Oleophobic fluoropolymers and filter materials prepared therefrom
The disclosure provides an improved process for preparing oleophobic fluoropolymers. The resulting fluropolymers were found to be effective in imparting hydrophobic and oleophobic properties to porous polymeric membranes such as PTFE. The treated PTFE membrane can reach an oleophobic level of 6 or above, (according to the AATCC-118-1997 oil repellency test method) with a low air flux loss.
1 . A process for preparing a fluoropolymer, comprising the free-radical polymerization of monoethylenically-unsaturated monomers consisting of fluorine-containing monoethylenically-unsaturated monomer and fluorine-free monoethylenically-unsaturated monomer, which comprises combining:
a. about 80 weight percent, or greater than 80 and less than 100 weight percent of the fluorine-containing monoethylenically-unsaturated monomer; and
b. about 20 weight percent, or greater than 0 and less than 20 weight percent of the fluorine-free monoethylenically-unsaturated monomer;
under free-radical polymerization conditions, in a solvent comprising at least one solvent having ester moieties, wherein the total weight percent of a. and b. is 100, and
allowing the polymerization to proceed to a desired end point,
wherein the fluorine-free monoethylenically-unsaturated monomer is one or more compounds of the following formulae:
wherein each R is independently chosen from hydrogen or an alkyl group of up to 18 carbon atoms.
2 . The process of claim 1 , wherein the free radical polymerization conditions comprise the addition of at least one free-radical initiator.
3 . The process of claim 2 , wherein the free-radical initiator is a compound chosen from hydrogen peroxide, potassium peroxydisulfate, ammonium peroxydisulfate, potassium persulfate, sodium persulfate, ammonium persulfate, dibenzoyl peroxide, lauryl peroxide, di-tertiary butyl peroxide, 2,2′-azobisisobutyronitrile, t-butyl hydroperoxide, azodiisobutylamidine hydrochloride, and benzoyl peroxide.
4 . The process of claim 1 , wherein the fluorine-containing monoethylenically-unsaturated monomer is chosen from
(a) acrylates,
(b) (C 1 -C 14 alkyl)acrylates, and
(c) vinyl esters,
having from about 3 to about 33 fluorine atoms.
5 . The process of claim 1 , wherein the fluorine-containing monoethylenically-unsaturated monomer has the formula
wherein R is chosen from hydrogen or an alkyl group of up to 18 carbon atoms,
and R 1 is chosen from groups of the formulae:
wherein m is 3, 5, 7, 9, 11, 13, or 15.
6 . The process of claim 1 , wherein the fluorine-containing monoethylenically-unsaturated monomer is one or more compounds chosen from perfluorooctylethylene, perfluorononylethylene, perfluorododecylethylene, perfluorotetra-decylethylene, perfluorohexadecylethylene, perfluorooctyl ethyl acrylate, perfluorododecyl ethyl acrylate, perfluoro tetradecyl ethyl methacrylate, perfluoro tetradecyl ethyl acrylate, perfluoro hexadecyl ethyl acrylate, perfluorooctylethyl methacrylate, perfluorononylethyl methacrylate, perfluorododecylethyl methacrylate, and perfluorohexadecylethyl methacrylate.
7 . The process of claim 1 , wherein the fluorine-containing monoethylenically-unsaturated monomer is one or more compounds chosen from 2-(perfluorooctyl) ethyl acrylate, perfluorononyl ethyl acrylate, perfluorododecyl ethyl acrylate, perfluorotetradecyl ethyl acrylate, perfluorohexadecyl ethyl acrylate, perfluorooctyl ethyl methacrylate, perfluorononyl ethyl acrylate methyl methacrylate, perfluorododecyl ethyl methacrylate, and perfluoro hexadecyl ethyl methacrylate.
8 . The process of claim 1 , wherein the fluorine-containing monoethylenically-unsaturated monomer comprises 2-(perfluorooctyl) ethyl acrylate.
9 . The process of claim 1 , wherein the fluorine-free monoethylenically-unsaturated monomer is one or more compounds chosen from methyl acrylate, ethyl acrylate, butyl acrylate, butyl, isobutyl acrylate, ethylhexyl acrylate, octyl acrylate, vinyl acetate, vinyl caprylate.
10 . The process of claim 1 , wherein the fluorine-free monoethylenically-unsaturated monomer is one or more compounds chosen from, vinyl acetate, vinyl butyrate, and vinyl caprylate.
11 . The process of claim 1 , wherein the solvent having ester moieties is chosen from compounds of the formula:
wherein R 1 and R 2 are independently chosen from (a) C 1 -C 12 alkyl, and (b) C 1 -C 12 alkyl groups substituted one or more times with a group chosen from halo, nitro, cyano, and alkoxy.
12 . The process of claim 1 , wherein the solvent having ester moieties is chosen from methyl acetate, ethyl acetate, propyl acetate, and butyl acetate.