Note: Descriptions are shown in the official language in which they were submitted.
CA 0224~689 l998-08-o~
WO97/30101 PCT~97/007~3
; IMPROVED CHEMIGAL CURING OF EPOXIDIZED DIENE
POLYMERS USING AROMATIC ANHYDRIDE CURING AGENTS
This invention relates to a process for curing
epoxidized diene polymers which may be used in sealant,
coatings, and adhesives applications. More
particularly, the present invention relates to such
S process in which an aromatic anhydride curing agent is
used. The use of an aromatic anhydride curing agent
provides a high level of crosslinking and enhanced
mechanical properties in the cured polymer.
The chemical curing of epoxidized diene polymers is
of interest for sealant, coatings, and adhesives
applications. U.S. Patent 5,229,464 describes low
molecular weight epoxidized diene block copolymers and
states that they may be crosslinked by the addition of
multifunctional carboxylic acids and acid anhydrides.
lS U.S. Patents 5,478,885 and 5,461,112 describe similar
polymers which are used as toughening modifiers for
epoxy resins. These epoxidized diene polymers are
shown to be curable with carboxylic acid or anhydride
curing agents. In this latter application, partially
and fully saturated aliphatic carboxylic acids or
anhydrides have been found to be very useful and to
allow the production of very good products. However, a
number of problems have been encountered when the same
partially or fully saturated aliphatic carboxylic acids
2~ or anhydrides have been used as curing agents to cure
the epoxidized diene polymers when epoxy resins are not
present in the compositions to be cured. Such is the
case when these polymers are used in sealant, coatings,
and adhesive applications.
~0 I have discovered that when such carboxylic acid
anhydrides are used to cure these epoxidized diene
CA 0224~689 1998-08-o~
WO97/30101 PCT~P97/00713
polymers alone, bubbles form in the crosslinked
product. Relative~y low conversion levels are achieved
with these curing agents and the products exhibit low
strength because of both a low level of crosslinking
conversion of the epoxy and defects introduced into the
product as bubbles.
It has been found that the bubbles are produced as
a result of the evolution of carbon dioxide during the
decarboxylation of the anhydride. This side reaction
competes with the desired crosslinking reaction and the
kinetics are such that it takes up enough of the epoxy
groups to significantly lessen the total curing while
producing CO2 bubbles in the product. This problem
does not occur to any noticeable extent in the epoxy
resin impact modification as described in U.S. patents
5,478,885 and 5,461,112 above because the reaction of
the anhydride with the epoxy resin is much faster than
the reaction between the epoxidized diene polymer and
the anhydride and also because in that patent, the
majority of the composition is the epoxy resin.
It is clear from the above that when there is a
desire for a high strength, defect free sealant,
coating, or adhesive utilizing an epoxidized diene
polymer, a curing agent different from the partially
2s and fully saturated aliphatic carboxylic acid
anhydrides is needed. There are other types of curing
agents which can be used, but acid anhydride curing
agents are preferable in the curing of epoxidized diene
polymers because amines will not rapidly cure such
polymers without an epoxy resin present. The Applicant
here has found that certain aromatic acid anhydride
curing agents are capable of curing epoxidized diene
polymers to a high degree of cure and high strength
without the formation of bubbles, especially when used
CA 0224~689 1998-08-0~
WO 97130101 PCT~P97JOO713
in a certain molar ratio relative to the epoxidized
diene polymers.
This invention is a method for chemically curing
epoxidized diene polymers for use in sealants,
coatings, and adhesives applications. The method
involves curing said epoxidized diene polymers with
aromatic anhydrides, preferably aromatic carboxylic
acid anhydrides. The curing process generally takes
place at elevated temperatures, 100 to 200~C, for a
period of 10 minutes to 6 hours, preferably 30 minutes
to 6 hours, and is often referred to as "bake cure.'~
Preferred aromatic carboxylic acid anhydrides are
chosen from phthalic anhydride and alkyl-substituted
phthalic anhydrides. The alkyl-substituted phthalic
anhydrides may be mono-, di- or tri- substituted
phthalic anhydrides. More preferably, the aromatic
carboxylic acid anhydride is chosen from phthalic
anhydride and mono-alkyl substituted phthalic
anhydride. The alkyl substituents may contain from 1
to 18 carbon atoms, preferably from 1 to 12 carbon
atoms, even more preferably from 1 to 4 carbon atoms.
