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SURFACE-CHARGED POLYMER COLLOIDS

The 2000 Korean Polymer Society Fall Conference October 13-14, 2000 Chungnam University. SURFACE-CHARGED POLYMER COLLOIDS. Do Ik Lee Emulsion Polymers R&D The Dow Chemical Company Midland, Michigan 48674 USA dilee@dow.com. Short Course on Polymer Colloids

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SURFACE-CHARGED POLYMER COLLOIDS

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  1. The 2000 Korean Polymer Society Fall Conference October 13-14, 2000 Chungnam University SURFACE-CHARGED POLYMER COLLOIDS Do Ik Lee Emulsion Polymers R&D The Dow Chemical Company Midland, Michigan 48674 USA dilee@dow.com

  2. Short Course on Polymer Colloids National Laboratory for Nanoparticle Technology, Yonsei University October 5-6, 2000 SURFACE-CHARGED POLYMER COLLOIDS Do Ik Lee Emulsion Polymers R&D The Dow Chemical Company Midland, Michigan 48674 USA dilee@dow.com

  3. Surface-Charged Polymer Colloids Outline of the Presentation • Introduction • The Critical Review of Emulsion Polymerization Mechanisms: Homogeneous and Micellar Particle Nucleations • Preparation of Surface-Charged Polymer Colloids • Ionic Initiators • Ionic Comonomers • pH-Dependent Ionogenic Comonomers such as Weak Acids and Bases • Hydrolysis of Esters • Post-Reactions

  4. Surface-Charged Polymer Colloids(Continued) • Various Methods of Controlling the Placement of Charge or Functional Groups: • Surface-Modification by Shot Additions • Gradient-Composition by Power-Feed or Computer-Aided Processes • Core-Shell Latexes • Inverted Core-Shell Latexes • Cleaning and Characterization of Surface-Charged Polymer Colloids • General Colloidal and Some Unique Properties • Applications • Summary and Conclusions

  5. Introduction • Surface-charged polymer colloids are anionic (negative), cationic (positive), or amphoteric (both negative and positive). • Surface-charged polymer colloids are ubiquitous in both scientific and industrial applications. • Surface charges impart electrostatic stabilization to polymer colloid particles. • Surface-charged polymer colloids are often functionalized in addition to charge groups on the particle surfaces. • Surface-charged polymer colloids are widely used for both scientific and industrial applications.

  6. Introduction(Continue) • Especially, well-defined, monodisperse surface-charged polymer colloids are widely used as: • Model colloids for basic scientific studies such as crystallization, self-assembly, colloidal stability / particle interactions, dispersion rheology, packing, etc. • Calibration standards for electron microscopes, HDC. CHDF, etc. • Surface-charged polymer colloids are quite extensively used for: • Biomedical applications such as diagnostic assays, immunoassays / cell separation, enzyme immobilization, drug delivery gene therapy, etc.

  7. Introduction(Continued) • Over 10 Million Metric Tons (20 Billion Pounds) of surface-charged polymer colloids are used in industrial applications: • Architectural coatings (Paints): interior and exterior • Paper coatings • Carpet backing: conventional and foam backing • Maintenance and industrial coatings • Textile coatings • Adhesives and Pressure-Sensitive Adhesives • Caulks and Sealants • Inks • Latex foams • Thickeners, etc.

  8. Micelle Formation Entry into Particle Continuous Propagation Current Views on Emulsion Polymerization Mechanisms Reactions in Aqueous Phase I2 > 2 I• I• + M > IM• IM• + (j-1)M > IMj• IMj• + IMj• > IM2jI (Termination > Water-Soluble Species) IMcrit j• (Surface-Active)

  9. Current Views on Emulsion Polymerization Mechanisms (Continued) IMcrit j• (Surface-Active) Micelle Formation Entry into Particle Continuous Propagation IMn• Entry into Particle Homogeneous Nucleation

  10. Radical Entry from the Aqueous Phase Current Views on Emulsion Polymerization Mechanisms (Continued) Reactions in the Particle Propagation Propagation Termination Transfer + M Exit M

