[0001] The subject invention relates to thermosetting resin systems which contain certain
secondary amine-terminated siloxane modifiers. The modified resins find uses as heat-curable
matrix resins in fiber-reinforced prepregs, as laminating films, and as structural
adhesives.
[0002] Modern high-performance thermosetting resin systems contain a variety of heat-curable
resins. Among these are epoxy resins, maleimide-group-containing resins, and the cyanate
resins. All these resins are noted for their high tensile and compressive strengths
and their ability to retain these properties at elevated temperatures, and all find
extensive use in the aerospace and transportation industries. Other thermosetting
systems which may be useful at lower temperatures or for specific applications include
the polyurethanes, polyureas, polyacrylics, and unsaturated polyesters.
[0003] Unfortunately, many of these resin systems tend to be brittle. Thus while exhibiting
high strengths under constant or slowly changing stress/strain, these systems and
the structures which contain them may be susceptible to impact-induced damage. It
would be desirable to prepare matrix resin and adhesive formulations which maintain
their high strength properties while having enhanced toughness.
[0004] In the past, functionalized elastomers such as the amino- or carboxy-terminated butadiene-acrylonitrile
copolymers (ATBN and CTBN, respectively) available from B.F. Goodrich Corp. under
the trademark HYCAR® have been used with some degree of success in toughening both
adhesive and matrix resin formulations. See, for example, the article by J. Riffle,
et. al., entitled "Elastomeric Polysiloxane Modifiers" in
Epoxy Resin Chemistry II, R. Bauer, Ed., ACS Symposium Series No. 221, American Chemical Society, and the
references cited therein.
[0005] The use of ATBN elastomers having carbon backbones, while increasing toughness, does
not provide sufficient thermal and/or oxidative stability for many modern applications
of adhesives and matrix resins, particularly those in the aerospace field. Thus it
has been proposed to utilize functionalized polysiloxanes for these applications,
relying on the thermal-oxidative stability of the silicon-containing backbone to lend
increased thermal stability to the total resin system. Several such approaches have
been discussed in Riffel,
supra, and involve primary amine terminated polysiloxanes such as bis(3-aminopropyl)polysiloxanes
and secondary amine terminated polysiloxanes such as bis(piperazinyl)polysiloxanes.
[0006] Perhaps due to their lower functionality, the secondary amine terminated, piperazinyl
polysiloxanes generally proved to have superior physical properties compared to the
primary amine terminated polysiloxanes (tetrafunctional). Unfortunately, these secondary
amine terminated polysiloxanes are difficult to prepare.
[0007] One preparation of piperazinyl functionalized polysiloxanes involves reaction of
2-aminoethylpiperazine with a previously synthesized carboxy-terminated polysiloxane
to form the bis(2-piperazinyl ethyl amide) of the polysiloxane:
[0008] A second approach is to react a large excess (to avoid polymer formation) of piperazine
with a bis-epoxy polysiloxane, producing a bis(2-hydroxy-3-piperazinyl) polysiloxane:
This method, of course, requires prior preparation of the epoxy-functional polysiloxane.
[0009] Ryang, in U.S. Patent 4,511,701, prepared both primary and secondary amine-terminated
polysiloxanes by reacting an appropriately substituted diamine with difunctional silylnorbornane
anhydrides, themselves prepared as disclosed by Ryang in U.S. Patent 4,381,396. Reaction
of these diamines with the bis(anhydride) functional polysiloxanes results in amino-imides
such as:
[0010] Only the last-mentioned process produces amino-functional polysiloxanes which are
truly difunctional. The amide hydrogen and hydroxyl hydrogen produced by the first
two preparations, though less reactive than the secondary amino hydrogens, are nevertheless
reactive species in most resin systems. Their presence, therefore can cause further,
and at times unpredictable crosslinking, either over an extended period of time in
normal service, or as a result of high curing temperatures.
[0011] Furthermore, all of the foregoing preparations involve many steps, and in the process
consume large quantities of relatively expensive chemical reagents. All these prior
art products are difficult to prepare, expensive products, and thus there remains
a need for thermally stable, secondary amine terminated polysiloxanes which may be
prepared in high yield and in an economic manner.
[0012] It has now been found that the use of certain secondary amine-functionalized organosilicones
may be used to modify a wide variety of thermosetting resin systems. These secondary
amine-functionalized organosilicones may be used as reactive modifiers in any resin
system which contains chemical groups which are reactive towards secondary amino groups.
