Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2002-03-05
2004-02-10
Robertson, Jeffrey B. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S031000, C528S032000, C528S033000, C528S034000, C528S043000, C528S015000, C525S477000, C525S478000
Reexamination Certificate
active
06689859
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a cured silsesquioxane resin having high fracture toughness and strength without loss of elastic modulus. With more particularity the invention relates to a cured silsequioxane resin that includes a mixture of silanes or siloxanes as a cross-linking compound resulting in an improved fracture toughness.
BACKGROUND OF THE INVENTION
Silsesquioxane resins have seen increased use in industrial applications in transportation (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 toughness of silicone resins, there is an additional need to further improve the toughness of silicone materials for use in high strength applications, such as those described above.
Therefore, it is an object of this invention to provide a process that may be utilized to prepare a cured silsesquioxane resin having high fracture toughness with minimal loss of modulus.
SUMMARY OF THE INVENTION
A hydrosilylation reaction curable composition including a silsesquioxane polymer, a mixture of silanes or siloxanes as a cross-linking compound, and a hydrosilylation reaction catalyst.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
This invention relates to a hydrosilylation reaction curable composition that is used to prepare a cured silsesquioxane resin. This curable composition comprises: (A) a silsesquioxane copolymer, (B) a mixture of silanes or siloxanes as a cross-linker, (C) a compound catalyst, (D) an optional reaction inhibitor and (E) an optional solvent.
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 mixture of silanes and/or siloxanes that contain silicon hydride functionalities that will cross-link with the vinyl group of component (A). The silanes or siloxanes utilized in the mixture should have at least two Si—H or silicon hydride functionalities and can be represented by the general formula:
H
a
R
1
b
Si wherein a≧2 and R
1
is a hydrocarbon for the silane, and H
a
R
1
b
Si
c
O
(4c−a−b)/
2 for the siloxane where a≧2, b≧4, c≧2 and R
1
is a hydrocarbon.
Component B should comprise a mixture of silanes and/or siloxanes that exhibit a synergistic effect. Such a synergistic effect is exemplified by a cured silsesquioxane resin produced utilizing the mixture that has a greater fracture toughness than a cured resin produced utilizing any of the components of the mixture alone as the cross-linking compound.
The mixture preferably includes 2 components in which the components range from 20 to 80 molar % of the mixture and even more preferably from 30 to 70 in molar % of the mixture. An example of a preferred mixture of silanes and siloxanes, is a mixture of diphenyl silane and hexamethyltrisiloxane. Such compounds are commercially available from Gelast, Inc. of TulIt, Pa. and United Chemical Technologies, Inc. of Bristol, Pa.
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 1.0:1.0 to 1.5:1.0. Preferably, the ratio is in the range of 1.1:1.0 to 1.5:1.0. If the ratio is less than 1.0:1.0, the properties of the cured silsesquioxane resin will be compromised because curing will be incomplete. The amounts of components (A) and (B) in the composition will depend on the number of C═C and Si—H groups per molecule. However, the amount of component (A) is typically 50 to 80 weight % of the composition, and the amount of component (B) is typically 2 to 50 weight % of the composition.
Component (C) is a hydrosilylation reaction catalyst. Typically, component (C) is a platinum catalyst added to the composition in an amount sufficient to provide 1 to 100 ppm of platinum based on the weight of the composition. Component (C) is exemplified by platinum catalysts such as chloroplatinic acid, alcohol solutions of chloroplatinic acid, dichlorobis(triphenylphosphine)platinum(II), platinum chloride, platinum oxide, complexes of platinum compounds with unsaturated organic compounds such as olefins, complexes of platinum compounds with organosiloxanes containing unsaturated hydrocarbon groups, such as Karstedts catalyst (i.e. a complex of chloroplatinic acid with 1,3-divinyl-1,1,3,3-tetramethyldisiloxane) and 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane, and complexes of platinum compounds with organosiloxanes, wherein the complexes are embedded in organosiloxane resins. A particularly preferred catalyst is a 1% platinum-divinyltetramethyldisiloxane complex commercially available from Chemical Technologies, Inc. of Bristol, Pa.
Component (D) may include an optional catalyst inhibitor, typically added when a one part composition is prepared. Suitable inhibitors are disclosed in U.S. Pat. No. 3,445,420 to Kookootsedes et al., May 20, 1969, which is hereby incorporated by reference for the purpose of describing catalyst inhibitors. Component (D) is preferably an acetylenic alcohol such as methylbutynol or ethynyl cyclohexanol. Component (D) is more preferably ethynyl cyclohexanol. Other examples of inhibitors include diethyl maleate, diethyl fumamate, bis (2-methoxy-1-methylethyl) maleate, 1-ethynyl-1-cyclohexanol, 3,5-dimethyl-1-hexyn-3-ol, 2-phenyl-3-butyn-2-ol, N, N, N′, N′-tetramethylethylenediamine, ethylenediamine, diphenylphosphine, diphenyl
Katsoulis Dimitris E.
Keryk John R.
Li Zhongtao
McGarry Frederick J.
Zhu Bizhong
Clark Hill PLC
Dow Corning Corporation
Robertson Jeffrey B.
LandOfFree
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