  11. Surfactant-Free Emulsion Polymerization Mainly Homogeneous Nucleation by the Precipitation of Oligomeric Radicals Some Micellar Nucleation In some cases, small amounts of surfactants will be used for stability. Conventional Emulsion Polymerization Mainly Micellar Nucleation by Monomer-Swollen Micelles Some Homogeneous Nucleation Seeded Emulsion Polymerization Particle Nucleation Step Eliminated Current Views on Emulsion Polymerization Mechanisms (Continued)

  12. - - - - M M M M M M M M - - M M M M M M M M - - - - - - M M M M M M M M - - M M M M M M M M - - - - - - M M M M M M M M - - M M M M M M M M - - - - Before Polymerization M - - M M M M I2 M M M M M M M M M M M M M Monomer Droplets (1-10 mm) I2 - M - M M M M M M M M Monomer-Swollen Micelles (5-10 nm) M M M M M M M M M M - - I2 M I2 Continuous Aqueous Phase - :Surfactant

  13. - - - - - - - - - - - - M M M M M M M M - - M M M M M M M M - - - - - - M M M M M M M M - - M M M M M M M M - - - Interval I: Micellar Particle Nucleation M M M M M M M M M M M M M M M - M - M M M M I2 M M M M M M M M M M M M M M Monomer Droplets (1-10 mm) I2 - M - M M M M M M M Seed Particle Formation M M M M M M M M M M M M I2 I2 - - M Continuous Aqueous Phase -

  14. - - - - - - - - - - - - M M M M M M M M - - M M M M M M M M - - - - - - M M M M M M M M - - M M M M M M M M - - - Interval II: Constant Particle Growth Period M M M M M M M M M M M M M M M - M - M M M M I2 M M M M M M M M M M M M M M Monomer Droplet (1-10 mm) I2 - M - M M M M M M M M Seed Particles M M M M M M M M M M M I2 I2 - - M Continuous Aqueous Phase -

  15. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Interval III: Decreasing Monomer Concentration and Finishing Step M M M I2 M M M M M M M M M M M M M I2 M M M M M M M M M M M M M M M M M M I2 M M I2 I2 M M M M M M M M M M M M I2 M M M M M M M M M M M M M I2 I2 M M M M M Continuous Aqueous Phase M

  16. MjOSO3- Surface-Charged Polymer Colloids Made with Ionic Initiators • Anionic Initiators • Persulfate (S2O82-) is the most widely used initiator in emulsion polymerization. • S2O82- > 2 •OSO3- •OSO3- + M > •MOSO3- + M > •M2OSO3- …….. •MjOSO3- (Surface-active) > Adsorbed onto either monomer-swollen micelles or particles • Persulfate produces surface-bound sulfate ion groups:

  17. Surface-Charged Polymer Colloids Made with Ionic Initiators (Continued) • In 1970, van den Hul and Vanderhoff* found both sulfate (-OSO3-)- and hyrdoxyl (-OH)-end groups on persulfate-initiated particles: • •OSO3- + H2O > •OH + HOSO3- • Shown by Kolthoff and Miller, especially at low pH’s • Also, hydrolysis of sulfate-end groups results in hydroxyl groups. * H.J. van den Hul and J.W. Vanderhoff, Br. Polym. J., Vol. 2, 121 (1970).

  18. Schematic Representation of Persulfate-InitiatedPolymer Colloid Particle The total number of end-groups was found to be close to two per polymer molecule, when hydroxyl end-groups were added. H.J. van den Hul and J.W. Vanderhoff, Br. Polym. J., Vol. 2, 121 (1970).

  19. Surface-Charged Polymer Colloids Made with Ionic Initiators (Continued) • In 1965, Matsumoto and Ochi and later in 1970, Kotera, Furusawa, and Takeda studied surfactant-free emulsion polymerizations using potassium persulfate as an initiator. • Then, in 1973, Goodwin, Hearn, Ho, and Ottewill made systematic studies on the effect of various polymerization variables on particle size in surfactant-free emulsion polymerization using potassium persulfate as an initiator:

