Micron-size structured particles via dispersion polymerization.

摘要

The focus of this research program is to investigate the experimental parameters controlling the dispersion and seeded dispersion polymerization using n-butyl acrylate (BA), and to understand the mechanism of particle formation and growth in dispersion polymerization.; The dispersion polymerization of n-butyl acrylate (BA) has been investigated using alcohol/water as dispersion medium, 4,4{dollar}spprime{dollar}-azobis-(4-cyanopentanoic acid) as the initiator and polyvinylpyrrolidone (PVP) as the stabilizer. The effects of polymerization parameters, such as alcohol/water ratio in the medium, type and concentration of polymeric stabilizer, etc., on the particle size and size distribution have been studied. Monodisperse micron-size PBA particles having controlled size and gel content have been prepared. The final particle size and the stability of the dispersion system have been found to be greatly influenced by the type of alcohol used in the mixture, i.e., methanol or ethanol, even through the apparent solubility parameters are almost the same for the two types of mixtures.; These PBA particles were used as seed in the second-stage seeded dispersion polymerizations. The effects of polymerization parameters on the morphology of structured particles resulting from the second-stage seeded dispersion polymerization have been studies and a series of uniform micron-size structured particles has been prepared.; Dispersion polymerization may be viewed as a special type of precipitation polymerization. A steric polymeric stabilizer (PVP) is chosen to stabilize the growing particles against flocculation in a dispersion polymerization rather than an ionic surfactant as is typical in an emulsion polymerization. It was found that in the seeded dispersion polymerizations, the type of the seed polymer and the PVP used in seed preparation, the cleaning procedure of the seed latex, and the type of monomer and additional PVP used in the second-stage greatly influence the outcome of the reaction.; In order to further understand the mechanism of particle formation and stabilization, the effects of PVP stabilizer on the preparation of PBA and PSt seeds by dispersion polymerization, especially on the colloidal stability and morphology of structured particles resulting from seeded dispersion polymerizations are discussed. {dollar}sp1{dollar}H NMR is used to analyze the conformation of different components in the PBA latex to determine the loci of PVP/PBA grafting polymers. Kinetics of the dispersion polymerization are studied by using the RC1 calorimeter. The Qr curve is divided into sections corresponding to three stages of the dispersion polymerization, i.e., the initiation stage, the nucleation stage, and the particle growth stage. The particle size distribution was found to be related to the shape of the Qr curve, primarily the shape and the length of the nucleation stage. This technique may be used to adjust the polymerization parameters to obtain desired outcome via dispersion polymerization. (Abstract shortened by UMI.)