472 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS property is to be utilized. They have found application, for example, in emulsion paints and latex compounds for carpet sizing. Resins of this type can be prepared by copolymerizing vinyl acetate with maleic anhydride (1), a monoalkyl ester of maleic acid (2) or crotonic acid (3). Such copolymers are useful in certain adhesive and other appli- cations where removability by aqueous alkali is required (4) and, in the non-aqueous state, as hair spray compositions (5). A possible disadvantage of vinyl acetate-crotonic acid copolymers, which are otherwise particularly suitable, is that they are generally of low molecular weight, due to the chain transfer property of crotonic acid in free-radical polymerization addition- ally, most vinyl acetate copolymers are readily hydrolyzed by aqueous alkali (6). If long term storage of alkali-soluble copolymers in aqueous systems at higher pH is required, acrylic and especially methacrylic ester copolymers are more suitable. In the present paper, the alkali-thickening of a group of alkyl metha- crylate-methacrylic acid copolymer emulsions is described. Methacrylic acid was used in preference to acrylic acid because of its good copoly- merization with methacrylate esters in aqueous emulsion systems. With methyl methacrylate, for example, 97% of the methacrylic acid introduced has been found to have copolymerized (7). EXPERIMENTAL The polymer emulsions were prepared to the following basic formula: Monomers Dodecyl mercaptan Polyoxyethylene (4-5) monolaurate Sodium dodecyl sulfate Sodium bicarbonate Sodium sulfate Ferric chloride (to 5 ppmFe on monomer wt) Sodium persulfate Sodium metabisulfite Parts by weight 100.00 0.20 1.00 1.00-3.00 0.12 0.50 0.24 0.24 Materials The monomers were commercial grades of high purity (99%) and were used as received the inhibitor contents were as follows:

ALKALI-THICKENABLE METHACRYLATE COPOLYMER EMULSIONS 473 methyl methacrylate, 0.01% 2:4-dimethyl-6-tert-butylphenol ethyl metha- crylate, 0.1% hydroquinone n-butyl methacrylate, 0.004% p-methoxy- phenol methacrylic acid, 0.025% p-methoxyphenol. Polyoxyethylene (4-5) monolaurate was a 93% pure grade containing 1.1% free polyethylene glycol (supplied by Rex Campbell & Co. Ltd.). Sodium dodecyl sulfate was 99.9% pure (supplied by Cyclo Chemicals Ltd.). The remaining ingredients were reagent grades. Process The water phase, contained in a 11 glass flask, was purged free of oxygen with nitrogen. At a temperature of 18-20øC, the monomers, dodecyl mercaptan, ferric chloride, sodium persulfate and sodium metabisulfite, were added with stirring. Agitation was continued throughout at such a rate as to ensure continuous uniform mixing of the ingredients. The temper- ature rose rapidly to about 80øC and was maintained at this temperature for 30 min. The emulsion was cooled down, its pH adjusted to 4.4-4.5 with 20% aq. sodium hydroxide and filtered through 400 mesh nylon. The emulsions were prepared in random order. Conversions of monomer to polymer were greater than 98%. Viscosities A portion of each emulsion was diluted to a non-volatile of 10% and its pH adjusted to 8.4-8.6 with aq. NaOH. The viscosity was determined after 60 min using a Ferranti portable concentric cylinder viscometer. Particle diameters were estimated by a turbidimetric technique {8). Optical densities were determined on the products adjusted to pH 8.4-8.6 at a non-volatile of 10%, through a 10 mm glass cell using filtered light of wavelength 580 nm. RESULTS AND DISCUSSION Increase in the quantity of surfactant in emulsion polymerization usually results in a decrease in diameter of the polymer particles, often in inverse proportion to the surfactant: monomer ratio. In the present series {Fig. 1 ), for given copolymer compositions the particle size in the emulsion state showed a similar reduction with increase of the anionic surfactant {i.e. sodium dodecyl sulfate) concentration.