  20. Persulfate-Initiated Emulsion Polymerization Low pHs High pHs -OSO3- -OSO3- -O3SO- -OSO3- -OH HO- -O3SO- -OSO3- -O3SO- -OSO3- HO- -OH -O3SO- -OSO3- -O3SO- -O3SO- Sulfated/Hydroxylated Latex Sulfated Latex Hydrolysis Hydrolysis Hydrolysis/Oxidation -OH -COO- HO- -OOC- -COO- -OH HO- -OH -OOC- -COO- HO- -OH -OOC- -COO- HO- -OOC- Hydroxylated Latex Carboxylated Latex Persulfate-Initiated Polymer Colloids Leading to Sulfated, Sulfated/Hydroxylated, Hydroxylated, and Carboxylated Polymer Colloids

  21. Surface-Charged Polymer Colloids Made with Ionic Initiators (Continued) • Various anionic Initiator Systems • S2O82- + Fe2+ > Fe3+ + •OSO3- • OSO3- + Fe3+ > Fe2+ + •OSO3- • S2O82- + HSO3- > SO42- + •OSO3- + H+ +•SO3- • S2O82- + HOCH2SO2- > SO42- + •OSO3- + H+ +•S(CH2OH)O2- • Also, ter-Butyl Hydroperoxide and Diisopropylbezene Hydroperoxide are used with sodium formaldehyde sulfoxylate (NaHOCH2SO2-) as a reducing agent at low temperatures.

  22. Surface-Charged Polymer Colloids Made with Ionic Initiators (Continued) • Cationic Initiators • Azo-bis(isobutyramidine hydrochloride) (AIBA: 2,2’-azo-bis(2-amidinopropane) dihydrochloride known as V-50 from Wako Chemicals) is widely used as a cationic initiator:

  23. Surface-Charged Polymer Colloids Made with Ionic Initiators (Continued) • Cationic Initiators (Continued) • In 1979, Goodwin, Ottewill, and Pelton made similar systematic studies on the effect of various polymerization variables on particle size in surfactant-free emulsion polymerization using AIBA as aninitiators: • Azo-bis(N,N’-dimethylene isobutyramidine hydrochloride) (ADMBA) is also used.

  24. Surface-Charged Polymer Colloids Made with Ionic Comonomers • Anionic Comonomers • In 1976, Juang and Krieger prepared monodisperse sulfonated latexes by surfactant-free polymerization of styrene with small amounts of sodium styrene sulfonate (NaSS): • Chonde and Krieger prepared sulfonated latexes by surfactant-free emulsion polymerization of styrene and sodium vinylbenzyl sulfonate (NaVBS) in the water-menthanol mixtures persulfate as an initiator.

  25. Surface-Charged Polymer Colloids Made with Ionic Comonomers (Continued) • Anionic Comonomers (Continued) • In 1992, Kim, Chainey, El-Aasser, and Vanderhoff studied the kinetics of the surfactant-free emulsion copolymerization of styrene and NaSS over a wide range of comonomer compositions: • The polymerization rate increased dramatically in the presence of small amounts of NaSS. • This increas was due to the increased number of particles by a homogenous nucleation. • At low NaSS concentrations, monodisperse latexes were obtained. • At high NaSS concentrations, broader and bimodal size distributions were obtained. • This was due to significant aqueous phase polymerization of NaSS. • The occurrence of this aqueous phase side reaction made the preparation of highly sulfonated latexes impossible.

  26. Surface-Charged Polymer Colloids Made with Ionic Comonomers (Continued) • Cationic Comonomers • van Streun, Welt, Piet, and German studied the effect of the amount of 3-(methacrylamidinopropyl) trimethylammonium chloride (MAD) on the emulsion copolymerization of styrene and MAD using AIBA as a cationic initiator: • MAD accelerated the polymerization and decreased the particle size. • Declair, Maguet, Pichot, and Mandrand prepared amino-functionalized by emulsion copolymerization of styrene and vinylbenzylamine hdrochloride (VBAH) using AIBA: • The use of divinylbenzene (DVB) improved monodispersity.

