Note: Descriptions are shown in the official language in which they were submitted.
ELASTOMERIC ORGANOPOLYSILOXANES CONTAINING POLYCARBO-
: DIIMID~-POLYSILOXANE COPOLYMERS
The present invention relates to compositions which
can be heat-cured to give elastomers; the compositions
have improved resistance to hydrolytic degradation and are
based on highly viscous organopolysiloxane compositions,
with the addition of polycarbodiimide-polysiloxane copoly-
mers.
It is known that organopolysiloxane elastomers, for
example polydimethylsiloxane rubbers, retain their elasto-
meric properties over a wide temperature range. Because
of these properties, they have found numerous applications.
However, a difficulty w~ich continues to exist in
the field o~ siloxane elastomer technology is the degrada-
tion of the polymer structure if the elastomer is exposed
to certain environmental conditions for a long time.
For example~ with some polysiloxane elastomers, when used
as sealing materials in certain systems, hydrolytic
degradation occurs to such an extent that there is consider-
able loss of their elastomeric properties. In the
absence of atmospheric oxygen the degradation takes place
so rapidly that, for example, vulcanize~ polydimethyl-
siloxane polymers heated in a sealed tube at 200C as a
rule are completely destroyed a~ter only 3 days.
Admittedly, it is known (compare, for example,
French Patent Specification 1,440,466 and U.S. Patent
Speci~ication 3,031,430) that certain metals and metal com-
pounds retard hydrolytic degradation and hence act as
stabilizers; for example, bismuth and cadmium, incorpora-
ted in the form o~ a low-melting alloy, provide a good pro-
tective ef~ect, but the use of these metals in siloxane
elastomers suffers from disadvantages. Furthermore,
stabilization against thermal ageing is possible, for
example by adding iron oxide or iron hydroxide in small
amounts (0.001 to 0.75 part by weight per 100 parts by
weigh~ o~ silicone elastomer), o~ by adding nickel salts,
such as nickel chloride, nickel acetate or nickel octoate.
However, all these known additives produce only inade~uate
stabilization of organopolysiloxane polymers against
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hydrolytic degradation. Dicyclohexylcarbodiimide, used
in rubber tecnnology to protect certain elastomers against
hydrolytic degradation, disperses so poorly when incorpora-
ted into silicone rubber that it has not been possible to
observe a protective effect.
It was therefore the object of the present invention
to provide novel advantageous organopolysiloxane elastomers
which are resistant to hydrolytic degradation and which
exhibit the heat resistance, solvent resistance and mechani~
cal ~a~ior of known polysiloxane elastomers.
Accordingly, the present invention relates to com-
positions which are heat-curable to give elastomers, have
improved resistance to hydrolytic degradation and are based
on organopolysiloxanes, and which are characterized by the
following constituents:
a) an organopolysiloxane polymer having a viscosity of
; 1,000,000 to-~200,~00,0~0 mPas at 25C and comprising the
; structural units
(R)a SiO4_a
wherein
R represents a monovalent hydrocarbon radical, which
can optionally be halogen-substituted, and
a is between a~out 1.95 and 2.01,
b) polycarbodiimide-polysiloxane copolymers,
c) a curing catalyst and
d) ~illers.
The compositions according to the invention, which
are heat-curable to give elastomers, can for example con-
sist of highly viscous organopolysiloxanes which are in
themselves known, especially those cont~ng about ~5 to 100 1
per cent of methylvinylsiloxane units and/or dimethylvinyl-
siloxane units, mixed with reinforcing and/or non-reinforc-
ing fillers and in most cases also with agents for reducing
the stiffening-up l~hich occurs on storage, especially
organosilanols and/or organosiloxanols, and curing agents.