Of the alkyl substituents, linear substituents are most
'preferred. The most preferred aromatic carboxylic acid
anhydride curing agents for use in the present
invention are phthalic anhydride and 4-methyl-phthalic
anhydride.
The process may be accelerated by using a curing
accelerator.
Polymers containing ethylenic unsaturation can be
prepared by copolymerizing one or more olefins,
particularly diolefins, by themselves or with one or
more alkenyl aromatic hydrocarbon monomers. The
copolymers may, of course, be random, tapered, block or
a combination of these, as well as linear, star or
radial.
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WO97/30101 PCT~P97/00713
- 4 -
In general, when solution anionic techniques are
used, copolymers of conjugated diolefins, optionally
with vinyl aromatic hydrocarbons, are prepared by
contacting the monomer or monomers to be polymerized
simultaneously or sequentially with an anionic
polymerization initiator such as group IA metals,
preferably lithium, their alkyls, amides, silanolates,
napthalides, biphenyls or anthracenyl derivatives. The
polydienes are synthesized by anionic polymerization of
conjugated diene hydrocarbons with these lithium
initiators. This process is well known as described in
U.S. Patents Nos. 4,039,593 and Re. 27,145.
Polymerization commences with a monolithium initiator
which builds a living polymer backbone at each lithium
lS site. Specific processes for making the preferred
polymers for use herein are described in detail in
International PCT Application No. W0 96/11215 and U.S.
Patent 5,461,112.
Conjugated diolefins which may be polymerized
anionically include those conjugated diolefins
containing from 4 to 24 carbon atoms such as
1,3-butadiene, isoprene, piperylene, methylpentadiene,
phenyl-butadiene, 3,4-dimethyl-1,3-hexadiene,
4,5-diethyl-1,3-octadiene and the like. Preferably,
conjugated diolefins containing from 4 to 8 carbon
atoms are used. Isoprene and butadiene are the
preferred conjugated diolefins for use in the present
invention because of their low cost and ready
availability. Alkenyl (vinyl) aromatic hydrocarbons
3() which may be copolymerized include vinyl aryl compounds
such as styrene, various alkyl-substituted styrenes,
alkoxy-substituted styrenes, vinyl napthalene,
alkyl-substituted vinyl napthalenes and the like, the
alkyl and alkoxy groups typically comprising from 1 to
~5 6, preferably from 1 to 4 carbon atoms.
CA 0224~689 1998-08-0~
WO 97130101 PCT~~97JOD7~3
Epoxidized polymers which may be cured in
accordance with the present invention are those
described in U.S. Patents 5,229,464, 5,247,026. For
instance, the following block copolymers, preferably
S containing from 0.1 to 7.0 millie~uivalents (meq) of
epoxy per gram of polymer, may be used:
(A-B-Ap)n-Yr- (Aq~B)m
wherein Y is a coupling agent, coupling monomers or an
initiator, and wherein A and B are polymer blocks which
may be homopolymer blocks of conjugated diolefin
monomers, copolymer blocks of conjugated diolefin
monomers or copolymer blocks of conjugated diolefin
monomers and monoalkenyl aromatic hydrocarbon monomers,
and wherein the A blocks have a greater number of di-,
tri- and tetra-substituted unsaturation sites per unit
of block mass than do the B blocks, and wherein the A
blocks have a weight average molecular weight from
about 100 to about 3000 and the B blocks have a weight
average molecular weight from about 1000 to about
15,000, and wherein p and q are 0 or 1 and n >0, r is 0
or 1, m 0 and n + m ranges from 1 to 100.
