Organopolysiloxane compositions which can be crosslinked to give

Details Organopolysiloxane compositions which can be crosslinked to give Organopolysiloxane compositions which can be crosslinked to give

1995-05-31

1998-01-06

Glass, Margaret W.

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

Synthetic resins

From silicon reactant having at least one...

524588, 525477, C08G 7708

Patent

active

057055882

DESCRIPTION:

BRIEF SUMMARY
The invention relates to organopolysiloxane compositions which can be crosslinked by means of free radical formation to give elastomers, and to a process for their preparation.
Compositions which can be crosslinked by means of free radical formation to give elastomers, are based on high-viscosity diorganopolysiloxanes and fillers and are crosslinked by addition of organic peroxides are known. To achieve favourable mechanical properties, such as good elongation at break and tear propagation resistance, mixtures of 2 to 3 different types of high-viscosity diorganopolysiloxanes having a different vinyl content and different siloxane units are employed. Reference may be made in this context to, for example, U.S. Pat. No. 3,652,475 and U.S. Pat. No. 3,660,345.
However, the use of different types of high-viscosity diorganopolysiloxanes has disadvantages in the logistics of the polymers and in the preparation of the compositions, in particular by continuous operation, since several metering pumps are required for the various polymers.
U.S. Pat. No. 2,803,619 describes compositions which can be crosslinked by means of free radical formation to form elastomers, comprise vinyl-free diorganopolysiloxanes and vinyl-containing, linear organopolysiloxanes having at least 12 silicon atoms and give elastomers having a low compression set.
There was the object of providing organopolysiloxane compositions which can be crosslinked by means of free radical formation to give elastomers and comprise a reduced number of high-viscosity diorganopolysiloxanes, with which the abovementioned disadvantages are avoided and with which elastomers having favorable mechanical properties, such as good elongation at break and tear propagation resistance, are obtained. The object is achieved by the invention.
The invention provides organopolysiloxane compositions which can be crosslinked by means of free radical formation to give elastomers and comprise
(1) high-viscosity diorganopolysiloxanes having a value of at least 3000 Nm determined in a Brabender Plastograph at 23.degree. C. and 60 revolutions per minute,
(2) low-viscosity vinyl-containing organopolysiloxanes having an average viscosity of 20 to 1.times.10.sup.6 mPa.multidot.s at 25.degree. C., consisting of siloxane units (M units) of the formulae radical having 1 to 18 carbon atoms per radical and R.sup.1 is a vinyl radical, with the proviso that the organopolysiloxanes contain at least 1.0% by weight of Si-bonded vinyl groups, and
(3) fillers.
The invention further provides a process for the preparation of the organopolysiloxane compositions which can be crosslinked by means of free radical formation to give elastomers, by mixing
(1) high-viscosity diorganopolysiloxanes with
(2) low-viscosity vinyl-containing organopolysiloxanes and
(3) fillers
The high-viscosity diorganopolysiloxanes used as
(1) in the compositions according to the invention are those of the general formula SiR.sub.3-z R.sub.z.sup.1 (I) 1 to 18 carbon atoms per radical, determined in the Brabender Plastograph at 23.degree. C. and 60 revolutions per minute is at least 3000 Nm.
Although not shown in formula (I), up to 1 mol % of the diorganopolysiloxane units can be replaced by other siloxane units, but usually only siloxane units which are present as impurities which are more or less difficult to avoid, such as R.sub.3 SiO.sub.1/2, RSiO.sub.3/2 and SiO.sub.4/2 units, in which R has the meaning given above for this radical.
Examples of radicals R are alkyl radicals, such as the methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl, neo-pentyl and tert-pentyl radical; hexyl radicals, such as the n-hexyl radical; heptyl radicals, such as the n-heptyl radical; octyl radicals, such as the n-octyl radical, and iso-octyl radicals, such as the 2,2,4-trimethylpentyl radical; nonyl radicals, such as the n-nonyl radical; decyl radicals, such as the n-decyl radical; dodecyl -radicals, such as the n-dodecyl radical; octadecyl radicals, such as the n-octadecyl radical; alkenyl radicals, such as

REFERENCES:
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patent: 3652475 (1972-03-01), Wada et al.
patent: 3660345 (1972-05-01), Bobear
patent: 4008198 (1977-02-01), Krohberger et al.
patent: 4725643 (1988-02-01), Burkhardt
patent: 5122562 (1992-06-01), Jeram et al.

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