Note: Descriptions are shown in the official language in which they were submitted.
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SEALANTS AND POTTING FORMULATIONS INCLUDING MERCAPTO
TERMINATED POLYMERS PRODUCED BY THE
REACTION OF A POLYTHIOL AND POLYVINYL ETHER MONOMER
Cross-Reference to Related Applications
This application is a continuation-in-part of U.S. Patent Application No.
08/928,972 filed September 12, 1997, which is a continuation-in-part of now
U.S. Patent No. 5,912,319. Also, this application is a continuation-in-part of
U.S. Patent Application No. 09/318,500 filed May 25, 1999, which is a division
of now U.S. Patent No. 5,912,319. This application also claims the benefit of
U.S. provisional application no. 60/182,396 filed February 14, 2000 and U.S.
provisional application no. 60/215,548 filed June 30, 2000.
Field of the Invention
The present invention relates to a sealant or potting formulation
prepared from a mercapto-terminated polymer produced by the reaction of
polythiol(s) and polyvinyl ether monomer(s), the formulation having good low
temperature flexibility and fuel resistance.
Background of the Invention
Commercially available polymeric materials which have sufficient sulfur
content to exhibit desirable sealing and fuel resistance properties for
aerospace sealants and electrical potting compounds are the polysulfide
polyformal polymers described, e.g., in U.S. Pat. No. 2,466,963, and the alkyl
side chain containing polythioether polyether polymers described, e.g., in
U.S.
Pat. No. 4,366,307 to Singh et al. Materials useful in this context also have
the desirable properties of low temperature flexibility characterized by a low
glass transition temperature (T9) and liquidity at room temperature.
An additional desirable combination of properties for aerospace
sealants which is much more difficult to obtain is the combination of long
application time (i.e., the time during which the sealant remains usable) and
short curing time (the time required to reach a predetermined strength). Singh
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et al., U.S. Pat. No. 4,366,307, disclose such materials. Singh et al. teach
the
acid-catalyzed condensation of hydroxyl-functional thioethers. The hydroxyl
groups are in the ~i-position with respect to a sulfur atom for increased
condensation reactivity. The Singh et al. patent also teaches the use of such
hydroxyl-functional thioethers with pendant methyl groups to afford polymers
having good flexibility and liquidity. However, the disclosed condensation
reaction has a maximum yield of about 75% of the desired condensation
product. Furthermore, the acid-catalyzed reaction of ~i-hydroxysulfide
monomers yields significant quantities of an aqueous solution of thermally
stable and highly malodorous cyclic byproducts, such as 1-thia-4-oxa-
cyclohexane which limits the suitable application of the disclosed polymers.
Another desirable feature in polymers suitable for use in aerospace
sealants is high temperature resistance. While incorporating sulfur to carbon
bonds into a polymer generally enhances high temperature performance, the
polysulfide polyformal polymers disclosed in U.S. Pat. No. 2,466,963 have
multiple -S-S- linkages in the polymer backbones which result in compromised
thermal resistance. In the polymers of Singh et al., U.S. Pat. No. 4,366,307,
enhanced thermal stability is achieved through replacement of polysulfide
linkages with polythioether (-S-) linkages. However, the thermal resistance of
these polythioethers is limited as a result of residual acid condensation
catalyst.
Morris et al., U.S. Pat. No. 4,609,762, describes reacting dithiols with
secondary or tertiary alcohols to afford liquid polythioethers having no
oxygen
in the polymeric backbone. Cured polymeric materials formed from these
polymers have the disadvantage, however, of reduced fuel resistance due to
the large number of pendant methyl groups that are present. In addition, the
disclosed process generates undesirable aqueous acidic waste.
Cameron, U.S. Pat. No. 5,225,472, discloses production of
polythioether polymers by the acid-catalyzed condensation of dithiols with
active carbonyl compounds such as HCOOH. Again, this process generates
undesirable aqueous acidic waste.
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The addition polymerization of aromatic or aliphatic dithiols with diene
monomers has been described in the literature. See, e.g., Klemm, E. et al., J.
Macromol. Sci.-Chem., A28(9), pp. 875-883 (1991); Nuyken, O. et al.,
Makromol. Chem., Rapid Commun. 11, 365-373 (1990). However, neither
Klemm et al. nor Nuyken suggest selection of particular starting materials to
form a polymer that is liquid at room temperature and, upon curing, has
excellent low-temperature flexibility (low T9) and high resistance to fuels,
i.e.,
hydrocarbon fluids. Nor do Klemm et al. suggest production of a polymer that
also is curable at room or lower temperatures. Moreover, the reactions
disclosed by Klemm et al. also generate undesirable cyclic byproducts.
There exists a need in the art for sealant, coating and electrical potting
formulations or compositions that can provide good pot life as well as good
performance properties, such as fuel resistance, flexural strength, thermal
resistance and longevity in use.
Summar)i of the Invention
The present invention provides a sealant or potting formulation
prepared from components comprising (a) at least one ungelled mercapto-
terminated polymer prepared by reacting reactants comprising at least one
polyvinyl ether monomer and at least one polythiol material; (b) at least one
curing agent reactive with a mercapto group of the mercapto-terminated
polymer; and (c) at least one additive selected from the group consisting of
fillers, adhesion promoters, plasticizers and catalysts.
Another aspect of the present invention is a sealant or potting
formulation prepared from components comprising: (a) at least one ungelled
mercapto-terminated polymer prepared from reactants comprising diethylene
glycol divinyl ether and dimercapto dioxaoctane; (b) at least one curing agent
reactive with a mercapto group of the mercapto-terminated polymer; and (c) at
least one additive selected from the group consisting of fillers, adhesion
promoters, plasticizers and catalysts.
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The above sealant formulations are useful in a variety of applications,
such as for example aerospace applications or as electrical potting
compounds.
Other than in the operating examples, or where otherwise indicated, all
numbers expressing quantities of ingredients, reaction conditions, and so
forth
used in the specification and claims are to be understood as being qualified
in
all instances by the term "about". Also, as used herein, the term "polymer" is
meant to refer to oligomers, homopolymers and copolymers.
Brief Description of the Drawings
The invention may be more readily understood by referring to the
accompanying drawings in which:
FIG. 1 depicts linear graphs of extrusion rate (E) versus time (T) for
sealant compositions of the invention in comparison to extrusion rate curves
for known types of sealant composition, and
FIG. 2 is a semi-log graph of the extrusion rate curve of a polythioether
sealant composition of the invention (~) and a prior art polysulfide sealant
composition (~).
