Compositions: ceramic – Ceramic compositions – Carbide or oxycarbide containing
Reexamination Certificate
1999-06-21
2001-05-01
Dawson, Robert (Department: 1712)
Compositions: ceramic
Ceramic compositions
Carbide or oxycarbide containing
C501S049000, C501S097200, C522S075000, C522S077000, C522S079000, C522S148000, C525S474000, C525S477000, C525S478000, C528S005000, C528S015000, C528S031000, C528S032000
Reexamination Certificate
active
06225247
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to cross-linked polymers and in particular to polymer precursor compositions, and polymers, thermosets and ceramics made by reacting silyl/siloxyl substituted carboranes having unsaturated organic end groups with hydrosilanes and hydrosiloxanes.
2. Description of the Related Art
The search for high temperature oxidatively stable materials has led to the development of organoboron polymers, particularly silyl or siloxyl polymers containing carboranyl and acetylenic groups incorporated into the polymer backbone. Polymers that include carboranyl, silyl or siloxyl and acetylenic groups in the same polymeric chain combine the desirable features of both inorganics and organics: the carborane groups provide thermal and oxidative stability, the silane or siloxane groups provide chain flexibility and the acetylenic groups allow cross-linking of adjacent polymer strands to form thermosets. The acetylene groups remain inactive during processing at lower temperatures and react either thermally or photochemically to form conjugated polymeric cross-links without the evolution of volatiles. Carborane-silane/siloxane-acetylene polymers have the advantage of being extremely easy to process and convert into thermosets or ceramics since they are either liquids at room temperature or low melting solids and are soluble in most organic solvents. The polymers are thus well-suited to serve as ceramic or thermoset polymeric precursors.
Thermoset polymers that include carborane, silane or siloxane and acetylene units are disclosed in U.S. Pat. No. 5,272,237; U.S. Pat. No. 5,292,779; U.S. Pat. No. 5,348,917; U.S. Pat. No. 5,483,017, and U.S. Pat. No. 5,681,870, each incorporated herein by reference in its entirety and for all purposes. The thermoset polymers described in U.S. Pat. Nos. 5,272,237; 5,292,779 and 5,348,917 are made from linear polymer precursors that include repeating units containing carborane-silane/siloxane-acetylene or related groups. The thermoset polymers described in U.S. Pat. No. 5,483,017 are made from linear polymer precursors that include, on each strand, both repeating units of carborane-silane/siloxane-acetylene or related groups and repeating units of siloxane/silane-acetylene or related groups. U.S. Pat. No. 5,681,870 describes a linear polymer with randomly distributed carborane, silane/siloxane and acetylene units. U.S. Pat No. 5,348,917, U.S. Pat. No. 5,483,017 and U.S. Pat. No. 5,681,870 further disclose boron-arbonsilicon ceramics made by pyrolyzing carborane-silane/siloxane-acetylene thermoset polymers.
While these polymers show outstanding thermal and thermo-oxidative stabilities, their use is limited due to the high cost and limited availability of carboranes and the high cost of dilithiated acetylenes used in making the polymers.
U.S. Pat. No. 5,679,818, incorporated herein by reference, describes compounds of the formula R
1
—Ac
1
—Ar
1
—M—Ar
2
—Ac
2
—R
2
, wherein M is a silyl/siloxyl substituted carborane, Ar
1
and Ar
2
are aromatic groups, and Ac
1
and Ac
2
are alkynyl groups. The compounds are described as being useful as precursors for thermosets. Synthesis of these compounds involves the steps of attaching aromatic groups Ar
1
and Ar
2
to the silyl/siloxyl group and then attaching the alkynyl-containing groups R
1
—Ac
1
— and R
2
—Ac
2
— to the aromatic groups.
