Curable fluoropolyether rubber compositions

Details Curable fluoropolyether rubber compositions Curable fluoropolyether rubber compositions

2001-06-29

2003-04-22

Moore, Margaret G. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

C528S031000, C528S015000, C528S025000

Reexamination Certificate

active

06552152

ABSTRACT:

This invention relates to curable fluoropolyether rubber compositions which cure into parts having good water repellency, oil repellency, heat resistance, solvent resistance, chemical resistance, weather resistance and parting property as well as improved acid resistance.
BACKGROUND OF THE INVENTION
Japanese Patent No. 2,990,646 (JP-A 8-199070) discloses a composition comprising (A) a straight-chain fluoropolyether compound having at least two alkenyl groups in a molecule and a perfluoroalkyl ether structure in the backbone, (B) an organosilicon compound having at least two H—SiOSi structures in a molecule, and (C) a hydrosilylation catalyst, which cures into parts having a good profile of heat resistance, chemical resistance, solvent resistance, parting property, water repellency, oil repellency and weather resistance.
Although this fluoropolyether rubber composition performs well in most applications, a need for higher acid resistance exists in special applications associated with semiconductors, engine oils and the like where acid resistance is necessary.
SUMMARY OF THE INVENTION
An object of the invention is to provide curable fluoropolyether rubber compositions which cure into parts having good heat resistance, chemical resistance, solvent resistance, parting property, water repellency, oil repellency and weather resistance as well as improved acid resistance.
It has been found that by compounding (A) a straight-chain fluoropolyether compound having at least two alkenyl groups in a molecule and a perfluoropolyether structure in the backbone, (B) an organosilicon compound having in a molecule at least two silicon atom-bonded hydrogen atoms, which all form H—SiCH
2
— structures, and (C) a hydrosilylation catalyst, there is obtained a curable fluoropolyether rubber composition which cures into parts having good heat resistance, chemical resistance, solvent resistance, parting property, water repellency, oil repellency and weather resistance as well as improved acid resistance.
Fluoropolyether rubber compositions using an organosilicon compound having H—SiOSi structures as disclosed in Japanese Patent No. 2,990,646 are not so strong against acid since the SiOSi linkage can undergo silicon-oxygen cleavage under the action of acid. By contrast, in the organosilicon compound having H—SiCH
2
— structures, the silicon-carbon bond is highly stable against acid. Thus use of the organosilicon compound having H—SiCH
2
— structures provides a fluoropolyether rubber composition with excellent acid resistance.
Accordingly the invention provides a curable fluoropolyether rubber composition comprising
(A) a straight-chain fluoropolyether compound having at least two alkenyl groups in a molecule and a perfluoropolyether structure in the backbone,
(B) an organosilicon compound having in a molecule at least two silicon atom-bonded hydrogen atoms, which all form H—Si(CH
2
)
c
— structures, wherein c=1 to 4, and
(C) a hydrosilylation catalyst.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Component (A) of the curable fluoropolyether rubber composition according to the invention is a straight-chain fluoropolyether compound having at least two alkenyl groups in a molecule and a divalent perfluoroalkyl ether structure in the backbone.
The perfluoroalkyl ether structure may be a structure comprising a multiplicity of recurring units: —C
d
F
2d
O— wherein d in each unit is independently an integer of 1 to 6, for example, a structure of the following general formula (5):
(C
d
F
2d
O)
q
  (5)
wherein q is an integer of 1 to 500, preferably 2 to 400, and more preferably 10 to 200.
The recurring units —C
d
F
2d
O— constituting the structure of formula (5) are exemplified by the following units:
—CF
2
O—,
—CF
2
CF
2
O—,
—CF
2
CF
2
CF
2
O—,
—CF(CF
3
)CF
2
O—,
—CF
2
CF
2
CF
2
CF
2
O—,
—CF
2
CF
2
CF
2
CF
2
CF
2
CF
2
O—, and