Detailed Description of the Preferred Embodiments
The sealant and potting formulations of the present invention comprise
one or more ungelled mercapto-terminated polymers or polythioethers. It has
surprisingly been discovered that polythioethers prepared from the
combination of polythiol(s) with polyvinyl ether monomers) according to the
present invention result in ungelled mercapto-terminated polymers that are
liquid at room temperature and pressure and that have desirable physical and
theological properties, and that furthermore are substantially free of
malodorous cyclic by-products. The inventive materials also are substantially
free of deleterious catalyst residues, and have superior thermal resistance
properties.
_q._
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The mercapto-terminated polymers useful in the sealant and potting
formulations of the present invention are preferably liquid at room
temperature
and pressure and cured sealants including such polymers have excellent low
temperature flexibility and fuel resistance. As used herein, the term "room
temperature and pressure" denotes conditions of approximately 77°F.
(25°C)
and 1 atmosphere (760 mm Hg) pressure.
The mercapto-terminated polymer is ungelled or substantially free of
crosslinking. By "ungelled" is meant that the mercapto-terminated polymer is
substantially free of crosslinking and has an intrinsic viscosity when
dissolved
in a suitable solvent, as determined, for example, in accordance with ASTM-
D1795 or ASTM-D4243. The intrinsic viscosity of the mercapto-terminated
polymer is an indication of its finite molecular weight. A gelled reaction
product, on the other hand, since it is of essentially infinitely high
molecular
weight, will have an intrinsic viscosity too high to measure.
Preferably, the mercapto-terminated polymer has a glass transition
temperature (T9) that is not higher than -50°C, more preferably not
higher than
-55°C and most preferably not higher than -60°C. Generally, it
is preferred
that the glass transition temperature of the mercapto-terminated polymer
ranges from -85°C to-50°C, and more preferably -70°C to -
50°C, as
determined by differential scanning calorimetry (DSC).
Low temperature flexibility can be determined by known methods, for
example, by the methods described in AMS (Aerospace Material
Specification) 3267 ~4.5.4.7, MIL-S (Military Specification) -8802E ~3.3.12
and MIL-S-29574, and by methods similar to those described in ASTM
(American Society for Testing and Materials) D522-88, which are incorporated
herein by reference. Cured formulations having good low temperature
flexibility are desirable in aerospace applications because the formulations
are
subjected to wide variations in environmental conditions, such as temperature
and pressure, and physical conditions such as joint contraction and expansion
and vibration.
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An advantage of the formulations of the present invention is that they
exhibit very desirable fuel resistance characteristics when cured, due at
least
in part to the use of the mercapto-terminated polymers discussed herein. The
fuel resistance of a cured sealant can be determined by percent volume swell
after prolonged exposure of the cured sealant to a hydrocarbon fuel, which
can be quantitatively determined using methods similar to those described in
ASTM D792 or AMS 3269, which are incorporated herein by reference. For
fuel resistance testing, the cured sealant can be prepared from 100 parts by
weight of mercapto-terminated polymer, 50 parts by weight of precipitated
calcium carbonate and an epoxy curing agent in a 1:1 equivalent ratio of
mercapto groups to epoxy groups. The epoxy curing agent is prepared from a
60:40 weight ratio of EPON 828 bisphenol A diglycidyl ether (available from
Shell Chemical) to DEN 431 bisphenol A novolac resin (available from Dow
Chemical).
In a preferred embodiment, the cured sealants of the present invention
have a percent volume swell not greater than 40%, and preferably not greater
than 25% after immersion for one week at 140°F (60°C) and
ambient pressure
in jet reference fluid (JRF) type 1. More preferably, the percent volume swell
of the cured polymers is not greater than 20%, and more preferably ranges
from zero to 20%. Jet reference fluid JRF type 1, as employed herein for
determination of fuel resistance, has the following composition (see AMS
2629, issued July 1, 1989), ~3.1.1 et seq., available from SAE (Society of
Automotive Engineers, Warrendale, Pennsylvania) (that is incorporated herein
by reference):
Toluene 28 t 1 % by volume
Cyclohexane (technical) 34 t 1 % by volume
Isooctane 38 ~ 1 % by volume
Tertiary dibutyl disulfide
(doctor sweet) 1 t 0.005% by volume
Tertiary butyl mercaptan 0.015% t 0.0015 by weight of the other
four components
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Preferably, the ungelled mercapto-terminated polymers have a number
average molecular weight ranging from about 500 to about 20,000 grams per
mole, more preferably from about 1,000 to about 10,000, and most preferably
from about 2,000 to about 5,000, the molecular weight being determined by
gel-permeation chromatography using a polystyrene standard.
Liquid mercapto-terminated polymers within the scope of the present
invention can be difunctional, that is, linear polymers having two end groups,
or polyfunctional, that is, branched polymers having three or more end
groups.
The mercapto-terminated polymers are prepared by reacting reactants
comprising one or more polyvinyl ether monomers and one or more polythiol
materials. Useful polyvinyl ether monomers include divinyl ethers having the
formula (V):
CH2 = CH-O-(-R2-O-)",-CH = CH2 (V)
where R2 is C~_6 n-alkylene, C2_6 branched alkylene, C6_$ cycloalkylene or
C6_10
alkylcycloalkylene group or -[(CH2-)p-O-]q-(-CH2-)~- and m is a rational
number
ranging from 0 to 10, p is an independently selected integer ranging from 2 to
6, q is an independently selected integer ranging from 1 to 5 and r is an
independently selected integer ranging from 2 to 10.
