HIGH SOLID CONTENT MULTISIZED EMULSION COPOLYMERIZATION OF STYRENE, BUTYL ACRYLATE, AND METHACRYLIC-ACID

Polymer lattices with a multimodal particle size distribution (PSD) po lymer latex were prepared by introducing additional surfactants during the semicontinuous emulsion polymerization of styrene, butyl acrylate , and methacrylic acid. The polymerization was investigated by followi ng the variation of the particle size, the size distribution, the numb er of particles, the T-g of the different particle sizes, and the tota l conversion at different steps of the polymerization process. The res ults show that bimodal and trimodal PSD polymer lattices can be obtain ed by this method and that the secondary generation of particles is gr eatly influenced by the nature and the amount of additional surfactant s, as well as the moment when they are introduced. When the amount of additional surfactants is increased, the diameters of both the small a nd large particles decrease and the number of particles in each of the populations increases. Earlier introduction of these surfactants favo rs the generation and the growth of the small particles and thereby le ads to a reduction of the relative fraction of large particles in the final latex. On introduction of 7 wt % of additional surfactants, base d on the total monomers, 100% of the monomers of the second-stage poly merization were consumed to form the small particles. This fraction de creases with a decreasing amount of the additional surfactants. These results were further demonstrated by measuring the T-g's of both the l arge and the small particles of two lattices, in which the T-g's of th e copolymers produced in each of the stages were different. High solid content (>65%), low viscosity, and coagulum-free lattices have been o btained through secondary nucleation, and a minimum in viscosity was f ound when the weight fraction of the large particles was around 80%. ( C) 1998 John Wiley & Sons, Inc.