Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to curable organo-
polysiloxane resins containing a reactive diluent.
Organopolysiloxane resins in which the substituent
organic groups are methyl, phenyl, vinyl and/or similar organic
groups are well-known~ These materials cure through a variety of
mechanisms, such as peroxide catalyzed vinyl groups on silicon or
by the platinum catalyzed addition of silicon hydride to alken~l
groups on silicon. The properties of these organopolysiloxane
resins such as toughness and retention of strength at high
temperatures make them useful in casting resin applications.
The resins that are useful for casting applications are
those that have higher viscosities, on the order of 5.0 to 200
Pa-s or higher. These resins, even though they have the desir~d
strengths, have one important disadvantage. Because of their high
viscosities they are extremely difficult to handle in use. They
do not pour rapidly and have slow flow when cast into place.
The problem is, therefore, posed as to how one can use
the high viscosit~ resins for their desirable properties and at
the same time obtain desirable handling properties.
An obvious solution is to dilute the resins with solvent
but this approach leads to bubble entrapment when the casting
resin is heated to cure it. It also leads to the time-consuming
step of solvent removal ~rom the cast resin.
Most recent attempts to solve the handling problem have
been to incorporate a low molecular weight crosslinker in the
system. For example, Clark in U.S. Patent 2,894,930 shows a
one-part, curable casting resin wherein he sugyests using
(CH2-C~(C~3)2SiO)2Si(C6Hs)2 as a portion of the reactive alkenyl
containing resin. The materials are cured through the use of
peroxide catalysts. These materials have the advantage of being
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one-part, that is, all the essential ingredients can be mixed
together and stored without the material curing. The
disadvantage r of course, is that fact that the peroxide cured,
one-part materials require a long period of time to cure.
Mink et al., in U.S. Patent 3,944/519, overcome the
latter problem by increasing the rate of cure oE such resins by
changing ~he cure system from the peroxide cured vinyl to the
platinum catalysis of the silicon hydride addition to alkenyl
groups, i.e. --SiH ~ CH2=CHSi-~ P >
-SiCH2CH2Si--. Thus, Mink et al. utilized low molecular ~eight
(low viscosity) silicon hydride crosslin~er organopolysiloxanes in
a vinyl containing organopolysiloxane to enhance the cure rate and
also to reduce the viscosity of the vinylsiloxane resin so that it
could be easily handled. The patent teaches that only specific
silicon hydride containing crosslinkers work. The use of low
molecular weight vinyl containing diluents is not shown or
; suggested therein.
It has been found that by adding a specific low molecular
weight vinyl containing diluent, lower viscosities of the casting
resins can be obtained without sacrificing the desirable
mechanical properties of the higher viscosity casting resin.
This invention consists of an improved curable
composition consisting essentially of a mixture of ~a) an
organopolysiloxane containing from 67 to 85 mol percent C6H5SiO3/2
units and 33 to 15 mol percent of CH2=CH(CH3)2SiOl/2 units, said
organopolysiloxane having an average of at least 8 silicon atoms
per molecule; (b) a silicon hydride containing polysiloxane
crosslinker for (a), said (b) being present in an amount
sufficient to provide about 0.9 to 1.1 mol of silicon hydride per
.nol of CH2=CHSi present in (a) and (d); (c) a platinum catalyst in
~3~
an amount sufficient to catalyze the reaction of the silicon
hydride with the CH2=CHSi-; the improvement comprising adding a
reactive diluent ~d) having the formula
[CH2=CH(CH3)2siO]2si(c6H5)2-
In this invention, the organopolysiloxane resin (a) isthe base resin. The critical feature of the resin (a) is that it
have a sufficiently high viscosity to give the desired mechanical
strength to the cured composition. The resin (a) is essentially
the same as that described in Mink et al., discussed above~ and
~ 10 consists of monophenylsiloxy units in the range 67 to 85 mol
- percent; dimethylvinylsiloxy units in the range of 33 to 15 mol
percent. Preferred for the resin (a) are 75 mol percent
monophenylsiloxy units and 25 mol percent of the dimethylvinyl-
siloxy units.
This resin is easily prepared by conventional hydrolysis
of the corresponding chloro or alkoxysllanes and condensation
techniques. Although there does not appear to be any upper limit
on the molecular weight of the resin ~a), it should have a degree
of polymerization of at least 8 silicon atoms per molecule. This
is to ensure adequate physical strengths in the final product.
The resin (a) can also be treated, for example, by alkaline
condensation catalysts, to reduce the silanol content of the
resin.
