SynopsisViscosity-versus-pH relationships for a large number of methacrylic acid-containing emulsion polymers have been measured. The monomers chosen for this study were so selected because they represent synthesized latexes of high and low To and comparative hydrophilicity. These were styrene, methyl methacrylate, ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate. The postulated mechanism involved in the t,ransition from an unneutralized latex particle to the neutralized species is accounted for in terms of varying degrees of particle swelling. In the limiting case, particle swelling is followed by complete solution of the polymer. The most important variables are the per cent methacrylic acid and the polymer T, and hydrophilicity as determined by the comonomers present. The degree of particle swelling ranges from none for high styreriecontaining latexes to high degrees of swelling followed by polymer solubilization for high ethyl acrylate-containing latexes.

We have used small-angle neutron scattering (SANS) technique to study the micellization of a series of alternating comb-shaped copolymers, poly[l-alkene-co-(maleic anhydride)], in the fully neutralized state in water with the 1-alkenes ranging from 1-octene to 1-octadecene and weight-average molecular weights from 6000 to 20000. The structural parameters of the amphiphilic aggregates are determined by analyzing the intraparticle structure factor of the SANS intensity data. The analysis has shown that the copolymer derived from 1-octadecene forms cylindrical-shaped micelles while the copolymers derived from lower 1-alkenes form ellipsoidal-shaped micelles with the transition occurring at the 1-hexadecene copolymer. Analysis of the absolute neutron scattering intensity at zero scattering angle has shown a strong dependence of the mass of the aggregates on the side-chain length, namely, there are approximately 200 monomer repeating units per aggregate for the 1-octadecene copolymer versus about 20 monomer repeating units per aggregate for the 1-octene copolymer. The effect of molecular weight on aggregation is not observed possibly due to the polydispersity in the copolymers.

synopsisThe mechanism of alkali thickening of acid-containing emulsion polymers has been confirmed by visual examination of the swelling and disappearance of latex particles with the light microscope. Specially prepared large particle-sized latexes were used in this study.The particle swelling and dissolution behavior correlated with viscosity measurements, high viscosity being present for swollen particle systems and low viscosity for true solutions. The neutralized state of all acid-containing latexes can be pictured in a cube with the important variables being per cent acid, hydrophilicity of the comonomers, and T,.A t the bottom will be latexes only slightly affected by neutralization, above this will be a swollen particle zone, and the largest area will be a true solution zone. The true solution zone will be enlarged by lowering the molecular weight of the latex polymer.Each latex was examined from 0%-200y0 neutralization with base. INTRODUCTlONThe change undergone by an acid-containing emulsion polymer upon neutralization is accounted for in terms of varying degrees of a single mechanism. This mechanism consists of swelling of the latex particles plus an accompanying solubilization of polymer molecules when the hydrophilicity of the polymer is high enough. ' If the particles of alkali-soluble latexes were made large enough, it should be possible to visually observe the swelling and disappearance of these particles in the dispersed state with the light microscope. Latexes were prepared of some representative compositions whose average particle size was 500 mp in diameter.The latexes were neutralized with base to varying degrees of neutralization and the equilibrated samples were observed and photographed with the light microscope.