Abstract: Making a fluoroelastomer by feeding to an aqueous polymerization medium in a reactor about 25-75% by weight of the total monomers, vinylidene fluoride, at least one other fluorine-containing ethylenically unsaturated monomer containing at least as many fluorine atoms as carbon atoms and copolymerizable with vinylidene fluoride, an inorganic free-radical initiator, a chain transfer agent added in an amount sufficient to maintain a concentration in the aqueous polymerization medium of from about 0.5.times.10.sup.-3 to 5.times.10.sup.-3 moles per 100 grams of total monomers, and from about 0.02-2% by weight, based on the weight of the aqueous medium, of a surfactant which is a compound having the formula:F--CF.sub.2 CF.sub.2).sub.n CH.sub.2 CH.sub.2 --OSO.sub.3 Mwhere n is an integer of from 2-8 or mixtures thereof and M is an alkali metal cation, hydrogen or ammonium, maintaining the pH of the aqueous polymerization medium within a range of from about 2.

Abstract: Core/shell fluoropolymer compositions in particulate form, wherein the core is a highly crystalline polymer such as, for example, tetrafluoroethylene, and the shell is an elastomeric fluoropolymer such as, for example, a vinylidene fluoride/hexafluoropropene copolymer, optionally also containing a cure site monomer are outstanding additives for uncured fluoroelastomer compositions, which after curing in the presence of dispersed core/shell fluoropolymers have improved tear strength, tear strength to modulus ratio, and certain other physical properties.

Abstract: Copolymerization in aqueous emulsion of ethylene with one or two comonomers having different water solubilities is more efficient when at least two but no more than three comonomer solubility-affecting additives are present in the copolymerization medium, at least one of which increases the solubility in water of one of the comonomers, while at least another one decreases the solubility in water of another comonomer. In this manner, the diffusion rates of comonomers to the copolymerization locus are well controlled; the rate of polymerization often is increased; the concentrations of the comonomers at the copolymerization locus remain constant; and the copolymer composition remains constant. This process improvement can be applied to the copolymerization of many comonomer combinations of great commercial interest, including, for example ethylene/tetrafluoroethylene and ethylene/ethyl acrylate copolymerizations.

Abstract: A continuous process for polymerizing tetrafluoroethylene alone or with selected comonomers to prepare a polymer which employs a perfluoroalkyl ethane sulfonic acid or its salt or a perfluoroalkyl ethane sulfate salt as dispersing agent.

Abstract: In the batch process for copolymerizing tetrafluoroethylene and selected comonomers to prepare a copolymer thereof, the improvement which comprises employing a perfluoroalkylethane sulfonic acid or its salts as the dispersing agent.