The most highly preferred polymers for use herein
are epoxidized diblock polymers which fall within the
scope of the formula:
(HO)X-A-Sz-B-(OH)y
wherein A and B are polymer blocks which may be
homopolymer blocks of conjugated diolefin monomers,
copolymer blocks of conjugated diolefin monomers, or
copolymer blocks of diolefin monomers and monoalkenyl
3() aromatic hydrocarbon monomers. These polymers may
contain up to 60~ by weight of at least one vinyl
aromatic hydrocarbon, preferably styrene. Generally,
it is preferred that the A blocks should have a greater
concentration of more highly substituted aliphatic
CA 0224~689 1998-08-0~
WO97130101 PCT~P~7/00713
double bonds than the B blocks have. Thus, the A
blocks have a greater concentration of di-, tri-, or
tetra-substituted unsaturation sites (aliphatic double
bonds) per unit of block mass than do the B blocks.
This produces a polymer wherein the most facile
epoxidation occurs in the A blocks. The A blocks have
a weight average molecular weight of from l00 to 6000,
pre~erably 500 to 4,000, and most preferabLy l000 to
3000, and the B blocks have a weight average molecular
weight of from l000 to 15,000, preferably 2000 to
l0,000, and most preferably 3000 to 6000. S is a vinyl
aromatic hydrocarbon block which may have a weight
average molecular weight of from l00 to l0,000. x and
y are 0 or l. Either x or y must be l, but only one at
a time can be l. z is 0 or l.
The overall weight average molecular weight of such
diblocks may range from 1500 to 15000, preferably 3000
to 7000. Either of the blocks in the diblock may
contain some randomly polymerized vinyl aromatic
hydrocarbon as described above. For example, where I
represents isoprene, B represents butadiene, S
represents styrene, and a slash (/) represents a random
copolymer block, the diblocks may have the following
structures:
2s I-B-OH I-B/S-OH I/S-B-OH I-I/B-OH or
B/I-B/S-OH B-B/S-OH I-EB-OH I-EB/S-OH or
I-S/EB-OH I/S-EB-OH HO-I-S/B HO-I-S/EB
where EB is hydrogenated butadiene, -EB/S-OH means that
the hydroxyl source is attached to a styrene mer, and
-S/EB-O~ slgnifies that the hydroxyl source is attached
to a hydrogenated butadiene mer. Thls latter case,
-S/EB-OH, requires capping--of the S/EB "random
copolymer" block with a mini EB block to compensate for
the tapering tendency of the styrene prior to capping
with ethylene oxide. These diblocks are advantageous
CA 0224~689 1998-08-0~
WO 97130101 PC:~TJ1~1~97J01~713
-
in that they exhibit lower viscosity and are easier to
manufacture than the corresponding triblock polymers.
It is preferred that the hydroxyl be attached to the
butadiene block because the epoxidation proceeds more
S favorably with isoprene and there will be a separation
between the functionalities on the polymer.
Epoxidation of the base polymer can be effected by
reaction with organic peracids which can be preformed
or formed in situ. Suitable preformed peracids include
peracetic and perbenzoic acids. In situ formation may
be accomplished by using hydrogen peroxide and a low
molecular weight acid such as formic acid. These and
other methods are described in more detail in U. S.
Patents 5,229,464, 5,247,026, 5,478,885, and 5,461,112.
The epoxidized polymers to be used in the process
according to invention preferably contains from 0.1 to
7.0 meq of epoxy per gram of polymer depending upon the
desired end use for the product.
The molecular weights of linear polymers or
unassembled linear segments of polymers such as mono-,
di-, triblock, etc., arms of star polymers before
coupling are conveniently measured by Gel Permeation
Chromatography (GPC), where the GPC system has been
appropriately calibrated. For anionically polymerized
linear polymers, the polymer is essentially
monodisperse ~weight average molecular weight/number
average molecuiar weight ratio approaches unity), and
it is both convenient and adequately descriptive to
report the "peak" molecular weight of the narrow
molecular weigh~ distribution observed. Usually, the
peak value is between the number and the weight
average, but for monodisperse polymers, all three are
very similar. The peak molecular weight is the
~ molecular weight of the main species shown on the
~ chromatograph. For polydisperse polymers the weight
CA 0224~689 1998-08-0~ .
WO g7/30101 rCT/EP97tO0713
average molecular weight should be calculated from the
chromatograph and used. For materials to ~e used in -
the columns of the GPC, styrene-divinyl benzene ~els or
silica gels are commonly used and are excellent
materials. Tetrahydrofuran is an excellent solvent for t
polymers of the type described herein. A refractive
index detector may be used.