—C(CF
3
)
2
O—,
Of these, —CF
2
O—, —CF
2
CF
2
O—, —CF
2
CF
2
CF
2
O— and —CF(CF
3
)CF
2
O— are especially preferred. It is noted that the perfluoroalkyl ether structure may be comprised of such recurring units of one type or a combination of two or more types.
The alkenyl groups in the straight-chain fluoropolyether compound (A) are preferably those groups having 2 to 8 carbon atoms, especially 2 to 6 carbon atoms, and terminated with a CH
2
═CH— structure, for example, vinyl, allyl, propenyl, isopropenyl, butenyl, and hexenyl. Of these, vinyl and allyl are preferred. The alkenyl groups may be located at any position within the molecule, but preferably attached to opposite ends of the molecular chain. In this preferred arrangement, the alkenyl groups may be attached to opposite ends of the straight-chain fluoropolyether compound backbone directly or through a divalent linking group: —CH
2
—, —CH
2
O— or —Y—NR—CO—. Herein Y is —CH
2
— or a group of the following structural formula (Z):
(wherein the free valence bond may be at the o, m or p-position), and R is hydrogen, methyl, phenyl or allyl.
The fluoropolyether compound (A) is preferably a straight-chain one of the following general formula (2) or (3).
CH
2
═CH—(X)
p
—Rf
0
—(X)
p
—CH═CH
2
  (2)
CH
2
═CH—(X)
p
—Q—Rf
0
—Q—(X)
p
—CH═CH
2
  (3)
Herein X is independently —CH
2
—, —CH
2
O— or —Y—NR′—CO— wherein Y is —CH
2
— or a group of the following structural formula (Z):
(o, m or p-position), and R′ is hydrogen, methyl, phenyl or allyl. Rf
0
is a divalent perfluoropolyether structure, preferably of the formula (5), that is, (C
d
F
2d
O)
q
. Letter p is independently 0 or 1. Q is a divalent hydrocarbon group of 1 to 15 carbon atoms which may contain an ether bond, for example, an alkylene group or an alkylene group containing an ether bond.
Of these straight-chain fluoropolyether compounds (A), those of the following general formula (4) are preferred.
Herein X is independently —CH
2
—, —CH
2
O— or —Y—NR′—CO— wherein Y is —CH
2
— or a group of the following structural formula (Z):
(o, m or p-position), and R′ is hydrogen, methyl, phenyl or allyl. Letter p is independently 0 or 1, r is an integer of 1 to 6, u is an integer of 2 to 6, and m and n each are an integer of 0 to 200.
Desirably the straight-chain fluoropolyether compounds of formula (4) have a weight average molecular weight of about 4,000 to 100,000, more desirably about 1,000 to 50,000.
Illustrative, non-limiting, examples of the straight-chain fluoropolyether compounds of formula (4) are given below. In the formulas, m and n are as defined above.
In the practice of the invention, to tailor the straight-chain fluoropolyether compound of formula (4) to a weight average molecular weight desired for a particular purpose, it is possible that the straight-chain fluoropolyether compound be previously subjected to hydrosilylation reaction with an organosilicon compound having two SiH groups in a molecule by a conventional method under ordinary conditions to form a chain-extended product, which can be used as component (A).
Component (B) serves as a crosslinking agent and chain extender for component (A). Any desired organosilicon compound may be used as long as it has at least two silicon atom-bonded hydrogen atoms in a molecule in which every silicon atom-bonded hydrogen atom forms an H—Si(CH
2
)
c
, wherein c=1 to 4, structure. The organosilicon compound is preferably of the following general formula (1).
Herein c is 1, 2, 3 or 4. R is a monovalent hydrocarbon group of 1 to 20 carbon atoms, preferably 1 to 6 carbon atoms, and may be the same or different. Z is hydrogen or —Q—M, —Q—Rf, —Q—, —Rf′— or —Q—Rf′—Q— wherein Q is a divalent hydrocarbon group of 1 to 15 carbon atoms which may contain an ether bond, Rf is a monovalent perfluoroalkyl or perfluorooxyalkyl group, and Rf′ is a divalent perfluoroalkylene or perfluorooxyalkylene group. Letter s is 1, 2 or 3, t is 0, 1, 2 or 3, and a and b each are 0 or 1, with the proviso that a and b are not 0 at the same time.
The hydrocarbon groups represented by R will be described later in detail. Examples of Q include alkylene groups

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