and methacrylates, and combinations of these.
  • Typical amines include the vinyl pyridines, dimethyl aminoethyl methacrylate and tert-butyl amino ethyl methacrylate.
  • the acrylic monomers employed in the process of the present invention include acrylic acid or ethacrylic acid, either alone or admixed wrth at least one other unsaturated monomer such as an ester of acrylic or methacrylic acid, 2- hydroxyethyl methacrylate, methacrylonitrile, acrylonitrile, and the like, and combinations of these.
  • unsaturated acid monomers can also be substituted in minor part for the preferred acrylic acids of the present invention.
  • unsaturated acid monomers include maleic acid, crotonic acid, fumaric acid, itaconic acid, vinyl benzoic acid, isopropenyl benzoic acid, and combinations thereof.
  • the glass-transition temperature (Tg) of the first-stage polymer is an important .factor in achieving the desired film forming properties of a particular stabilized late product. Therefore, monomers are selected such that the first-stage polymer will exhibit a Jig suitable for a particular end-use application. ---- - -
  • the first-stage monomers are, accordingly, selected so that a hydrophilic first-stage polymer will be produced. Additionally, the monomers are selected with a view toward the ultimate use of the latex film that is to be produced as well as the chemical resistance required of the thus-produced latex film. If the resulting emulsion is to be crosslinked, for example, then crosslinkable monomers should be used to form the first-stage polymer.
  • Preferred monomer formulations for the first-stage polymer include ethyl acrylate (EA) and methacrylic acid (MAA) and, particularly, the combination 80 EA/20 MAA.
  • EA ethyl acrylate
  • MAA methacrylic acid
  • S Styrene
  • AA acrylic acid
  • the ratio of water-insoluble monomer to functional-group monomer is from 20:1 to 1:3. A more preferred ratio is from 10:1 to 1:1. The most preferred embodiment is where the water- insoluble monomer to functional-group monomer ratio varies from 7:1 to 3:2.
  • a chain-transfer agent is preferably added to the first stage monomers during emulsion polymerization to regulate th molecular weight of the first-stage polymer.
  • the addition of a chain- transfer agent will enable one to regulate not only the number-average molecular weight but also the weight-average molecular, weight of the first-stage polymer.
  • the number- average molecular weight should generally not exceed about 20,000, otherwise the first-stage polymer will usually cause the system to become exceedingly viscous upon pH adjustment.
  • employing higher molecular weight might be useful for some compositions, especially those where high viscosity is desirable.
  • molecular weight refers to the number-average (Mn) molecular weight, ⁇ unless indicate otherwise.
  • the first-stage polymer must be capable of dissolving upon proper adjustment of the pH.
  • the preferred molecular weight for the first-stage polymer is from about 3,000 to 15,000.
  • the most preferred molecular weight is fro about 5,000 to 10,000.
  • Chain-transfer agents for molecular weight control is important for obtaining homogeneous, low molecular weight polymers.
  • Chain-transfer agents must be efficient, must exhibit high transfer activity, must produce controllable molecular weight distribution, and must not adversely affect the polymerization rates.
  • Conventional chain-transfer agents which meet these standards, such as mercapto carboxylic acids having 2 to 8 carbon atoms, and their esters, may be employed.
  • Suitable chain-transfer agents are ercaptoacetic acid, 2- mercaptopropionic acid, 3-mercaptopropionic acid, 2- mercaptobenzoic acid, mercaptosuccinic acid, mercaptoisophthalic acid, and alkyl esters thereof, and combinations thereof. It may also be desirable to employ a mercapto monocarboxylic acid and/or a mercapto dicarboxylic acid containing 2 to 6 carbon atoms such as mercaptopropionic acid and the alkyl ester thereof, or the butyl or isooctyl ester of mercaptopropionic acid.
  • organic-type chain-transfer agents including halogenated hydrocarbons such as bromoform, carbon tetrachloride and bromotrichloromethane, may also be desirable.
  • the chain-transfer agent is preferably selected from the group consisting of bromotrichloromethane, butyl mercaptopropionate, dodecyl mercaptan, mercaptoethanol, octyl mercaptan, and combinations of these.
