The progressive dissolution of carboxylated latex particles with increasing pH was utilized to investigate the internal structure of core‐shell latex particles, in comparison with that of copolymeric latex particles formed from the same monomers. The results indicated that in those latex particles which are formed when ethyl acrylate (EA) ‐methacrylic acid (MAA) or methyl acrylate (MA) ‐MAA mixture is polymerized in the presence of poly(MA‐MAA) or poly(EA‐MAA) seeds the shell is composed of the more hydrophilic poly(MA‐MAA) molecules relatively high in MAA content and the core is composed of both poly(MA‐MAA) and poly(EA‐MAA) molecules, regardless of the order of the stage feed, while the copolymeric latex particles are relatively uniform from surface to center in distribution of all components except MAA. Examination of the distribution of the carboxylic groups in all of the latex particles showed their concentration to be highest at the surface and to decrease with proximity to the center in accordance with other findings reported in the literature.

SynopsisConduct,omet,ric and potentiometric titration behavior of emulsions of ethyl acry1at.e copolymers with acrylic acid and methacrylic acid was investigat.ed. On the conductometric tit,ration curves of the emulsions of the copolymers with more than 5 mole-% of the acids, two equivalence points, based on the copolymerized acids, were observed, but only one equivalence point was observed on potentiometric titration. Almost all of the copolymerized acids could be detected by both titration methods. The change in optical density of the dilute emulsions with their pH was measured. The particles of these emulsions were st,udied under an electron microscope. These results showed that,. when the pH of the emulsions was raised, the surface layers of the part.icles began to dissolve and their cores started to swell near the pH of their first equivalence points. When the pH was again lowered the dissolved polymers coagulated, tiny particles were formed, and the swollen cores were dehydrated. The surface layers thickened with increasing amount, of the copolymerized acid. These behaviors were very similar in the emulsions of the copolymers with acrylic acid and methacrylic acid. The quantity of watersoluble polymers formed in the course of the emulsion copolymerization was approximately 3-4y0 or slightly more. This quantit,y depended only slightly upon the amount and type of the copolymerized acid. The acid contents of the water-soluble polymers were higher in cases of the copolymers with acrylic acid than in those with methacrylic acid. No relationship with the amount of copolymerized acid was established.

SynopsisThe solubility of carboxylated polymer emulsions in an aqueous alkaline solution was studied. The alkali solubility was shown to depend on the degree of carboxylation, the hydrophilic nature of the noncarboxylic main components, the degree of polymerization, the glass transition temperature, the chain configuration, and the dissolution temperature. Emulsions of the copolymer containing acrylic acid units showed considerably different dissolution behavior from those containing methacrylic acid units, possibly owing to the difference in the distribution state of carboxylic units inside the particle. It is deduced that methacrylic acid units are distributed more homogeneously inside the particle than acrylic acid units.