Note: Descriptions are shown in the official language in which they were submitted.
lO~S995
The present invention relates to the catalyzation of
methylene dianiline complexes utilized in the curing of amine
curable polymers and particularly polyurethane polymers so that
cure proceeds rapidly and at reasonably low temperatures.
Heretofore, the curing of amine curable polymers or
prepolymers such as epoxy resins, millable halogen containing
hydrocarbon polymers and particularly isocyanate terminated poly-
urethane prepolymers have generally involved the blending of
an amine curing agent, forming of the resulting mixture into a
useful form and heating to complete the curing reaction.
However, a problem generally encountered by this procedure was
the premature reaction of the curing agent with the curable
polymer during the mixing and formation operations. This problem
was particularly acute in highly reactive systems such as in the
curing of isocyanate terminated polyurethane prepolymers which
necessitated the use of special low residence time mixers and
selected diamine curing agents having reduced reactivity which
generally limited the physical properties of the vulcanizates.
A class of widely used curing agents which have over-
come many of the above-noted problems are the complexes of
methylene dianiline and a salt which upon heating generally in
excess of temperatures of 100C liberated the methylene dianiline
from the complex and allowed it to commence curing of the poly-
mers (U.S. Patent No. 3,755,261~. Although an improvement in
the art, such class of curing agents still tended to be time
consuming, required undesirable demolding time and thus tended
to be uneconomical due to the number of molds re~uired. The
only way to overcome these disadvantages was to increase the
cure temperature which resulted, of course, in an increased cure
rate. However, increased cure temperatures caused larger thermal
expansion and subsequent shrinkage in the molded article which
often led to strains and cracks in the product.
Accordingly, the presen~ invention proposes to provide
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catalytic compounds for a methylene dianiline complex or a racemic
2,~3-di(4-aminophenyl) butane complex curing agent used in the
curing of amine curable polymers or prepolymers, which catalytic
compounds have a high dielectric constant and are relatively non-
reactive with amines or isocyanates.
More particularly, the invention provides a catalyst
cured polymer, comprising by weight, 100 parts of an amine curable
polymer or prepolymer selected from the group consisting of (a)
urethanes containing free isocyanate groups, epoxy resins,
polymers containing acid halide and haloformate groups and
polymers containing anhydride groups which on reaction with
diamines, yield amide-acide linkages, or (b) halogen containing
hydrocarbon polymers, chlorosulfonated polymers and organo-poly-
siloxanes an amine containing curing agent in an amount of 0.8
to 1.2 equivalents based upon the free active groups of the amine
curable polymer or prepolymer of group (a), or of 0.0005 to about
0.05 equivalents based upon the active groups of the amine curable
polymer or prepolymer of group (b), the curing agent selected
from the group consisting of a complex of 4,4'-methylene dianiline
and a salt, the salt selected from the group consisting of sodium
chloride, sodium bromide, sodium iodide, sodium nitrate, li.thium
chloride, lithium bromide, lithium iodide, lithium nitrate and
sodium cyanide, and a complex of racemic 2,3-di(4-aminophenyl)
butane and a salt selected from the group consisting of sodium
chloride, sodium bromide, sodium iodide, potassium chloride,
potassium bromide, potassium iodide, rubidium chloride, rubidium
bromide, rubidium iodide, cesium chloride, cesium bromide and
cesium iodide, the ratio of the dianiline or butane to the
salt in the complex being about 3 moles per 1 mole and from
0.1 to about 35 parts of a curing agent catalyst selected from
the group consisting of oleic acid, benzaldehyde, adiponitrile,
acetic anhydride, polydimethylsiloxane and diethyl sulfate.
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It has been found that the use of a specific catalyst
in combination with a curing agent utilized for curing amine
curable polymers or prepolymers generally results in increased
cure rates, decreased curing temperatures or both. According to
the present invention, the curing agent catalyst is selected
from the group consisting of oleic acid benzaldehyde, adipo-
nitrile, acetic anhydride, polydimethylsiloxane and diethyl sulfate.
A specific curing agent is a complex of 4,4'-methylène
dianiline (MDA) and a salt. The preparation of the specific
curing agent complex is set forth in U.S. Patent 3,755,261.
