Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-03-18
2003-11-04
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S293000, C525S200000, C526S247000, C526S243000, C526S248000
Reexamination Certificate
active
06642319
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a method for forming graft copolymers from perfluoroolefins and perfluorovinyl ethers having fluorosulfonyl and fluorosulfonate functionality with selected polymers, and the uncrosslinked graft copolymers resulting therefrom.
TECHNICAL BACKGROUND OF THE INVENTION
Howard, U.S. Pat. No. 5,798,417, discloses (perfluorovinyl ether)-grafted polyolefins. The grafting process involves contacting the polymer in the form of a powder or a shaped article with a free-radical initiator and the monomer. The reaction medium is heterogeneous and the polymer is invariably crosslinked during the grafting reaction. The degree of grafting varies with the initiator concentration and the reaction temperature. Up to 17 mol % incorporation of grafted monomer is claimed (up to 9 mol % shown in the examples). The polymers are useful as catalysts and as membranes in electrochemical cells.
U.S. Pat. No. 4,396,727 claims cation exchange membranes having fluorovinyl sulfonic acid monomers grafted onto high molecular weight substrates. Grafting is carried out directly on films by using ionizing radiation. Substrate polymers have the following repeat units: CH
2
—CXY where X is H, F, or CH
3
, and Y is H or F. Polyethylene is the most preferred substrate. Solvents miscible with the monomer can be used to achieve thorough impregnation of the substrate. Graft ratios of up to 75% are reported (although graft ratio is not defined, it is commonly found in the grafting literature as (w−w
0
)/w
0
where w
0
is the weight of the substrate and w is the weight after grafting. So 75% graft ratio is equivalent to 43 weight % grafting). The membranes are useful in electrochemical cells. U.S. Pat. No. 4,384,941 claims a process for electrolysis of pure water using these membranes.
Drysdale et al., WO 98/31716 discloses free radical grafting of partially fluorinated functionalized vinyl monomers to polyethylene. In the process, the polyethylene is first dissolved and the grafting reaction takes place in solution. Incorporation of up to ca. 13 mol-% is achieved. The polymers are useful as molding resins, for coatings and as catalysts.
DesMarteau, U.S. Pat. No. 5,463,005 discloses fluoromonomers containing sulfonimide groups and their copolymers with tretrafluoroethylene. Conductive compositions of these materials are also disclosed.
Armand et al., EP 0,850,920 A2, teaches salts of perfluorinated amides and their use as materials for ionic conduction. Polymers containing sulfonimide side groups are disclosed. Examples include several condensation and addition polymers containing hydrocarbon backbones.
Narang et al., U.S. Pat. No. 5,633,098 disclose ionic polymers having sulfonic acid and sulfonimide functional groups. Polymers disclosed include polysiloxanes, polymethacrylates, and poly(alkene oxides).
Considerable interest has developed in the application of fluorinated ionomers as solid polymer electrolyte membranes in secondary lithium batteries and fuel cells. Key to these applications is the use of fluorosulfonates or derivatives thereof as cation exchange groups. It is believed that the cations associated with these functional groups only become sufficiently labile when highly electron-withdrawing fluorines are employed proximate to the sulfonate and sulfonate derivatives, typically, in groups represented by the formula —CF
2
CF
2
SO
3
H or —CF
2
CF
2
SO
3
Li or sulfonyl imide or sulfonyl methide derivatives thereof. See for example Doyle et al., WO 9820573, Doyle et al., WO 9941292(A1), Feiring et al., WO 9945048(A1).
Polymer having a backbone of methylene groups and pendant groups having the formula —CH
2
CH
2
—(CF
2
)
2
0(CF
2
)
2
SO
2
F is prepared by a grafting reaction in Choi et al., WO 9952954.