SUMMARY OF THE INVENTION
Silyl or siloxyl substituted carboranes have now been made with unsaturated organic end groups attached directly to the silanes or siloxanes on the terminal ends of the compounds. These compounds can be made by a relatively simple reaction scheme and can be used as crosslinkers in other polymer systems such as hydrosilanes and hydrosiloxanes to impart strength and thermal/oxidative stability to these polymers. Thermoset polymers can be formed by partially crosslinking silyl or siloxyl substituted carboranes having acetylene end groups and then further curing of the partially crosslinked polymer. Ceramics can be formed by crosslinking silyl or siloxyl substituted carboranes and then pyrolyzing the crosslinked polymer.
Accordingly, the invention is directed to a precursor composition comprising:
(1) at least one crosslinking compound represented by the formula:
wherein:
(a) u and x are independently selected positive integers;
(b) v and w are independently selected integers greater than or equal to zero;
(c) R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
and R
8
are independently selected from the group consisting of alkyl, aryl, alkylaryl, haloalkyl, haloaryl and mixtures thereof;
(d)
represents a carboranyl group;
(e) q and q′ are integers from 3 to 16;
(f) A and E are independently selected from the group consisting of O, an aliphatic bridge, an aryl bridge and mixtures thereof; and
(g) R
9
and R
10
are independently selected from the group consisting of
wherein R
11
, R
12
and R
13
are independently selected and are H, alkyl, aryl or silyl and
wherein R
14
is H, alkyl or aryl, p
1
(2) at least one silicon hydride-containing organosilicon compound containing at least two silicon hydride moieties per molecule, and
(3) a hydrosilation catalyst.
The invention is further directed to a cross-linked polymer formed by reacting the crosslinking compound of formula I with the silicon hydride-containing organosilicon compound by way of a hydrosilation reaction. The invention is further directed to a thermoset polymer formed by thermally further curing of the crosslinked polymer. The invention is further directed to a boron-carbon-silicon ceramic formed by pyrolyzing the thermoset polymer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The crosslinking compounds used in the present invention are carborane-silane/siloxane compounds having unsaturated organic end groups, as represented by the formula:
wherein: u and x are independently selected positive integers, v and w are independently selected integers greater than or equal to zero, R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
and R
8
are independently selected from the group consisting of alkyl, aryl, alkylaryl, haloalkyl, haloaryl and mixtures thereof; A and E are independently selected from the group consisting of O, an aliphatic bridge, an aryl bridge and mixtures thereof; and R
9
and R
10
are independently selected from the group consisting of
wherein R
11
, R
12
and R
13
are independently selected and are H, alkyl, aryl or silyl, and
wherein R
14
is H, alkyl, aryl or silyl.
Particular values for u, v, w and x, and particular choices for the side chains R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, R
8
, the linking groups A and E and the end groups R
9
, R
10
, R
11
, R
12
, R
13
and R
14
may be selected according to particular properties desired for the compound and for polymers made using the compound. For example, increasing the number of silane or siloxane groups (increasing u, v, w and x) would lower the melting point of the compound and increase the chain flexibility. Using larger alkyl groups for the side chains R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, R
8
would increase the solubility of the compound in organic solvents and increase the hydrophobicity and decrease the thermo-oxidative stability of polymers made using the compound. Using aryl groups for the side chains R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, R
8
would increase the stiffness and slightly increase the thermo-oxidative stability of polymers made using the compound. Using aryl linking groups for A and E would add considerable stiffness to polymers made from the compound, but would decrease the thermo-oxidative stability as compared to using oxygen for the linking group. Using alkyl groups for A and E would give similar mechanical properties as using oxygen, but would result in a decreased thermo-oxidative stability.
The selection of particular end groups for R
9
and R
10
and the particular choices for R
11
, R
12
, R
13
and R
14
affect the rate of hydrosilation and curing of the compound. For example, vinyl groups typically cure faster than et
Houser Eric J.
Keller Teddy M.
Dawson Robert
Karasek John J.
Ketner Philip
Robertson Jeffrey B.
The United States of America as represented by the Secretary of
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