Extrudable silicone elastomer compositions

• US 4,427,801 A
• Filed: 06/03/1983
• Issued: 01/24/1984
• Est. Priority Date: 04/14/1982
• Status: Expired due to Term

• Current Assignee: Dow, Inc.
• Original Assignee: Dow, Inc.
• Inventors: Sweet, Randall P.
• Primary Examiner(s): Jacobs, Lewis T.
• Application Number:
  US06/500,012
• Time in Patent Office: 235 Days
• Field of Search: 524/862, 524/906, 523/212
• US Class Current: 523/212
• CPC Class Codes: C08G 77/12 containing silicon bound to hydrogen C08G77/045 takes precedence
• CPC Class Codes: C08G 77/20 containing silicon bound to unsaturated aliphatic groups C08G77/045 takes precedence
• CPC Class Codes: C08G 77/70 Siloxanes defined by use of the MDTQ nomenclature
• CPC Class Codes: C08L 2666/54 Inorganic substances
• CPC Class Codes: C08L 83/00 Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
• CPC Class Codes: C08L 83/04 Polysiloxanes
• CPC Class Codes: Y10S 524/906 Multipackage compositions

Abstract

This invention provides organopolysiloxane elastomers exhibiting a desirable combination of high durometer hardness, tensile strength and tear strength, and a level of heat stability sufficient to retain these properties following prolonged exposure to temperatures above 150° C. The elastomers are prepared by curing a vinyl endblocked polydiorganosiloxane, an organopolysiloxane resin having a specified concentration of vinyl groups, a treated silica filler containing vinylsiloxy groups bonded to the silica particles and a organohydrogenpolysiloxane in the presence of a suitable platinum catalyst.

Claims

1. An elastomeric organopolysiloxane obtained by curing an extrudable, curable composition consisting essentially of

(1) 100 parts by weight of a liquid triorganosiloxy endblocked polydiorganosiloxane exhibiting a viscosity of from 5,000 to 200,000 centipoises at 25°

C., wherein the triorganosiloxy groups are vinyldimethylsiloxy or vinylmethylphenylsiloxy and at least 95% of the diorganosiloxane groups are dimethylsiloxane;

(2) from 20 to 60 parts by weight of finely divided amorphous silica particles having a surface area greater than 100 square meters per gram, wherein at least a portion of the silicon atoms on the surface of the particles are bonded to trimethylsiloxy groups and vinyl-containing siloxy groups selected from the group consisting of

(a) CH₂ ═

CH(CH₃)₂ SiO[(CH₃)₂ SiO--_x

(b) CH₂ ═

CH(CH₃) (C₆ H₅)SiO[(CH₃)₂ SiO--_x where the average value of x is from 0 to 20, and

(c) organosiloxy groups consisting essentially of repeating units of the general formulae ##STR4## the total number of repeating units in each organosiloxy group being from 2 to about 20, and the molar ratio of dimethylsiloxy units to methylvinylsiloxy units having an average value of from 1;

1 to 5;

1, the relative concentrations of trimethylsiloxy and vinyl-containing siloxy groups being sufficient to provide (1) from 0.01 to 0.5 percent of vinyl groups, based on the weight of silica, and (2) from 1 to 100 moles of trimethylsiloxy groups for each mole of vinyl-containing siloxy groups;

(3) from 10 to 50 parts of a organopolysiloxane resin consisting essentially of

(d) R₂¹ (CH₂ ═

CH--SiO₀.5 units,

(e) R₃² SiO₀.5 units and

(f) SiO_4/2 units wherein the molar ratio of the combination of (d) and (e) units to (f) units is from 0.6 to 1.1, and the concentration of (d) units is from 0.2 to 8% based on the weight of said organopolysiloxane resin, and R¹ and R² are alkyl containing from 1 to 4 carbon atoms or phenyl, with the proviso that at least 95% of the R¹ and R² groups are methyl;

(4) a liquid organohydrogensiloxane in an amount sufficient to provide from 1 to 3 silicon-bonded hydrogen atoms per vinyl group present in components (1), (2) and (3) combined, said organohydrogensiloxane having an average of at least three silicon-bonded hydrogen atoms per molecule and consisting essentially of units selected from the group consisting of methylhydrogensiloxy, dimethylsiloxy, dimethylhydrogensiloxy, trimethylsiloxy and SiO_4/2 units; and

(5) a platinum-containing catalyst in sufficient amount to provide at least 0.1 part by weight of platinum per million parts by weight of said triorganosiloxy endblocked polydiorganosiloxane.

