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Swelling of Latex Particles by Water-Soluble Solvents. 1. Experimental Results R. Popli,' M. H. Luccas, and S. L. Tsaur Louis Laboratory, S. C. Johnson and Son, Inc., Racine, Wisconsin 53403 Received March 22, 1990. I n Final Form: J u n e 28, 1990 Equilibrium swelling of polymer latexes by solvents with varying degree of solubility in water was studied. Monodisperse latexes of acrylate terpolymer (butyl methacrylate/ butyl acrylate/methacrylic acid) and sulfonated polystyrene were dialyzed and treated with ion-exchange resin. The solvents were chosen to represent a broad spectrum of the solubility parameter and the degree of solubility in water. The solvent partitioning data show that glycols and ethanol partition to the polymer phase at high solvent concentrations, whereas methyl ethyl ketone and diethylene glycol monobutyl acetate partition to the polymer phase at all concentrations. The polymer nature also influences the solvent partitioning behavior.
Introduction Many practical examples of thermodynamic equilibrium of polymer-solvent systems are known. One of the important systems is the swelling of polymer latex particles by solvents or monomers. This is of considerable importance in industry due to the role it plays in emulsion polymerization and latex film formational+ Several studies have shown that the swelling of latex particles by monomers occurs during the emulsion polymerization.+' However, the actual transport behavior of monomer and morphological changes of the latex particle are not fully understood. The effect of monomer or solvent solubility in the polymer and the dispersion phase (water generally) has not been examined in detail. Nevertheless, the swelling behavior has been successfully employed to control the latex particle size made from emulsion polymerization.&" The objective of our work is to examine the following: (1)the solvent parameters that affect the partition behavior (In particular, the solubility of solvent in the continuous phase (water) is examined); (2) The effect of polymer hydrophobicity on the solvent partition behavior. Previous studies have considered solvents with low solubility,less than 10%in water.12-14 In the present work, the solvent solubility in water varies from a low of approximately 3% to complete solublity in water. The solvents were chosen based on two considerations: (1) solvent solubility in water; (2) solubility parameter of the solvent, as an indicator of the strength of solvent-polymer interaction. (1) Gardon, J. L. J. Polym. Sci., Part A-1 1968,6,2859. ( 2 ) Ugelstad, J.; El-Aasser, M. S.; Vanderhoff, J. W. J.Polym. Sci., Polym. Lett. 1973,11, 505. (3)Dillon, R. E.;Bradford, E.B.; Andrews, R. D., Jr. Ind. Eng. Chem. 1963,45,728. (4)Hansen, C. M. Prog. Org. Coat. 1982,10,331. (5)Bovey,F. A.; Kolrthoff,I. M.;Medalia, A. I.; Meehan, E. J.Emulsion Polymerization; Interscience: New York, 1955. (6) Ching-Li, Y.; Goodwin, J. W.; Ottewill, R. M. Prog. Colloid Polym. Sci. 1976,60,163. (7)Goodwin, J . W.;Ottewill, R. M.; Harris, N. M.; Tabony, J. J. Colloid Interface Sci. 1980,78,253. (8)Ugelstad, J.; Hansen, F. K.; Lange, S. Makromol. Chem. 1974,175, 507. (9)Ugelstad, J. Makromol. Chem. 1978,179,815. (10) Ugelstad, J.; Kaggarud, K. H.; Hansen, F. K.; Berge, A. Makromol. Chem. 1979,180,737. (11) Ugelstad, J.; Kaggerud, K. H.; Fitch, R. M. Polym. Colloids 2, [Proc. Symp. Phys. Chem. Prop. Colloidal Part.] 1980,83. (12)Bindechaedler, C.; Gurny, R.; Doekler, E.; Peppas, N. A. J. Colloid Interface Sci. 1985,108,75. (13)Bindschaedler, C.; Gurny, R.; Doekler, E.; Peppas, N. A. J. Colloid Interface Sci. 1985, 108, 83. (14)Bindschaedler, C. PhD Thesis, University of Geneva, 1984.
The solubility parameters used are either the literature values or the estimates based on group contribution c a l c ~ l a t i o n s . ~These ~ J ~ and other solvent characteristics are listed in Table I.
Experimental Section Materials. Two monodisperse latexes were prepared for this study. The latexes used were a polystyrene (PS)latex containing sulfonate groups and a terpolymer latex of butyl methacrylate/ butyl acrylate/methacrylic acid (BMA/BA/MAA). These latexes were synthesized in a semicontinuousprocess. The latexes were dialyzed against distilled water and subsequently treated with highly purified mixed bed ion exchange resin. The particle size measurements were carried out by using quasi-elasticlight scattering (QELS). A few characteristics of these latexes are given in Table 11. Glass transition temperatures of the latexes were measured by differential scanning caloriometry (DSC). Electron microscopy and DSC studies of the acrylate terpolymer latex showed a single phase morphology. The solvents for this study were selected on the basis of their solubility parameter values and solubilityin water. The solubility parameter of the solvents covered a large span to provide a wide representation of the interactions between solvent and polymer or water. These solventswere diethyleneglycol monoethyl ether (DEGEE),dipropyleneglycol monomethylether (DPGME),ethanol (ET), methyl ethyl ketone (MEK), and diethylene glycol monobutyl ether acetate (DEGBA). The measurement of solvent partition between the aqueous and the polymer phase is done by ultracentrifugationof a mixture of a known concentration of a polymer latex, water, and the solvent. The composition of the supernatant is analyzed by gas chromatography. This procedure has been used previously for similar measurements.13J7 In a second procedure employed for these measurements, the solvent vapor pressure in equilibrium with the solvent-polymer latex mixture is measured.18 The latter technique lacks sensitivityfor the high boiling solvents. However, measurements using the vapor pressure technique were done in selected cases and a comparison of the two techniques for a latex is shown in Table 111. Specimen Preparation. A predetermined composition of the solvent-water mixture was added dropwise to a measured quantity of the polymer latex. The polymer-solvent-water mixture was continuously stirred during addition. The solvent, (15)Fredenslund, A.;Jones, R. L.; Prausnitz, J. M. AIChE J . 1975,22, 1086. (16)Gmehling, J . ; Rasmussen, P.; Fredenslund, A. Ind. Eng. Chem. Process Des. Deu. 1982,21,118. (17)Hoy, K.L. J. Paint Technol. 1973,45,51. (18)Lohr, G., Polym. Colloids 2, [Proc. Symp. Phys. Chem. Prop. Colloidal Part.] 1980,71. (19)CRC Handbook of Solubility Parameters and Other Cohesion Parameters; Barton, A. F. M., Ed.; CRC Press: Boca Ratan, FL, 1983.
0 1991 American Chemical Society
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solvent diethylene glycol monoethyl ether
Table I. Characteristics of Solvents Used designation molar volume, m3/mol solubility in water, 7% DEGEE 130.0 100
dipropylene glycol monomethyl ether diethylene glycol butyl ether acetate ethanol methyl ethyl ketone
DPGME DEGBA ethanol MEK
water
water
a
100
