Peroxide curable fluoroelastomers

Details Peroxide curable fluoroelastomers Peroxide curable fluoroelastomers

1999-06-21

2001-11-27

Nutter, Nathan M. (Department: 1711)

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

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S200000

Reexamination Certificate

active

06323283

ABSTRACT:

The present invention relates to new fluoroelastomers cured by peroxides having improved mechanical and elastic properties.
Various fluoroelastomers are known, and they are widely used in those fields when outstanding elastic properties combined with high thermochemical stability are required. For a review of such products see, for instance, “Ullmann's Encyclopedia of Industrial Chemistry”, vol. A-11, pp. 417-429 (1988, VCH Verlagsgesellschaft).
Fluoroelastomer curing can be carried out both ionically and with peroxides. In peroxidic curing, the polymer must contain curing sites capable of forming radicals in the presence of peroxides. To this purpose, cure-site monomers containing iodine and/or bromine can be introduced in the polymeric backbone as described, for example, in U.S. Pat. No. 4,035,565, U.S. Pat. No. 4,745,165 and EP 199,138. Alternatively, chain transfer agents containing iodine and/or bromine, which produce iodinated and/or brominated end groups (see for example U.S. Pat. No. 4,243,770 and U.S. Pat. No. 5,173,553), can be used during polymerization.
A drawback of the compounds for curing resides in difficult processing. In particular, it is well known that the fluoroelastomers cured by peroxides with respect to those cured ionically, exhibit poor elastic properties as shown by the high compression set values. In addition, there is a remarkable mold fouling leading to decreases in productivity and increases in waste.
The Applicant has surprisingly and unexpectedly found that it is possible to obtain new fluoroelastomers having superior mechanical, and compression set properties and excellent mold release properties.
An object of the present invention consists in curable fluoroelastomers substantially consisting of mixtures of the following fluoroelastomers:
a) from 20 to 70% by weight of a fluoroelastomer having a Mooney viscosity, ML (1+10) at 121° C., measured according to ASTM D 1646, greater than 60 points and containing from 0.01 to 3% by weight of iodine;
b) from 0 to 70% by weight of a fluoroelastomer having a Mooney viscosity, ML (1+10) at 121° C., measured according to ASTM D 1646, greater than 20 to 60 points and containing from 0.2 to 5% by weight of iodine;
c) from 5 to 60% by weight of a fluoroelastomer having a Mooney viscosity, ML (1+10) at 121° C., measured according to ASTM D 1646 method, in the range of 1-20 points and containing an iodine percentage by weight greater than 0.3; said fluoroelastomers comprising monomeric units derived from bis-olefins having the formula:
 wherein:
R
1
, R
2
, R
3
, R
4
, R
5
and R
6
are equal to or different from each other, and are H or C
1
-C
5
alkyls; Z is a C
1
-C
18
alkylene or cycloalkylene radical, linear or branched, optionally containing oxygen atoms, preferably at least partially fluorinated, or Z is a (per)fluoropolyoxyalkylcne radical.
Preferred compositions are:
a) from 20 to 50% by weight of a fluoroelastomer having a Mooney viscosity, ML (1+10) at 121° C., measured according to ASTM D 1646, greater than 70 points and containing from 0.05 to 2% by weight of iodine;
b) from 0 to 50% by weight of a fluoroelastomer having a Mooney viscosity, ML (1+10) at 121° C., measured according to ASTM D 1646, in the range of 30-50 points and containing from 0.2 to 3% by weight of iodine;
c) from 10 to 30% by weight of a fluoroelastomer having a Mooney viscosity, ML (1+10) at 121° C., measured according to ASTM D 1646, in the range of 5-15 points and containing an iodine percentage by weight greater than 0.5.
In formula (I), Z preferably is a C
4
-C
12
perfluoroalkylene radical, wherein R
1
, R
2
, R
3
, R
4
, R
5
and R
6
preferably are hydrogen.
When Z is a (per)fluoropolyoxyalkylene radical, it preferably has the formula:
—(Q)
p
—CF
2
O—(CF
2
CF
2
O)
m
(CF
2
O)
n
—CF
2
—(Q)
p
—  (II)
wherein:
Q is a C
1
-C