The materials of formula V are divinyl ethers. Such divinyl ether
monomers as described herein can provide polymers having superior fuel
resistance and low temperature performance as compared to prior art
polymers prepared from alkenjrl ether and conjugated dienes such as 1,3
butadiene copolymerized with a dithiol such as DMDS. Divinyl ether (m=0) is
operative herein. Preferred divinyl ethers include those compounds having at
least one oxyalkylene group, more preferably from 1 to 4 oxyalkylene groups
such as those compounds in which m is an integer from 1 to 4. More
preferably, m is an integer from 2 to 4. It is also possible to employ
commercially available divinyl ether mixtures in producing mercapto-
terminated polymers according to the invention. Such mixtures are
characterized by a non-integral average value for the number of alkoxy units
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per molecule. Thus, m in formula V can also take on rational number values
between 0 and 10.0; preferably betvueen 1.0 and 10.0; very preferably
between 1.0 and 4.0, particularly between 2.0 and 4Ø
Suitable polyvinyl ether monomers include divinyl ether monomers,
such as divinyl ether, ethylene glycol divinyl ether (EG-DVE) (R2=ethylene,
m=1), butanediol divinyl ether (BD-DVE) (R2=butylene, m=1), hexanediol
divinyl ether (HD-DVE) (R2=hexylene, m=1), diethylene glycol divinyl ether
(DEG-DVE) (R2=ethylene, m=2) (preferred), triethylene glycol divinyl ether
(R2=ethylene, m=3), tetraethylene glycol divinyl ether (R2=ethylene, m=4),
cyclohexanedimethanol divinyl ether, polytetrahydrofuryl divinyl ether;
trivinyl
ether monomers such as trimethylolpropane trivinyl ether, tetrafunctional
monomers such as pentaerythritol tetravinyl ether and mixtures thereof. The
polyvinyl ether material can have one or more pendant groups selected from
alkyl groups, hydroxyl groups, alkoxy groups and amine groups.
Useful divinyl ethers in which R2 is C2_~ branched alkylene can be
prepared by reacting a polyhydroxy compound with acetylene. Exemplary
compounds of this type include compounds in which R2 is an alkyl-substituted
methylene group such as -CH(CH3)- (for example "PLURIOL~" blends such
as PLURIOLO E-200 divinyl ether (BASF Corp. of Parsippany, New Jersey),
for which R2=ethylene and m=3.8) or an alkyl-substituted ethylene (for
example -CH2CH(CH3)- such as "DPE" polymeric blends including DPE-2 and
DPE-3 (International Specialty Products of Wayne, New Jersey)).
Other useful divinyl ethers include fluorinated compounds or
compounds in which R2 is polytetrahydrofuryl (poly-THF) or polyoxyalkylene,
preferably having an average of about 3 monomer units.
Two or more polyvinyl ether monomers of the formula V can be used in
the foregoing method. Thus in preferred embodiments of the invention, two
polythiols of formula IV (discussed below) and one polyvinyl ether monomer of
formula V, one polythiol of formula IV and two polyvinyl ether monomers of
formula V, two polythiols of formula IV and two polyvinyl ether monomers of
formula V, and more than two compounds of one or both formulas, can be
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used to produce a variety of polymers according to the invention, and all such
combinations of compounds are contemplated as being within the scope of
the invention.
Generally, the polyvinyl ether monomer comprises 20 to less than 50
mole percent of the reactants used to prepare the mercapto-terminated
polymer, and preferably 30 to less than 50 mole percent.
Suitable polythiol materials for preparing the mercapto-terminated
polymer include compounds, monomers or polymers having at least two thiol
groups. Useful polythiols include dithiols having the formula (IV):
HS-R~-SH (IV)
where R~ can be a CZ_6 n-alkylene group; C3_6 branched alkylene group,
having one or more pendant groups which can be, for example, hydroxyl
groups, alkyl groups such as methyl or ethyl groups; alkoxy groups, C6_$
cycloalkyfene; C6_~o alkylcycioalkylene group; -[(-CH2)p-X]q-(-CH2)r-; or -[(-
CH2)p-X]q-(-CH2)~- in which at least one -CH2- unit is substituted with a
methyl
group and in which p is an independently selected integer ranging from 2 to 6,
q is an independently selected integer ranging from 1 to 5 and r is an
independently selected integer ranging from 2 to 10.
Further preferred dithiols include one or more heteroatom substituents
in the carbon backbone, that is, dithiols in which X includes a heteroatom
such as O, S or another bivalent heteroatom radical; a secondary or tertiary
amine group, i.e., -NR6-, where R6 is hydrogen or methyl; or another
substituted trivalent heteroatom. In a preferred embodiment, X is O or S, and
thus R~ is -[(-CHI-)p-O-]q -(-GH2-)~- or -[(-CH2-)p S-]q-(-CH2-)r-.
Preferably, p
and r are equal, and most preferably both have the value of 2.
Useful polythiols include but are not limited to dithiols such as 1,2-
ethanedithiol, 1,2-propanedithiol, 1,3-propanedithiol, 1,3-butanedithiol, 1,4-
butanedithiol, 2,3-butanedithiol, 1,3-pentanedithiol, 1,5-pentanedithiol, 1,6-
hexanedithiol, 1,3-dimercapto-3-methylbutane, dipentenedimercaptan,
ethylcyclohexyldithiol (ECHDT), dimercaptodiethylsulfide, methyl-substituted
dimercaptodiethylsulfide, dimethyl-substituted dimercaptodiethylsulfide,
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dimercaptodioxaoctane, 1,5-dimercapto-3-oxapentane and mixtures thereof.
The polythiol material can have one or more pendant groups selected from
lower alkyl groups, lower alkoxy groups and hydroxyl groups. Suitable alkyl
pendant groups include C~-C6 linear alkyl, C3-C6 branched alkyl, cyclopentyl,
and cyclohexyl.
Preferred dithiols include dimercaptodiethylsulfide (DMDS) (p= 2, r=2,
q=1, X=S); dimercaptodioxaoctane (DMDO) (p=2, q=2, r=2, X=0); and 1,5-
dimercapto-3-oxapentane (p=2, r=2, q=1, X=O). It is also possible to use
dithiols that include both heteroatom substituents in the carbon backbone and
pendant alkyl groups, such as methyl groups. Such compounds include
methyl-substituted DMDS, such as HS-CHZCH(CH3)-S-CH2CH2-SH, HS-
CH(CH3)CH2-S-CH2CH2-SH and dimethyl substituted DMDS such as HS-
CH2CH(CH3)-S-CH(CH3)CH2-SH and HS-CH(CH3)CH2-S-CH2CH(CH3)-SH.
Two or more different polythiols can be used if desired to prepare
useful polythioethers.
Preferably, the polythiol material has a number average molecular
weight ranging from 90 to 1000 grams per mole, and more preferably 90 to
500 grams per mole.