Alternatively, the secondary amine-functionalized organosilicones may be prereacted
with a monomeric, oligomeric, or polymeric reagent to form a "prereact" which is compatible
but not necessarily reactive with the primary resin. Such modified resins display
considerably enhanced toughness while maintaining their elevated temperature performance.
Adhesives formulated with such modifiers show surprisingly enhanced lap shear strengths.
[0013] These modifiers may be readily prepared in quantitative or nearly quantitative yields,
by reacting a secondary N-allylamine corresponding to the formula:
or an analogous secondary N-(γ-butenyl)- or N-(δ-pentenyl)amine with an Si-H functional
organosilicone, preferably a 1,1,3,3-tetrasubstituted disiloxane or silane functional
persubstituted polysiloxane, in the presence of a suitable catalyst. In the disclosure
which follows, references to the reaction of secondary N-allylamines should be taken
to include, where appropriate, the corresponding reaction of secondary-N-(γ-butenyl)amines
and secondary-N-(δ-pentenyl)amines. Higher molecular weight polysiloxanes may be prepared
by the equilibrium polymerization of the product of the above reaction with additional
siloxane monomer to form secondary amine-functionalized homopolymers of higher molecular
weight, or block or heteric organosilicones which correspond to the general formula
wherein each R¹ may be individually selected from the group consisting of alkyl,
preferably C₁-C₁₂ lower alkyl; alkoxy, preferably C₁-C₁₂ lower alkoxy; acetoxy; cyanoalkyl;
halogenated alkyl; and substituted or unsubstituted cycloalkyl, aryl, and aralkyl;
wherein k is an integer from 3 to 5, preferably
wherein R³ is selected from the group consisting of alkyl, preferably C₁-C₁₂ lower
alkyl; alkoxy, preferably C₁-C₁₂ lower alkoxy; acetoxy; cyanoalkyl; halogenated alkyl;
cycloalkyl; aryl; and aralkyl; wherein m is a natural number from 1 to about 10,000
preferably from 1 to about 500; wherein n is a natural number such that the sum of
m+n is from about 1 to 10,000, preferably from 1 to about 1000, and more preferably
from 1 to about 500; and wherein at least one of R¹ or Y is
wherein k is an integer from 3 to 5. Most preferably, the secondary amino functional
organosilicones are bis[secondary γ-amino-functionalized] organosilicones which correspond
to the formula
where R may be a substituted or unsubstituted alkyl, cycloalkyl, aryl, or aralkyl
group which does not carry a primary amino group, and where each R¹ may be individually
selected from cyano, alkyl halogenated alkyl, preferably C₁-C₁₂ lower alkyl, alkoxy,
preferably C₁-C₁₂ lower alkoxy, acetoxy, cycloalkyl, aryl, or aralkyl groups, and
wherein m is an integer from 1 to about 10,000, preferably 1 to about 500.
[0014] As indicated, the R¹ substituents may be the same as each other, or may be different.
The phrase "may be individu ally selected," or similar language as used herein, indicates
that individual R¹s may be the same or different from other R¹ groups attached to
the same silicon atom, or from other R¹ groups in the total molecule. Furthermore,
the carbon chain of the ω-aminoalkylene-functional organosilicone may be substituted
by inert groups such as alkyl, cycloalkyl, aryl, arylalkyl, and alkoxy groups. References
to secondary aminopropyl, aminobutyl, and aminopentyl groups include such substituted
ω-aminoalkyl groups.
[0015] In addition to the preferred bis(N-substituted, secondary aminopropyl)polysiloxanes,
tris- or higher analogues may also be prepared by the subject process if branched
or multi-functional siloxanes are utilized. Such higher functionality secondary amino-functionalized
siloxanes, for example, may be useful as curing agents with resins of lesser functionality.
Monofunctional N-substituted, secondary 4-aminobutyl-, 5-aminopentyl, and 3-aminopropylsiloxanes
may also be prepared. Such monofunctional siloxanes have uses as reactive modifiers
in many polymer systems.
[0016] The secondary-amine-functional organosilicone modifiers of the subject invention
may be prepared through the reaction of an N-allyl secondary amine with an Si-H functional
organosilicone. In the discussion which follows, references to organosilicone reactants,
in general, are intended to include silanes and di- and polysiloxanes which have Si-H
functionality. The preferred reaction may be illustrated as follows:
[0017] Of course, by varying the nature of the Si-H functional organosilicone, a variety
of products may be obtained. For example, a polysiloxane having one or more pendant
secondary amino functionalities may be prepared readily from an Si-H functional cyclic
siloxane:
[0018] A wide variety of allylamines and corresponding γ-butenyl and δ-pentenylamines are
useful in this synthesis. However, as is well known, amines such as the secondary
alkylamines, for example dimethylamine and dipropylamine, as well as (primary) allylamine
itself, fail to react in a satisfactory and reproducible manner. For example, U.S.