Measurement of the absolute molecular weight o~ a
polymer is not as straightforward or as easy to make
using GPC. A good method to use for absolute molecular
weight determination is to measure the weight average
molecular weight by light scattering techniques. The
sample is dissolved in a suitable solvent at a
concentration less than 1.0 gram o~ sample per 100
milliliters of solvent and filtered using a syringe and
porous membrane filters of less than 0.5 microns pore
sized directly into the light scattering cell. The
light scattering measurements are performed as a
function of scattering angle, polymer concentration and
polymer size using standard procedures. The
differential refractive index (DRI) of the sample is
measured at the same wave length and in the same
solvent used for the light scattering. The folIowing
references relate to this sub~ect:
2s 1. Modern Size-Exclusion Liquid Chromatography, M. W.
Yau, J. J. Kirkland, D. D. Bly, John Wiley and
Sons, New York, New York, 1979.
2. Light Scattering From Polymer Solutions, M. B.
Huglin, ed., Academic Press, New York, New York,
1972.
3. W. K. Kai and A. J. Havlik, A~plied Optics, 12, 541
(1973).
4. M. L. McConnell, American Laborator~, 63, May,
1978.
CA 0224j689 1998-08-oj
WO97/30101 PCT~P97/00713
If desired, these block copolymers can be partially
hydrogenated. Hydrogenation may be effected
selectively as disclosed in U.S. Patent Reissue 27,145.
The hydrogenation of these polymers and copolymers may
S be carried out by a variety of well established
processes including hydrogenation in the presence of
such catal~sts as Raney Nickel, nobel metals such as
platinum and the like, soluble transition metal
catalysts and titanium catalysts as in U.S. Patent
5,039,755. The polymers will have dif~erent diene
blocks and these diene blocks may be selectively
hydrogenated as described in U.S. Patent 5,229,464.
U.S. Patents 5,478,885 and 5,461,112 describe
anhydride curing agents as commonly used to cure the
epoxidized diene polymers described above. Anhydrides
are used herein because a bake cure system is desired.
Amine curing agents, which work well in compositions
containing epoxy resins as described in said patent,
will not cure epoxidized diene polymers. The anhydride
curing agents described as useful in said patents may
be any compound containing one or more anhydride
functional groups and specific examples given include
phthalic anhydride, substituted phthalic anhydrides,
hydrophthalic anhydrides (which are not aromatic
2~ compounds because they are hydrogenated), substituted
hydrophthalic anhydrides, succinic anhydride,
substituted succinic anhydrides, halogenated
anhydrides, multifunctional carboxylic acids, and
polycarboxylic acids.
Because of their ease of handling, saturated or
partially saturated anhydrides, such as hydrophthalic
anhydrides and substituted hydrophthalic anhydrides,
are regularly used in this type of curing. I have
foun~i that, unknown to those skilled in the art, these
anhydrides cause problems when used to cure epoxidized
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WO97/30101 ~CT~P9710071
-- 10 --
diene polymers by themselves (as opposed to in
combination with epoxy resins as described in U.S.
Patents 5,478,885 and 5,461,112~. Specifically, carbon
dioxide generated during the reaction of the epoxidized
polymer and the curing agent creates bubbles in the
cured product and causes the product to have diminished
physical properties.
I have found that it is necessary to use an
anhydride curing agent which is aromatic in nature to
achieve a good bake cure without the formation of
bubbles in the product. Carbon dioxide is not
generated in the reaction of an epoxidized diene
polymer and an aromatic anhydride curing agent.
According to my invention, the aromatic anhydride is
combined with the epoxidized diene polymer such that a
suitable epoxidized diene polymer/aromati$ anhydride
molar ratio is achieved. This ratio should range from
0.5/l.0 to 2.0/l.0, preferably 0.8/l.0 to 1.2/l.0, and
most preferably about l/l, to achieve sufficient
crosslinking to produce a product with desirable
physical properties. The crosslinking occurs through
the epoxy groups and aromatic anhydride such that
aromatic ester linkages are formed. Typically, the
aromatic anhydride cures are conducted at elevated
2~ temperatures - temperatures of from lO0 to 200~C are
possible but 130 to 180~~ is the preferred operating
range - for a period of lO minutes to 6 hours, and are
often referred to as "bake cures."