Generally, the complexes which are utilized as curing agents for
amine curable polymers include the reaction product of 4,4'-
methylene dianiline with the following salts at a ratio of
about 3 moles of methylene dianiline to about 1 mole of salt;
sodium chloride, sodium bromide, sodium iodide, sodium nitrite,
lithium chloride, lithium bromide, lithium iodide, lithium nitrate
and sodium cyanide.
Another complex which can be used as a curing agent are
the reaction products of racemic 2,3-di(4-aminophenyl) butane
with the following salts in approximately a ratio of 3 moles of
diamine to about 1 mole of salt; sodium chloride, sodium bromide,
sodium iodide, potassium chloride, potassium bromide, potassium
iodide, rubidium chloride, rubidium bromide, rubidium iodide,
cesium chloride, cesium bromide and cesium iodide. The complex
of methylene dianiline and the salt are generally preferred with
the preferred salt being sodium chloride or lithium chloride.
Utilization of the preferred curing agent in the curing of
amine curable prepolymers or polymers upon heating to a temperature
of approximately 100C causes methylene dianiline to be liberated
from the complex and cure the polymers of prepolymers in a manner
thought to be identical to that which occurs when free methylene
dianiline is used as a curing agent.
The above-noted complexes can cure many amine curable
prepolymers or polymers as noted and set forth in the above-noted
~ ~ - 3 -
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106S~9S
U.S. Patent No. 3,755,261. Generally, the preferred class of
such prepolymers or polymers are the urethanes which are general-
ly formed by the reaction of a diisocyanate and a glycol or
diol having a molecular weight of generally 400 to 8,000 and
preferably from 600 to 3,000. Such urethanes typically may be
formed by the reaction of a polyether, a polyol, a polyester
polyol, polybutadiene diols, and combinations thereof with an
equivalent amount of slight excess of diisocyanate or triiso-
cyanate to form a prepolymer having therminal isocyanate groups.
The present invention pertains to such formed urethanes as well
as to other formed urethanes as fully apparent to those skilled
in the art. Patents describing some general types of urethanes
are 2,620,516, 2,777,831, 2,843,568, 2,866,774, 2,900,368,
2,929,800, 2,948,691, 2,948,707 and 3,141,735. Other groups of
amine curable prepolymers or polymers set forth in U.S. Patent
3,755,261, are epoxy resins, polymers containing acid halide
groups such as O
- C - Cl o
and haloformate groups, such as - O - C- Cl
polymers containing anhydride groups which on reaction with
diamines yield amide-acid linkages, halogen containing hydrocarbon
polymers such as chloroprene polymers, chlorinated butyl rubber
and chlorinated polyethylene and polypropylene, chlorosulfonated
polymers and organopolysiloxanes.
The specific catalyst when used in combination with
the complex curing agents has been found to have a catalytic
effect in the curing of polyurethane as well as the other noted
amine curable polymers or prepolymers. That is, the use of the
above selected catalysts causes the various polymers or pre-
polymers to proceed at a more rapid cure rate or at a lowertemperature than otherwise possible with solely the use of the
complex curing agents. Based upon 100 parts of polymer or pre-
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1065S~9S
polymer, from 1.0 to approximately 35 parts of curing agentcatalyst ls utilized. A more preferred range extends from
about 2 to about 10 parts with approximately 5 parts being high~
ly preferred. As should be apparent to one skilled in the art,
the exact amount of catalyst may vary somewhat depending upon
the amount of curing agent complex utilized, the amount of
poly~ner or prepolymer active groups, curing temperature and the
like.