Patent 3,665,027 discloses the reaction of allylamine with a monofunctional hydrogen
alkoxysilane. Despite the presence of the activating alkoxy groups and exceptionally
long reaction times, the reaction provided at most an 85 percent yield. Furthermore,
the reaction produces considerable quantities of potentially dangerous peroxysilanes
as by-products. For these reasons, the preparation disclosed is not a desirable one
for producing even monofunctional γ-aminopropyl trialkoxy siloxanes. Attempts to
utilize the reaction for the preparation of higher functionality siloxanes, particularly
alkyl-substituted siloxanes such as the poly(dimethyl)silicones, have not proven successful.
It is also known that use of vinylamine leads only to intractable products of unspecified
composition.
[0019] One reason that such processes produce poor and irreproducible results is the well
known fact that primary amines poison platinum catalysts. The greater amount of amine
present per mole of catalyst, the greater the degree of catalyst alteration. Thus
where an amine such as allylamine or vinylamine is added in mole-to-mole correspondence
with the hydrogen functionality of the hydrogen functional organosilicone, the expected
catalyst function is disrupted and numerous side reactions, including polymerization
of the vinyl or allyl compounds may occur. Thus it is necessary that the amine be
a secondary, N-allylamine or secondary, N-(unsaturated alkylamino) wherein the double
bond is located at least two carbons from the secondary amino nitrogen.
[0020] In the list of suitable secondary allylamines which follows, it should be noted that
the corresponding γ-butenyl and δ-pentenylamines are also suitable. Examples of amines
which are suitable, include N-alkyl-N-allyl amines such as N-methyl, N-ethyl, N-propyl,
N-isopropyl, N-butyl, N-isobutyl, N-tert-butyl, and N-(2-ethylhexyl)allylamines and
the like; cycloaliphatic-N-allylamines such as N-cyclohexyl, N-(2-methylcyclohexyl),
and N-(4-methylcyclohexyl)-N-allylamines; aliphatic cycloaliphatic-N-allylamines such
as N-cyclohexylmethyl and N-(4-methylcyclohexylmethyl)-N-allylamines; aralkyl (aromatic-aliphatic)-N-allylamines
such as N-benzyl, N-(4-methylbenzyl), N-(2-methylbenzyl), and N-(4-ethylbenzyl)-N-
allylamines; aryl (aromatic)-N-allylamines such as N-phenyl, N-(4-methylphenyl),
N-(4-nonylphenyl), and N-naphthyl-N-allylamines; and aromatic N-allylamines where
the aromatic component has the formula
[0021] While these and many other N-allyl secondary amines are useful for the practice of
the subject invention, it must be recognized that some are more preferred than others.
In general, the cycloaliphatic and aryl-N-allylamines are preferred. Particularly
preferred are N-cyclohexyl-N-allylamine and N-phenyl-N-allylamine. It should be noted
that the secondary N-allyl amines are more preferred than their γ-butenyl and δ-pentenyl
analogues.
[0022] As the Si-H functional organosilicone may be used compounds of the formula:
wherein R² is selected from the group consisting of hydrogen; alkyl, preferably C₁-C₁₂
lower alkyl; alkoxy, preferably C₁-C₁₂ lower alkoxy; acetoxy; cyanoalkyl; halogenated
alkyl, preferably perhalogenated alkyl; and substituted or unsubstituted cycloalkyl,
aryl, or aralkyl; and
wherein m and n are natural numbers from 1 to about 10,000, preferably from 1 to
about 500 and more preferably from 1 to about 100; wherein p is a natural number from
3 to about 20, preferably from 4 to about 8; and wherein the sum n+m is less than
about 10,000, preferably less than about 500, more preferably less than about 100;
and wherein at least one R² is hydrogen. Most preferably, the Si-H functional organosilicone
is an Si-H functional disiloxane, preferably
where R₂ is cyanoalkyl, halogenated alkyl, alkyl, alkoxy, cycloalkyl, or aryl. Examples
of such Si-H functional organosilicones are trimethoxy- and triethoxysilane, tetramethyldisiloxane,
tetraethyldisiloxane, 1,1,3,3,5,5-hexamethyltrisiloxane, methyltris(dimethylsiloxysilane),
1,1,3,3,5,5,7,7-octamethyltetrasiloxane, tetramethoxydisiloxane, tetraethoxydisiloxane,
1,1-bis(trifluoropropyl)-3,3-dimethyldisiloxane, pentamethylcyclopentasiloxane, heptamethylcyclotetrasiloxane,
tetramethylcyclotetrasiloxane, methylhydrosiloxane-dimethylsiloxane copolymers, tetraphenyldisiloxane,
tetramethyldisiloxane and tetraphenyldisiloxane. Particularly preferred because of
its low cost and ready availability is tetramethyldisiloxane. Mixed-substituted alkyl-aryl
siloxanes such as 1,3-dimethyl-1,3-diphenyldisiloxane are also useful.
