Conventional Emulsion Polymerization
In this study, composite particles with a core/shell structure, containing a high silicon content [m (organosilicon): m (acrylate) = 76], were synthesized. The influence of the polymerization process on the particle size distribution and morphology of the lotion was investigated. The results demonstrated that by using a composite emulsifier with a m (sodium dodecyl sulfate): m (polyethylene glycol octyl phenyl acyl) ratio of 1:1, a silicone acrylic lotion with small particle size (100nm) and narrow distribution could be obtained. Furthermore, increasing the concentration of the emulsifier led to smaller particle sizes and increased monomer conversion rate. The nucleation mechanism of the composite lotion was also discussed.
During the polymerization process, the MMA monomer was gradually added, causing the latex particles to be in a "hungry" state. MMA was then adsorbed onto the surface of the seed latex particles, which were rich in alkenyl groups from the polysiloxane. This led to copolymerization and restricted the reaction to the "transition layer" on the surface of the latex particles. Due to the limited compatibility between PMMA and polysiloxane, the subsequent MMA monomer enriched the "transition layer" surface, eventually forming the acrylate shell. This microphase separation resulted in the formation of composite particles with a core/shell structure.
Conventional lotion polymerization produces homogeneous latex particles, while shell/core lotion polymerization yields heterogeneous ones. In this study, a copolymer lotion with polyacrylate (core)/polysiloxane (shell) latex particles was prepared using simultaneous polycondensation and free radical copolymerization. The lower hydrophilicity and surface free energy of polysiloxane compared to polyacrylate create an increased interfacial tension between water and polymer, leading to an increase in Gibbs free energy. Consequently, this colloidal structure is thermodynamically unstable. After storing the lotion (with a siloxane mass fraction of 20%) for 54 days, the morphology of the latex particles transformed into a relatively stable polysiloxane (core)/polyacrylate (shell) structure in accordance with thermodynamics. The siloxane mass fraction in the polymer increased, and the phase inversion time was shortened.
Finally, lotion particles with a shell/core structure were prepared. The core, composed of polysiloxane, polyacrylate, and styrene polymer, was synthesized using a two-step swelling method. The shell, consisting of an organosilicon acrylate polymer with styrene and acrylate, was grafted onto the core. This polymer exhibited excellent coloration and collision resistance, making it widely applicable in electronic product coatings.
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