Relative amounts of dithiol and divinyl ether materials used to prepare
the polymers are chosen to yield terminal mercapto groups (-SH). These
mercaptan-terminated polymers can include thiol terminal groups that are not
further reacted ("uncapped"), or include one or more thiol groups that are
further reacted with other materials to provide reactive or non-reactive
terminal or pendant groups ("capped"). Capping the polymers of the present
invention enables introduction of additional terminal functionalities, for
example, hydroxyl or amine groups, to the polymers, or in the alternative,
introduction of end groups that resist further reaction, such as terminal
alkyl
groups. Preferably, the stoichiometric ratio of polythiol to divinyl ether
materials is less than one equivalent of polyvinyl ether to one equivalent of
polythiol, resulting in mercapto-terminated polymers. More preferably, the
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stoichiometric ratio is selected to fully terminate the polymer with mercapto
groups.
Hydroxyl- or amino-functional terminal polymers can be produced, for
example, by reacting a vinyl terminated material with mercaptoalcohols such
as 3-mercaptopropanol or mercaptoamines such as 4-mercaptobutylamine,
respectively, or by reacting a mercaptan terminated material with a vinyl
terminated material having hydroxyl functionality such as butane diol
monovinyl ether or amine functionality such as aminopropyl vinyl ether.
Preferably, the mercapto-terminated polymer comprises 30 to 90
weight percent of the sealant formulation on a basis of total weight of the
sealant formulation, and more preferably 30 to 60 weight percent.
The reactants from which the mercapto-terminated polymers are
prepared can further comprise one or more free radical catalysts. Preferred
free radical catalysts include azo compounds, for example azobis-nitrite
compounds such as azo(bis)isobutyronitrile (AIBN); organic peroxides such
as benzoyl peroxide and t-butyl peroxide; inorganic peroxides and similar
free-radical generators. The reaction can also be effected by irradiation with
ultraviolet light either with or without a cationic photoinitiating moiety.
Ionic
catalysis methods, using either inorganic or organic bases, e.g.,
triethylamine,
also yield materials useful in the context of this invention.
Mercapto-terminated polymers within the scope of the present
invention can be prepared by a number of methods. According to a first
preferred method, (n+1 ) moles of a material having the formula IV:
HS-R~-SH (IV)
or a mixture of at least two different compounds having the formula IV, are
reacted with n moles of a material having the formula V:
CH2 = CH-O-(-R2-O-)~,-CH = CH2 (V)
or a mixture of at least two different compounds having the formula V, in the
presence of a catalyst. This method provides an uncapped, mercapto-
terminated difunctional polymer.
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Although, as indicated above, compounds of the formulas IV and V
which have pendant alkyl groups, for example pendant methyl groups, are
useful according to the invention, it has surprisingly been discovered that
compounds of the formulas IV and V which are free of pendant methyl or
other alkyl groups also afford mercapto-terminated polymers that are ungelled
at room temperature and pressure.
Capped analogs to the foregoing mercapto-terminated polymers can
be prepared by reacting a material having the formula IV or a mixture of at
least two different compounds having the formula IV and a material having the
formula V or a mixture of at least two different compounds having the formula
V in a stoichiometric ratio of less than one equivalent of dithiol per vinyl
equivalent of formula V, with about 0.05 to about 2 moles of a material having
the formula VI
CH2 = CH-(CH2) S-O-R5 (VI)
or a mixture of two different materials having the formula VI, in the presence
of an appropriate catalyst.
Materials of the formula VI are alkyl ~-alkenyl ethers having a terminal
ethylenically unsaturated group which react with terminal thiol groups to cap
the polythioether polymer.
In formula VI, s is an integer from 0 to 10, preferably 0 to 6, more
preferably 0 to 4 and R5 is an unsubstituted or substituted alkyl group,
preferably a C~_6 n-alkyl group which can be substituted with at least one -OH
or -NHR' group, with R' denoting H or C~_6 alkyl. Exemplary useful R5 groups
include alkyl groups, such as ethyl, propyl and butyl, hydroxyl-substituted
groups such as 4-hydroxybutyl; amine substituted groups such as
3-aminopropyl; etc.
Specific preferred materials of the formula VI are monovinyl ethers
(s = 0), including amino- and hydroxyalkyl vinyl ethers, such as 3-aminopropyl
vinyl ether and 4-hydroxybutyl vinyl ether (butanediol monovinyl ether), as
.well as unsubstituted alkyl vinyl ethers such as ethyl vinyl ether.
Additional
preferred materials of the formula VI include allyl ethers (s = 1 ), such as
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4-aminobutyl allyl ether, 3-hydroxypropyl allyl ether, etc. Although materials
in
which s is greater than 6 can be used, the resulting polymers may have less
fuel resistance than those in which s is 6 or less.
Use of equivalent amounts of materials of the formula Vl relative to
thiol groups present in formula IV provides fully capped mercapto polymers,
while use of lesser amounts results in partially capped polymers.
Preferably, an equivalent of polyvinyl ether is reacted with dithiol or a
mixture of polythiols.
A preferred linear structured mercapto-terminated polymer useful in the
sealant and potting formulations of the present invention has the structure of
formula (I):
HS-R~-[-S-(CH2)n-O-(-R2-O-)m-(CH2)q-S-R1-]n -SH (I)
wherein
R~ denotes a CZ_~o n-alkylene, C2_g branched alkylene, C6_$ cycloalkylene
or C6_~o alkylcycloalkylene group, heterocyclic, -[(-CH2)p-X]q-(-CH2)r ; or
-[(-CH2)p-X]q-(-CHZ)r- in which at least one -CH2- unit is substituted with
a methyl group;
R2 denotes a Cz_~o n-alkylene, C2_6 branched alkylene, C6_$ cycloalkylene
or C6_~4 alkylcycloalkylene group, heterocyclic, -[(-CH2)p-X]q-(-CH2)r;
X denotes one selected from the group consisting of O, S and
_N Rs_;
R6 denotes H or methyl;
m is an independently selected rational number from 1 to 50; and
n is an independently selected integer from 9 to 60;
p is an independently selected integer ranging from 2 to 6;
q is an independently selected integer ranging from 1 to 5; and
r is an independently selected integer from 2 to 10.
In a more preferred embodiment of the foregoing polymer, R~ is C2-C6
alkyl and R2 is C2-C6 alkyl.