[0023] The N-allyl secondary amine and Si-H functional organosilicone are preferably reacted
neat, in the absence of solvent. However solvents which are inert under the reaction
conditions may be utilized if desired. The use of solvent may affect both the average
molecular weight of the product polysiloxane and the molecular weight distribution.
[0024] The reaction temperature is preferably maintained between about 20°C and 150°C depending
upon the nature and amount of catalyst and reactants. A catalyst is generally necessary
to promote reaction between the amine and the Si-H functional organosilicone. Surprisingly,
it has been found that even rather inefficient catalysts such as hexafluoroplatinic
acid and hexachloroplatinic acid are highly effective, frequently resulting in quantitative
yields. Other catalysts which are useful include those well known in the art, typically
platinum catalysts in which the platinum is present in elemental or combined states,
particularly di- or tetravalent compounds. Useful catalysts are, for example, platinum
supported on inert carriers such as aluminum or silica gel; platinum compounds such
as Na₂PtCl₄, and the previously mentioned platinic acids, particularly hexachloro-
and hexafluoroplatinic acids. Also useful are alkylplatinum halides; siloxyorganosulfur-platinum
or aluminoxyorganosulfurplatinum compositions, and those catalysts prepared through
the reaction of an olefinic-functional siloxane with a platinum compound as disclosed
in U.S. Patents 3,419,593; 3,715,334; 3,814,730; and 4,288,345. Other catalysts may
also be effective, such as those found in U.S. Patent 3,775,452. All the foregoing
U.S. Patents are herein incorporated by reference. However, because of its (relatively)
low cost and the high yields it produces, hexachloroplatinic acid is the catalyst
of choice. Purification of the secondary amine-functionalized organosilicone product
is accomplished by methods well known to those skilled in the art of purifying silicones.
Generally, vacuum distillation is utilized, for example distillation at pressures
less than about 1 torr. In some cases, purification may be effectuated by stripping
off light fractions under vacuum, optionally with the aid of an inert stripping agent
such as nitrogen or argon.
[0025] The secondary amine-functionalized organosilicones may be utilized as such, or they
may be further polymerized with additional silicon-containing monomers to produce
higher molecular weight secondary amine-functionalized polysiloxanes. For example,
a secondary amine-functionalized tetramethyl disiloxane may be converted easily to
a secondary amineterminated poly(dimethylsiloxane) by equilibration with octamethylcyclotetrasiloxane:
The equilibration co-polymerization is facilitated through the use of catalysts well
known to those skilled in the art. A particularly useful catalyst which is relatively
inexpensive and readily available is tetramethylammonium hydroxide. However, many
other catalysts are also suitable, such as potassium hydroxide, cesium hydroxide,
tetramethylammonium siloxanolate, and tetrabutylphosphonium hydroxide, which are also
preferred.
[0026] If copolymer polysiloxanes are desired, then a different siloxane comonomer may be
added to the reaction mixture. For example, a secondary amine-terminated tetramethyldisiloxane
may be reacted on a mole to mole basis with octaphenylcyclotetrasiloxane to produce
a copolymer polysiloxane having the nominal formula:
Or, in the alternative, the secondary amine-terminated disiloxane or polysiloxane
may be reacted with mixtures of siloxane monomers to form block and block heteric
structures.
[0027] The synthesis of secondary amine-functionalized organosilicone modifiers may be illustrated
by the following preparative examples, which should not be considered as limiting
in any way. All reagent quantities are by weight or by gram-mole,as indicated.
Example 1
Synthesis of 1,3-bis(N-phenyl-3-aminopropyl)-1,1,3,3-tetramethyldisiloxane.