The radicals R in the organopolysiloxane polymer or
the mixtures of such organopolysiloxane polymers and
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especially in a diorganopolysiloxane polymer having a vis-
cosity of ~x~t 1,000,000 to 200,000,OGO centipoise at 25C are
'selected,'~for example, from'amongst monovalent hydrocarbon
radicals, halogen-substituted-monovalent hydrocarbon radi-
cals and cyanoalkyl radicals. Such radicals are, forexample alkyl radicals, such as methyl, ethyl and propyl,
cycloalkyl radicals, such as cyclohexyl and cycloheptyl,
alkenyl radicals, such as vinyl and allyl, halogen-substitu-
ted alkyl radicals, such as fluoropropyl and trifluoro-
propyl and in particular fluorinated alkyl radicals of theformula R4CH2CH2-, R4 being a perfluoroalkyl radical, mono-
nuclear aryl radicals, such as phenyl, alkaryl radicals,
such as methylphenyl and ethylphenyl, aralkyl radicals, such
as phenylmethyl and phenylethyl, cyanoalkyl radicals, such
as cyanopropyl and the like, as well as other ~ubstituents
which are usually encountered as substituents of linear
diorganopolysiloxanes. It is particularly preferred to
select the radicals R from amongst alkyl radicals with 1 to
8 carbon atoms, alkenyl radicals with 2 to 8 carbon atoms,
halogen-substituted alkyl radicals, such as fluoroalkyl
radicals with 3 to 8 carbon atoms, and mononuclear aryl
radicals.
Further additives used as a rule are pigments, an~i-
oxidants and hot air stabilizers based on known metal oxides.
Examples of reinforcing fillers are, in particular, silicon
dioxide produced pyrogenically in the gas phase, precipita-
ted 3ilicon dioxide having a surface area of at least
50 m2/g, and silicic acid hydrogels dehydrated' in such a
way as to retain the structure. Examples of non-rein-
forcing fillers are, in particular, diatomaceous earth,quartz powder and chalk. Titanium dioxides, iron oxide,
A1203, CaC03, silicates and the like are also suitable.
Examples of curing agents are alkyl peroxides, aryl
peroxides or acyl peroxides, used individually or in com-
bination. However, the organopolysiloxane compositionscan also be cured by gamma-rays.
The specific peroxide curing catalysts which are
preferred include di-tertiary-butyl peroxide, tertiary-
butyl triethylmethyl perGxide, tertiary-butyl triphenyl-
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methyl peroxide, tertiary-butyl perbenzoate and di-tertiary-
alkyl peroxides, such as dicumyl peroxide. ~ther suit-
able peroxide catalysts which cause curing both via satura-
ted and via unsaturated hydrocarbon groups on the silicone
chain are aryl peroxides, the benzoyl peroxides, mixed alkyl-
aryl peroxides, such as tertiary-butyl perbenzoate, chloro-
aroylperoxides. such as 1.4-dichlorobenzovl peroxide Z 4-
dichlorobenzoyl percKide and moncchlor~zGyl peroxide, benzcylperoxide
~ methyl ethyl ketone peroxide and the like. In general,
0.1 ~o 8% by weight of the peroxide, relative to the rubber,
are employed. Preferably, about 0.5 to 4 % by weight are
employed.
The choice of the crosslinking agent depends on the
processing conditions. Thus, for example, most peroxides
are employed for w lcanization under pressure at tempera-
tures above 100C. In industrial practice, bis-(2,/l
dichlorobenzoyl) peroxide has proved a valuable peroxide
which, during vulcanization without externally applied
pressure, gives bubble-free and pore-freevulcanized
products.
Since the peroxides used belong to different chemi-
cal categories of compounds, their decomposition products
exert different effects in silicone rubber which as a rule
adversely influence the pattern of properties of the sili-
cone rubber. In particular, the acids liberated on
decomposition of acyl peroxides and per esters accelerate
thedepolymerization of silicone polymers. The cause
for this is a shift in the pH value, which favors attack
by water in every form.
According to the present invention, effective pro-
tection against the deterioration of the pattern o~ proper-
ties of organopolysiloxane rubber materials under hydroly-
tic environmental conditions is achieved by using siloxane
polymers which contain polycarbodiimide groups.
This finding was surprising inasmuch as the incor-
poration of monomeric carbodiimides, such as, ~or example,
dicyclohexylcarbodiimide, or of mixtures of higher-mole-
cular carbodiimides, such as are employed in the plastics
industry as agents for protecting certain polyester-based
v
or polyether-based polymers against hydrolysis, provided
in~ffective in silicone rubber.
Furthermore, it was surprising that the good hot air
resistance of silicone rubber is not adversely affected by the
presence of the relatively large organic radicals of the poly-
carbodiimide constituent.
Suitable polycarbodiimide-polysiloxane copolymers are
modified polysiloxanes such as are described, for example, in our
copendlng Canadian Applica~ion No. 306,352, filed June 5, 1978,
and United States Patent No. 4,076,763. It is preferred to employ
those copolymers in which the polysiloxanes and polycarbodiimide
are present as distinguishable phases, optionally with partial
chemical and/or physical bonding.
