Patent ID: 6277937
Filing Date: 2001-08-21
Classification: C08F

Abstract:
A suspension polymerization process for producing a fluoroelastomer having a selected molar ratio of copolymerized monomer units, said fluoroelastomer comprising copolymerized units of vinylidene fluoride major monomer, at least one other copolymerizable fluorinated major monomer, and at least one cure site monomer, comprising the steps of:(A) charging a reactor with a quantity of an aqueous medium comprising a suspension stabilizer, said suspension stabilizer being present in said aqueous medium at a concentration of 0.001 to 3 parts by weight per 100 parts of said aqueous medium; said quantity of aqueous medium being such that a sufficient vapor space is left in said reactor for receiving gaseous monomer;(B) charging the vapor space in said reactor with an initial quantity of a gaseous monomer mixture comprising vinylidene fluoride major monomer and at least one other fluorinated major monomer; and continuously mixing said aqueous medium and said monomer mixture to form a dispersion;(C) initiating polymerization of said monomers at a temperature of 45.degree. C. to 70.degree. C. by adding to said dispersion an oil soluble organic peroxide polymerization initiator in an amount of 0.001 to 5 parts by weight per 100 parts of said aqueous medium, said initiator being added as a solution consisting essentially of 0.1 to 75 wt. % of an oil soluble organic peroxide in a water-soluble solvent, said solvent selected from the group consisting of compounds of the formulas R.sub.1 OH, R.sub.2 COOR.sub.1, and R.sub.1 COR.sub.3, where R.sub.1 and R.sub.3 are methyl or t-butyl groups, and R.sub.2 is hydrogen, a methyl group or a t-butyl group; and(D) incrementally feeding to said reactor, during polymerization, so as to maintain a constant pressure in said reactor, said major monomers and at least one cure site monomer, said major monomers and said cure site monomer being fed to the reactor in said selected molar ratio until a fluoroelastomer product having a number average molecular weight of between 50,000 to 2,000,000 daltons is obtained.