The anhydride bake cures can be accelerated by
~) us-ng a curing accelerator and accelerators are highly
reoommended for practical operation. Suitable curing
accelerators include trialkyl amines,
hydroxyl-containing compounds and lmidazoles.
Benzyldimethylamine (BDMA), 2-ethyl-4-methylimidazole
(EMTj, triphenylphosphine (TPP), and BF3 amine
CA 0224~689 1998-08-o~
W097/30101 PCTn~97tO0713
complexes have been found to work well in curing the
blends of the present invention. The accelerator is
used in an amount of O.l to lO, preferably about l part
of accelerator per lOO parts of polymer.
The crosslinked materials of the present invention
are useful in adhesives (including pressure sensitive
adhesives, contact adhesives, laminating adhesives,
assembly adhesives and structural adhesives), sealants,
coatings, films (such as those requiring heat and
solvent resistance), etc. However, it may ~e necessary
for a formulator to combine a variety of ingredients
together with the polymers of the present invention in
order to obtain products having the proper combination
of properties (such as adhesion, cohesion, durability,
low cost, etc.) for particular applications. Thus, a
suitable formulation might contain only the polymers of
the present invention and the aromatic anhydride curing
agent. This is especially true for coatings, sealants,
and structural adhesives. However, in applications
such as pressure sensitive adhesives, suitable
formulations would also contain various combinations of
resins, plasticizers, fillers, solvents, stabilizers
and other ingredlents such as asphalt. In particular,
a suitable pressure sensitive formulation would
2S comprise the epoxidized diene polymers, the aromatic
anhydride curing agent and a tackifying resin. The
following are some typical examples of formulating
ingredients for adhesives, coatings and sealants.
In adhesive applications, as well as in coatings
3() and sealants, it may be necessary to add an adhesion
promoting or tackifying resin that is compatible with
the polymer. A common tackifying resin is a
diene-olefin copolymer of piperylene and
2-methyl-2-butene havlng a softening point of about
~ ~5~C. Thls resin is available commercially under the
CA 0224~689 1998-08-o~
WO97/30101 PCT~97/00713
tradename Wingtack 95 and is prepared by the cationic
polymerization of 60% piperlene, 10% isoprene, ~%
cyclo-pentadiene, 15% 2-methyl-2-butene and about 10% .
dimer, as taught in U.S. Patent No. 3,577,398. Other
tackifying resins may be employed wherein the resinous
copolymer comprises 20-80 weight percent of piperylene
and 80-20 weight percent of 2-methyl-2-butene. The
resins normally have ring and ball softening points as
determined by ASTM method E28 between about 80~C and
115~C.
To obtain good thermo-oxidative and color
stability, it is preferred that the tackifying resin be
a saturated resin, e.g., a hydrogenated dicyclopenta-
diene resin such as Escorez 5000 series resin made by
Exxon or a hydrogenated polystyrene or polyalphamethyl-
styrene resin such as Regalrez resin made by Hercules.
The amount of tackifying resin employed typically
varies from 0 to 400 parts by weight per hundred parts
rubber (phr), preferably between 20 to 350 phr, most
preferably 20 to 150 phr. The selection of the
particular tackifying agent is, in large part,
dependent upon the specific polymer employed in the
respective adhesive composition.
Resins, in particular aromatic resins, may also be
employed as reinforcing agents, provided that they are
compatible with the particular polymer used in the
formulation. Normally, these resins should also have
ring and ball softening points between about 80~C and
115~C although mixtures of resins having high and low
.~() softening points may also be used. ~seful resins
include coumarone-indene resins, polystyrene resins,
vinyl toluene-alpha methylstyrene copolymers and
polyindene resins. Examples of such reinforcing resins
useful in the present invention are the hydrogenated
Regalrez and Regalite resins from Hercules.
