Model-Guided and Scalable Approach to Synthesize Snowman Polymer Particles

Some specific high-performance latex applications require nonequilibrium anisotropic particle morphologies, as they exhibit distinct properties compared to isotropic particles. In this work, snowman particles (a type of an anisotropic morphology) are sought. Even though several strategies have been reported in the literature to create these kinds of particles, the methods used are still limited by the particle size obtained and the small production scale. In the present work, a scalable two-step semibatch emulsion polymerization process is proposed to obtain snowman particles with sizes below 500 nm and localized functionalization in the core of the particles (head of the snowman particle). Cross-linked, functionalized, and soft (Tg: 40 °C) polymer latexes of different sizes have been synthesized as the first-stage polymer, using methyl methacrylate (MMA) and n-butyl acrylate (BA) as main monomers, acrylic acid (AA) and acrylamide (AM) as functional monomers, and allyl methacrylate (AMA) as a cross-linker. For the second-stage polymerization, a styrene (S)/BA monomer system has been used. Using a mathematical model, the necessary conditions for achieving particles with a snowman morphology are determined. It has been shown that the obtained morphology is strongly dependent on the V2/A1 parameter, which represents the ratio of the volume of the second-stage polymer to the surface area of the first-stage polymer. Model-guided experiments have been carried out in a wide range of V2/A1 ratios, successfully obtaining snowman particles of different sizes.