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 process for polymerizing fluoromonomer to form a dispersion of fluoropolymer particles in an aqueous medium in a polymerization reactor comprising an initial period and a stabilization period subsequent to the initial period, wherein the initial period comprises:
preparing an initial dispersion of fluoropolymer particles in the aqueous medium in the polymerization reactor, and
the stabilization period comprises:
polymerizing fluoromonomer in the polymerization reactor, and
adding hydrocarbon-containing surfactant to the polymerization reactor,
wherein during the stabilization period no fluorosurfactant is added; and
wherein a solids content of dispersed fluoropolymer particles of at least 16 wt % is achieved in the polymerization reactor by the process.
2. The process according to claim 1 wherein the initial dispersion of fluoropolymer particles is essentially free of fluorosurfactant.
3. The process according to claim 1 wherein the hydrocarbon-containing surfactant is metered into the polymerization reactor during the stabilization period.
4. The process according to claim 3 wherein the hydrocarbon-containing surfactant is metered at a rate sufficient to reduce the telogenic activity of said hydrocarbon-containing surfactant.
5. The process according to claim 4 wherein the hydrocarbon-containing surfactant is metered at a rate sufficient to reduce the telogenic activity of said hydrocarbon-containing surfactant and while maintaining surface activity to stabilize the dispersion of fluoropolymer particles in the medium during the polymerizing.
6. The process according to claim 1 wherein the hydrocarbon-containing surfactant is anionic.
7. The process according to claim 1 wherein said hydrocarbon-containing surfactant is hydrocarbon surfactant.
8. The process according to claim 1 wherein the hydrocarbon-containing 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 2− , —PO 3 − and —COO − , wherein Ar is an aryl group, and M is a univalent cation selected from the group consisting of H + , Na + , K + and NH 4 + .
9. The process according to claim 1 wherein said polymerizing is carried out in the presence of polymerization initiator.
10. The process according to claim 1 which further comprises passivating said hydrocarbon-containing surfactant.
11. The process according to claim 10 wherein the hydrocarbon-containing surfactant is passivated by reacting the hydrocarbon-containing surfactant with an oxidizing agent.
12. The process according to claim 11 wherein the oxidizing agent is hydrogen peroxide or polymerization initiator.
13. The process according to claim 10 , wherein the passivation of the hydrocarbon-containing surfactant is carried out in the presence of a passivation adjuvant.
14. The process according to claim 13 wherein the passivation adjuvant is a metal in the form of metal ion.
15. The process according to claim 14 wherein the metal ion is ferrous ion or cuprous ion.
16. The process according to claim 1 wherein the fluoromonomer is selected from tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro-2,2-dimethyl-1,3-dioxole (PDD), perfluoro-2-methylene-4-methyl-1,3-dioxolane (PMD), perfluoro(alkyl vinyl ether) (PAVE) and mixtures thereof.
17. The process according to claim 1 wherein the initial period of the polymerization process comprises providing polymerization sites in the aqueous medium.
18. The process according to claim 1 wherein the polymerization sites are provided by a dispersed particulate of fluorinated ionomer.
19. The process according to claim 1 wherein fluoropolymer in the dispersion of fluoropolymer particles is selected from the group consisting of PTFE, modified PTFE, and copolymer comprising tetrafluoroethylene units and at least one other monomer.
20. A dispersion of fluoropolymer particles obtained from the process of claim 1 .
21. The process of claim 1 wherein the solids content of dispersed fluoropolymer particles is at least 20 wt %.
22. The process of claim 1 wherein the solids content of dispersed fluoropolymer particles is at least 33 wt %.
23. The process of claim 1 wherein the solids content of dispersed fluoropolymer particles is at least 45 wt %.
24. The process of claim 1 wherein the solids content of dispersed fluoropolymer particles is at least 50 wt %.
25. The process of claim 1 wherein the solids content of dispersed fluoropolymer particles is at least 60 wt %.
26. The process of claim 1 wherein the process forms no greater than 5 wt % of the fluoropolymer as coagulum.