The effectiveness of reactive dispersants in non-aqueous dispersion polymerization
May 10-15, 2015
Non-aqueous dispersion (NAD) polymerization is used to produce poly(acrylic) nanoparticles for solvent‐borne automotive coatings formulations. During nucleation and growth, the nanoparticles are stabilized sterically by a low molecular weight polymer dispersant that is often functionalized with a reactive double bond. In this work, the performance of two types of reactive dispersants are evaluated, both based on radical polymerization of butyl methacrylate (BMA). The first contains a small amount of methacrylic acid (MAA) in the formulation, which is subsequently reacted with glycidyl methacrylate (GMA) in the presence of amino catalyst to form a dispersant with functional unsaturated groups grafted to random positions along the backbone. The second is a vinyl-terminated BMA macromer prepared by cobalt chain transfer polymerization. It has been found that the effectiveness of the surfactant, characterized by the amount of free dispersant remaining in solution as well as NAD particle size and overall dispersion viscosity, is dependent on the composition of the NAD being produced as well as the dispersant choice and double bond content (macromer chain length). For an acrylate-rich recipe, the macromer dispersant is found to be incorporated more effectively than the randomly grafted dispersant, a result attributed to the uniform distribution of reactive double bonds across the entire dispersant molar mass distribution. When methacrylates are added as components to the NAD recipe, however, the effectiveness of the macromer dispersant decreases, due to the chain transfer reaction that occurs with methacrylate radicals.1
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