Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-03-05
2003-11-11
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S588000, C528S015000, C528S025000, C528S031000, C528S032000
Reexamination Certificate
active
06646039
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for producing a cured silsesquioxane resin having high fracture toughness and strength without loss of elastic modulus and glass transition temperature. With more particularity the invention relates to a cured silsequioxane resin having colloidal silica having a surface coating formed thereon dispersed within the silsesquioxane resin.
BACKGROUND OF THE INVENTION
Silsesquioxane resins have seen increased use in industrial applications in the automotive, aerospace, naval and other manufacturing industries. Silsequioxane resins exhibit excellent heat and fire resistant properties that are desirable for such applications. These properties make the silsesquioxane resins attractive for use in fiber-reinforced composites for electrical laminates, structural use in automotive components, aircraft and naval vessels; Thus, there exists a need for rigid silsesquioxane resins having increased flexural strength, flexural strain, fracture toughness, and fracture energy, without significant loss of modulus or degradation of thermal stability. In addition, rigid silsesquioxane resins have low dielectric constants and are useful as interlayer dielectric materials. Rigid silsesquioxane resins are also useful as abrasion resistant coatings. These applications require that the silsesquioxane resins exhibit high strength and toughness.
Conventional thermoset networks of high cross-link density, such as silsesquioxane resins, typically suffer from the drawback that when measures are taken to improve a mechanical property such as strength, fracture toughness, or modulus, one or more of the other properties suffers a detriment.
Various methods and compositions have been disclosed in the art for improving the mechanical properties of silicone resins including: 1) modifying the silicone resin with a rubber compound, as disclosed in U.S. Pat. No. 5,747,608 which describes a rubber-modified resin and U.S. Pat. No. 5,830,950 which describes a method of making the rubber-modified resin; 2) adding a silicone fluid to a silicone resin as disclosed in U.S. Pat. No. 5,034,061 wherein a silicone resin/fluid polymer is adapted to form a transparent, shatter-resistant coating.
While the above referenced patents offer improvements in the strength of silicone resins, there is an additional need to further improve the strength and toughness of silicone materials for use in high strength applications, such as those described above. There is also a strong need to further increase the strength, toughness, modulus and to raise the glass transition temperature simultaneously.
Therefore, it is an object of this invention to provide a process that may be utilized to prepare a cured silsesquioxane resin having high strength and fracture toughness without loss of modulus and glass transition temperature. It is also an object of the invention to provide a process to prepare a cured silsesquioxane resin having simultaneously increased strength, toughness, modulus with an increased glass transition temperature.
SUMMARY OF THE INVENTION
A hydrosilylation reaction curable composition including a silsesquioxane polymer, a cross-linking compound, a hydrosilylation reaction catalyst and colloidal silica having a surface coating formed thereon.
There is also included a process for preparing a hydrosilyation reaction curable composition and producing a cured silsesquioxane resin comprising the steps of:
a) providing a silsesquioxane polymer;
b) providing a cross-linking compound;
c) providing colloidal silica with a surface treatment formed thereon;
d) mixing the components of a), b), c) to form a curable composition;
e) adding a hydrosilylation reaction catalyst to the curable composition of step d)
f) curing the curable composition of step e) to form a cured resin having high fracture toughness and strength without the loss of elastic modulus and glass transition temperature.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
This invention relates to a hydrosilylation reaction curable composition and process that is used to prepare a cured silsesquioxane resin. This curable composition comprises: (A) a silsesquioxane copolymer, (B) a silicon hydride containing hydrocarbon, silane or siloxane as a crosslinker, (C) a catalyst, (D) an optional solvent (E) a catalyst inhibitor and (F) colloidal silica having a surface coating of various compositions formed thereon.
Component (A) is a silsesquioxane copolymer comprising units that have the empirical formula R
1
a
R
2
b
R
3
c
SiO
(4-a-b-c)/2
, wherein: a is zero or a positive number, b is zero or a positive number, c is zero or a positive number, with the provisos that 0.8≦(a+b+c)≦3.0 and component (A) has an average of at least 2 R
1
groups per molecule, and each R
1
is independently selected from monovalent hydrocarbon groups having aliphatic unsaturation, and each R
2
and each R
3
are independently selected from monovalent hydrocarbon groups and hydrogen. Preferably, R
1
is an alkenyl group such as vinyl or allyl. Typically, R
2
and R
3
are nonfunctional groups selected from the group consisting of alkyl and aryl groups. Suitable alkyl groups. include methyl, ethyl, isopropyl, n-butyl, and isobutyl groups. Suitable aryl groups include phenyl groups. Suitable silsesquioxane copolymers for component (A) are exemplified by (PhSiO
3/2
)
0.75
(ViMe
2
SiO
1/2
)
0.25
, where Ph is a phenyl group, Vi represents a vinyl group, and Me represents a methyl group.
Component (B) is a silicon hydride containing hydrocarbon having the general formula H
a
R
1
b
SiR
2
SiR
1
c
H
d
where R
1
is a monovalent hydrocarbon group and R
2
is a divalent hydrocarbon group and where a and d≧1, and a+b=c+d=3. The general formula H
a
R
1
b
SiR
2
SiR
1
c
H
d
although preferred in the present invention is not exclusive of other hydrido silyl compounds that can function as cross-linkers of the component (A). Specifically a formula such as the above, but where R
2
is a trivalent hydrocarbon group can also be suitable as component (B). Other options for component (B) can be mixtures of hydrido-silyl compounds as well.
Suitable silicon hydride containing hydrocarbons of component (B) can be prepared by a Grignard reaction process. For example, one method for making a silyl-terminated hydrocarbon for use in this invention includes heating to a temperature of room temperature to 200° C., preferably 50° C., a combination of magnesium and a solvent such as diethylether or tetrahydrofuran. A di-halogenated hydrocarbon, such as dibromobenzene is then added to the magnesium and solvent over a period of several hours.
After complete addition of the di-halogenated hydrocarbon, a halogenated silane, such as dimethylhydrogenchlorosilane, is then added, and an optional organic solvent can also be added. The resulting mixture is then heated for a period of several hours at a temperature of 50 to 65° C. Any excess halogenated silane is then removed by any convenient means, such as neutralization with a saturated aqueous solution of NH
4
Cl. The resulting product can then be dried with a drying agent such as magnesium sulfate and then purified by distillation.
An example of such a silicon hydride containing hydrocarbon produced by a Grignard reaction includes p-bis(dimethylsilyl)benzene which is commercially available from Gelest, Inc. of Tullytown, Pa.
Component (B) may also be a silane or siloxane that contain silicon hydride functionalities that will cross-link with the vinyl group of component (A). Examples of suitable silanes and siloxanes that may be utilized as component (B) include di phenylsilane and hexamethyltrisiloxane. Such compounds are commercially available from Gelast, Inc. of Tullytown, Pa. and United Chemical Technologies of Bristol, Pa. Component (B) can also be mixtures of hydrido containing silane and siloxanes.
Components (A) and (B) are added to the composition in amounts such that the molar ratio of silicon bonded hydrogen atoms (SiH) to unsaturated groups (C═C) (SiH:C═C) ranges from 1.0:1
Bergstrom Debora F.
Katsoulis Dimitris E.
Keryk John R.
Kwan Kermit S.
Li Zhongtao
Clark Hill PLC
Dawson Robert
Dow Corning Corporation
Zimmer Marc S.
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