[0028] N-allylaniline (0.200 mole) and 1,1,3,3-tetramethyldisiloxane (0.100 mole) are introduced
along with 0.05 g hexachloroplatinic acid into a 100 ml cylindrical glass reactor
equipped with reflux condenser, nitrogen inlet, and stir bar. The contents of the
reaction are heated and maintained while stirring, at approximately 70°C, for a period
of ten hours. The IR spectrum of the resulting viscous oil shows no peaks corresponding
to Si-H, indicating completion of the reaction. The crude product is mixed with carbon
black and stirred overnight at room temperature. The product is filtered through silica
gel and the filter cake washed with toluene. Volatile fractions are removed by stripping
under vacuum at 150°C to give a slightly colored oil. The oil is further purified
by vacuum distillation at <1 torr at 223-230°C. The yield of 1,3-bis(N-phenyl-3-aminopropyl)-1,1,3,3-tetramethyldisiloxane
is virtually quantitative.
Example 2
Synthesis of 1,3-bis(N-cyclohexyl-3-aminopropyl)-1,1,3,3-tetramethyldisiloxane.
[0029] Following the technique described in Example 1, N-allylcyclohexylamine (0.173 mole),
1,1,3,3,-tetramethyldisiloxane (0.0783 mole), and 0.05 g hexachloroplatinic acid
are stirred at 70°C for eight hours at 110°C under nitrogen. The product, in nearly
quantitative yield, is purified by vacuum distillation at <1 torr at a temperature
of 207-210°C.
Example 3
Synthesis of α,ω-bis(N-phenyl-3-aminopropyl)polysiloxane copolymer.
[0030] Into a 500 ml glass reactor equipped with a reflux condenser, mechanical stirrer,
and nitrogen inlet are introduced 1,3-bis(N-phenyl-3-aminopropyl)-1,1,3,3-tetramethyldisiloxane
(0.100 mole), octamethylcyclotetrasiloxane (0.270 mole), octaphenylcyclotetrasiloxane
(0.100 mole), and tetramethylammonium hydroxide (0.3 g). The reaction mixture is
stirred at 80°C for 44 hours followed by an additional 4 hours at 150°C, all under
nitrogen. The resultant viscous oil is filtered and volatiles removed under vacuum
at 300°C. The resulting copolymer is obtained in high yield as a slightly colored
viscous oil.
Example 4
Synthesis of α,ω-bis(N-cyclohexyl-3-aminopropyl capped polysiloxane copolymer.
[0031] Utilizing the procedure of Example 3, 1,3-bis(N-cyclohexyl-3-aminopropyl)-1,1,3,3-tetramethyl
disiloxane (0.0485 moles), octamethylcyclotetrasiloxane (0.179 moles), octaphenylcyclotetrasiloxane
(0.067 mole) and tetramethylammonium siloxanolate (1.20 g) are allowed to react over
a period of 40 hours at 90°C and an additional 4 hours at 150°C. After cooling to
room temperature, the filtered reaction mixture is vacuum stripped at <1 torr and
250°C to yield a viscous oil in high yield.
Example 5
Synthesis of α,ω-bis(N-phenyl-3-aminopropyl) Capped Polydimethylsiloxane
[0032] 1,3-Bis(N-phenyl-3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (30.0 g), octamethylcyclotetrasiloxane
(12.0 g), and tetramethylammonium hydroxide (0.06 g) are charged to a 500 ml glass
reactor equipped with a reflux condenser, nitrogen inlet, and mechanical stirrer.
The contents of the reactor are stirred at 80°C for 30 hours, then at 150°C for four
hours under N₂ blanket. After filtration, the filtrate was further purified by eliminating
volatile fractions under vacuum at 180°C. The resulting oligomer was a colorless viscous
oil.
Example 6
Synthesis of an α,ω-bis(N-phenyl-3-aminopropyl) Capped Polydimethylsiloxane
[0033] 1,3-Bis(N-phenyl-3-aminopropyl)-1,1,3,3,-tetramethyldisiloxane (4.0 g) is treated
with octamethylcyclotetrasiloxane (100 g) and tetramethylammonium hydroxide (0.06
g) in a manner similar to that described in Experiment 5. The resulting oligomer is
a colorless viscous oil having an average molecular weight of about 10,000.
Example 7
Synthesis of a Siloxane Polymer
[0034] 1,3-Bis(N-cyclohexyl-3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (4.0 g) is treated
with octamethylcyclotetrasiloxane (100 g) and tetrabutylphosphonium hydroxide (0.06
g) at 110°C for four hours and 150°C for three hours under nitrogen. Filtration followed
by elimination of volatile fractions under vacuum at 160°C gives a secondary amine
terminated silicone oligomer having an average molecular weight of about 10,000.