  27. Surface-Charged Polymer Colloids Made with pH-Dependent Ionogenic Comonomers • Carboxylated Latexes • Carboxylated latexes are the most widely used of all commercial latexes: • They were invented in the 1940s. • Their benefits were recognized through the incorporation of MAA, AA, IA, FA, etc. onto the surface of latex particles. • Since then, there has been phenomenal success in developing a variety of commercial carboxylated latexes for various applications. • Thus, carboxylated latexes amount to more than 90% of all the commercial latexes. • The distribution of carboxylic groups, on the particle surface, in the aqueous phase, and inside the particle, was studied extensively in the 1970s and 1980s.

  28. Surface-Charged Polymer Colloids Made with pH-Dependent Ionogenic Comonomers (Continued) • Carboxylated Latexes (Continued) • The distribution (on surface, in medium, and within particle) of carboxylic groups depends on: • Type of carboxylic monomers in terms of hydrophilicity: MMA <AA < IA < FA in order of increasing hydrophilicity • The degree of neutralization, that is, the degree of ionization • Mode of addition: Early or late addition, continuous addition, shot addition, etc. • The use of more water-soluble comonomers, such as MMA, VCN, etc., acting as coupling agents • Latex particle size: The smaller particle size, the more carboxylic groups on the particle surface • Ionic strength, etc.

  29. Emulsion Polymerization of Nonionic Monomers with Carboxylic Monomers Low pHs High pHs MAA MAA, AA, IA and FA AA IA and FA -COO- -COOH -COOH -COOH -OOC- -COO- -OOC- -OOC- -OOC- -COOH -COOH -COOH -OOC- -COO- HOOC- -COO- HOOC- -COO- HOOC- -COO- -OOC- -COO- HOOC- HOOC- HOOC- -COOH -COOH -COOH- -OOC- -OOC- -OOC- -OOC- Increasing Hydrophilicity Acid Distribution on the Particle Surface Medium Low High Very High Acid Distribution inside the Particle Medium High and Uniform Low Very Low Acid Distribution in the Aqueous Phase Medium Very Low High High The Acid Distribution in the Carboxylated Latexes as a Function of Acid Type and Polymerization pH

  30. Surface-Charged Polymer Colloids Made with pH-Dependent Ionogenic Comonomers (Continued) • A Special Class of Carboxylated Latexes: Alkali-Swellable and Soluble Latexes (ASwL’s and ASL’s) • In 1959, Fordyce, Dupre, and Toy invented alkali-soluble latexes. • In 1966, Muroi established the factors affecting the alkali swelling of carboxylated latexes. • In 1970, Verbrugge further delineated the properties of alkali-soluble latexes as a function of acid level, backbone hydrophilicity, Tg, molecular weight and crosslinking, etc. • In 1981, Nishida, El-Aasser, Klein, and Vaderhoff showed that carboxylated latex particles had non-uniform distribution of carboxylic groups: High on the surface and low in the core.

  31. COO-Na+ H2O COOH Add Base H2O H2O H2O HOOC Neutralize COOH HOOC COOH Na+ -OOC Na+ -OOC COO-Na+ COO-Na+ H2O COOH COO-Na+ or NH4+ References: 1. D. B. Fordyce, J. Dupre, and W. Toy, Official Digest, 31, 284 (1959). 2. S. Muroi, J. Appl. Polym. Sci., 11, 1963 (1967). 3. C. J. Verbrugge, J. Appl. Polym. Sci., 14, 897 (1970). The Alkali-Swelling of Carboxylated Latex Particles Depends on: Acid Type and Content (1-3) Polymer Backbone Hydrophilicity (2, 3) Dissolution Temperature (2) / Polymer Tg (2-3) Molecular Weight (2) / Crosslinking Degree of Neutralization, pH Etc. Brief Literature Review of the Alkali-Swelling of Carboxylated Latex Particles

  32. Unionized carboxylic group Emulsion Polymerization of Nonionic Monomers with Varying Amounts of Methacrylic Acid at Low pHs Conventional Carboxylated Latex Alkali-Swellable Latex Alkali-Soluble Latex -COOH -COOH -COOH -OOC- -OOC- -COOH -COOH -OOC- -COOH HOOC- -COO- HOOC- -COO- HOOC- -COO- HOOC- HOOC- -COOH -COOH HOOC- -COOH -OOC- -OOC- -OOC- Increasing Methacrylic Acid -COO- -OOC- -COO- -COO- -OOC- -COO- -OOC- -COO- -OOC- -COO- -OOC- -COO- -OOC- -COO- -OOC- -COO- -COO- -OOC- -OOC- -COO- -OOC- -COO- -OOC- -COO- -OOC- -COO- -OOC- -OOC- Ionized carboxylic group Neutralization A Special Class of Carboxylated Latexes; Alkali-Swellable and Soluble Latexes and Their Swelling Behaviors