  • chain-transfer agent no less than about 0.5 mol % chain- transfer agent is normally employed. If it is desirable to make polymers of greater molecular weight and/or polydispersity values, then the amount of chain-transfer agent employed can be reduced to below 0.5 mol %, say, to at least about 0.3 mol %. Depending upon the end-use, however, it may be desirable to use from about 1-3 mol % of a chain- transfer agent.
  • the chain-transfer agent is normally added to the reaction mix incrementally, along with the monomers of the first stage.
  • a portion of the chain-transfer agent may be added to a functional group-containing monomer precharge, usually in the same relative proportion as the functional group monomer.
  • the precharge preferably contains about 10 weight percent (wt.-%) of the entire charg of chain-transfer agent.
  • Initiation is a factor to consider in connection with the emulsion polymerization process; and choice of suitable initiator is important for the preparation of homogeneous products. For example, to enhance initiator efficiency, to provide desired polymerization rates, and to provide product of a particular fine-particle size, it may be preferable to gradually add initiator to a particular reaction mixture. Precharging initiator prior to the onset of polymerization, or rapidly adding initiator along with the monomers, may yield premature destruction of initiator from the high concentrations of radical thereby produced. Employing high polymerization temperatures may also induce early consumptio of initiator. For the above and other purposes, low- temperature initiators are preferred.
  • persulfate initiators such as sodium persulfat or potassium persulfate or barium persulfate and, especially with ammonium persulfate (APS) .
  • APS ammonium persulfate
  • Mixtures of such initiators may also be employed.
  • the particular identity and quantity of initiator selected will of course depend, in part, upon the desired polymerization rate, the co-monomer mixture addition rate, the polymerization reaction temperature, and the like.
  • initiator may be employe to drive the reaction to completion.
  • the choice of type of initiator, and amount of initiator, as well as the effect will be apparent to those skilled in the art.
  • An emulsifier typically an anionic emulsion- polymerization surfactant such as sodium lauryl sulfate, can be utilized to promote desired emulsion polymerization and t stabilize a particular polymerization reaction.
  • Other emulsifiers such as alkali metal sulfates, sulfonates and/or sulfosuccinic esters and so-called “non-ionics", as well as combinations of these, can also be utilized.
  • the selection of the monomers that make up the hydrophobic second-stage polymer is important. These monomers can be selected from the group of monomers set forth hereinabove (described in connection with the first-stage polymer) ; however, such monomers as well as their relative ratios are selected so that the resulting polymer will not be water soluble upon pH adjustment. Further, the resulting second-stage polymer must be capable of partitioning into the first-stage polymer, so as to form "domains" on or within the first-stage polymer. Accordingly, the second-stage polymer must be relatively incompatible with the first-stage polymer. The molecular weight of the second-stage polymers may also be modified or regulated by use of the chain-transfer agents discussed hereinabove.
  • One function of the second- stage polymer may be to enhance film strength.
  • the molecular weight should be significantly higher than that employed for the first-stage polymer.
  • molecular weights 15,000 to 200,000 are acceptable for the second-stage polymers of this invention.
  • Higher molecular weights if desired, can be obtained by methods known in the art, such as cross-linking.
  • Preferred molecular weights are from 20,000 to 150,000.
  • the most preferred molecular weight range for the second-stage polymer is 25,000 to 100,000.
  • the weight ratio of first-stage polymer to second-stage monomer can range from about 1:20 to 1:1. Preferably, the ratio is from about 1:15 to 1:2. In the most preferred embodiments, the ratio of first-stage polymer to second-stage monomer is from about 1:10 to 1:3.
  • the process of the present invention is conducted at the temperature range for conventional emulsion polymerization, known to those skilled in the art.
  • the reaction temperatures are maintained at about 70 C. to about 90 C. and preferably at about 80 C. Lower temperatures, if desired, may be utilized using re-dox polymerization techniques, as is well known to those skilled in the art.
  • the second-stage monomers be polymerized at a temperature above the glass- transition temperature (Tg) for the first-stage polymer.
  • reaction mixture may be maintained at the desired reaction temperature for a period of about 1 hour, or more, after the final additions of co-monomers, initiator, and chain-transfe agent.
  • the second-stage emulsion polymer is formed from monomers which polymerize so as to form a "hydrophobic" polymer, as defined hereinabove.