The silicon hydride containing siloxane (b) serves as a
crosslinker and curing agent in the curable composition. This
material can be any silicon hydride containing silane or siloxane
that is compatible and gives the cured composition the desired
properties. This material can be, for example, the polymer found
in the Mink et al. patent at column 2, lines 23-25 or
[H(CH3)2SiO]2Si(C6H5)2 or ~H(CH3)2SiO~3SiC6H5. The crosslinker
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must have at least two (2) silicon hydrogens per molecule. There
must be enough of (b) present to give from 0.9 to 1.1 mol of
silicon hydride per mol of alkenyl groups in the curable
composition. Preferred is a ratio of 1 mol of silicon hydride to
1 mol of alkenyl for the best results. The crosslinkers (b) can
be prepared by conventional techniques known to those skilled in
the art, for example, the cohydrolysis of the corresponding
silanes. -
The platinum catalyst (c) can be any of the well-known
forms of catalytic platinum, ran~ing from finely divided platinum
metal to platinum on various carriers to the chloroplatinic acid
and complexed platinum compounds. Chloroplatinic acid in a small
amount of solvent or [(R3P)2PtCl]2 where R is methyl, ethyl,
propyl or butyl are preferred
There should be at least 0.1 parts by weight of platinum
per million parts by weight of the combined total of components
(a), (b) and (d) and 1-20 parts Pt per million parts is preferred.
The unique component of this invention is the component
(d), the vinyl containing siloxane diluent,
[CH2=CH(cH3)2siO]2si(c6H5)2-
On mixing this diluent (d) with the componen~ ~a) in a
ratio of (d) to (a) of from 20/80 to 50/50, a solventless material
is produced which has a maximum viscosity of about 2.5 Pa-s. The
preferred ratio is 25 parts of (d) to 75 parts of (a)~ This
specific material is the only one of many similar materials that
was effective in this invention. [CH2=CH(CH3)2Si]2O was too
volatile while [(C6H5)(CH3)(CH2=CH)Si]2O and
[CH2=CH(CH3)2Sio]2SiCH3(C6Hs), although non-volatile, reduced the
mechanical properties of the cured resin. This material is easily
~3~
prepared by the same methods as indicated for the component (b)
above
Generally for a two-component system, the component (d)
is mixed, with a small portion of the base resin (a) and the
catalyst required for cure, into one package. The remainder of
the base resin (a) and the crosslinker (b) are mixed together and
form a second package. The means and manner for mixing these
individual materials is not critical as long as the materials are
homogeneous. The two packages can then be mixed together at the
appropriate time for their use and cast into place. Upon heating,
the composition cures. If other materials are to be mixed with
the composition, they should be incorporated in the individual
packages during their preparation rather than adding those
materials at the final mixing of the whole composition. Other
materials that can be incorporated in ~he resin composition of
this invention are the conventional fi:Llers such as glass fibers,
inely divided silica, crushed quartz, powdered glass, asbestos,
talc, carbon black, iron oxide, titanium oxide, magnesium oxide or
mixtures thereof. Also included are pigments, dyes, oxidation
inhibitors, cure inhibitors and release a~ents. -
The curable composition can be employed in any
conventional manner for casting or impregnating.
The components (a), (b), (c) and (d) are mixed together
with any of ~he above desired additives and mixed to make
homogeneous. It is then fabricated into the desired ~orm and
cured, usually at elevated temperatures, for example, 100-150C.
It may be desirable in some cases to post cure the cured material
at elevated temperatures, for example, up to 200C.
The following examples are by way of comparison with the
systems currently in the prior art. The examples are not intended
~L33:~60~
as limiting the invention delineated in the claims.
Example 1
A base resin was prepared consisting of 75 mol percent
monophenylsiloxy units and 25 mol percent of vinyldimethylsiloxy
units and was designated "A". Various types of crosslinkers
; designated "B", "C" and "D" were prepared and mixed with A
; according to conventional techniques in the amounts shown in Table
I. The mixture of B with A is the example of the prior art shown
in Mink et al., U.S. 3,944,519 at Table II, middle columnO B is
10 [H(CH3)2siO72si(c6H5)2; C is [H(cH3)2sio]3sic6Hs and D is 35 mole
percent diphenylsiloxy units; 55 mole % HCH3SiO units and 10 mole
percent (CH3)3SiOl/2 units. The catalyst was 1% [(C4Hg)3P]2PtC12
in toluene. Runs 1, 2 and 3 are outside the scope of the
invention and represent the prior art.
Runs 4, 5 and 6 illustrate the invention and show the
effect of the addition of (d) (CH2=CH(CH3)2SiO)2Si(C6H5)2.
Two-part compositions were prepared wherein part one was the base
resin (a) and the crosslinker (b) and the second part was the
component (d) and the catalyst and, a small amount of component
(a) as a carrier. The ratio of part one to part two was 10:1.
The results are shown in Table II helow.
Example 2
This example serves to illustrate the comparison between
the prior art diluent (~ViMeSi)2O and the present diluent. As the
amount of the prior art diluent is increased, the flex strength of
the resulting resin is reduced. The increase in diluent is to
decrease the viscosity so that the base resin can be easily
handled.
Runs 7, 8 and 9 on Table III show the use of (~ViMeSi)2O
as the reactive diluent wherein 0 is C6Hs-, Vi is CH2=CH- and Me
~L~3~
is CH3~. Two part compositions were again prepared wherein part
one was the base resin (a) and the crosslinker (b) and the second
part was (~ViMeSi)2O, the catalyst and a small amoun~ of component
(a) as a carrier. The ratio of part one to part two was 10:1.
; The catalyst was the same as used in Example 1.
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