Non-Aqueous Dispersion Polymerization for Automotive Coating Applications
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Non-aqueous dispersion polymerization (NAD) is used to produce submicron sized particles utilized by the solvent-borne automotive coatings industry to prevent crack propagation, improve toughness and reduce energy requirements for drying. Despite its industrial significance, there have been few studies about particle nucleation and other qualities of the semibatch process. The dispersion features high solids (50-60 wt%) of higher molecular weight acrylic polymer, with the polymeric nanoparticles sterically stabilized by low molecular weight dispersant polymer chains anchored to the particle surface either by chemical or physical interaction. The work presented in this thesis investigates three aspects influencing particle formation in the NAD system, i.e., the dispersant type, the multi-component core composition and the dispersant feeding procedure in the starved feed semibatch process. Three categories of unsaturated poly(methacrylate) dispersants are examined, a butyl methacrylate (BMA) based material with grafted vinyl functionality, vinyl-terminated BMA homopolymer macromers, and hydroxyl group functionalized macromers. The macromers provided more effective stabilization than the grafted dispersant, but the addition of 2-hydroxyethyl methacrylate (HEMA) to the dispersant reduced stability. Average particle size of the dispersion increased with the addition of methyl methacrylate and styrene to the mix of monomers used to produce the particles. The increased effectiveness of the dispersant led to an investigation of reduced dispersant levels, increased monomer loading, and simplified dispersant feeding strategies while producing small particles (<150 nm) and keeping dispersion viscosity low (<500 cp). The findings are interpreted by considering the relative polarity of the dispersant, core polymer, and solvent mixture in the NAD system.