  33. Surface-Charged Polymer Colloids Made with pH-Dependent Ionogenic Comonomers (Continued) • Aminated Latexes • Amine-containing monomers such as dimethyl aminoethyl methacrylate (DMAEMA), 4-vinylpyridine (VP), etc. can be copolymerized with varous noionic monomers such as styrene, MMA, etc. either by in-situ seeded or seeded emulsion polymerization with either anionic, cationic or nonionic surfactant or by surfactant-free emulsion polymerization using various initiators such as persulfate, azo-bis(isobutyronitrile) (AIBN), and cationic inititiators, depending on the pH of polymerization.

  34. Surface-Charged Polymer Colloids Made with pH-Dependent Ionogenic Comonomers (Continued) • Amphoteric Latexes • Aphoteric latexes can be made by emulsion copolymerizations of weak acid and weak base monomers with various nonionic monomers either at low pHs or at high pHs. • Also, amphoteric latexes can be made by emulsion copolymerization of various combinations of cationic monomers and weak acid monomers at low pHs and anionic monomers and weak base monomers at high pHs, with nonionic monomers using appropriate initiators and surfactants.

  35. Special Emulsion Polymerization Techniques for Controlling the Placement of Functional Monomers in Surface-Charged Polymer Colloids • It is highly desirable to be able to control the placement of functional monomers for designing latexes. • It is generally advantageous to place functional groups on or near the particle surface for various reasons such as colloidal stability, surface functionality, post-reactions, etc. • For this reason, great efforts have been made to maximize the placement of functional monomers.

  36. Special Emulsion Polymerization Techniques for Controlling the Placement of Functional Monomers in Surface-Charged Polymer Colloids (Continued) • Some of the Techniques Explored: • Inverted core-shell approaches by Ceska (1974), Lee et al. (1983), Okubo, Kanaida, and Matsumoto (1987), etc. • A shot addition by Sakota and Okaya (1976) • Power feed process to make gradient-composition latexes by Bassett and Hoy (1980, 1981) • Computer-aided processes of making gradient-composition latexes • Core-shell approaches

  37. Special Emulsion Polymerization Techniques for Controlling the Placement of Functional Monomers in Surface-Charged Polymer Colloids (Continued) Inverted Core-Shell Formation D.I Lee and T. Ishikawa, “The Formation of Inverted Core-Shell Latexes”, J. Polym. Sci., Polym. Chem. Ed., 21, 147 (1983).

  38. Special Emulsion Polymerization Techniques for Controlling the Placement of Functional Monomers in Surface-Charged Polymer Colloids (Continued) Inside Particle Inside Particle On Surface On Surface In Serum In Serum M. Okubo, K. Kanaida, and T. Matsumoto, “Preparation of Carboxylated Polymer Emulsion Particles in Which carboxyl Groups are Predominantly Localized at Surface Layer by Using the Seeded Emulsion Polymerization Technique”, J. Appl. Polym. Sci., 33, 1511 (1987).

  39. Special Emulsion Polymerization Techniques for Controlling the Placement of Functional Monomers in Surface-Charged Polymer Colloids (Continued) Functional Monomer Tank

  40. Special Emulsion Polymerization Techniques for Controlling the Placement of Functional Monomers in Surface-Charged Polymer Colloids (Continued) Power Feed Process Power Feed Tanks D.R. Bassett and K.L. Hoy, “Nonuniform Emulsion Polymer: Process Description and Polymer Properties” in Bassett, D.R., Hamielec, A.E. (Eds), Emulsion Polymers and Emulsion Polymerization, ACS Symposium Series 165, Washington, DC, 1981, p. 371-403.

