| An experimental study of emulsifier-free emulsion polymerization of styrene has been made. The process has been characterized by kinetic measurement, SEM, NMR, GPC, pH measurement, surface tension measurement and potentiometric titration. The rate of polymerization, particle size, particle number concentration, molecular weights of oligomers and polymers and their distributions, concentration of radicals, particle surface sulfate coverage, and other quantities are obtained. A relatively constant rate of polymerization stage and an auto-acceleration stage and monodispersity of latex particle size were observed. The termination rate of free radicals, initiator efficiency, and the diffusion coefficient of macromolecular radicals in latex particle were estimated. Some new experimental findings are made and explained. These include: the abrupt end of polymerization, sustained oligomerization in the aqueous phase throughout the whole process, Shortness of oligomers and dominance of oligomers in number, insufficient surface activity of oligomeric species and low polymer molecular weights. Possibilities of radical transfer in latex particles, and partial association of polymer-chain attached sulfate groups, are discussed. An oligomer aggregation and aggregate nucleation mechanism is proposed. A homogeneous particle structure for the constant rate stage and an inhomogeneous structure for the auto-acceleration stage are suggested.; A theoretical study has been made on the swelling of latex particles. The Flory-Morton governing equation for swelling equilibrium was modified. Based on the new equation, an analysis of the preparation of micron-sized, surface-clean, monodisperse polymer microparticles was made. |