  • Monomers similar to those employed for the first stage can be used in the second stage, except that lesser amounts of functional group-containing polymers are employed to prevent solubilization upon dissolution of the first-stage polymers; In this instance, it is preferred that the second-stage polymer contain no mor than about 10 mol % of functional monomer.
  • Copolymers of monomers such as monovinyl aromatic monomers, monoethylenically-unsaturated carboxylic acids and esters thereof, conjugated dienes, acrylonitrile, vinyl acetate, vinyl dichloride, and the like, and combinations of these, can thus be employed as second-stage monomers.
  • reaction conditions for second-stage emulsion polymerization reaction are similar to those of the first- stage reaction, at least with regard to initiator, chain- transfer agent, emulsifier, and reaction parameters.
  • the solids content of the resulting aqueous polymer latex can be adjusted to the level desired by adding water thereto or by distilling water therefrom.
  • a desired level of polymeric solids content is from about 20 to about 65 wt.-%, and preferably from about 30 to about 55 wt.-%, on a total weight basis.
  • reaction conditions for the second-stage polymerization reaction it should be understood that sufficient initiator may still be present from the first- stage reaction to conduct the second-stage reaction. Addition of more chain-transfer agent may, however, be necessary to bring about the desired second-stage polymerization reaction, depending upon the desired molecular weight of the second-stage polymer. On the other hand, use of additional emulsifier is often unnecessary in the second- stage polymerization reaction.
  • reaction parameters and adjuvants can be modified, as needed, to provide optimum second-stage reaction conditions.
  • the emulsion-polymerization process can, moreover, be conducted as a batch process, or as a semi-continuous process, as desired.
  • first-stage monomer may be important, particularly if there is difficulty in obtaining uniformity of composition, for example, due to the tendency of certain monomers to partition to different phases.
  • a particular example is a first stage of styrene and acrylic acid wherein monomer-starved conditions are necessary. In such a case, a one-hour addition may be unsatisfactory, whereas a three-hour addition might be preferable.
  • an addition rate of about 0.5 to about 4 hours is sufficient for most semi-continuous polymerization reactions, dependent, of course, on the type and amount of initiator, the monomers employed, and the polymerization rate, as is well known to those skilled in the art.
  • the rate of addition of the second-stage monomer may also be important. Providing a high rate of second-stage monomer addition may make the first-stage polymer more- soluble. This can affect morphology and grafting. Similar rates of addition, as compared to first-stage addition, are normally employed but this also depends on polymerization rates.
  • the pH of the emulsion is adjusted to dissolve the first-stage polymer. If acidic functional group monomers are selected for the first-stage polymer, addition of a suitable base is appropriate. If basic functional group monomers are selecte for the first-stage polymer, addition of an acid is appropriate.
  • Suitable bases which can be used to adjust the pH include organic and inorganic bases.
  • suitable organic bases include amines, morpholine, and alkanol amines.
  • suitable inorganic bases include ammonia, NaOH, KOH, and LiOH.
  • Suitable acids for adjusting pH include various known organic and inorganic acids such as acetic acid, hydrochlori acid, and phosphoric acid.
  • the rate of addition of the base or acid to the latex emulsion is usually not important.
  • Sufficient base or acid should be added to achieve dissolution of the first-stage polymer.
  • the degree of dissolution of the first-stage polymer can be estimated by measuring the change in optical density (O.D.) of the emulsion before and after addition of the pH-adjusting agent.
  • additives for various applications, it is sometimes desirable to employ small amounts of various known additives in the latex.
  • Typical examples of such additives are bacteriocides, antifoamers, etc.
  • Such additives can be added in a conventional manner to such latexes.
  • the resulting stabilized emulsion can be used to produce a variety of coatings known in the art, including films, polishes, varnishes, paints, inks, and adhesives.
  • the process of this invention can typically be conducted as semi-continuous polymerization as follows. Unless otherwise specified, percentages shall refer to weight percen .
  • a suitable reactor Internally subjected to a nitrogen (N 2 ) atmosphere, a suitable reactor is filled with water and emulsifier and stirred until a homogeneous solution is formed. The solution is heated, utilizing conventional heating equipment, to the desired reaction temperature.
  • the first-stage monomers and chain-transfer agent are combined to produce a first-stage mixture.
  • a pre-charge of about 15% of the first-stage mixture is introduced into the reactor.