In a preferred embodiment, the polythioether has the formula (fl):
A-(--~R3]v ~R4)2 (II)
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wherein
A denotes a structure having the formula I,
y is0or1,
R3 denotes a single bond when y = 0
and - S - (CH2)2 - [-O-R2 ]m--0 - when y = 1,
R4 denotes -SH or - S --(--CH2--)Z+S - O - R5 when y = 0
and - CH= CH2 or - (CH2-)2-- S - R5 when y = 1,
s is an integer from 0 to 10,
R5 denotes C~_6 alkyl group which is unsubstituted or substituted with at
least one -OH or -NHR' group, and
R' denotes H or a C~_6 n-alkyl group.
Thus, polythioethers of the formula 11 are linear, difunctional polymers
which can be uncapped or capped. When y = 0, the polymer includes
terminal thiol groups or capped derivatives thereof. In an alternative
embodiment, when y = 1 (not preferred), the polymer includes terminal vinyl
groups or capped derivatives thereof.
According to a preferred embodiment, the inventive polythioether is a
difunctional thiol-terminated (uncapped) polythioether. That is, in formula
II,
y = 0 and R4 is - SH. Thus, the polythioether has the fohlowing structure:
HS - R~ ~ S --(CHZ)2 - O -{- R2 - O -]r~,- (CH2)2 - S - R~ -]"- SH
In a preferred embodiment, R~=-[(-CH2)p-X]q-(-CHZ)~ , where p=2, X=O,
q=2 and r=2, R2 is ethylene group, m=2 and n is about 9.
The foregoing polymers are produced, for example, by reacting a
divinyl ether or mixfiure thereof with an excess of a dithiol or mixture
thereof,
as discussed in detail below.
In an alternative embodiment of the foregoing polythioether, when
m = 1 and R2 = n-butylene in formula II, R~ is not ethylene or n-propylene.
Also preferably, when m = 1, p = 2, q = 2, r = 2 and R2 = ethylene, X is not
O.
Although not preferred, polythioethers according to the invention can
also include difunctional vinyl-terminated polythioethers. That is, in formula
II,
y = 1 and R4 is - CH = CH2. These polymers are produced, for example, by
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reacting a dithiol or mixture thereof with an excess of a divinyl ether or
mixture
thereof, as discussed in detail below. Analogous capped polythioethers
include terminal - (CH2-)2- S - R5.
Preferably, the mercapto-terminated polymers are essentially free of
sulfone, ester or disulfide linkages, and more preferably free of such
linkages.
The absence of these linkages can provide good fuel and temperature
resistance and good hydrolytic stability. As used herein, "essentially free of
sulfone, ester or disulfide linkages" means that less than 2 mole percent of
the
linkages in the mercapto-terminated polymer are sulfone, ester or disulfide
linkages. Disulfide linkages are particularly susceptible to thermal
degradation, sulfone linkages are particularly susceptible to hydrolytic
degradation.
Mercapto-terminated polymers useful in the formulations of the present
invention have a mercapto functionality of at least 2. Polyfunctional analogs
of the foregoing difunctional mercapto-terminated polymers can be prepared
by reacting one or more compounds of formula IV and one or more
compounds of formula V, in appropriate amounts, with one or more
polyfunctionalizing agents.
The term "polyfunctionalizing agent" as employed herein denotes a
compound having more than two moieties that are reactive with -SH and/or -
CH=CH2 groups. The polyfunctionalizing agent preferably includes from 3 to
6 such moieties, and thus is denoted a "z-valent" polyfunctionalizing agent,
where z is the number (preferably from 3 to 6) of such moieties included in
the
agent, and hence the number of separate branches which the polyfunctional
mercapto-terminated polymer comprises.
The polyfunctionalizing agent can be represented by the formula
B-(R$)~
where R$ denotes a moiety or several moieties that are reactive with -SH or
-CH=CH2 groups, and B is the z-valent residue of the polyfunctionalizing
agent, i.e., the portion of the agent other than the reactive moieties R8.
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Polyfunctional mercapto-terminated polymers according to the present
invention thus preferably have the formula:
B-{R8~-CH2CH2-O-(R2-O)mCH2CH2-S-R~-[-S-CHzCH~-O-(RZ-O)m -CHz-S-R~~~ SH}z
or
B-{R8~-S-R~-[-S-C H2CH2-O-(R2-O),r-CH2-S-R~ ]~-S H}Z
wherein
B denotes a z-valent residue of a polyfunctionalizing agent,
R~, R2, n and m denote structures and values discussed above with
reference to Formula I,
R$ denotes a moiety which is reactive with a terminal vinyl group or
mercapto group, and
z is an integer from 3 to 6.
Polyfunctional polythioethers according to the present invention can
preferably have the formula (III):
B --(A- [R3]y - R4)z (I I I)
wherein
A denotes a structure having the formula I,
Y is0or1,
R3 denotes a single bond when y = 0
and - S - (CH2)2 -[- O - R2-]m- O - when y = 1,
R4 denotes -SH or - S -(-CH2-)2+S - O - R5 when y = O
and - CH = CH2 or - (CH2-)2- S - R5 when y = 1,
R5 denotes C~_6 alkyl that is unsubstituted or substituted with at least one
-OH or -NHR' group,
R' denotes H or a Cq_g n-alkyl group,
s is an integer from 0 to 10,
z is an integer from 3 to 6, and
B denotes a z-valent residue of a polyfunctionalizing agent.
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As with the preceding difunctional embodiments, the foregoing
polyfunctional polythioethers of the present invention optionally include
terminal -SH or -CH=CH2 groups, or are capped and thus include terminal -S-
(-CH2-)2+S -O-R5 or -(CH2-)2-S-R~ groups. Partially capped polyfunctional
polymers, i.e., polymers in which some but not all of the branches are capped,
are also within the scope of the present invention.
Specific polyfunctionalizing agents include trifunctionalizing agents,
that is, compounds with z=3. Preferred trifunctionalizing agents include
triallylcyanurate (TAC), which is reactive with dithiol, and 1,2,3-
propanetrithiol,
which is reactive with polyvinyl ether. Agents having mixed functionality,
i.e.,
agents that include moieties which are typically separate moieties that react
with both thiol and vinyl groups, can also be employed.
Other useful polyfunctionalizing agents include trimethylolpropane
trivinyl ether, and the polythiols described in U.S. Pat. No. 4,366,307; U.S.
Pat. No. 4,609,762 and U.S. Pat. No. 5,225,472, the disclosures of each of
which are incorporated in their entireties herein by reference. Mixtures of
polyfunctionalizing agents can also be used.
