Particle Formation Mechanism And Kinetic Of Suspended Emulsion Polymerization Of Methyl Methacrylate

Suspended emulsion polymerization is a new heterogeneous polymerization process developed from emulsion polymerization and suspension polymerization, to prepare porous polymer particles. Porous structure resin has applications in the absorption treatment, enzyme immobilization catalyst etc, so the study on suspended emulsion polymerization exhibits theoretical and application importance. The present work investigates the particle formation mechanism and kinetic of suspended emulsion polymerization of methyl methacrylate (MMA) based on the fundamental investigation of polymerization technology.Comparing with the suspended emulsion polymerization of monomer/polymer dissoluble system (such as vinyl chloride), non-solvent of PMMA, such as cyclohexane, must be added to the polymerization system, to obtain porous PMMA resin. The influences of cyclohexane/MMA mass ratio, water/oil mass ratio, initiator, emulsifier, suspending agent on the particle properties were studied. It showed that the porosity and diethylhexyl phthalate (DOP) plasticizer absorption of PMMA resin increased with the increase of cyclohexane/MMA and water/oil mass ratios. The addition of emulsifiers and the amount of initiator had no significant influences on the porosity of PMMA resin, but the size of primary particles decreased as emulsifiers added. The average particle size of PMMA resin increased as the HLB value of emulsifier decreased. The average particle size increased and the particle size distribution became wider, and DOP absorption decreased when PVA suspending agent was added to the polymerization system.The electrical conductivity measurement showed that water acted as the dispersed phase and oil as the continuous phase in the polymerization system with no emulsifier and TweenZO emulsifier, at the experiment water/oil ratio. Sampling of PMMA was carried out during the polymerization process for polymerization system with no emulsifier and with Tween20 emulsifier, and the particle size distribution and morphology of PMMA latex or particles were investigated. It showed that the stabilized PMMA latex was formed in the early polymerization stage, and the particles size and particle distribution were close with that of normal emulsion polymerization PMMA latex. The size of latex particles (primary particle) increased as conversion increased and the coagulation of primary particles occurred at acertain conversion. The particle size of PMMA grains increased and the particle size became wider. The final product was mainly composed of PMMA grains developed from the coagulation of primary particles. The scanning electron micrograph showed that PMMA grains were composed of primary particles, which almost did not fuse and had higher porosity.According the above results, the mechanism of particle formation of MMA suspended emulsion polymerization, which included the formation of latex(primary) particles by emulsion polymerization, growth and coagulation of primary particles in the dispersed water droplets. Polymerization in water droplets was initiated by radicals produce by the decomposition of potassium persulphate (KPS) in water droplets. The growing PMMA chains precipitated from the water phase to form microdomains when they reached a critical length. The microdomains would capture free radicals and grow up to primary nucleus. The stability of the primary nucleus was poor and they tended to agglomerate to form primary particles. PMMA was dissoluble in the cyclohexane/MMA mixture and the stability of primary particles was still poor, so primary particles would further coagulate to form porous PMMA grains.The polymerization kinetics of MMA suspended emulsion polymerization was also studied. For MMA suspended emulsion polymerization initiated by KPS, it showed that the initial polymerization rate (Rp) was proportional to the water/oil ratio, [I]0.71 ,and [S]0.58where [I], and [S] were the concentrations of initiator and emulsifier, respectively. The activation energy was 124KJ/mol. It also showed that the molecular weight of PMMA...