  • An initiator, dissolved in water, is thereafter added into the reactor to induce the pre-charge to polymerize.
  • the balance of the first-stage monomers and chain- transfer agent are thereafter slowly added to the reaction mixture, over a time period of about 20 minutes to 2 hours. Assuming that an acidic monomer is included in the first-stage mixture, the pH of the first-stage emulsion- polymerization reaction mixture is optionally raised to about 4.5 to 7 to cause the first-stage polymer to "swell". (If a desired second-stage polymerization mixture has not been prepared beforehand, such can now be prepared.)
  • the second-stage polymerization mixture (of second-stage monomers) is added at the desired reaction temperature.
  • the pH of the reaction mix is slowly raised (over ca. 50 minutes) to about 8 to 10 to release the first-stage polymer into solution.
  • the pH of the stirred mixture was approximately 2.5, and the optical density (O.D.), measured on a Bausch and Lomb Spec 70 unit (at 500 nm in a 10 mm cell at 0.2% N.V.) was found to be 1.4
  • the pH was adjusted to 9.5 using a 28 weight- percent aqueous ammonium hydroxide solution (28 wt.-% aq.
  • the second-stage MMA polymer was stabilized b dissolution of the first-stage EA/MAA polymer.
  • the O.D. after pH adjustment was found to be 0.37.
  • Example 2 The procedure of Example 1 was followed, except that 10 g of styrene (S) was used as the second-stage monomer in place of the 100 g of MMA. Similar results were obtained; and an emulsion latex was formed. When the O.D. was measure at a pH of approximately 2.5, the O.D. was found to be greater than 2. After adjustment to approximately pH 9, the O.D. was found to be reduced to 0.82.
  • S styrene
  • Example 3 The procedure of Example 1 was again followed, except that no emulsifier was added to the first-stage polymerization step. Similar results were obtained. When measured at a pH of approximately 2.5, the O.D. was found to be 0.4. After adjustment to approximately pH 9, the O.D. was found to be 0.18.
  • EXAMPLE 4 To provide a clear model to show inverse core/shell emulsion polymerization and also to obtain additional confirmation of release and stabilization of the domains by base solubilization of the first stage, a monomodal first- stage alkali-soluble emulsion polymer was formulated as follows. Such an emulsion was made via a so-called "seeded” approach, wherein a fine particle size 80/20 EA/MAA polymer, made by emulsion-polymerization techniques, was used as the "seed" for the second-stage manufacturing step of the same composition.
  • the resulting alkali-soluble, relatively low molecular weight thus-produced "seed” was then characterized, at low and high pH, utilizing known transmission electron microscopy (T.E.M.) techniques and was shown to be both monodisperse, 94 nm (nanometers) , and alkali-soluble.
  • T.E.M. transmission electron microscopy
  • Such a seed was then utilized in connection with second-stage monomers of both styrene (S) and methyl methacrylate (MMA) at 5:1 and 1:1 S/MMA weight ratios, and resultant mixtures were subjected to emulsion polymerization.
  • the resulting emulsions were then characterized by known T.E.M techniques. In all cases, phase inversion was noted. At high pH, the EA/MAA first-stage polymer was shown to be in a dissolved state and the discrete second-stage domains remained. These results correlated well with the particle size distributions at low and high pH. The distributions tended to show lower, monomodal particle sizes at high pH, indicating the presence of the second-stage domains after the EA/MAA phase was solubilized. The T.E.M. analytical results also correlated well with the observation of the lower O.D. value of the emulsions after the pH was raised from 2.5 to 9.
  • EXAMPLE 5 To a 1-liter round-bottom flask equipped with a conventional paddle stirrer, and internally subjected to a N atmosphere, was added 48 g of water and 0.8 g of sodium lauryl sulfate emulsifier (28%) . These ingredients were the mixed until homogeneous, while heating to a temperature of 8 C.
  • first-stage monomers were next combined along with 2.6 g of the chain-transfer agent bromotrichloromethane, to produce a first-stage monomer mixture:
  • the balance of the chain-transfer agent- containing first-stage monomer mixture was added to the flask, over a time period of 30 minutes, while maintaining the desired 80 C. reaction temperature.