Polyfunctionalizing agents having more than three reactive moieties
(i.e., z > 3) afford "star" polymers and hyperbranched polymers. For example,
two moles of TAC can be reacted with one mole of a dithiol to afford a
material having an average functionality of 4. This material can then be
reacted with a diene and a dithiol to yield a polymer, which can in turn be
mixed with a trifunctionalizing agent to afFord a polymer blend having an
average functionality between 3 and 4.
Inventive polymers as described above have a wide range of average
functionality. For example, trifunctionalizing agents afford average
functionalities from about 2.05 to 3.0, preferably about 2.1 to 2.6. Wider
ranges of average functionality can be achieved by using tetrafunctional or
higher polyfunctionalizing agents. Functionality will also be affected by
factors
such as stoichiometry, as is known to those skilled in the art.
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It is contemplated that other functional groups may be employed as a
substitute for the thiol groups discussed herein to react with the curing
agent
in order to form the polyfunctional material of the present invention. These
functional groups include, for example, hydroxyl functional groups and amine
groups. These thiol substitutes may be employed in the reaction chemistry by
one of ordinary skill in the art of sealant formation based upon the examples
and methodology discussed herein.
Thus, according to one method for making polyfunctional polymers of
the present invention, (n+1 ) moles of a compound or compounds having the
formula IV, (n) moles of a compound or compounds having the formula V, and
a z-valent polyfunctionalizing agent in an amount sufficient to obtain a
predetermined molecular weight and functionality, are combined to form a
reaction mixture. The mixture is then reacted in the presence of a suitable
catalyst as described above to afford mercapto-terminated polyfunctional
polymers. Capped analogs of the foregoing mercapto-terminated
polyfunctional polymers are prepared by inclusion in the starting reaction
mixture of about 0.05 to about (z) moles one or more appropriate capping
compounds VI. Use of (z) moles affords fully capped polyfunctional polymers,
while use of lesser amounts again yields partially capped polymers.
The inventive polymers preferably are prepared by combining at least
one compound of formula IV and at least one compound of formula V,
optionally together with one or more capping compounds VI and/or VII as
appropriate, and/or a polyfunctionalizing agent, followed by addition of an
appropriate catalyst, and carrying out the reaction at a temperature from
about 50 to about 120°C for a time from about 2 to about 24 hours.
Preferably, the reaction is carried out at a temperature from about 70 to
about
90°C for a time from about 2 to about 6 hours.
Since the inventive reaction is an addition reaction, rather than a
condensation reaction, the reaction typically proceeds substantially to
completion, i.e., the inventive mercapto-terminated polymers are produced in
yields of approximately 100%. No or substantially no undesirable by-products
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are produced. In parfiicular, the reaction does not produce appreciable
amounts of malodorous cyclic by-products such as are characteristic of
several known methods for producing polythioethers. Moreover, the polymers
prepared according to the invention are substantially free of residual
catalyst.
Methods of making the foregoing polyfunctional inventive polymers are
discussed in detail below.
Preferably, the mercapto-terminated polymer has a viscosity of less
than about 500 poise at a temperature of about 25°C and a pressure of
about
760 mm Hg determined according to ASTM D-2849 ~ 79-90 using a
Brookfield viscometer.
The mercapto-terminated polymer or combination of mercapto-
terminated polymers as detailed herein preferably is present in the
polymerizable sealant composition in an amount from about 30 wt% to about
90 wt%, more preferably about 40 to about 80 wt%, very preferably about 45
to about 75 wt%, with the wt% being calculated based on the weight of total
solids of the composition.
The sealant or potting formulations of the present invention further
comprise one or more curing agents, such as polyolefins, polyacrylates, metal
oxides, polyepoxides and mixtures thereof as appropriate. Curing agents
useful in polymerizable sealant compositions of the invention include
polyepoxides or epoxy functional resins, for example, hydantoin diepoxide,
bisphenol-A epoxides, bisphenol-F epoxides, novolac type epoxides, aliphatic
polyepoxides, and any of the epoxidized unsaturated and phenolic resins.
Other useful curing agents include unsaturated compounds such as acrylic
and methacrylic esters of commercially available polyols, unsaturated
synthetic or naturally occurring resin compounds, TAC, and olefinic
terminated derivatives of the compounds of the present invention. In addition,
useful cures can be obtained through oxidative coupling of the thiol groups
using organic and inorganic peroxides (e.g., Mn02) known to those skilled in
the art. Selection of the particular curing agent may afFect the Tg of the
cured
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composition. For example, curing agents that have a T9 significantly lower
than the Tg of the polythioether may lower the Tg of the cured composition.
Depending on the nature of the mercapto-terminated polymers) used
in the composition, the composition can comprise about 90% to about 150%
of the stoichiometric amount of the selected curing agents) based upon -SH
equivalents, preferably about 95 to about 125%.
Fillers useful in the polymerizable compositions of the invention for
aerospace application include those commonly used in the art, such as
carbon black and calcium carbonate (CaC03). Potting compound fillers
illustratively include high band gap materials such as zinc sulfide and
inorganic barium compounds. Preferably, the compositions include about 10
to about 70 wt% of the selected filler or combination of fillers, more
preferably
about 10 to 50 wt% based upon the total weight of the composition.
The sealant and potting compositions of the present invention can
comprise one or more adhesion promoters. Suitable adhesion promoters
include phenolics such as METHYLON phenolic resin available from
Occidental Chemicals, organosilanes such as epoxy, mercapto or amino
functional silanes such as A-187 and A-1100 available from OSi Specialities.
Preferably, an adhesion promoter is employed in an amount from 0.1 to 15
wt% based upon total weight of the formulation.
Common substrates to which the sealant compositions of the present
invention are applied can include titanium, stainless steel, aluminum,
anodized, primed, organic coated and chromate coated forms thereof, epoxy,
urethane, graphite, fiberglass composite, ICEVLAR~, acrylics and
polycarbonates.
Preferably, a plasticizer is present in the sealant formulation in an
amount ranging from 1 to 8 weight percent based upon total weight of the
formulation. Piasticizers that are useful in polymerizable compositions of the
invention include phthalate esters, chlorinated paraffins, hydrogenated
terphenyls, etc.
