Vinylidene fluoride → Hfp tfe

Beteiligte Stoffe

Reaktionsschritte

A VF2/HFP/TFE fluoroelastomer was prepared by a continuous emulsion polymerization process of the prior art in a well-stirred 4.0-liter stainless steel liquid full reaction vessel at 115° C. An aqueous solution, consisting of 3.59 g/hour (g/h) ammonium persulfate, 8.30 g/h sodium phosphate dibasic heptahydrate, 7.20 g/h ammonium perfluorooctanoate, and 2.30 g/h isopropanol in deionized water, was fed to the reactor at a rate of 10 L/hour. The reactor was maintained at a liquid-full level at a pressure of 6.2 MPa by means of a back-pressure control valve in the effluent line. After 30 minutes, polymerization was initiated by introduction of a gaseous monomer mixture consisting of 584 g/h tetrafluoroethylene (TFE), 1103 g/h vinylidene fluoride (VF2), and 921 g/h hexafluoropropylene (HFP) fed through a diaphragm compressor. After 2.0 hours, collection of the resulting fluoroelastomer latex was begun and continued for 6 hours. The latex, which had a pH of 3.5 and contained 19.3 wt. % solids, was separated from residual monomers in a degassing vessel at atmospheric pressure. Fluoroelastomer crumb product was isolated using aluminum sulfate solution. The coagulated fluoroelastomer polymer was allowed to settle, supernatant serum was removed, and the polymer was washed by reslurrying in water three times before filtering. The wet crumb was dried in an air oven at approximately 50°-65° C. to a moisture content of less than 1 wt. %. About 14 kg of fluoroelastomer was recovered at an overall conversion of 92.2%. The product, containing 24.0 wt. % TFE units, 44.3 wt. % VF2 units, and 31.7 wt. % HFP units, was an amorphous elastomer having a glass transition temperature of −12° C., as determined by DSC (heating mode, 10° C./minute, inflection point of transition). Inherent viscosity of the elastomer was 0.79 dL/g, measured at 30° C. in methyl ethyl ketone, and Mooney viscosity, ML (1+10), was 64.

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