Aqueous polymerization of perfluoromonomer using hydrocarbon surfactant
A process is provided for the polymerization of fluoromonomer to an dispersion of fluoropolymer particles in an aqueous medium in a polymerization reactor, by (a) providing the aqueous medium in the reactor, (b) adding the fluoromonomer to the reactor, (c) adding initiator to the aqueous medium, the combination of steps (b) and (c) being carried out essentially free of hydrocarbon-containing surfactant and resulting in the kickoff of the polymerization of the fluoromonomer, and (d) metering hydrocarbon-containing surfactant into the aqueous medium after the kickoff of polymerization, e.g. after the concentration of the fluoropolymer in the aqueous medium is at least 0.6 wt %, the metering being at a rate reducing the telogenic activity of said surfactant while maintaining surface activity.
1. A directly polymerized dispersion of polytetrafluoroethylene (PTFE) particles in an aqueous medium obtained without a concentration step having a solids content of said particles in said aqueous medium of 45 wt % or greater than 45 wt %, wherein said dispersion is maintained stable within said aqueous medium by hydrocarbon surfactant, the hydrocarbon surfactant being present in an amount in the range of 3000 parts-per-million to 5500 parts-per-million based on the weight of the PTFE particles, wherein 100% of the monovalent substituents on the carbon atoms of the hydrocarbon surfactant are hydrogen and said hydrocarbon surfactant is an anionic hydrocarbon surfactant, said polytetrafluoroethylene of said polytetrafluoroethylene particles having a molecular weight (M n ) of at least 1,000,000.
2. The dispersion of PTFE particles of claim 1 wherein said aqueous medium is free of halogen-containing surfactant.
3. The dispersion of PTFE particles of claim 1 wherein said anionic hydrocarbon surfactant is a compound of the formula R-L-M wherein R is an alkyl group containing from 6 to 17 carbon atoms, L is selected from the group consisting of —ArSO 3 − , —SO 3 − , —SO 4 − , —PO 3 − , and —COO − , wherein Ar is an aryl group, and M is a univalent cation selected from H + , Na + , K + , and NH 4 + .
4. The dispersion of PTFE particles of claim 1 wherein said anionic hydrocarbon surfactant is sodium dodecyl sulfate.
5. The dispersion of PTFE particles of claim 1 wherein said solids content of said particles in said aqueous medium is 50 wt % or greater than 50 wt %.
6. The dispersion of PTFE particles of claim 1 wherein said solids content of said particles in said aqueous medium is 55 wt % or greater than 55 wt %.
7. The dispersion of PTFE particles of claim 1 wherein said polytetrafluoroethylene of said polytetrafluoroethylene particles has a molecular weight (M n ) of at least 2,000,000.