The improved organopolysiloxane compositions according to
the present invention are, accordingly, polysiloxanes which contain
polycarbodiimide-filled organopolysiloxane mixtures which in turn
are composed of the following two phases: (i) a continuous phase
of an organopolysiloxane liquid and (ii) a discontinuous phase of
finely dispersed par-ticles of a carbodiimide polymer which has
been obtained by polycondensation of the corresponding monomer or
monomer mixture in the presence of the organopolysiloxane and of
a carbodiimidation catalyst.
The polycarbodiimide-filled organopolysiloxane compositions
are prepared, for example, by thoroughly mixing the organopoly-
siloxane liquid with diisocyanates or polyisocyanates or mixtures
thereof in the presence of a catalyst which accelerates the
carbodiimide formation, or by mixing the organopolysiloxane liquid
~,
with polycarbodiimides prepared in situ and in themselves known.
The polymer mixture contains about 3-80% by weight, preferably
about 5-70% by weight, of polycarbodiimide (based on the total
mixture).
Instead of starting from pure polymer it is possible to
employ mixtures of customary polysiloxanes with polycarbodiimide-
polysiloxane copolymers. This can be done by premixing polymers
with one another and then mixing with
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the fillers and auxiliaries already mentioned, or by
blending a premix of a customary polysiloxane polymer,
fillers and auxiliaries, with the polycarbodiimide polymer,
or by premixing polycarbodiimide-polysiloxane polymer with
fillers and auxiliaries, or by blending premixes of both
types of polymers with one another in the desired ratio.
It follows from the above that the sequence of
mixing is not critical.
Equally, the mixing temperature is not subject to
any special res-trictions. All procedures customary with
silicone rubber can also be employed in the present case.
To prepare the compositions according to the inven-
-tion, a polycarbcdiimide content of about 0.1 to 70 % by weight, pre-
ferably abcut 1 to 20 % by weight, and very particularly prefentially
a~out 6 to 15 - by weight, relative to total polymer, is
employed.
If the content of polycarbodiimide in the polymer
is greater than abcut 70 mol per cent, technical disadvantages in
respect of processability manifest themselves, since, in
order to achieve satisfactory vulcanization characteristics,
either uneconomically large amounts of peroxide-must be
employed or the polymer must contain several times the
usual content of vin~l groups. Furthermore, the high
content of rigid molecular unit structures causes deteriora-
tion of the elastomeric properties.
The examples which follow are intended to explainthe silicone elastomers according to the invention in more
detail. Mixtures o~ the abovementioned type were pro-
duced under the usual conditions on a rubber mixing mill.
The composition of the samples is given in parts by weight.
The test specimens were vulcanized in a heated press.
The test specimens were examined in accordance with
the ~ollowing standard specifications:
Strength, elongation, 100 and 300~0 modulus:
DIN 53,504.
Hardness: DIN 53,505.
Elasticity: DIN 53,512~
Tear propagation resistance (crescent): ASTM-D
624 B.
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Example l
This example illustrates a method of preparation of
the polycarbodiimide-polysiloxane copolymer.
For this preparation, 20 kg of a polydimethylsilox-
ane with terminal hydroxyl groups, having a viscosity Gf10,000 mPas are stirred by means of a stirring disc at 400
to 500 rpm, and warmed to 70C. 30 g of a l-meth~lphos-
pholine oxide isomer mixture are added and 20 kg of an
isomer mixture of 80 per cent of toluylene-2,4-diisocyanate
and 20 per cent of toluylene-2,6-diisocyanate are metered
into this mixture in a uniform stream over the course of 2
hours, with constant stirring. The carbon dioxide formed
is led away. After completion of the addition of the
isocyanate, stirring is continued for one hour at the same
temperature, after ~hich the product is cooled to room tem-
perature.
The product is a white to pale yellowish, viscous
composition having a viscosity of about 200,000 mPas.
xample 2
This example describes the preparation of a poly-
carbodiimide-polysiloxane copolymer based on diphenyl-
methane-4,4'-diisocyanate~
750 g of polydimethylsiloxane with terminal hydroxyl
groups and having a viscosity of 18,000 mPas are heated to
80C and o.6 ml of l~methyl-phospholine oxide iso~er mixture
is added. 750 g of diphenylmethane-4,4'-diisocyanate
are mete~d in over the course of 2 hours at 80C, with
constant stirring, and after completion of the addition
stirring is continued for 1 hour at 80C. A white,
homogeneous and pourable product having a viscosity of
330,000 mPas is obtained.
