Process for preparing fluororubber graft copolymer

A process for preparing a fluororubber graft copolymer, comprising the step of graft-copolymerizing, onto (A) a fluororubber, (B) at least one organosilicon compound having the general formula (I): ##STR1## wherein R.sup.3 represents a monovalent unsaturated aliphatic hydrocarbon group; and R.sup.N represents as nitrogen-containing organic group having the general formula (II): ##STR2## or the general formula (III): ##STR3## where R.sup.4 and R.sup.5 each represent a hydrogen atom or a C.sub.1 -C.sub.15 organic group, and l is an integer of from 0 to 6, R.sup.6 and R.sup.7 have the same meaning as R.sup.3 and R.sup.4 or may form together a divalent hydrocarbon group represented by the formula: EQU --(CH.sub.2).sub.k -- where k represents an integer of 4 to 9, n represents an integer of 1 to 3, and m is an integer of from 0 to 10. The fluororubber graft copolymer has good workability in roll milling, and is vulcanizable under normal pressure. The cured products have good mechanical strength and low temperature properties.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for preparing a fluororubber 
graft copolymer. 
2. Description of the Prior Art 
Fluororubbers are recently noted as a material having good oil resistance, 
solvent resistance and heat resistance. 
The fluororubbers, however, have the drawbacks that they have poor 
workability in kneading processes such as roll milling, and that, when 
cured molded products such as tubing are produced, treatment with 
pressurized water steam or long time heat-treatment was required for 
vulcanization after a molding step. The cured products obtained have also 
drawbacks that they have too high rigidity or poor elongation in spite of 
good tensile strength, or exhibit poor low temperature properties 
according to the Gehman torsion test or the T-R test. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a process 
for preparing a fluororubber graft copolymer that has not only good oil 
resistance, solvent resistance and heat resistance but also has good 
workability in roll milling, and is vulcanizable under normal pressure and 
capable of producing cured products having good mechanical strength and 
good low temperature properties. Thus, the present invention provides a 
process for preparing a fluororubber graft copolymer, comprising the step 
of graft-copolymerizing, onto (A) a polyaminevulcanizable fluororubber, 
(B) at least one organosilicon compound having the general formula (I): 
##STR4## 
wherein plural R.sup.1 and R.sup.2 may be the same or different each 
represent a substituted or unsubstituted monovalent organic group; R.sup.3 
represents a monovalent unsaturated aliphatic hydrocarbon group; and 
R.sub.N presents a nitrogen-containing organic group having the genera 
formula (II): 
##STR5## 
where R.sup.4 and R.sup.5 may be the same or different and each represent 
a hydrogen atom or a substituted or unsubstituted C.sub.1 -C.sub.15 
organic group, and 1 is an integer of from 1 to 6, or the general formula 
(III): 
##STR6## 
where R.sup.6 and R.sup.7 have the same meaning as R.sup.4 and R.sup.5 as 
defined above or may form together a divalent hydrocarbon group 
represented by the formula: 
EQU --(CH.sub.2).sub.k 
where k represents an integer of from 4 to 9, and 1 is as defined above, n 
represents an integer of 1 to 3, and m is an integer of from 0 to 10. 
According the present process, it is possible to obtain a fluorine graft 
copolymer that has not only good oil resistance, solvent resistance and 
heat resistance but also has good workability in roll milling, and is 
vulcanizable under normal pressure and capable of producing cured products 
having good mechanical strength and good low temperature properties. 
Further, compositions having good physical properties can be prepared by 
adding the copolymer obtained to silicone rubbers, for instance.