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
2001-10-01
2003-02-11
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S326400, C525S359300, C525S378000, C525S379000
Reexamination Certificate
active
06518366
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a nitrile group-containing fluoroelastomer having nitrile group in a molecular chain, particularly at the end of the molecular chain and a process for preparation thereof. The elastomer can give a crosslinked product having a very good sealing property, mechanical strength and ultra high heat resistance of not less than 300° C.
BACKGROUND ART
Fluoroelastomers comprising a fluoromonomer unit as a recurring unit such as tetrafluoroethylene (TFE) are used widely as a sealing material to be used under strict environment since they exhibit excellent chemical resistance, solvent resistance and heat resistance. Particularly in the fields of aviation and space industries, semi-conductor production apparatuses and chemical plants, which are major applications of the fluoroelastomers, heat resistance of sealing at 300° C. or more is demanded.
Such a crosslinked product having excellent heat resistance is obtained by firstly preparing a nitrile group-containing fluoroelastomer having nitrile group in a molecular chain as a cure site by copolymerizing perfluoro(vinyl ether) (CNVE) having nitrile group with TFE and perfluoro(alkyl vinyl ether) (PAVE) and then crosslinking the fluoroelastomer by triazine crosslinking with organotin, oxazole crosslinking with a bisaminophenol compound or tetraamine compound or imidazole crosslinking, as described, for example, in JP-A-58-152041 and JP-A-59-109546.
However CNVE for introducing nitrile group as a cure site requires a long synthesis step and is very expensive, and also the nitrile group in the obtained nitrile group-containing fluoroelastomer is unstable. Further a mechanical strength and sealing property at high temperature (compression set) of the obtained crosslinked product are insufficient.
The inventors of the present invention have made various studies with respect to conventional nitrile group-containing fluoroelastomers and assumed that a reason why sufficient properties were not obtained was the fact that nitrile cure site group is present only as a pendant of a molecular chain. Thus the inventors have studied introduction of nitrile group into an end of the molecular chain. However in a conventional method described in Polymer Journal, Vol. 17, No. 1, pp 253 to 263, in which a solid dehydrating agent such as phosphorus pentoxide is used (Formula 10 at page 261), it is possible to carry out conversion of an end group of liquid fluorooil into nitrile group but a solid fluoroelastomer cannot be dehydrated uniformly and the dehydrating agent remains in the obtained product. Therefore an intended solid fluoroelastomer having nitrile group at the end could not be obtained.
An object of the present invention is to provide a solid fluoroelastomer having, at the end, nitrile group functioning as a cure site, and an economical preparation process thereof.
Another object of the present invention is to provide a novel synthesis process for converting amide group into nitrile group, and a dehydrating agent to be used therefor.
DISCLOSURE OF INVENTION
The present invention relates to a process for preparing a nitrile group-containing fluoroelastomer by converting amide group contained in a polymer molecular chain of a solid fluoroelastomer into nitrile group in the presence of a dehydrating agent.
It is preferable that the dehydrating agent to be used is in the form of gas or liquid. Particularly COF
2
is preferable.
The solid nitrile group-containing fluoroelastomer to be prepared in the present invention, which has nitrile groups at both ends and is represented by the formula (I):
NC—(R
f
)—CN
wherein R
f
is a divalent fluoroelastomer chain, is a novel fluoroelastomer.
It is preferable that the fluoroelastomer chain R
f
is a perfluoroelastomer chain of copolymer or terpolymer represented by the formula (1):
wherein m/(n+p) is 95 to 50/5 to 50, n/p is 0/100 to 100/0, m+n+p is from 100 to 10,000, R
f
1
is a perfluoroalkyl group having 1 to 8 carbon atoms, R
f
2
is —(CF
2
CFYO)
q
R
f
3
, in which R
f
3
is a perfluoroalkyl group having 1 to 6 carbon atoms, Y is fluorine atom or a trifluoromethyl group, q is an integer of 1 to 5, or
a perfluoroelastomer chain of terpolymer or tetrapolymer represented by the formula (2):
wherein 1/m/(n+p) is 95 to 35/0 to 30/5 to 35, n/p is 0/100 to 100/0, 1+m+n+p is from 100 to 10,000, R
f
1
and R
f
2
are as defined above.
The fluoroelastomer composition particularly comprising a solid nitrile group-containing fluoroelastomer having nitrile groups at ends in the number of more than ½ of a total number of end groups of molecular chains of the fluoroelastomer provides a crosslinked product having excellent properties.
Further the present invention relates to the process for preparing an amide group-containing fluoroelastomer which is a starting substance for the above-mentioned reaction for converting into nitrile group, by reacting a solid fluoroelastomer having ester group in a molecular chain thereof, particularly at the end of the molecular chain with ammonia or aqueous ammonia.
Further the present invention relates to a solid amide group-containing fluoroelastomer having amide groups at both ends and. represented by the formula (II):
H
2
NOC—(R
f
)—CONH
2
wherein R
f
is a divalent fluoroelastomer chain.
Also the present invention relates to a novel process for synthesis of a nitrile compound which is represented by the formula (IV):
R—CN
wherein R is a monovalent organic group, and is prepared by dehydrating an amide compound represented by the formula (III):
R—CONH
2
wherein R is as defined above, in the presence of COF
2
. It is advantageous to use COF
2
as the dehydrating agent for such a reaction for converting into nitrile group, from the viewpoint of yield, low boiling point and easy removal of un-reacted gas after the reaction.
BEST MODE FOR CARRYING OUT THE INVENTION
Firstly the present invention relates to the process for preparing a nitrile group-containing fluoroelastomer by converting amide group contained in a polymer molecular chain of a solid fluoroelastomer into nitrile group in the presence of a dehydrating agent.
A fluoropolymer which is a starting material in the process for preparing the nitrile group-containing fluoroelastomer of the present invention is firstly (1) in the form of solid. This means that a liquid fluorooil which is described in the above-mentioned Polymer Journal, has a relatively low molecular weight (10,000 or less) and comprises essentially a fluoroether unit, is excluded. As mentioned above, in case of a liquid fluoropolymer, conventional dehydrating agents can be used, but in case of a solid fluoropolymer, non-uniform reaction arises and a desired object cannot be obtained.
Secondly (2) the fluoropolymer has amide group in a molecular chain thereof. The amide group may be present in the molecular chain as a pendant or may be present as end group of the molecular chain. It is a matter of course that the amide groups may be present in the both forms. The present invention has an important meaning that it becomes possible to introduce nitrile group as end group, which has been so far impossible. Particularly the solid fluoroelastomer having nitrile groups at both ends, which can be prepared by the process of the present invention and is represented by the above-mentioned formula (I) is a novel fluoroelastomer.
In the present invention, an elastomer chain (R
f
in the formula (I)) on a trunk chain portion of the fluoroelastomer does not change substantially. Examples of the fluoroelastomer chain R
f
are, for instance,
a perfluoroelastomer chain of copolymer or terpolymer represented by the formula (1):
wherein m/(n+p) is 95 to 50/5 to 50, n/p is 0/100 to 100/0, m+n+p is from 100 to 10,000, R
f
1
is a perfluoroalkyl group having 1 to 8 carbon atoms, R
f
2
is —(CF
2
CFYO)
q
R
f
3
, in which R
f
3
is a perfluoroalkyl group having 1 to 6 carbon atoms, Y is fluorine atom or a trifluoromethyl group, q is an integer of 1 to 5,
a perfluoroelastomer chain of
Irie Masaki
Kawasaki Kazuyoshi
Kishine Mitsuru
Daikin Industries Ltd.
Lipman Bernard
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