[0035] Examples of thermosetting resin systems with which the subject invention modifiers
are useful include but are not limited to epoxy resins, cyanate resins, maleimide-group-containing
resins, isocyanate resins, unsaturated polyester resins, and the like. Particularly
preferred are those resins which are reactive with secondary amines. Most preferred
are the epoxy, cyanate, and maleimide resins.
[0036] Epoxy resins are well known to those skilled in the art. Such resins are characterized
by having an oxiranyl group as the reactive species. The most common epoxy resins
are the oligomeric resins prepared by reacting a bisphenol with epichlorohydrin followed
by dehydrohalogenation. Preferred bisphenols are bisphenol S, bisphenol F, and bisphenol
A, particularly the latter. Such resins are available in wide variety from numerous
sources. Aliphatic epoxy resins are also useful, particularly those derived from dicyclopentadiene
and other polycyclic, multiply unsaturated systems through epoxidation by peroxides
or peracids.
[0037] For high temperature, high strength applications, epoxy resins containing dehydrohalogenated
epichlorohydrin derivatives of aromatic amines are generally used. The most preferred
of these resins are the derivatives of 4,4′-methylenedianiline and p-aminophenol.
Examples of other epoxy resins which are useful may be found in the treatise
Handbook of Epoxy Resins by Lee and Neville, McGraw-Hill, New York, c. 1967.
[0038] The epoxy resins described above are seldom used alone but are generally cured by
means of a curing agent reactive with the oxirane group. Suitable curing agents include
primary and secondary amines, carboxylic acids, and acid anhydrides. Examples of suitable
curing agents may be found in Lee and Neville,
supra, in chapters 7-12. Such curing agents are well known to those skilled in the art.
A particularly preferred curing agent for elevated temperature use is 4,4′-diaminodiphenylsulfone.
[0039] The maleimide-group containing resins useful for the practice of the subject invention
are generally prepared by the reaction of maleic anhydride or a substituted maleic
anhydride such as methylmaleic anhydride with an amino-group-containing compound,
particularly a di- or polyamine. Such amines may be aliphatic or aromatic. Preferred
maleimides are the bismaleimides of aromatic diamines such as those derived from
the phenylenediamines, the toluenediamines, and the mehtylenedianilines. A preferred
polymaleimide is the maleimide of polymethylenepolyphenylenepolyamine (polymeric MDA).
[0040] In addition to the aromatic diamines described above, aliphatic maleimides derived
from aliphatic di- and polyamines are useful. Examples are the maleimides of 1,6-hexanediamine,
1,8-octanediamine, 1,10-decanediamine, and 1,12-dodecanediamine. Particularly preferred
are low melting mixtures of aliphatic and aromatic bismaleimides. These and other
maleimides are well known to those skilled in the art. Additional examples may be
found in U.S. Patents 3,018,290; 3,018,292; 3,627,780; 3,770,691; 3,770,705; 3,839,358;
3,966,864; and 4,413,107. In addition, the polyaminobismaleimides which are the reaction
product of an excess of bismaleimide with a diamine as disclosed in U.S. Patent 3,562,223
may be useful. Also useful are bismaleimide compositions containing alkenylphenolic
compounds such as allyl and propenyl phenols as disclosed in U.S. Patents 4,298,720
and 4,371,719. In addition to being useful with bismaleimides, such comonomers may
be useful in resin compositions containing epoxy and cyanate resins.
[0041] Cyanate resins may also be used to advantage in the subject invention. Such resins
containing cyanate ester groups are well known to those skilled in the art. The cyanates
are generally prepared from a di- or polyhydric alcohol by reaction with cyanogen
bromide or cyanogen chloride. Cyanate resin preparation is described in U.S. Patent
3,740,348, for example. Preferred cyanates are the cyanates derived from phenolic
hydrocarbons, particularly hydroquinone, the various bisphenols, and the phenolic
novolak resins such as those disclosed in U.S. Patents 3,448,071 and 3,553,244.
[0042] The cyanate and epoxy resins are frequently used in combination, as these resins
appear to be compatible with each other. Examples of epoxy/cyanate compositions are
disclosed in U.S. Patents 3,562,214 and 4,287,014.
[0043] The following examples illustrate the use of secondary amine-functionalized siloxanes
in matrix resin and adhesive formulations.