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The formulation can further comprise one or more organic solvents,
such as isopropyl alcohol, in an amount ranging from 0 to 15 percent by
weight on a basis of total weight of the formulation, preferably less than 15
weight percent and more preferably less than 10 weight percent.
A typical sealant formulation is provided in Example 18.
Polymerizable sealant composition cure time is reduced considerably
by using an organic amine catalyst having a pKb of 10 or above. Preferred
organic amine catalysts are organic tertiary amines. Specific catalysts which
are useful in the present invention are triethylene diamine, diazabicyclo
(2,2,2)
octane (DABCO) (preferred), diazabicycloundecene (DBU), 2,4,6-
tri(dimethylamino methyl) phenol (DMP-30) and tetramethyl guanidine (TMG).
The reaction time when utilizing the organic amine catalysts, and particularly
the organic tertiary amine catalysts, is in general between about one hour to
about 20 hours which is a considerable difference compared to using no
amine catalyst.
Generally the amount of catalyst ranges from 0.05 wt% to 3 wt%,
based on the total weight of the starting reactants.
The foregoing sealant or potting formulations preferably are cured at
ambient temperature and pressure, however the formulations generally can
be cured at a temperature ranging from about 0°C to about 100°C.
In addition to the foregoing ingredients, polymerizable sealant
compositions of the invention can optionally include one or more of the
following: pigments; thixotropes; retardants; and masking agents.
Useful pigments include those conventional in the art, such as carbon
black and metal oxides. Pigments preferably are present in an amount from
about 0.1 to about 10 wt% based upon total weight of the formulation.
Thixotropes, for example fumed silica or carbon black, are preferably
used in an amount from about 0.1 to about 5 wt% based upon total weight of
the formulation.
An additional advantage of sealant formulations according to the
invention is their improved curing behavior. The extent of cure of a sealant
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formulation as a function of time is often difficult to measure directly, but
can
be estimated by determining the extrusion rate of the composition as a
function of time. The extrusion rate is the rate at which a mixed sealant
formulation, i.e., a sealant formulation together with an accelerator system,
is
extruded from an applicator device. As the sealant formulation is mixed with
the accelerator system, curing begins, and the extrusion rate changes with
time. The extrusion rate thus is inversely related to the extent of cure. When
the extent of cure is low, the viscosity of the mixed ungelled sealant
formulation is low and thus the extrusion rate is high. When the reaction
approaches completion, the viscosity becomes very high, and the extrusion
rate thus becomes low. The extrusion rate can be measured according to
AMS Method 3276 (section 4.5.10), which is incorporated herein by reference.
With reference to FIG. 1, the viscosity of some known types of sealant
formulations remains low for an extended time, because the compositions are
slow to cure. Such formulations have extrusion curves qualitatively similar to
curve A. Other known types of sealant formulations cure very quickly, and
thus their viscosity rapidly increases. Consequently, the extrusion rate
rapidly
decreases, as shown in curve B. Desirably, a mixed sealant formulation
should have a low viscosity, and thus a high extrusion rate, for a length of
time sufficient to allow even application of the sealant formulation to the
area
requiring sealing, but then should cure rapidly after application, i.e., their
extrusion rate should quickly decrease. Sealant formulations according to the
present invention are characterized by this desirable extrusion curve, as
illustrated qualitatively in curve C.
Sealant formulations according to the present invention can have,
depending on the particular formulation, initial extrusion rates as high as
500
g/min or higher, together with low extrusion rates on the order of about 5 to
10
g/min or less after curing times on the order of one hour.
As shown in FIG. 2, the initial extrusion rate of a sealant containing a
polymer of the present invention (Example 1, below, cured with an epoxy
curing agent as described below) is about 550 g/min, then falls rapidly to
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about 20 g/min after 70 minutes. In comparison, a known polysulfide polymer
based sealant (cured with Mn02) has an initial extrusion rate of about 90
g/min, which slowly falls to about 20 g/min after 70 minutes.
Another preferred curable sealant formulation combines one or more
plasticizers with the mercapto-terminated polymer(s), curing agents) and
fillers) described above. Use of a plasticizer allows the polymerizable
formulation to include mercapto-terminated polymers which have higher Tg
than would ordinarily be useful in an aerospace sealant or potting compound,
i.e., use of a plasticizer effectively reduces the Tg of the formulation, and
thus
increases the low-temperature flexibility of the cured polymerizable
formulation beyond that which would be expected on the basis of the T9 of the
mercapto-terminated polymers alone.
The present invention is illustrated in more detail by means of the
following non-limiting examples which are presently representative of
preferred embodiments. These examples are exemplary and are not intended
as a limitation on the scope of the invention as detailed in the appended
claims.
EXAMPLES
In Examples 1-8, liquid polythioethers were prepared by stirring
together one or more dithiols with one or more divinyl ethers and a
trifunctionalizing agent. The reaction mixture was then heated and a free
radical catalyst was added. All reactions proceeded substantially to
completion (approximately 100% yield).
Example 1
In a 2 L flask, 524.8 g (3.32 mol) of diethylene glycol divinyl ether
(DEG-DVE) and 706.7 g (3.87 mol) of dimercaptodioxaoctane (DMDO) were
mixed with 19.7 g (0.08 mol) of triallylcyanurate (TAC) and heated to
77°C.
To the heated reaction mixture was added 4.6 g (0.024 mol) of an azobisnitrile
free radical catalyst (VAZO~ 67 [2,2'-azobis(2-methylbutyronitrile),
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commercially available from DuPont). The reaction proceeded substantially to
completion after 2 hours to afford 1250 g (0.39 mol, yield 100%) of a liquid
polythioether resin having a Tg of -68°C and a viscosity of 65 poise
and a
number average molecular weight of about 3165 grams per mole and a thiol
functionality of 2.2. The polymer was faintly yellow and had low odor.
Example 2
In a 1 L flask, 404.4 g (1.60 mol) of PLURIOL~ E-200 divinyl ether and
355.88 g (1.94 mol) of DMDO were mixed with 12.1 g (0.049 mol) of TAC and
reacted as in Example 1. The reaction proceeded substantially to completion
after 5 hours to afford 772 g (0.024 mol, yield 100%) of a resin having a T9
of
-66°C and a viscosity of 48 poise. The polymer was yellow and had low
odor.