  • the resultant reaction mixture was held at 80 C. for one additional hour. Then, a premix of 10.1 g of an 80% aqueous solution of 2- dimethylamino-2-methyl-l-propanol, 1.4 g of 28 wt.-% aq. NH 4 OH soln. , and 20 g of water was added to the reaction mixture, using the same feed rate as for the first-stage monomer mixture. After such addition was completed, the resultant reaction mixture was then held at 80 C. for 5 minutes. The pH was thereafter found to be 7.0-7.5.
  • the second-stage monomer mixture was then added to the thus-neutralized first-stage polymer mixture, over a time period of 60 minutes, at a temperature of 80 C. After such addition of the second-stage monomer mixture was completed, the resultant batch was. held at a temperature of 80 C. for 5 minutes. Next, a pre-mix of 5.6 g of 28 wt.-% aq. NH 4 0H soln. and 20 g of water was added at the same fee -rate as for the second monomer feed. The resultant reaction mixture was then maintained at 80 C. for 50 minutes.
  • the resulting latex emulsion was thereafter cooled and filtered.
  • the emulsion was observed to exhibit the characteristics of an "inverted" core-shell emulsion, within which the first-stage polymer had become solubilized.
  • a latex for use in a floor polish which can provide both the low molecular weight leveling resins and the high molecular weight colloidal components, can be made from the latexes produced according to the present invention, using known procedures and formulations.
  • an emulsion polymer was prepared according to the above general preparation example (2-hour first-stage monomer addition) utilizing the following raw materials: Step 1; Preparation of Emulsion Polymer Stage 1 monomers: Styrene Acrylic Acid Iso-octyl Mercapto propionate
  • Step 2 Floor Finish Prepared Employing Step 1 Polymer An 18.7% non-volatile, high-gloss floor polish was formulated, in a conventional manner, from the above emulsion. The ingredients are listed below: Ingredients
  • Emulsion (a 1:1 blend of AC-392 and Eplene E-43 polyethylene waxes) 20% Zinc Ammonium Carbonate 3.0 g
  • Triton X 405 is a commercially- available 70 wt.-% soln. of a 40-EO octylphenol surfactant.
  • EXAMPLE 8 An architectural coating was prepared using the polymer prepared according to Example 5. The coating had the following formulation: Paint Base:
  • Dispose Ayd W22 is a blend of anionic and non-ionic surfactants, sold by Daniel Products, Jersey City, NJ.
  • 2- "Drew Plus T4500” is an anti-foam agent for water-based paints, based on mineral oil and a silica derivative, sold by Drew Ameroid.
  • the above paint possessed good gloss as well as good coating and adhesion properties.
  • the next three examples are directed to the production of adhesives..
  • a first-stage hydrophilic polymer emulsion was produced as follows. To a 2-liter round-bottom flask fitted with a conventional paddle stirrer and containing 580.7 g of water at 80 C. under a N 2 atmosphere was added 8.0 g of a first emulsifier, sodium lauryl sulfate, together with 8.5 g of a second emulsifier, sodium dodecyl diphenyl oxide disulfonate. Next, 2.0 g of the free-radical initiator (NH4) 2 S 2 0g was added to the flask contents.
  • NH4 2 S 2 free-radical initiator
  • first-stage monomers namely, 310.0 g of ethyl acrylate (EA) and 78.0 g of methacrylic acid (MAA) , were added to the agitated flask contents over a time period of 60 minutes, along with 7.8 g of the chain-transfer agent butyl mercaptopropionate.
  • the monomer-containing agitated flask contents were then held at 80 C. for 30 minutes; and, thereafter, 5.0 g of a 28 wt -% aq. NH4OH soln. was added, to maintain a pH value of from 5 to 6.
  • the second-stage polymer was produced as follows.
  • the resultant mixture was then held at 80 C. for one hour, while maintaining agitation. Th pH of the thus-agitated emulsion was approximately 5.5 and the viscosity was approximately 75 centipoises (cps) .
  • the pH of the thus-agitated emulsion was adjusted to 7.0-7.5, utilizing 5.0 g of the above-mentioned 28 wt.-% aq. NH 4 OH soln. With the addition of the NH4OH solution, the first- stage EA/MAA polymer particles were observed to dissolve in their emulsion and the viscosity of such an emulsion was observed to increase to approximately.1000 cps.
