Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-07-18
2004-10-12
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S249000, C526S255000
Reexamination Certificate
active
06803435
ABSTRACT:
TECHNICAL FIELD
This invention relates to peroxide-curable fluoropolymer compositions having interpolymerized units of a C
2
-C
10
fluorinated olefin, which may contain one or more heteroatom(s), and a hydrogen-containing C
2
-C
9
olefin, which may be made in the presence of a brominated salt. The invention also relates to methods of making such fluoropolymer compositions and articles made from the cured compositions.
BACKGROUND
Fluoroelastomers having up to one iodine or bromine atom at the end of a polymeric chain, with a bromine content in the chain from 0.05-2 weight percent (wt %) are described in U.S. Pat. No. 5,173,553. These fluoroelastomers are said to have improved proccessability, particularly in injection molding processes, mold release, and heat stability. The fluoroelastomers are made from fluorinated monomeric units of vinylidene fluoride and/or tetrafluoroethylene, and optionally hexafluoropropene and/or perfluoroalkyl-perfluorovinylethers. These fluorinated copolymers can be combined with amounts up to 40 mole percent (mol %) of monomeric units derived from ethylene, propylene, butene, and/or isobutylene.
Copolymers of tetrafluoroethylene and propylene have been prepared and cured with peroxides. The physical properties of such polymers after curing have undesirably high compression set values.
SUMMARY
Briefly, the present invention provides a curable composition comprising (a) a fluoropolymer comprising interpolymerized units derived from (i) CF
2
═CF—R
f
, wherein R
f
is fluorine or a C
1
-C
8
perfluoroalkyl, (ii) at least about 10 mole percent of a hydrogen-containing C
2
-C
9
olefin, based on the total moles of said CF
2
═CFR
f
and said olefin, (iii) an average of two or more bromine atoms including one or more terminal bromine atom(s) per fluoropolymer chain, (iv) optionally CX
2
═CX—R, wherein each X is independently H, F, or Cl and R is a halogen or a C
1
-C
8
alkyl or alkenyl group that may include one or more ether linkage(s), (v) optionally a bromine-containing cure site monomer; (b) optionally, a peroxide curing agent; and (c) optionally, a crosslinking co-agent. The fluoropolymer in the curable composition preferably is polymerized in the presence of a bromine salt.
In another aspect, the invention provides a cured fluoroelastomer composition comprising the reaction product of (a) a copolymer comprising tetrafluoroethylene and propylene having an average of two or more bromine atoms including one or more terminal bromine atom(s) per polymer chain, (b) a peroxide curing agent, and (c) optionally, a crosslinking co-agent; wherein the composition has a compression set value lower than a comparative copolymer having a similar comonomer ratio and having an average of less than two bromine atoms per chain. This comparative copolymer is similar to the inventive fluoropolymer in that the ratio of monomers are within about 5 mol % or even closer, but the comparative material has lower amounts of bromine such that it contains less than two bromine atoms per polymer chain and/or has fewer than the one or more terminal bromine atoms of the inventive fluoropolymer.
In still another aspect, the present invention provides a method of preparing a fluoropolymer composition comprising (a) combining CH
2
═CF—R
f
, wherein R
f
is fluorine or a C
1
-C
8
perfluoroalkyl, with at least about 10 mole percent of a hydrogen-containing C
2
-C
9
olefin, based on the total moles of said CH
2
═CFR
f
and said olefin, a brominated salt, optionally CX
2
═CX—R, wherein each X is independently H, F, or Cl and R is a halogen or a C
1
-C
8
alkyl or alkenyl group that may include one or more ether linkage(s), and optionally a bromine-containing cure site monomer, together with an initiator, and polymerizing the combination.
In still another aspect, the present invention provides fluoropolymer articles containing cured compositions.
The invention provides fluorinated elastomers (e.g., tetrafluoroethylene-propylene or “TFE-P”) that are made in the presence of radical initiators and a bromine salt. Surprisingly, the initiator system of the present invention provides curable fluoropolymer, such as TFE-P, with excellent physical properties even where cure site monomers are absent from the fluoropolymer. These fluoroelastomers exhibit improvements in physical properties. Another advantage of the present invention is that the fluoroelastomers of the invention, after curing, exhibit significantly reduced compression set as compared to known TFE-P elastomers.
Other features and advantages of the invention will be apparent from the following detailed description of the invention and the claims. The above summary of principles of the disclosure is not intended to describe each illustrated embodiment or every implementation of the present disclosure. The following detailed description more particularly exemplifies certain preferred embodiments utilizing the principles disclosed herein.
DETAILED DESCRIPTION
The fluoroelastomer compositions of the invention are derived from interpolymerized units of fluorinated monomers, having the formula CH
2
═CF—R
f
, wherein R
f
is fluorine or a C
1
-C
8
perfluoroalkyl, along with hydrogen-containing C
2
-C
9
olefins, which have less than half of the hydrogen atoms substituted with fluorine, more preferably less than one-fourth of the hydrogen atoms substituted with fluorine, and which are non-fluorinated in other embodiments.
The polymer may optionally contain one or more bromine-containing cure site monomer such as bromotrifluoroethylene (BTFE), bromodifluoroethylene (BDFE), bromotetrafluorobutene (BTFB), perfluoro vinyl ethers having one or two fluorine atoms substituted with bromine atoms, an iodine-containing cure site monomer, and the like. The amount of bromine-containing cure site monomer in the fluoropolymer is up to about 5 mole percent (mol %) or less. The amount of bromine-containing cure site monomer, when included, preferably is from about 0.01 to about 4 mol %, and more preferably from about 0.05 to about 2 mol %, based on the total fluoropolymer composition. In cases where the fluoropolymer contains a bromine-containing cure site monomer, the amount of the hydrogen-containing C
2
-C
9
olefin is at least 10 mol % of the total fluoropolymer composition. Propylene is one preferred C
2
-C
9
olefin.
The curable compositions have an average of two or more bromine atoms per fluoropolymer chain. These bromine atoms typically are found at the polymer chain ends, i.e., terminal bromine atoms. Bromine atoms also may be found substituted along the polymer backbone, such as when a linear polymer is polymerized using, e.g., a brominated perfluorovinyl ether or a bromotetrafluorobutene (BTFB) cure site monomer. These fluoropolymers have at least one terminal bromine atom.
In another embodiment of the invention, a bromine-containing cure site monomer is not necessary to enable crosslinking of the inventive fluoroelastomer compositions. In this aspect, the curable compositions have an average of two or more terminal bromine atoms per fluoropolymer chain. Such terminal bromine atoms occur on the main chain and/or chain branches.
The fluoropolymer chains in the inventive composition may be linear, branched, or a combination thereof. The curable compositions yield fluoroelastomer with excellent, physical properties, including low compression set, whether or not a bromine-containing cure site monomer is included. In contrast, comparable materials similar in every respect except having less than one bromine atom per chain do not cure to provide desirable properties. Also in contrast, comparable materials having levels of bromine-containing cure site monomers similar to the inventive fluoropolymer but lacking the additional bromine atoms at the polymer chain ends (provided in the inventive fluoropolymer) have much higher compression set levels.
When the fluoropolymer does not contain a cure site monomer, the amounts of the hydrogen-containing C
2
-C
9
olefins ranges from at least about 10 mol %, more preferably at le
Coggio William D.
Hare Erik D.
Hintzer Klaus
Scott Peter J.
3M Innovative Properties Company
Harts Dean M.
Lipman Bernard
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