Example 8 - Epoxy Resin Prereact
[0044] A prereact is prepared by heating to 145°C, for two hours under nitrogen, a mixture
containing 15.0 g of the secondary amine-functionalized silicone oligomer of Example
4 and 13.8 g of DER® 332, an epoxy resin which is a diglycidyl ether of bisphenol
A available from the Dow Chemical Company, Midland, MI, which has an epoxy equivalent
weight of from 172 to 176. The resulting product is a homogenous, viscous oil.
Example 9 - Curable Resin Adhesive Composition
[0045] To 2.88 g of the prereact of Example 8 is added 2.0 g Tactix® 742, a glycidyl ether
of tris(4-hydroxyphenyl)methane, and 2.62 g DER® 332, both products of the Dow Chemical
Company. The mixture was stirred at 100°C for 30 minutes. Upon cooling to 70°C, 2.0
g of 4,4′-diaminodiphenylsulfone and 0.5 g of a fumed silica (CAB-0-SIL® M-5, available
from Cabot Corporation) are introduced with stirring. A catalyst solution is prepared
separately by mixing 0.8 g 2-methylimidazole with 10.0 g DER® 332 at room temperature.
Following addition of 0.35 g of the catalyst solution to the resin, the mixture was
coated onto a 112 glass fabric.
Example 10 - Comparison Adhesive
[0046] A comparison resin similar to the resin of Example 9 was prepared by coating 112
glass fabric with a similarly prepared mixture containing 2.0 g Tactix® 742, 4.0 g
DER® 332, 2.0 g 4,4′-diaminodiphenylsulfone, 0.5 g CAB-0-SIL M-5, and 0.35 g of the
catalyst solution as prepared in Example 9.
[0047] The adhesive films of Examples 9 and 10 were cured by heating at 177° for four hours,
200°C for two hours, and 250° for one hour. Single lap shear strengths were measured
by the method of ASTM D-1002. The comparative test results are presented in Table
I below.
TABLE I
Al/Al Lap Shear Strengths of Cured Adhesive Compositions |
Test Conditions |
Lap Shear Strength lb/in² |
|
Example 9 (with modifier) |
Example 10 (comparative - no modifier) |
Ambient, initial |
2840 |
2130 |
177°C, initial |
3290 |
2660 |
Ambient, aged¹ |
2370 |
1810 |
177°C, aged¹ |
3010 |
2560 |
¹Aging at 177°C for 500 hours |
Examples 11, 12 - Curable Resin Elastomer Compositions
[0048] The secondary amine-functionalized silicone oligomers from Examples 6 and 7 respectively
(1.6 g) were treated with 0.1 g Tactix® 742 and 0.3 g DER® 332 at 130°C for one hour.
Following addition of 0.15 g 4,4′-diaminiodiphenylsulfone, the resulting resin systems
were cured at 177°C for two hours and 200°C for three hours. The cured elastomers
demonstrated improved strength as compared to cured silicone homopolymers. Thermal
stabilities of the cured elastomers were examined by thermogravimetric analysis (TGA).
The results are illustrated in Table II.
TABLE II
|
TGA (°C) in Air |
|
5% wt. loss |
10% wt. loss |
Example 11 |
380 |
405 |
Example 12 |
350 |
380 |
Example 13 - Prereact
[0049] A mixture of the secondary amine-functionalized silicone oligomer from Example 4
(30.0 g) Taxtix® 742 (33.8 g), and DER® 332 (22.1 g) is heated to 140°C for three
hours. The resulting product is a homogeneous viscous oil.
Example 14 - Resin Adhesive
[0050] The prereact of Example 13 (28.5 g) is mixed with Tactix® 742 (12.8 g), DER® 332
(4.3 g), and Compimid® 353 (maleimid resin of Boots-Technochemie, 16.0 g) at 130°C
for 30 minutes. At 70°C, 3,3′-diaminodiphenylsulfone (13.8 g), 4,4′-bis(p-aminophenoxy)-diphenylsulfone
(6.1 g), and CAB-O-SIL M-5 (1.8 g) are introduced. The final resin mixture is coated
on a 112 glass fabric. The adhesive film is cured by being heated for four hours at
177°C, two hours at 220°C, and one hour at 250°C. The single lap shear strengths (A1/A1)
are 2200-psi at 20°C and 2500 psi. at 205°C, respectively.
Example 15 - Curable Resin Compositions
[0051] A mixture of the secondary amine-functionalized silicone oligomer (15.0 g) from Example
3, Compimide 353 (10.0 g), and benzoic acid (0.1 g) is heated to 140°C for six hours
under N₂ with vigorous stirring. To the resulting mixture, additional Compimide (10.0
g) and tetra(o-methyl)bisphenol F dicyanate (70.0 g) are added. The mixture is stirred
at 120°C for 30 minutes under vacuum. At 70°C, CAB-0-SIL (N70-TS, 2.6 g0) and dibutyltindilaurate
(0.15 g) are introduced. The final resin mixture is coated on a 112 glass fabric.