10
alkylene or oxyalkylene radical; p is 0 or 1; m and n are integers such that the m
ratio is between 0.2 and 5 and the molecular weight of said (per)fluoropolyoxyalkylene radical is in the range of 500-10,000, preferably 1,000-4,000. Preferably, Q is selected from:
—CH
2
OCH
2
—; —CH
2
O(CH
2
CH
2
O)
s
CH
2
—; or s=1-3.
The bis-olefins of formula (I) wherein Z is an alkylene or cycloakylene radical can be prepared, for example, according to I.L. Knunyants et al. in Izv. Akad. Nauk. SSSR, Ser. Khim., 1964(2), pp. 384-386, while the bis-olefins containing (per)fluoropolyoxyalkylene sequences are described in U.S. Pat. No. 3,810,874.
The units derived from bis-olefins in the backbone are generally in the range of 0.01-1.0 moles, preferably 0.03-0.5 moles, still more preferably 0.05-0.2% moles per 100 moles of the other monomer in the backbone.
The base structure of the fluoroelastomer can be in particular selected from:
(1) VDF-based copolymers, wherein VDF is copolymerized with at least a comonomer selected from: C
2
-C
8
perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropene (HFP); chloro- and/or bromo- and/or iodo-C
2
-C
8
fluoroolefins, such as chlorotrifluoroethylene (CTFE) and bromotrifluoroethylene; (per)fluoroalkylvinylethers (PAVE) CF
2
═CFOR
f
, wherein R
f
is a C
1
-C
6
perfluoroalkyl, for example trifluoromethyl, bromodifluoromethyl, penta-fluoropropyl; perfluoro-oxyalkylvinylethers CF
2
═CFOX, wherein X is a C
1
-C
12
perfluoro-oxyalkyl having one or more ether groups, for example perfluoro-2-propoxy-propyl; non-fluorinated (Ol) C
2
-C
8
olefins, for example ethylene and propylene;
(2) TFE-based copolymers, wherein TFE is copolymerized with at least a comonomer selected from:
(per)fluoroalkylvinylethers (PAVE) CF
2
═CFOR
f
, wherein R
f
is as above defined; perfluoro-oxyalkylvinylethers CF
2
=CFOX,wherein X is as above defined; C
2
-C
8
fluoroolefins containing hydrogen and/or chlorine and/or bromine and/or iodine atoms; non-fluorinated (Ol) C
2
-C
8
olefins.
Within the above defined classes, preferred base monomer compositions are:
(a) VDF 45-85%, HFP 15-45%, TFE 0-30%;
(b) VDF 50-80%, PAVE 5-50%, TFE 0-20%;
(c) VDF 20-30%, Ol 10-30%, HFP and/or PAVE 18-27%, TFE 10-30%;
(d) TFE 50-80%, PAVE 20-50%;
(e) TFE 45-65%, Ol 20-55%, VDF 0-30%;
(f) TFE 32-60%, Ol 10-40%, PAVE 20-40%; and
(g) TFE 33-75%, PAVE 15-45%, VDF 5-30%.
The fluoroelastomer mixtures of the invention are obtained by separately polymerizing the fluoroelastomers of a), b) and c) supra and subsequently coagulating the latexes obtained in the above mentioned ratios. Alternatively, a), b) and c) fluoroelastomer mixtures can be produced in situ in a single polymerization by suitably dosing the polymerization components during the polymerization reaction, as well-known to those of ordinary skill in the art.
The preparation of the fluoroelastomers of the present invention can be carried out by copolymerizing the monomers in an aqueous emulsion according to well known methods, in the presence of radical initiators (for example alkaline or ammonium persulphates, perphosphates, perborates or percarbonates), optionally in combination with ferrous, cuprous or silver salts, or of other easily oxidizable metals. In the reaction medium surfactants of various types are usually present, among which the fluorinated surfactants of formula:
R
f
—X
−
M
+
are particularly preferred, wherein R
f
is a C
5
-C
16
(per)fluoroalkyl chain or a (per)fluoropolyoxyalkylene chain, X
−
is —COO
−
or —SO
3
−
, M
+
is selected from: H
+
, NH
4
+
, or an alkaline metal ion. The most commonly used are: ammonium perfluoro-octanoate, (per) fluoropolyoxyalkylenes ended with one or more carboxyl groups, etc.
The amount of bis-olefin to be added to the reaction mixture depends on the amount desired in the final product. It has to be noted that, at the low amounts used according to the purposes of the present invention, practically all the bis-olefin present in the reaction medium enters into the chain.
When the copolymerization is completed, the fluoroelastomer is isolated by conventional methods, such as by coagulati

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