E~ es 3 to 8
A silicone rubber premix is prepared on a rubber
mixing mill by mixing, in the usual manner, l part of hexa-
methyldisilazane, 58 parts of a pyrogenic silica having asurface area of 200 m2/g and 12.76 parts of a silicone oil
containing hydroxyl groups and possessing 3.1 mol % of
vinyl-methyl-siloxane units into lO0 parts of a polydi-
methylsiloxane containing vinyl groups (0.003 mol ,b of
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vinyl-methyl groups3.
This premix is divided Into six parts and each is
mixed, on a rubber mixing mill, with a 50 ~ strength Dis-
(2,4-dichlorobenzoyl) peroxide paste in silicone oil, and,
optionally, with a polycarbo~iimide-polysiloxane copolymer
according to Example 1 or dicyclohexylcarbodiimide, in
accordance with Table 1 below.
Sheets of 2 and 6 mm thickness of these six mixtures
are vulcanized in a heated press at 120Co The vulcan-
ization time is 10 minutes. The test specimens accord-
ing to the abovementioned standard specifications are cut
from these sheets. Post-vulcanization in hot air is
dispensed with, so that the concentration of crosslinking
agent decomposition products in the vulcanized materials
should be preserved, This is done in order deliberately
to create more severe ageing conditions.
The test specimens are examined in accordance with
the abovementioned DIN or ASTM instructions. Some o~
the samples are aged, after vulcanization, for 70 or 120
hours at 200C in sealed glass tubes, and are then tested
in accordance with the abovementioned DIN instructions.
The progress of hydrolytic ageing is followed by measuring
the strengths.
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Examples 9 to 11
100 partC of a polydimethylsiloxane containlng vinyl
groups, 1 part of hexamethyldisilazane, 58.0 parts of a
pyrogenic silica having a surface area of 200 m2/g, 12.8
parts of a polydimethylsiloxane oil containing hydroxyl
groups, 2 parts of a 50% strength paste of black iron oxide
pigment in polydimethylsiloxane containing vinyl groups,
and 0.8 part of bis-tert.-butyl-(peroxydiisopropyl)-benzene
are mixed on a mill, in one and the same pass, with the
amounts, shown in Table 2, of polycarbodiimide-polysiloxane
polymer according to Example 1 and of a 50% strength bis~
(2,4-dichlorobenzoyl) peroxide paste.
2 and 6 mm thick sheets of these mixtures are vul-
canized for 10 minutes in a heated press at 120 to 180C,
using rapid heating. The test specimens are cut from
these sheets in accordance with standard specifications and
are tested appropriately. ~ome of the samples, after
having been vulcanized, are heated for 10 days at 200C by
means of hot air and others for 3 days at 225C. Yet a
further number of the samples are heated for 70 hours in a
sealed glass tube at 200C.
Following their vulcanization with or without sub-
sequentheat ageing, all the samples are tested in accordance
with the DIN instructions. The progress of the hydroly-
tic ageing is followed by measuring the strengths.
Table 2
Example 9 Example 10 Example 11
containing vinyl groups100.0lO0.0 100.0
30 Hexamethyldisilazane 1.0 1.0 1.0
Silica 58.0 58.0 58.0
Polydimethylsiloxane 12 8 12 8 12 8
containing hydroxyl groups
Iron oxide pigment 2.0 2.0 2.0
35 ~icumyl peroxide 0.8 0.8 0.8
Polycarbodiimide- 4 0 4 0 6 0
polysiloxane copolymer
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Table 2
(Continuation)
Example 9 Example 10 Example 11
.- ., . . . .. .....