2. An elastomeric organopolysiloxane according to claim 1 wherein the triorganosiloxy endblocked polydiorganosiloxane (1) exhibits a viscosity from 35,000 to 75,000 centipoises and is represented by the formula ##STR5## where R⁴ is methyl or phenyl and R⁵ and R⁶ are individually methyl, ethyl, propyl or phenyl, with the proviso that at least 95% of the R⁵ and R⁶ groups are methyl and n has an average value from 650 to 1000;

the surface area of the silica particles (2) is from 120 to 600 square meters per gram;

the silicon atoms on the surface of the silica particles are bonded to organosiloxane groups of the formula (CH₃)₃ SiO-- and groups consisting essentially of repeating units of the general formulae ##STR6## in a molar ratio of from 1;

1 to 2;

1, respectively; and

the concentration of silica particles is from 30 to 40 parts by weight;

the organopolysiloxane resin (3) contains at least two vinyl groups per molecule and the molar ratios of (d) units;

(e) units;

(f) units are within the range 5-10;

40-45;

45-50, with the proviso that the concentration of (d) units does not exceed about 8%, based on resin weight;

the organohydrogen siloxane (4) contains at least 4 silicon-bonded hydrogen atoms per molecule; and

the platinum-containing catalyst (5) is a reaction product of chloroplatinic acid and sym-divinyltetramethyl disiloxane.

3. An elastomeric organopolysiloxane according to claim 2 wherein in (1) R⁴, R⁵ and R⁶ are methyl;

all of the groups represented by R¹ and R² in the organopolysiloxane resin (3) are methyl;

the organohydrogen siloxane (4) is a trimethylsiloxy terminated polymethylhydrogensiloxane; and

the concentration of platinum-containing catalyst (5) is equivalent to from 5 to 50 parts by weight Pt per million parts of the triorganosiloxy endblocked polydiorganosiloxane.

4. An elastomeric organopolysiloxane according to claim 3 where the concentration of vinyl groups present in the organosiloxane groups bonded to the silica particles is from 0.05 to 0.5%, based on the weight of sand particles;

the organopolysiloxane resin contains 0.8 mole of trimethylsiloxane units and 0.09 mole (CH₃)₂ CH₂ ═

CH--SiO₀.5 units for each mole of SiO_4/2 units; and

the concentration of the organopolysiloxane resin is from 15 to 30 parts by weight.

5. An elastomeric organopolysiloxane according to claim 1 where said extrudable, curable composition contains a platinum catalyst inhibitor in an amount sufficient to inhibit curing of the curable composition at ambient temperature.

6. An elastomeric organopolysiloxane according to claim 5 where said platinum catalyst inhibitor is selected from the group consisting of acetylenic alcohols, olefinic siloxanes and polymethylvinylcyclosiloxanes having three to six methylvinylsiloxane units per molecule.

7. An elastomeric organopolysiloxane according to claim 6 where said platinum catalyst inhibitor is an acetylenic alcohol.

8. An elastomeric organopolysiloxane according to claim 7 where the acetylenic alcohol is 2-methyl-3-butyn-2-ol.

9. An elastomeric organopolysiloxane according to claim 1, 2, 3 or 4 where the organopolysiloxane exhibits a tear strength greater than 40 kilonewtons/meter and a Shore A durometer hardness greater than 65.

10. An elastomeric organopolysiloxane according to claim 1 where the curable composition is post cured at a temperature above 150°

C.

11. An extrudable, curable composition consisting essentially of

(1) 100 parts by weight of a liquid triorganosiloxy endblocked polydiorganosiloxane exhibiting a viscosity of from 5,000 to 200,000 centipoises at 25°

C., wherein the triorganosiloxy groups are vinyldimethylsiloxy or vinylmethylphenylsiloxy and at least 95% of the diorganosiloxane groups are dimethylsiloxane;

(2) from 20 to 60 parts by weight of finely divided amorphous silica particles having a surface area greater than 100 square meters per gram, wherein at least a portion of the silicon atoms on the surface of the particles are bonded to trimethylsiloxy groups and vinyl-containing siloxy groups selected from the group consisting of

(a) CH₂ ═

CH(CH₃)₂ SiO[(CH₃)₂ SiO--_x

(b) CH₂ ═

CH(CH₃) (C₆ H₅)SiO[(CH₃)₂ SiO--_x where the average value of x is from 0 to 20, and

(c) organosiloxy groups consisting essentially of repeating units of the general formulae ##STR7## the total number of repeating units in each organosiloxy group being from 2 to about 20, and the molar ratio of dimethylsiloxy units to methylvinylsiloxy units having an average value of from 1;

1 to 5;

