| 摘要 |
<p>TITLE PROCESS FOR MAKING VINYLIDENE FLUORIDE CONTAINING FLUOROELASTOMERS 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 x 10-3 to 5 x 10-3 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?CF2CF2?nCH2CH2-OSO3M where 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 2.5-5, continuously removing a portion of the resulting fluoroelastomer latex from the polymerization reactor and adding to said portion a mineral acid or a carboxylic acid containing no more than 5 carbon atoms and having a pk of less than about 4.2 to lower the pH to about 2 or below and a water-soluble salt of an alkaline earth meral to coagulate the fluoroelastomer and recovering the fluoroelastomer from the latex.</p> |