The current state of the commercial art is exemplified by Nafion® Perfluoroionomer Membranes available from E. I. du Pont de Nemours and Company, Wilmington, Del. Nafion® membranes were developed for the highly corrosive environment of a chloralkali cell wherein the corrosion resistance of the perfluorinated ionomers is an important attribute. It is believed that in certain other applications such as lithium batteries corrosion resistance may be of less importance. In such a case considerable reduction in materials cost may be achieved by reducing the fluorine content in parts of the molecule which do not affect ionic conductivity. See for example Choi et al., WO 9952954.
The present invention provides a method for combining a perfluorinated functional group with a polymer having a backbone which contains carbon hydrogen bonds with the aim of providing a non-cross-linked, highly processible lower cost ionomer of high ionic conductivity.
SUMMARY OF THE INVENTION
The present invention provides for a process comprising:
contacting a first polymer having a backbone which comprises at least 50% methylene units with a solvent which swells or dissolves said first polymer to form a solvent-swollen polymer or polymer solution;
contacting said solvent swollen polymer or polymer solution with a source of free-radicals and a compound of the formula F
2
C═CFR
1
R
2
SO
2
X wherein
R
1
represents a covalent bond or a perfluoroalkenyl radical having 1 to 20 carbon atoms; R
2
is a radical of the formula:
—O—[CF
2
CF(R
3
)—O
m
]
n
—CF
2
CF
2
—
wherein m=0 or 1, n=0, 1, or 2, and R
3
is F or a perfluoroalkyl radical having 1-10 carbons;
and X is F or the radical represented by the formula
—Y(M)(SO
2
R
4
)
p
wherein Y is C or N, M is an alkali metal, R
4
is a perfluoroalkyl radical having 1-10 carbons optionally substituted with one or more ether oxygens, and p=1 or 2 with the proviso that p=1 when Y is N and p=2 when Y is C;
to form a reaction mixture;
providing sufficient heat to said reaction mixture to cause the initiation of free-radical reaction; and, reacting said mixture to form a graft copolymer.
The present invention further provides for a non-crosslinked polymer comprising a polymer having a backbone which comprises at least 50 mol-% methylene units and up to 50 mol-% of methylene units having a pendant group comprising a radical represented by the formula
wherein R
1
represents a covalent bond or a perfluoroalkenyl radical having 1 to 20 carbon atoms; R
2
is a radical of the formula:
—O—[CF
2
CF(R
3
)—O
m
]
n
—CF
2
CF
2
—
wherein m=0 or 1, n=0, 1, or 2, and R
3
is F or a perfluoroalkyl radical having 1-10 carbons, and X is F, —OM, or the radical represented by the formula
—Y(M)(SO
2
R
4
)
p
wherein Y is C or N, M is hydrogen or an alkali metal, R
4
is a perfluoroalkyl radical having 1-10 carbons optionally substituted by one or more ether oxygens, and p=1 or 2 with the proviso that p=1 when Y is N and p=2 when Y is C.
DETAILED DESCRIPTION
The present invention provides a process for preparing non-crosslinked graft copolymers by reacting a perfluoro vinyl compound comprising a sulfonyl fluoride functionality or derivative thereof with a polymer in the presence of a free radical initiator and a suitable solvent.
As used herein, the term “reacting” is intended to mean allowing at least two components in a reaction mixture to react to form at least one product. “Reacting” may optionally include stirring and/or heating or cooling.
In the process of the invention, the polymer is contacted with a solvent, which swells or, preferably, dissolves the polymer. The swollen polymer or polymer solution is further contacted with a perfluorovinyl compound comprising a sulfonyl fluoride functionality or derivative thereof and a source of free radicals. Preferably the perfluorovinyl compound is soluble in the solvent which swells or dissolves the polymer.
Polymers suitable for the process of the invention are those which have hydrogens along the backbone which can be abstracted by a free radical initiator. Suitable are polymers having at least 50 mol-% of methylene units in the polymer backbone. Most olefinic type polymers are suitable; suitable olefinic type polymers may be
Asinovsky Olga
E. I. du Pont de Nemours and Company
Seidleck James J.
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