Peroxide paste as per 1 4 1 8 1.4
5 text
Vulcanization at 120-180C,
duration 10'
Strength (MPa) 8.5 8.3 7.9
Elongation (%) 450 460 450
10 Modulus (100%) 2.0 2.1 1.9
Modulus (300%) 5.4 5.4 5.0
Hardness (Shore A) 63 64 63
Elasticity (%) 37 31 29
Crescent (N/mm) 18 21 21
Vulcanization 120-* 180C7
10' + 10 days at 200C in
hot air
Strength 5.2 5.4 5.0
Elongation 250 250 250
20 Modulus ( lOOyo ) 3.1 3.2 3.1
Hardness 71 71 72
Elasticity 23 28 28
Vulcanization 120-~ 180C, _
- 10' + 3 days at 225C in
hot air
.. _ . .. . . . ..
Strength 4.0 4.5 4.o
Elongation 200 240 235
Modulus (100%) 2.9 3.0 3.1
Hardness 69 73 72
30 Elasticity 22 24 24
Vulcan zation 120-~ol80C,
10' + ~0 hrs at 200 C in
a sealed test-tube
Strength 1.1 1.2 1.6
35 Elongation 40 60 70
Exam~les 12 to 16
A silicone rubber premix is prepared in the usual
manner on a ~ubber mixer by adding, to 100 parts of a poly-
dimethylsiloxane containing vinyl groups, 27.5 parts o~
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pyrogenically produced silica o~ sur~ace area greater than
300 m2/g and 6.33 parts of a silanol-based processing
auxiliary,
This premix is divided into four parts and mixed on
a rubber mixer with polycarbodiimide-polysiloxane copol-ymer
according to Example 2 and with a 50% strength biS-(2,L~
dichlorobenzoyl) peroxide paste in silicone oil, in accord-
ance with Table 3 below.
2 and 6 mm thick sheets of these mixtures are cross-
lb linked in a heated press at 120C, with a vulcanization time
of 10 minutes. The test specimens cut from the sheets
in accordance with the appropriate standard specifications
are tested in accordance with the said specifications.
Some of the samples, after having been vulcanized, are
heated for 10 days at 200C by means of hot air and others
for 3 days at 225C. Yet a further number of the samples
are heated ~or 70 hours in a sealed glass tube at 200C.
Following their vulcanization, with or without subsequent
heat ageing, aIl the samples are-tested in accordance with
standard specification instructions. The progress of the
hydrolytic degradation is followed by measuring the
strengths.
.. ~
Example Example Example Example
12 13 14 15
Premix 100.0100.0 100.0 100.0
Polycarbodiimide- 8 0 6 0 4 0
polysiloxane copolymer
~Peroxide paste as per text 1.4 1.0 1.2 1.4
Vulcani~ation for
10'/120UC press temperature
Strength (mPa) 7.7 7.0 7.9 8,7
Elongation (%) 555 590 545 490
Modulus (100%) 1.4 1.3 1.5 1.7
Modulus (300/0) 0.7 3.1 4.0 4.7
Hardness (Shore A) 50 54 59 66
Elasticity (%) 19 18 20 25
Crescent (~/mm) 35 36 33 32
~,~
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Table 3
(Continuation)
Example Example Exa~ple Example
12 13 14 15
,. .. . . ..
Vulcanization for 10'/
5 120C press temperature
+ 10 days at 200C in
hot air
.,
Strength 5 ~ 2 4 ~ 7 4~ 7 5 ~ 1
Elongation 310 325 300 270
10 Modulus ( 100% ) 2 ~ 3 2 ~ 2 2 ~ 4 2 ~ 9
Modulus (200%) 3r7 3~3 3~6 4~3
Hardness 70 71 73 76
Elasticity 23 23 25 28
Vulcanization for 10'/
15 120C press temgerature
+ 3 days at 225 C in hot
air
.. . . . _ _ . , , "
- Strength 4~ 8 4~ 4 4~ 8 4~ 9
Elongation 360 335 310 245
20 Modulus (100%) 2 ~ 0 2 ~ 0 2 ~ 4 2 ~ 8
Modulus (200%) 3~0 2~9 3~6 4~2
Hardness 68 68 69 73
Elasticity 16 17 17 22
. . . .
-~ Vulcanization for 10'/
25 120C press temperature
+ 70 hours at 200C in a
test~tube
.. . .... ... .. .
Strength 2~ 6 2 ~ 0 1 ~ 3
Elongation 330 260 105
Modulus (100%) 1.1 1.2 1.3
Y~ulu~ ~ 200O
It will ~e appreciated that the instant specification
and examples are set forth by way of illustration and not
limitation, and that various modifications and changes may be
made without departing from the spirit and scope of the
present invention.
'
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