Process for the manufacture of fluoroelastomers having bromine or lodine atom cure sites

Abstract

Fluoroelastomers having bromine, iodine or both iodine and bromine cure sites are prepared by an emulsion polymerization process wherein any iodine or bromine containing comonomers and any iodine or bromine containing chain transfer agents are introduced to the reactor as aqueous emulsions, optionally containing a surfactant.

1 . A process for preparing a fluoroelastomer having bromine, iodine or both bromine and iodine cure sites, said process comprising: 
 (A) charging a reactor with a quantity of an aqueous solution;    (B) feeding to said reactor a quantity of an initial monomer mixture to form a reaction medium, said initial monomer mixture comprising i) a first monomer, said first monomer selected from the group consisting of vinylidene fluoride and tetrafluoroethylene, and ii) one or more additional copolymerizable monomers, different from said first monomer, wherein said additional monomer is selected from the group consisting of fluorine-containing olefins, fluorine-containing ethers, propylene, ethylene and mixtures thereof;    (C) feeding to said reactor at least one aqueous emulsion comprising a cure site source selected from the group consisting of i) an iodine-containing cure site monomer, ii) a bromine-containing cure site monomer, iii) an iodine-containing chain transfer agent, and iv) a bromine-containing chain transfer agent; wherein said emulsion has a mean droplet size of 50 microns or less; and    (D) polymerizing said monomers in the presence of a free radical initiator to form a fluoroelastomer having cure sites.    
   
   
       2 . A process of  claim 1  wherein said aqueous emulsion in step C) comprises a cure site source having a mean droplet size of 20 microns or less.  
   
   
       3 . A process of  claim 1  wherein said aqueous emulsion in step C) further comprises a surfactant.  
   
   
       4 . A process of  claim 3  wherein said surfactant is selected from the group consisting of sodium octyl sulfonate, sodium dodecylsulfonate, sodium lauryl sulfate, sodium decyl sulfate, sodium caprylate, sodium stearate, nonylphenolpoly(ethylene oxide), perfluorohexylethylsulfonic and salts thereof, perfluorooctanoic acid and salts thereof, tridecafluorohexylethyl sulfonic acid and salts thereof, and 3,3,4,4-tetrahydroundecafluorooctanoic acid and salts thereof.  
   
   
       5 . A process of  claim 3  wherein said aqueous emulsion in step C) is prepared by high shear mechanical mixing of water, cure site source and surfactant.  
   
   
       6 . A process of  claim 1  wherein said fluoroelastomer comprises copolymerized units selected from the group consisting of i) vinylidene fluoride and hexafluoropropylene; ii) vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene; iii) vinylidene fluoride, tetrafluoroethylene and perfluoro(methyl vinyl ether); and iv) tetrafluoroethylene and perfluoro(methyl vinyl ether) and cure sites selected from the group consisting of bromine atoms, iodine atoms and both iodine and bromine atoms.  
   
   
       7 . A process of  claim 1  wherein said cure site source is a bromine-containing cure site monomer selected from the group consisting of bromotrifluoroethylene; 4-bromo-3,3,4,4-tetrafluorobutene-1 vinyl bromide; 1-bromo-2,2-difluoroethylene; perfluoroallyl bromide; 4-bromo-1,1,2-trifluorobutene-1; 4-bromo-1,1,3,3,4,4,-hexafluorobutene; 4-bromo-3-chloro-1,1,3,4,4-pentafluorobutene; 6-bromo-5,5,6,6-tetrafluorohexene; 4-bromoperfluorobutene-1; 3,3-difluoroallyl bromide; 2-bromo-perfluoroethyl perfluorovinyl ether; CF 2 ═CFOCF 2 CF 2 CF 2 OCF 2 CF 2 Br; CH 3 OCF═CFBr and CF 3 CH 2 OCF═CFBr.  
   
   
       8 . A process of  claim 1  wherein said cure site source is an iodine-containing cure site monomer selected from the group consisting of iodoethylene; 4-iodo-3,3,4,4-tetrafluorobutene-1; 3-chloro4-iodo-3,4,4-trifluorobutene; 2-iodo-1,1,2,2-tetrafluoro-1-(vinyloxy)ethane; 2-iodo-1-(perfluorovinyloxy)-1,1,-2,2-tetrafluoroethylene; 1,1,2,3,3,3-hexafluoro-2-iodo-1-(perfluorovinyloxy)propane; 2-iodoethyl vinyl ether; 3,3,4,5,5,5-hexafluoro4-iodopentene; iodotrifluoroethylene; allyl iodide; and 2-iodo-perfluoroethyl perfluorovinyl ether.  
   
   
       9 . A process of  claim 1  wherein said cure site source is an iodine-containing chain transfer agent selected from the group consisting of i) CH 2 X 2  where X is I or Br; ii) X(CF 2 ) n Y where X is I or Br, Y is I or Br and n is an integer between 3 and 10 and iii) X(CF 2 ) n Y where both X and Y are I and n is an integer between 3 and 10.