Example 16 - Comparative Curable Resin Composition
[0052] A resin formulation is made in a similar manner to Example 15 from a 2-piperazinyl
ethyl amide terminated butadiene-acrylonitrile copolymer (Hycar® ATBN 1300 x 16,
B.F. Goodrich Co.,) (15.0 g), Compimide 353 (20.0 g), tetra(o-methyl)bisphenol F
dicyanate (70.0 g) CAB-0-SIL N70-TS (2.6 g) and the dibutyltindilaurate catalyst (0.15
g). In this case, pretreatment is carried out by adding the ATBN modifier to Compimide
353 at 120°C under N₂ while stirring.
[0053] The adhesive films of Examples 15 and 16 are cured by being heating for four hours
at 177°C, four hours at 200°C, and two hours at 230°C. The single lap shear strengths
(A1/A1) of these formulations are shown in Table III.
TABLE III
Al/Al Lap Shear Strengths of Cured Adhesive Compositions |
Test Conditions |
Shear Strength, lb,/in² |
|
Example 15 (silicone modified) |
Example 16 (ATBN modified) |
20°C |
3280 |
2670 |
205°C |
3800 |
2900 |
[0054] The foregoing examples illustrate the versatility of secondary amine-functionalized
organosilicones as modifiers for a variety of resin systems. The stoichiometry of
the systems may be readily adjusted to enable those skilled in the art to produce
elastomer modified high strength matrix resins, high-temperature, high-strength elastomers,
and high performance structural adhesives. Preferably, the weight ratio of the heat-curable
resin system and the silicone modifier is between 99:1 and 20:80 in particular between
97:3 and 50:50. In the claims which follow, the term "resin system" is utilized in
its conventional meaning, i.e. a system characterized by the presence of a substantial
amount of a heat curable resin together with customary catalysts and curing agents
but devoid of the secondary amine-functionalized silicone modifiers of the subject
invention.
[0055] The modified resin systems of the subject invention may be used as high performance
structural adhesives, matrix resins, and elastomers. These compositions are prepared
by techniques well known to those skilled in the art of structural materials.
[0056] The adhesives, for example, may be prepared as thin films from the melt, or by casting
from solution. Often, the films do not have enough structural integrity to be handled
easily. In this case, the adhesive is generally first applied to a lightweight support,
or scrim. This scrim may be made of a wide variety of organic and inorganic materials,
both woven and non-woven, and may be present in an amount of from about 1 to about
25 percent by weight relative to the weight of the total adhesive composition. The
scrim adds little or no strength to the cured adhesive film, but serves to preserve
the integrity of the film in its uncured state. Common scrim compositions include
fiberglass, carbon/graphite, polyester, and the various nylons.
[0057] When used as a matrix resin, the compositions of the subject invention are applied
to fiber reinforcement. The resin/reinforcement ratio can vary widely, but most prepregs
prepared using the subject compositions will contain from 10 to 60 percent by weight,
preferably from 20 to 40 percent by weight, and most preferably from about 27 to 35
percent by weight of matrix resin, the balance being reinforcing fibers. The reinforcing
fibers may be woven or non-woven, collimated, or in the form of two or three dimensional
fabric, or may, in the case of casting resins, be chopped.
[0058] In contrast to the scrim material used in adhesives, the reinforcing fibers in prepregs
contribute substantially to the strength of the cured prepreg or composite made from
them. Common reinforcing fibers utilized are carbon/graphite, fiberglass, boron, and
silicon; and high strength thermoplastics such as the aramids, high modulus polyolefins;
polycarbonates; polyphenylene oxides; polyphenylene sulfides; polysulfones; polyether
ketones (PEK), polyether ether ketones (PEEK), polyether ketone ketone (PEKK) and
variations of these; polyether sulfones; polyether ketone sulfones; polyimides; and
polyether imides. Particularly preferred are those thermoplastics having glass transition
temperatures (Tg) above 100°C, preferably above 150°C, and most preferably about 200°C
or higher.
[0059] When utilized as heat curable elastomers, the modified resins of the subject invention
may or may not contain fibrous reinforcement of any of the kinds previously discussed.
In contrast to their matrix resin kindred, the elastomers generally contain much higher
proportions by weight of secondary amine-functionalized silicones or prereacts formed
from them.