  • the thus-produced pH-adjusted second-stage polymeric emulsion was thereafter applied to commercially-available polyester film to provide a one-mil thick dry film of pressure-sensitive adhesive possessing so-called "removable performance" characteristics (i.e., the adhesive and so- called “face stock” onto which the adhesive is coated are together cleanly removable from a surface) .
  • the dried film was observed to have a glass-transition temperature (Tg) of minus 48 C.
  • Tg glass-transition temperature
  • Example 10 The procedure for Example 9 was repeated except that 4.3 g of diethylene glycol dimethacrylate was utilized to produce the second-stage polymer, in lieu of the 4.0 g of hexanediol diacrylate.
  • the initial 30-minute 180-degree peel value was determined to be 48 ounces per inch width; the 70-degree C, 24-hour aged 180-degree peel value was observed to be 110 ounces; the Polyken tack was observed to be 600 g per square centimeter; and the rolling-ball tack was observed to be 4 inches.
  • Example 9 produced a "removable” pressure-sensitive adhesive.
  • Example 10 produced a somewhat more “permanent” pressure-sensitive adhesive.
  • EXAMPLE 11 A heat-sealable (e.g., blister-pack) variety of adhesive was prepared as follows. The above-discussed procedures of Example 9 were again followed to produce yet another quantity of the first-stage hydrophilic polymer emulsion.
  • Another second-stage hydrophobic polymer was then produced as follows. To the 2-liter round-bottom flask, which was fitted with the conventional paddle stirrer and which contained 270 g of water at 78 C. under a N 2 atmosphere, was added 250 g of the first-stage hydrophilic polymer-containing emulsion along with 15 g of a 4-mole EO nonyl phenol surfactant. Next, 1.3 g of the free-radical initiator (NH4) 2 S 2 0g was added to the flask.
  • NH4 2 S 2 free-radical initiator
  • second-stage monomer namely 10 g of MAA, 225 g of BA, and 150 g of methyl methacrylate (MMA) , were simultaneously added to the agitated flask contents over a time period of 90 minutes to produce a second-stage monomer mixture.
  • the thus-produced second-stage monomer mixture was then held at 80 C. for one hour, while maintaining agitation.
  • the pH of the thus-agitated emulsion was approximately 5.5 and the viscosity was approximately 30 centipoises (cps) .
  • the pH of the thus-agitated emulsion was adjusted to 7.0-7.5, utilizing 12.5 g of the 28 wt.-% aq. NH4OH soln.
  • the first-stage EA/MAA polymer particles were observed to dissolve in their emulsion, and the viscosity of such emulsion was found to have increased to approximately 1900 cps. This emulsion was then reduced to 40 wt.-% solids with water, resulting in a viscosity of 85 cps.
  • the pH-adjusted second-stage polymeric emulsion was thereafter applied to commercially-available so called "SBS" paper stock to provide a dry film of heat- sealable adhesive.

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Polymerisation Methods In General (AREA)
  • Adhesives Or Adhesive Processes (AREA)
  • Graft Or Block Polymers (AREA)
  • Non-Portable Lighting Devices Or Systems Thereof (AREA)
  • Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
EP19900916634 1989-10-02 1990-09-17 Stable emulsion polymers and methods of preparing same Withdrawn EP0495000A4 (en)

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US5212251A (en) * 1990-09-24 1993-05-18 Rohm And Haas Company Alkali-resistant core-shell polymers
GB9110418D0 (en) * 1991-05-14 1991-07-03 Du Pont Howson Ltd Radiation-sensitive material
DE19542181A1 (de) 1995-11-13 1997-05-15 Hoechst Ag Lösemittel-freie Kunstharze und Kunstharzmischungen
US6767638B2 (en) * 2002-05-16 2004-07-27 Meadwestvaco Corporation Core-shell polymeric compositions
US11591472B2 (en) * 2016-12-02 2023-02-28 The Williamette Valley Company Llc Wax-organic extender emulsion and method for manufacture thereof
CN114456324B (zh) * 2021-12-30 2022-09-13 广东恒和永盛集团有限公司 一种水性低透水率单组份丙烯酸酯乳液及其制备方法
US12152151B2 (en) 2022-03-29 2024-11-26 The Willamette Valley Company Llc Adhesive mixture having an organic slurry dispersion and process for manufacture thereof

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