CA 0224~689 1998-08-o~
WO97130101 PCT~97J00713
- 13 -
Preferably, they are used in amounts from 1 to 50
percent by weight of the total composition.
Other resins which are also useful in the
compositions of this invention include hydrogenated
s rosins, esters of rosins, polyterpenes, terpenephenol
resins and polymerized mixed olefins, lower softening
point resins and liquid resins. An example of a liquid
resin is Adtac LV resin from Hercules.
Reactive co-curing components such as epoxy resins
and epoxidized natural products are also useful as
reinforcing agents. Examples of useful epoxy resins
are aromatic resins such as EPON 828 resin from Shell
and aliphatic resins such as EPONEX 1510 resin from
Shell and UVR 6110 resin from Union Carbide. Examples
of useful epoxidized or epoxy-containing natural
products are the DRAPEX series of epoxidized oils from
Witco and naturally occurring vernonia oil.
A composition of the instant invention may contain
plasticizers, such as rubber extending plasticizers, or
2~ compounding oils or organic or inorganic pigments and
dyes. Rubber compounding oils are well-known in the
art and include both high saturates content oils and
high aromatics content oils. Preferred plasticizers
are highly saturated oils, e.g. Tufflo 6056 and 6204
oil made by Arco and process oils, e.g. Shellflex 371
oil made by Shell. Reactive compounds can be used as
plasticizers. The amounts of rubber compounding oil
employed in the invention composition can vary from 0
to 500 phr, preferably from 0 to 100 phr, and most
preferably between 0 and 60 phr.
Optional components of the present invention are
stabilizers which inhibit or retard heat degradation,
oxidation, skin formation and color formation.
J Stabilizers are typically added to the commercially
available compounds in order to protect the polymers
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WO97/30101 PCT~P97/00713
- 14 -
against heat degradation and oxidation during the
preparation, use and hlgh temperature storage of the
..
composition. Additional stabilizers known in the art
may also be incorporated into the composition. These
may be for protection during the llfe of the article
against, for example, oxygen, ozone and ultra-violet
radiation. However, these additional stabilizers
should be compatible with the essential stabilizers
mentioned hereinabove and their intended function as
taught herein.
~arious types of fillers and pigments can be
included in the formulation. This is especially true
for exterior coatings or sealants in which fillers are
added not only to create the desired appeal but also to
improve the performance of the coatings or sealants
such as its weatherability. A wide variety of fillers
can be used. Suitable fillers include calcium
carbonate, clays, talcs, silica, zinc oxide, titanium
dioxide and the like. The amount of filler usually is
in the range of 0 to about 65~w based on the solvent
free portion of the formulation depending on the type
of filler used and the application for which the
coating or sealant is intended. An especially
preferred filler is titanium dioxide.
All adhesive, coating and sealant compositions
based on the epoxidized polymers of this invention will
contain some combination of the various formulating
ingredients disclosed herein. No definite rules can be
offered about which ingredients will be used. The
3() skilled formulator will choose particular types of
ingredients and adjust their concentrations to give
exactly the combination of properties needed in the
composition for any specific adhesive, coating or
sealant application.
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- 15 -
The only two ingredients that will always be used
in any adhesive, coatinq or sealant are the epoxidized
polymer and the curing agent. Beyond these two
ingredients, the formulator will choose to use or not
to use among the various resins, fillers and pigments,
plasticizers, reactive oligomers, reactive and
non-reactive diluents, stabilizers, and solvents.
Adhesives are frequently thin layers of sticky
compositions which are used in protected environ~ents
(adhering two substrates together). Therefore,
unhydrogenated epoxidized polymers will usually have
adequate stability so resin type and concentration will
be selected for maximum stickiness without great
concern for stability, and pigments will usually not be
used.
Coatings are ~requently thin, non-sticky, pigmented
compositions applied on a substrate to protect or
decorate it. Therefore, hydrogenated epoxidized
polymers may be needed to give adequate durability.
Resins will be selected to assure maximum durability
and minimum dirt pick-up. Fillers and pigment will be
selected carefully to give appropriate durability and
color. Coatings will frequently contain relatively
high solvent concentration to allow easy application
and give a smooth dry coating.
