Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1998-09-11
2001-04-03
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C525S379000, C525S381000, C525S382000, C526S247000, C526S248000, C526S254000, C528S492000
Reexamination Certificate
active
06211319
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to perfluoroelastomer compositions which have excellent processability, and which, when cured, have outstanding thermal stability and chemical resistance.
BACKGROUND OF THE INVENTION
Perfluoroelastomers (elastomeric perfluoropolymers) are polymeric materials which exhibit outstanding high temperature tolerance and chemical resistance. Consequently, such compositions are particularly adapted for use as seals and gaskets in systems in which elevated temperatures and/or corrosive chemicals are encountered. The outstanding properties of perfluoropolymers are largely attributable to the stability and inertness of the copolymerized perfluorinated monomer units which make up the major portion of the polymer backbone, e.g., tetrafluoroethylene and perfluoro(alkyl vinyl) ethers. In order to completely develop elastomeric properties, perfluoropolymers are typically crosslinked, i.e. vulcanized. To this end, a small percentage of cure site monomer is copolymerized with the perfluorinated monomer units. Cure site monomers containing at least one nitrile group, for example perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene, are especially preferred. Such compositions are described in U.S. Pat. Nos. 4,281,092 and 4,394,489; and in International Application WO 95/22575.
A recently-developed class of perfluoroelastomers having carbonyl-containing functional groups is disclosed in co-pending U.S. patent application Ser. No. 08/755,919, entitled “Fast-curing Perfluoroelastomer Compositions”, filed Nov. 25, 1996. These polymers are characterized by having carbonyl-containing functional groups, including carboxyl groups, carboxylate groups, carboxamide groups, and mixtures thereof. Preferably, the carbonyl-containing functional groups are endgroups generated as a result of persulfate initiation of the polymerization reaction and the reaction is carried out in the absence of sulfite or bisulfite reducing agents. The carbonyl-containing perfluoroelastomers exhibit outstanding cure characteristics but they are difficult to process in certain end-uses because of their relatively high viscosity. A method for decreasing viscosity of the carbonyl-containing perfluoroelastomers would permit use of these materials in a wider variety of end-use applications.
SUMMARY OF THE INVENTION
The present invention provides a composition comprising a perfluoroelastomer comprising copolymerized units of (1) a perfluoroolefin, (2) a perfluorovinyl ether selected from the group consisting of perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers, and mixtures thereof, and 3) a cure site monomer wherein the perfluoroelastomer is characterized by being substantially free of functional groups selected from the group consisting of i) ionized or ionizable endgroups, ii) bromine-containing endgroups, and iii) iodine-containing endgroups.
The invention is further directed to a curable perfluoroelastomer composition comprising
A) a perfluoroelastomer comprising copolymerized units of (1) a perfluoroolefin, (2) a perfluorovinyl ether selected from the group consisting of perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers and mixtures thereof, and 3) a cure site monomer, wherein the perfluoroelastomer is characterized by being substantially free of functional groups selected from the group consisting of i) ionized or ionizable endgroups, ii) bromine-containing endgroups, and iii) iodine-containing endgroups; and
B) a curing agent.
The invention is also directed to a process for preparation of an uncured perfluoroelastomer composition comprising the steps of
A) preparing a perfluoroelastomer having a plurality of carbonyl-containing functional groups selected from the group consisting of carboxyl endgroups, carboxylate endgroups, carboxamide endgroups, and mixtures thereof by copolymerizing a monomer mixture comprising a) a perfluoroolefin monomer, b) a perfluorovinyl ether monomer selected from the group consisting of perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers, and mixtures thereof, and c) a cure site monomer at a pressure of from 4-10 MPa, in the presence of a persulfate free radical initiator, in a polymerization mixture wherein i) the feed ratio of monomer to initiator is controlled so that the ratio of the radical flux to the polymerization rate, R
j
/R
p
, is from about 10 to 50 millimoles per kilogram, and ii) less than 5 mole percent of a sulfite or bisulfite reducing agent, based on the total moles of persulfate initiator and reducing agent, is present in the polymerization mixture;
B) isolating said perfluoroelastomer having a plurality of carbonyl-containing functional groups from the polymerization mixture; and
C) heating said isolated perfluoroelastomer having a plurality of carbonyl-containing functional groups at a temperature of at least 230° C. for a time sufficient to at least partially decarboxylate the perfluoroelastomer.
In addition, the present invention is directed to an uncured perfluoroelastomer composition prepared by a process comprising the steps of
A) preparing a perfluoroelastomer having a plurality of carbonyl-containing functional groups selected from the group consisting of carboxyl endgroups, carboxylate endgroups, carboxamide endgroups, and mixtures thereof by copolymerizing a monomer mixture comprising a) a perfluoroolefin monomer, b) a perfluorovinyl ether monomer selected from the group consisting of perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers, and mixtures thereof, and c) a cure site monomer at a pressure of from 4-10 MPa, in the presence of a persulfate free radical initiator in a polymerization mixture wherein i) the feed ratio of monomer to initiator is controlled so that the ratio of the radical flux to the polymerization rate, R
i
/R
p
, is from about 10 to 50 millimoles per kilogram, and ii) less than 5 mole percent of a sulfite or bisulfite reducing agent, based on the millimoles of persulfate initiator and reducing agent, is present in the polymerization mixture;
B) isolating said perfluoroelastomer having a plurality of carbonyl-containing functional groups from the polymerization mixture; and
C) heating said isolated perfluoroelastomer having a plurality of carbonyl-containing functional groups at a temperature of at least 230° C. for a time sufficient to at least partially decarboxylate the perfluoroelastomer.
The invention is further directed to curable compositions comprising the product produced by the above-described process and a curing agent.
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E. I. Du Pont de Nemours and Company
Zitomer Fred
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