| Dispersion polymerization is an attractive method to prepare micron-size polymer particles with narrow size distribution in one single step. The present research systematically studied the kinetics of dispersion polymerization of methyl methacrylate (MMA) and n-butyl acrylate ( n-BuA). Effects of reaction conditions on the kinetics were investigated using a reaction calorimeter (Mettler RC1). Coupled with characterization of produced polymer particles and comparison to other polymerizations (solution and precipitation), important mechanistic features of dispersion polymerization are illustrated.; In dispersion polymerizations leading to narrow particle size distributions, particle nucleation stops at low conversion and the number of particles remains constant afterwards. Nucleation occurs by aggregation of polymer chains longer than critical chain length (jcr) in the continuous phase. jcr was found to be larger in the MMA system than in the n-BuA system. Initial reaction rates ( Rp,ini) were found to differ from solution polymerization (in toluene) but were similar to the corresponding precipitation polymerizations.; Stabilization occurs simultaneously with aggregation through adsorption of graft or pure stabilizer. Although trace amounts of graft polymer can be detected by gel permeation chromatography (GPC), little difference was found between recycled and fresh stabilizer in the MMA system. The molecular weight distribution of the stabilizer remains virtually unchanged during polymerization of either MMA or n-BuA.; After nucleation, polymerization takes place in swollen particles (pseudo-bulk), continuous phase (solution), and unstable nuclei. The formation of unstable nuclei by aggregation during the particle growth period is still of importance by enhancing the termination rate of oligoradicals. In MMA system, nuclei formation reduced the radical concentration and colloidal entry is the main radical adsorption mechanism, while in the n-BuA case, termination more likely occurs in polymer particles.; In this research, the kinetics of seeded dispersion polymerization using micron-size or submicron seed latexes was investigated. It was discovered that with addition of submicron seed in dispersion polymerization, excellent control of particle properties (particle size, size distribution, and morphologies) compared to ab initio polymerization can be achieved. In addition, with elimination of the nucleation stage, seeded dispersion polymerization is also proven to be a better model system to study dispersion polymerization. |
