GB1057186A - Improvements in or relating to vinyl halide polymers - Google Patents

Abstract

A process for preparing vinyl fluoride polymers of controlled particle size comprises polymerizing in a reactor at moderately elevated temperature and under superatmospheric pressure a monomeric material comprising at least 50% of vinyl fluoride monomer suspended in an aqueous medium in the presence of a free-radical generating polymerization catalyst and reducing the size of the individual monomer droplets dispersed in the aqueous medium to substantially less than one micron in diameter by subjecting the reaction mixture to high shearing and impaction forces, whereby the droplets, when so reduced in size, are inhibited from coalescing into monomer droplets comparable in size to those which are obtained at lower shearing and impaction forces, and polymer products are produced therefrom are composed of particle agglomerates of controlled size. The forces may be applied by an agitator in the reactor, e.g. with a tip speed in excess of 600 feet per minute and with a clearance of no more than 3 inches between the tip and the reactor wall, or by circulating the reaction mixture through a dispersing device adjacent to the reactor. Small proportions of surface active agents may be added to the reaction mixture. The monomeric material may comprise minor proportions of di-, tri- and tetrahaloethylenes, vinyl esters, vinyl ketones, vinyl ethers, olefins, and acrylic, methacrylic, maleic and fumaric acids and the anhydrides, acid halides, nitriles, amides and esters thereof. Examples describe the polymerization of a suspension of vinyl fluoride in water in the presence of lauroyl peroxide, isopropanol, methyl cellulose and magnesium lauryl sulphate using rapid agitation and circulation through an adjacent dispersing device to effect the desired dispersion. The dispersions may be used for coating.