The compounds which have a catalytic effect upon the
curing of amine curable polymers or prepolymers according to the
concepts of the present invention generally are high polar com-
pounds, that is compounds which have a high dielectric constant,
and which generally have relatively slow reaction rates with
amines and free isocyanates. That is, it is desirable that the
high dielectric constant catalytic compounds do not react with
the amines of the curing agent or the isocyanates of the pre-
polymer but rather have a catalytic effect upon the curing agent
and are not deleterious to the prepolyrner or polymer. Hence, by
the words "a relatively slow reaction rate" is meant a rate such
that a substantial number of prepolymers or polymers are cured
by the curing agents to produee cured polymers since the reac-
tion rate with amines or diisocyanates ls sufficiently slow enough
such that competitive reactions are substantially abated. There-
fore, high dielectric constant compounds which react with amines
such as strong acids and high dielectric constant compounds
which react with isocyanates such as strong bases are not within
the scope of the present invention. Generally, compounds having
a high dielectric constant of 2.0 or above are preferred in the
present invention. Of course, compounds having a high dielectric
constant generally having a greater catalytic effect. General-
ly, high dielectric catalytic compoùnds which are liquid during
the curing temperature of the amine curable prepolymers or
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polymers, that is from about 80C to about 140C and even 170C
are desirable. It is generally thought that such liquid
catalytic compounds can then wet the surface of the curing
agent salts and thus sufficiently produce a catalytic effect.-
Based upon 100 parts of polymer or prepolymer, from
0.1 to about 35 parts of the high dielectric catalyst compound
is utilized. A preferred range extends from about 0.2 to about
10 parts. Of course, the exact amount of high dielectric
constant catalytic compound will vary depending upon particula'r
desirable curing temperature as well as the curing rates of the
compounds which varies with different catalytic compounds which
effect is clearly understood by one skilled in the art. Com-
pounds which are preferred include those which generally give
a demold time of less than 6.5 minutes when cured at a tempera-
ture of 120C utilizing approximately 2.9 parts per 100 parts of
polymer or prepolymer in accordance with the manner and test
set forth in Example II, hereinbelow. Such preferred compounds
include benzaldehyde, adiponitrile, acetic anhydride, poly-
dimethylsiloxane and diethyl sulfate.
When the amine curable polymer or prepolymer is
polyurethane, the amount of the curing agent complex will general-
ly range from 0.8 to about 1.2 equivalents of the diamine in the
curing agent to the free isocyanate groups in the polyurethane.
A more preferred range extends from 1.0 to about 1.1 equivalents.
These same ranges are applicable in situations wherein the
polymer or prepolymer are the above-noted epoxy resins, polymers
containing acid halide groups and haloformate groups(and halo-
formate groups,) and polymers containing anhydride groups which
on reaction with diamlnes yield amide-acid linkages~ That is,
the amount of curing agent complex such as methylene dianiline
and a salt will have the above-noted equivalent ranges which is
based upon the number~of free active groups in the polymer or
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prepolymer which react with methylene dianiline.
Considering the remaining polymers or prepolymers,
namely the halogen containing hydrocarbon polymers, the chloro-
sulfonated polymers and the organopolysiloxanes, since they do
not generally contain diamine reactive groups on the terminal
portions of the chain, a much smaller equivalent ratio is
desirable to cure these compounds such as through crosslinking.
Depending upon the desired final molecular weight of the
polymers, and the average molecular weight of the prepolymers,
the amount of curing agent complex can vary over a wide range.
Generally, such a range may extend from 0.0005 to about 0.05
equivalents of the reactive portion of the curing agent such as
diamine to the active groups contained in the polymer or pre-
polymer. A preferred range is from 0.005 to about 0.05
equivalents. As well known to one skilled in the art, the
equivalent amount for obtaining a cured polymer having a desired
average molecular weight or the like can be quickly and readily
determined.
The composition according to the present invention can
be prepared by blending the polymer or prepolymers with the
curing agent complex at ambient or slightly elevated temperatures
such as about 50C but below the curing temperature of the
complexed curing agent which is generally about 90C or 100C.
Preferably, the catalyst is added just before the composition is
cured such as prior to molding, extruding or the like. Since
the various high dielectric constant catalytic compounds lower
the cure initiation temperature of a curing agent, preferably
the polymer or prepolymer mixture is below 80 or 90 at the
incorporation or blending time of the catalytic compounds of the
present invention to prevent, of course, premature cure.
Various conventional additives and compounds may be
added to the composition of the present invention to impart
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various desirable characteristics or properties. These include
antiforming agents or solid articles, pigments, light stabilizers,
forming agents for foamed articles, fillers such as Hi Sil and
the like. Additionally, in the production of polyurethanes,
plasticizers are often added to increase the flexibility of the
article. A conventional plasticizer often employed is dioctyl
phthalate (DOP). The addition of DOP is also desirable in that
since it is a liquid,it is used to disperse the powder during
agent complexes.
The catalyzed amine curable polymers or prepolymers
have been found to increase the cure rate, to decrease the cure
time or both. Increased rate of cure, of course, allows the
use of fewer molds since each mold can be cycled more rapidly.