1, the relative concentrations of trimethylsiloxy and vinyl-containing siloxy groups being sufficient to provide (1) from 0.01 to 0.5 percent of vinyl groups, based on the weight of silica, and (2) from 1 to 100 moles of trimethylsiloxy groups for each mole of vinyl-containing siloxy groups;

(3) from 10 to 50 parts of a organopolysiloxane resin consisting essentially of

(d) R₂¹ (CH₂ ═

CH--SiO₀.5 units,

(e) R₃² SiO₀.5 units and

(f) SiO_4/2 units wherein the molar ratio of the combination of (d) and (e) units to (f) units is from 0.6 to 1.1, and the concentration of (d) units is from 0.2 to 8% based on the weight of said organopolysiloxane resin, and R¹ and R² are alkyl containing from 1 to 4 carbon atoms or phenyl, with the proviso that at least 95% of the R¹ and R² groups are methyl;

(4) a liquid organohydrogensiloxane in an amount sufficient to provide from 1 to 3 silicon-bonded hydrogen atoms per vinyl group present in components (1), (2) and (3) combined, said organohydrogensiloxane having an average of at least three silicon-bonded hydrogen atoms per molecule and consisting essentially of units selected from the group consisting of methylhydrogensiloxy, dimethylsiloxy, dimethylhydrogensiloxy, trimethylsiloxy and SiO_4/2 units; and

(5) a platinum-containing catalyst in sufficient amount to provide at least 0.1 part by weight of platinum per million parts by weight of said triorganosiloxy endblocked polydiorganosiloxane.

12. An extrudable composition according to claim 11 wherein the triorganosiloxy endblocked polydiorganosiloxane (1) exhibits a viscosity from 35,000 to 75,000 centipoises and is represented by the formula ##STR8## where R⁴ is methyl or phenyl and R⁵ and R⁶ are individually methyl, ethyl, propyl or phenyl, with the proviso that at least 95% of the R⁵ and R⁶ groups are methyl and n has an average value from 650 to 1000;

the surface area of the silica particles (2) is from 120 to 600 square meters per gram;

the silicon atoms on the surface of the silica particles are bonded to organosiloxane groups of the formula (CH₃)₃ SiO-- and groups consisting essentially of repeating units of the general formulae ##STR9## in a molar ratio of from 1;

1 to 2;

1, respectively; and

the concentration of silica particles is from 30 to 40 parts by weight;

the organopolysiloxane resin (3) contains at least two vinyl groups per molecule and the molar ratios of (d) units;

(e) units;

(f) units are within the range 5-10;

40-45;

45-50, with the proviso that the concentration of (d) units does not exceed about 8%, based on resin weight;

the organohydrogen siloxane (4) contains at least 4 silicon-bonded hydrogen atoms per molecule; and

the platinum-containing catalyst (5) is a reaction product of chloroplatinic acid and sym-divinyltetramethyl disiloxane.

13. An extrudable composition according to claim 12 wherein in (1) R⁴, R⁵ and R⁶ are methyl;

all of the groups represented by R¹ and R² in the organopolysiloxane resin (3) are methyl;

the organohydrogen siloxane (4) is a trimethylsiloxy terminated polymethylhydrogensiloxane; and

the concentration of platinum-containing catalyst (5) is equivalent to from 5 to 50 parts by weight Pt per million parts of the triorganosiloxy endblocked polydiorganosiloxane.

14. An extrudable composition according to claim 13 where the concentration of vinyl groups present in the organosiloxane groups bonded to the silica particles is from 0.05 to 0.5%, based on the weight of sand particles;

the organopolysiloxane resin contains 0.8 mole of trimethylsiloxane units and 0.09 mole (CH₃)₂ CH₂ ═

CH--SiO₀.5 units for each mole of SiO_4/2 units; and

the concentration of the organopolysiloxane resin is from 15 to 30 parts by weight.

15. An extrudable composition according to claim 11 where said extrudable, curable composition contains a platinum catalyst inhibitor in an amount sufficient to inhibit curing of the curable composition at ambient temperature.

16. An extrudable composition according to claim 15 where said platinum catalyst inhibitor is selected from the group consisting of acetylenic alcohols, olefinic siloxanes and polymethylvinylcyclosiloxanes having three to six methylvinylsiloxane units per molecule.

17. An extrudable composition according to claim 16 where said platinum catalyst inhibitor is an acetylenic alcohol.

18. An extrudable composition according to claim 17 where the acetylenic alcohol is 2-methyl-3-butyn-2-ol.

19. An extrudable composition according to claim 11 where the organopolysiloxane exhibits a tear strength greater than 40 kilonewtons/meter and a Shore A durometer hardness greater than 65.

20. An extrudable composition according to claim 11 where the curable composition is post cured at a temperature above 150°

C.