ANALYSIS, KINETICS AND ALKALI-SWELLABILITY OF CARBOXYLATED LATEXES (ACRYLIC ACID, 2-ETHYLHEXYL ACRYLATE, METHACRYLIC ACID, COPOLYMERIZATION)

This research has studied the preparation and characterization of carboxylated latexes in order to more fully understand their alkali-swelling behavior. Two systems were studied, 2-Ethylhexyl acrylate (EHA) and Styrene (ST), which were copolymerized with either Acrylic acid (AA) or Methacrylic acid (MAA) to provide the carboxyl functionality. The primary factors examined with respect to the alkali-swelling behavior were T(,g), hydrophobicity of the base monomer, type of carboxyl monomer (AA or MAA), amount of carboxyl functionality, preparation process (batch or semicontinuous polymerization) and effect of crosslinking.; In addition, a mechanism was developed to explain the emulsion copolymerization behavior of an oil-based monomer with the two types of carboxyl monomer. The use of AA resulted in fairly large particles close in size to the pure EHA latex, with large fractions of the AA on the surface of the particle and in the aqueous phase. In contrast, the latexes with MAA had a much smaller particle size, and had a greater fraction of the MAA in the core of the particle with little in the aqueous phase compared to the latexes containing AA. These results were contrary to current ideas where the absolute amounts of carboxyl groups at the surface stabilize the particle and control the particle size. The primary outcome of the copolymerization mechanism is that the time of incorporation of the carboxyl monomer during the reaction determines the final latex properties.; The classical mechanism of alkali-swelling behavior declares that the viscosity increase results from an increase in particle size as a function of increasing pH. The present results indicate that no true swelling is occurring for the hydrophobic ST and EHA systems. However, the viscosity still increases as a function of higher pH, with the magnitude of the increase being a function of the fraction and type of carboxyl monomer. This viscosity increase is the consequence of the extension of the surface carboxyl chains into the aqueous phase while still attached to the particle. Thus, the viscosity can be varied as a function of pH without true particle expansion. These results will be explained with respect to the copolymerization mechanism. (Abstract shortened with permission of author.)...