Another important advantage of the use of the present catalyst
cure systemps is that because possible lower temperature cures
can be effected, less thermal expansion and subsequent shrinkage
occurs in a molded article, Thus, the article contains less
strain and is much less likely to develop any cracks or fissures.
Yet another obvious advantage is that due to the lower tempera-
ture cure of the various catalysts, lower operating costs are
obtained due to energy conservation.
~ he amine curable prepolymers or polymers made in
accordance with the present invention can, of course, he used
for the same normal applications. Concerning the preferred
polyurethanes, they can be used for numerous applications such
as automotive parts, bumpers, commercial and passenger tires,
shoe soles, wearing apparrel, roller wheels and the like. Per-
haps the most important application will lie in the manufacutre
of tires.
The present invention will be more fully understood
by reference to tne following examples concerning preparation
and data.
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EXAMPLE I (COMPARATIVE)
To a 3 neck flask fitted with a stirrer, thermometer
and a vacuum takeoff was added 250 grams of DuPont's Adiprene
LD784 (polytetramethylene ether glycol of about 1,000 molecular
weight end capped with 2 molecules of Hylene TM, i.e. approxi-
mately a 80/20 mixture the 2,4/2,6 position isomers of toluene
diisocyanate) and 86.15 grams of a Caytur 21 (a complex of 4,4'-
methylene dianiline and a salt) dispersion (50 % in DOP). Then
7.15 grams of tributyl phosphate was added to a flask. The
mixture was seen to rapidly thicken and set up in the flask
after 3 minutes of mixing at 50C. Cures prepared from this
material were poor due to the partial cure which occurred in the
flask. Since it appeared that TBP catalyzed the reaction of the
Caytur 21 with the prepolymers, a series of various temperature
cures were run to determine if the TBP was a true catalytic
material. It was found that cure would occur at temperatures
down to 80~ in the catalyzed system whereas in the uncatalyzed
system, a cure temperature of at least 105C was necessary to
initiate reasonable cure rates.
A series of runs were made utilizing different levels
of TBP at various cure temperatures, the results of which are
set forth in Fig. 1 wherein the demold time represents the time
required for the molded articles to be sufficiently cured such
that it maintained it:s structural integrity upon removal from
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S995
the mold. In the drawing,,line 1 represents the prior art
composition of 100 parts of ~diprene LD784, 20 parts of DOP
and an equivalent ratio of 1.025 of the diamine to the free
active isocyanate groups in the Adiprene prepolymer. The
dotted portion of line 1 indicates that cures below a temperature
of approxLmately 100C were difficult to achieve and gave poor
properties. Lines 2, 3 and 4 represent mixtures of Adiprene
prepolymers, DOP, TBP, and Caytur 21' curing agent in the amounts
indicated.
As readily apparent from the drawing, the addition of
TBP greatly reduced the cure time at a specific curing temperature
and reduced the required curing temperature to cure in a
specific amount of time. The commencement of lines 2, 3 and 4 at
the lower temperatures generally represent the onset of initiation
or cure whereas the termination of lines 2, 3 and 4 at higher
tempexatures generally represent the upper desirable curing
temperature, Of course, compositions containing more or les~
TBP will generally result in correspondingly located lines
dependlng upon the amount of TBP, Moreover~ the equivalent
ratio of the complex such as methylene dianiline to free active
isocyanate groups can also be varied.
The effect of tributyl phosphate concentration on
physical properties is set forth in Table I.
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In general, as the amount of catalyst was increased,
the physical properties such as tensile strength and crescent
tear ~ere slightly reduced. Rowever, such reduction is generally
well within the r~quirements of a particular application for the
S cured polymer. Additionally, the 5% and 300~ modulus at ambient
temperature (73F) were reduced thus indicatin~ a more resilient
article is produced.
Table II shows the effect of prepolymers containing an
increased amount of isocyanate content.