  41. Surface-Charged Polymer Colloidsby Hydrolysis • Fitch et al. (1979) prepared polymethy, cyclohexyl, benzyl and b-naphtyl acrylate latexes and polymethyl methacrylate latexes snd studied the kinetics of their hydrolysis to form carboxylated latexes. • The acrylate latexes were treated with a mixed bed of strongly acid and strongly basic ion exchange resins. • The hydrolysis reactions were measured by conductometric titration. • Lee et al. (1992, 1996) developed hollow particles by hydrolysis of acrylate cores.

  42. Surface-Charged Polymer Colloidsby Post-Reactions • Lloyd et al. (1962) prepared linear and lightly crosslinked polyvinylbezyl chloride (PVBC) latexes and quaternized them with trimethylamine to form cationic latexes. • Chonde, Liu, and Krieger (1980) prepared a series of latexes with vinylbenzyl chloride (VBC) and carried out nucleophilic displacement of the surface chloride by sulfite ions by reacting them with aqueous sulfite to form anionic sulfonated latexes. • Wessling et al. (1980-1985) prepare cationic latexes by reacting VBC copolymer latexes with tertiary amines. • Kawaguchi et al. (1981) prepared styrene-acrylamide copolymer latex and reacted it with hypochlorite and sodium hydroxide to form amino and carboxyl groups by the Hoffman reaction and competitive hydrolysis of amide groups, respectively. • Ford et al. (1993) prepared monodisperse latexes with styrene (23-98%), VBC (0-75%), DVB (1%), and vinylbenzyl trimethyl ammonium chloride using a cationic initiator and reacted them with trimethylamine.

  43. - Anionic or Cationic Charge Group Surface Morphology of Charged Polymer Colloid Particles Smooth Charged Surface Hairy Charged Surface

  44. Methods of Cleaning • In order to remove free and adsorbed surfactants, water-soluble oligomers and polymers, electrolytes, etc., the following cleaning methods have been used: • Dialysis (Ottewill etal, Fitch et al., etc.) • Mixed ion exchange (Vanderhoff et al., etc.) • Continuous hollow dialysis / mixed ion exchange • Serum replacement (El-Aasser et al., etc.) • Serum replacement and ion exchange (El-Aasser et al., etc.) • Ultracentrifugation (Chonde nd Krieger, etc.)

  45. Characterization • Conductometric titration • Potentiometric titration • Electrophoresis (z Potential Measurement) • Turbidometric titration with a cationic surfactant • Viscosity • Particle swelling • Etc.

  46. Conductance Amount of NaOH Solution Added Conductometric Titration Conductance Amount of NaOH Solution Added Conductometric Titration of Persulfate-Initiated Latex Conductometric Titration of Persulfate-Initiated/Carboxylated Latex

  47. pH Amount of NaOH Solution Added Potentiometric Titration pH Amount of NaOH Solution Added Conductometric Titration of Persulfate-Initiated Latex Conductometric Titration of Persulfate-Initiated/Carboxylated Latex

  48. Zeta ( z ) Potential, mv 0 2 4 6 8 pH Electrophoresis - z Potential Measurement U = C(ez/h) z = chU/e for kR < 0.1, C = 1/6p for kR > 100, C = 1/4p 10-4M NaCl 10-3M NaCl 10-2M NaCl Zeta Potential of Amphoteric Colloids Vs. pH

  49. General Colloidal Propertiesof Surface-Charged Polymer Colloids • Most importantly, surface-charged polymer colloids are electrostatically stabilized by surface charges. • Their colloidal behaviors are strongly affected by the ionic strength of aqueous phase. • Their stability is generally governed by the Schulz-Hardy Rule: The effect of counter-ion valency. • Industrially, surface-charged polymer colloid particles are often combined with nonionic steric stabilizers to achieve electrosteric (both electrostatic/steric) stabilization. • Industrially, they are often modified with a variety of functional groups.

  50. Some Unique Properties of Surface-Charged Polymer Colloids - Iridescence Monodisperse Polyvinyl Toluene Latex R.M. Fitch, “Polymer Colloids: A Comprehensive Introduction”, Academic Press, New York, 1997.

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