Sealants are gap fillers. Therefore, they are used
in fairly thick layers to fill the space between two
substrates. Since the two substrates frequently move
relative to each other, sealants are usually low
modulus compositions capable of withstanding this
movement. Further, they generally have good adhesion
to the substrates. Since sealants are frequently
exposed to the weather, the hydrogenated epoxidized
polymers are usually used. Resins and plasticizers
will be selected to maintain low modulus and minimize
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- 16 -
dirt pick-up. Fillers and pigment will be selected to
give appropriate durability and color. Since sealants
are applied in fairly thick layers, solvent content is
as low as possible to minimize shrinkage.
A formulator skilled in the art will see tremendous
versatility in the epoxidized polymers of this
invention to prepare adhesives, coatings and sealants
having properties suitable for many different
applications.
The adhesive, coating and sealant compositions of
the present invention can be prepared by mixing the
components together until a homogeneous blend is
obtained. Various methods of blending are known to the
art and any method that produces a homogenous blend is
satisfactory. Frequently, the components can be
blended together using solvent to control viscosity.
Suitable solvents include common hydrocarbons, esters,
ethers, ketones and alcohols as well as mixtures
thereof. If solvent content is restricted or in
solvent-free compositions, it may be possible to heat
the components to help reduce viscosity durin~ mixing
and application.
A preferred use of the present formulation is in
weatherable bake-cured sealants. The sealant comprises
2~ a monohydroxylated epoxidized diene polymer, an
aromatic anhydride curing agent, an optional curing
accelerator, an optional reinforcing resin or co-curing
agent, and an optlonal tackifying resin.
Alternatively, when the amount of tackifying resin is
ero, the compositions of the present invention may be
used for adhesives that do not tear paper and molded
goods and the like.
Coating compositions of this invention can be used
in many applications, depending on the hardness,
adhesion, durability and cure conditions chosen by the
CA 0224~689 1998-08-0~
WC~ 97/30101 PCT/EP97/007i3
-
formulator. A fairly soft coating formulated for low
adhesion could be used as a protective strippable
coating. A fairly soft coating formulated for high
adhesion could be useful as a shatter retentive coating
for glass bottles ~or carbonated beverages. A fairly
hard coating formulated for high adhesion and long
durability could be used as a corrosion protective
coating for metals such as lawn equipment, automobiles,
etc.
Sealant compositions of this invention can be used
for many applications. Particularly preferred is their
use as gap fillers for constructions which will be
baked (for example, in a paint baking oven) after the
sealant is applied. This would include their use in
automobile manufacture and in appliance manufacture.
Another preferred application is their use in gasketing
materials, for example, in lids for food and beverage
containers.
EXAMPLE 1
A series of experiments were carried out using a
variety of anhydrides to cure a monohydroxylated
epoxidized polydiene block copolymer having the
structure I-B-OH where I is a block of polymerized
isoprene of weight average molecular weight 1000, B is
2s a block of polymerized butadiene of weight average
molecular weight 5000 and -OH is a terminal hydroxyl
group. The polymer was partially hydrogenated and then
fully epoxidized to yield an epoxy content of 1.5
Meq/g. Nonaromatic anhydridesmethyl tetrahydrophthalic
anhydride (MTHPA), hexahydrophthalic anhydride (HHPA),
methyl-5 norbornene-2,3-dicarboxylic anhydride (Nadic
methyl anhydride, NMA), and dodecenyl anhydride
(DSA)were compared with aromatic anhydridesphthalic
anhydride (PA), 4-methyl-phthalic anhydrlde (MPA), and
3~ 4-t-butylphthalic anhydride (tBPA). The amount of
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curing agent used in each experiment was chosen to give
a l:l molar ratio of epoxidized diene polymer to
aromatic anhydride functionality. The accelerator,
2-ethyl-4-methyl imidazole (EMI) was used in an amount
of one part per hundred parts of polymer. The
formulation components were mixed and then placed in
0.16 cm (l/~6 inch) glass molds.
The composition was cured at 150C for two hours.