TABLE II
r
EFFECT ~F NC~ CONTENT
COMPOSITION G H
Prepolymer %NCO 6.45 5~10
of Caytur Cure 102.5 102.5
Parts TBP 5 5
Parts DOP 17.2 14.0
212F
Tensile Str. (PSI)2050 2100
300% Mod (PSI) 1530 1020
Crescent Tear (LB/IN) 276 291
73F
Tensile Str. (PSI~4340 4400
5% Mod (PSI) 500 434
300% Mod (PSI) 1875 1275
Crescent Tear (LB/IN) 419 399
Tex-US Flex (2 low
of 8) 10,000 126,000
In general, the properties remain relati~ely the same
except that the 5% and 300% modulus of compound G containing
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106~5
the higher amount of free isocyanate was much higher and the
flex much lower indicating a stiffer or more brittle material.
Table III represents polyurethane compositions prepared
from poly THF (Tetrahydrofuran).
TABLE II I
PREPOLYME~ TYI?ES
COMPOS ITION I J
Prepolymer type loo IPO1Y THF 100 ~Poly T~F
TDI type~Hylene TM ~Hylene T
% Caytur Cure102.5 102.5
Parts DOP 17.1 20
10 Parts TBP 2 . 9 5
212F
Tensile Str. (PSI) 1970 1890
30096 Mod. (PSI) 1560 800
Crescent Tear (LB/IN) 274 137
73F
Tensile Str. (PSI) 5375 2075
5% Mod. (PSI) 494 168
15 30096 Mod. (PSI) 2125 890
Crescent Tear (LB/IN)417 269
Additionally, the various catalytic high dielectric
constant compounds according to the present invention other
than tributyl phosphate also give reduced cure time at
20 a specific curing temperature or reduced the required curing
temperature to cure in a specific amount of time. Moreover,
the properties of the amine curable polymers or prepolymers
according to the present invention wherein various high
dielectric catalytic compounds were utilized generally are the
25 same as pol~mers or prepolymers cured without said high dielectric
catalytic compounds.
~,~ . ,. _;
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~06sg~5
EXAMPLE II
To a three neck flask fitted with a stirrer, thermo-
meter and a vacuum takeoff was added 250 grams of DuPont's
Adiprene LD784 (polytetramethylene ether glycol of about 1,000
molecular weight end capped with two molecules of Hylene TM,
that is, approximately and 80/20 mixture of the 2,4/2,6 position
isomers of toluene diisocyanate) and 86.15 grams of Caytur 21
(the complex of 4,4-methylene dianiline and a salt) dispersion
(50 % in DOP). The mixture was heated to 50C and then 7.15
grams of various high dielectric constant catalytic compounds
was added constant stirring. The mixture was then stirred more
or less from about one half minute to a minute and a half
depending upon the catalytic effect of a specific high dielectric
constant compound. The mixture was then poured into a mold.
The time necessary for the material to become demoldable, that
is maintain a structural integrity which would not lose its
shape after separation from a mold, was compared to an un-
catalyzed mixture to determine whether the specific compoun~
was a true catalyst. The following Table sets forth the results
of a number of various types of high dielectric constant com-
pounds which were tested as catalyst. It was found that the
catalyzed systems could be cured as low as about 80C whereas
in the absence of a catalyst, cure temperature of at least
105C was necessary to initiate reasonable cure rates.
Table IV sets forth the mold time of various catalysts
wherein an amount of`2.9 grams per 100 grams of prepolymer
were utilized and the mixture cured at a temperature of 120C.
3 - 14 -
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TABLE IV
DEMOLD
SAMPLE CATALYST MOLD TEMP (C) TIME (MIN
Control DOP 120 10.0
Oleic Acid 100 7.5
B Benzaldehyde 120 5.0
C Adiponitrile 120 3.0
D Acetic Anhydride 120 6.0
E Polydimethylsiloxane 120 5.5
F Diethyl sulfate 120 4.5 ,
Of course, increased concentrations of a specific
catalyst will result in increased cure rates and thus shorter
demold times and/or lower curing temperatures. Variation of
concentrations, cure temperature and demold time of the catalysts
of the present invention when plotted will result in a graph
similar to Fig. 1.
Table V represents polyurethane compositions prepared
from poly THF (Tetrahydrofuran).
TABLE V
Parts, Wt Compound
100 Polypropylene glycol hylene TM prepolymer
(6.2~ NCO)
32.9 Caytur 21 Dispersion (49.5% in DOP)
2.9 Oleic Acid
The composition of Table V when cured according to
the same conditions as the compositions set forth in Table IV
gave a demold time of 4.0 minutes.
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