Table I shows some of the physical properties of the
cured compositions and also the reaction exotherm for
each of the reactions. The reaction exotherm is a
measure of the amount of reaction, i.e. crosslinking,
which took place during the curing process and is
measured calorimetrically. The maximum stress and
elongation at maximum stress are derived from tensile
deformation experiments.
Table I
anhydride melting point max. stress elongation rxn
(~C) MPa (psi) at stress exotherm
(~) (kJ/mole
epoxy)
MTHPAliquid at room 1.29 (187) 283 -20.6
temperature
HHPA 37 1.19 (173) 402 -18.9
DSA 43 0.34 (S0) 154 -19.9
NMAliquid at room 0.04 (6)1600 -9.1
temperature
PA 135 6.51 (944) 146 -47.0
MPA 94 3.50 (508) 165 -57.6
tBPA 78 - - -8.8
As can be seen from the reaction exotherms, the use
of PA and MPA aromatic anhydrides led to a higher
degree of conversion than the others. This increased
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level of crosslinking is also reflected in the
mechanical properties of the cured polymer. The
tensile strengths are significantly higher ~or the PA
and MPA systems. Thus, the aromatic anhydrides lead
- 5 not only to a bubble-free sample but also to a higher
level of crosslinking in the polymer. This may be
somewhat attributed to the lack of decarboxylation as
that side reaction would yield unreactive anhydride and
a necessarily lower conversion. However, another
feature observed is the steric character of the
anhydrides. The tri-substituted epoxy of this polymer
is a relatively crowded reaction site. Therefore,
bulky anhydrides like NMA and DSA may be unable to
easily accommodate the steric re~uirements for
reaction. PA and MPA are both flat molecules and as
such may more easily approach the reaction site. The
relative acid strengths may also play a role in extent
of reaction. TBPA did not lead to carbon dioxide
bubble formation. However, the extent of reaction was
low. This is attributable to the relatively bulky
nature of this curing agent.
Both PA and MPA lead to superior physical
properties. The lower melting point of MPA may present
a processing advantage, though. In our laboratory
2s experience we have found that the PA system must be
heated to 150~C to thoroughly melt and mix the
anhydride. At this elevated temperature, gel formation
proceeds rapidly upon addition of the catalyst. With
the MPA system, the anhydride is easily melted and
mixed at 120~C. Addition of catalyst at this
temperature does not lead to rapid gelation.
Rheological experiments show that the gel time for the
polymer/MPA/EMI system is near 1800 seconds at 120~C.
Because of the avoidance of the adverse decarboxy-
3~ lation reaction, superior mechanical properties, ease
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of processing, and commercial availability, MPA is the
most preferred aromatic anhydride curing agent for this
polymer.
EXAMPLE 2
s This example demonstrates the use of the epoxidized
monohydroxylated polymer of Example l with a variety of
accelerating agents. The sealants of this example were
formulated with a stoichiometric ratio of epoxy to
anhydride where the anhydride was MPA. An accelerator
was used at the l phr level. The formulations were
mixed and then cured in 0.16 cm (l/16 inch) glass molds
at l60~C for 2 hours. Table II lists the tensile
property results. All formulations cured without the
formation of carbon dioxide bubbles. These results
show that BDMA is an effective accelerant ~or MPA cures
of epoxidized polydiene polymers.
Table II
AcceleratorStrength MPa (psi) Elongation (%)
BDMA 1.59 (231) 320
TPP 0.35 (51) 630
None l.lO (159) 430
EXAMPLE 3
This example demonstrates the use of the epoxidized
monohydroxylated polymer of Example l with reinforcing
additives in MPA cures. The molar ratio of epoxy to
anhydride functionality was maintained at l:l in all
cases. This required consideration of the epoxy level
of the additives. EMI was used at l part per lDD parts
polymer to accelerate the cure. The cures were
conducted in glass molds as in Example l. The physical
properties of the resulting bake-cured sealants are t
shown in Table III. No carbon dioxide was evolved
during the cure of these sealants with the aromatic
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anhydride. Bubble-free test specimens with high
strength were obtained. The data demonstrate that both
hydrogenated hydrocarbon resins of elevated Tg and
epoxidized oils are effective at providing aromatic
s anhydride cured sealants of elevated Tg.
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