Example 3
In a 100 mL flask, 33.2 g (0.21 mol) of DEG-DVE and 26.48 g (0.244
mol) of 1,2-propanedithiol were mixed with 0.75 g (0.003 mol) of TAC and
heated to 71 °C. To the heated reaction mixture was added 0.15 g (0.8
mmol)
of VAZO~ 67. The reaction proceeded substantially to completion after 7
hours to afford 60 g (0.03 mol, yield 100%) of a resin having a Tg of -61
°C and
a viscosity of 22 poise. The polymer had a noticeable PDT (propane dithiol)
odor.
Example 4
In a 100 mL flask, 33.3 g (0.136 mol) of tripropylene glycol divinyl ether
(DPE-3) and 27.0 g (0.170 mol) of dimercaptodiethylsulfide (DMDS) were
mixed with 0.69 g (0.003 mol) of TAC and heated to 77°C. To the heated
reaction mixture was added 0.15 g (0.8 mmol) of VAZO~ 67. The reaction
proceeded substantially to completion after 6 hours to afford 61 g (0.028 mol,
yield 100%) of a polymer having a T9 of -63°C and a viscosity of 26
poise.
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Example 5
In a 250 mL flask, 113.01 g (0.447 mol) of PLURIOL~ E-200 divinyl
ether and 91.43 g (0.498 mol) of DMDO were mixed with 1.83 g (0.013 mol) of
1,2,3-propanetrithiol (PTT) and allowed to react exothermically for 72 hours.
The mixture was then heated to 80°C. To the heated reaction
mixture was
added 0.2 g (1 mmol) of VAZO~ 67. The reaction mixture was maintained at
80°C, and the reaction proceeded substantially to completion after 3
hours to
afford 200 g (0.06 mol, yield 100%) of a polymer having a Tg of -66°C
and a
viscosity of 55 poise.
Example 6
In a small jar, 14.0 g (0.055 mol) of PLURIOL~ E-200 divinyl ether,
6.16 g (0.0336 mol) of DMDO and 5.38 g (0.0336 mol) of DMDS were mixed
with 0.42 g (0.017 mol) of TAC (briefly heated to melt the TAC) and heated to
82°C. To the heated reaction mixture was added 0.2 g (0.001 mol) of
VAZO~
67. The reaction proceeded substantially to completion after 18 hours to
afford 26 g (8.4 mmol, yield 100%) of a polymer having a Tg of -63°C
and a
viscosity of 80 poise.
Example 7
In a small jar, 13.55 g (0.054 mol) of PLURIOL.~ E-200 divinyl ether,
10.44 g (0.057 mol) of DMDO and 1.44 g (8.1 mmol) of
ethylcyclohexanedithiol (ECHDT) were mixed with 0.40 g (1.6 mmol) of TAC
(heated briefly to melt the TAC) and heated to 82°C. To the heated
reaction
mixture was added 0.2 g (0.001 mol) of VAZO~ 67. The reaction proceeded
substantially to completion after 5 hours to afford 26 g (8.1 mmol, yield
100%)
of a polymer having a T9 of -66°C and a viscosity of 58 poise.
Example 8
!n a small glass jar, 9.11 g (0.036 mol) of PLURIOL~ E-200 divinyl
ether, 5.71 g (0.031 mol) of DMDO, 1.52 g (7.8 mmol) of ECHDT, 5.08 g
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(0.031 mol) of DMDS and 4.11 g (0.024 mol) of hexanediol divinyl ether
(HD-DVE) were mixed with 0.39 g (1.6 mmol) of TAC (heated briefly to
dissolve the TAC) and heated to 82°C. To the heated reaction mixture
was
added 0.6 g (3.1 mmol) of VAZO~ 67. The reaction proceeded substantially
to completion after about 45 hours to afford 2.6 g (7.8 mmol, yield 100%) of a
polymer having a T9 of -66°C and a viscosity of 304 poise. The polymer
had a
cloudy appearance.
Each of the foregoing polymers was evaluated for odor. The following
scale was employed: 3: strong, ofFensive odor; 2: moderate odor; 1: slight
odor; 0: substantially odorless.
The polymer described in Example 3 of U.S. Pat. No. 4,366,307 was
used as a control. This polymer (the "control polymer") had an odor of 3.
Results were as follows:
Pol Odor Pol mer Odor
mer
1 1 5 1
2 1 6 1
3 3 7 1
4 1 8 2
All of the liquid polythioethers thus had little or moderate odor except
polymer 3, which had a strong odor.
The polymers prepared in Examples 1-8 were then cured. Curing was
carried out using the uncompounded resins with a curing agent and DABCO
accelerator. The curing agent had the following composition:
epoxy novolac' (equivalent weight 175.5) 22 wt
hydantoin epoxy2 (equivalent weight 132) 34 wt
calcium carbonate 34 wt
carbon black 5 wt
silane adhesive promoter 5 wt
DEN-431 epoxy novolac available from Dow Chemical of Midland, Michigan.
Z ARACAST XU A4 238 hydantoin epoxy available from Ciba-Geigy.
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The cured resins were evaluated for odor according to the procedure
set forth above. The Tg and the percent weight gain after immersion in JRF
type 1 for one week at room temperature and pressure were also measured
for each of the cured resins. The volume swell and weight gain percentages
were determined for each cured material as follows:
w~ = initial weight in air
w2 = initial weight in H20
w3 = final weight in air
w4 = final weight in H20
% volume swell = 100 x [(w2 + w3)-(W~ + w4)]~(w1 - w2)
weight gain = 100 x (w3 - W1)~w1
The results are given in Table 1:
TABLE 1
Cured Resin 1 2 3 4 5 6 7 8
~
Odor 0 0 0 0 0 0 0 0
Tg (C) -59 -61 -61 -63 -62 -56 -59 -58
fuel swell 19 22 -- -- 23 19 24 27
wt. Gain ~ 14 15 15 23 15 15 19 20
In comparison, the control polymer had an odor of 1-2 when cured.
Example 9
Polythioethers having a number average molecular weight of 2100 and
an average SH functionality F of 2.1 were prepared by combining a divinyl
ether with a dithiol as shown in Table 2 and reacting the materials as
previously described herein. The uncompounded polythioethers were then
cured using 15 g of the curing agent described above and 0.30 g of DABCO.
For each polythioether so prepared, the following quantities were measured:
viscosity (uncured material, poise p); Shore A hardness (cured material, Rex
durometer value); % weight gain (cured material) after one week at
140°F
(60°C) and atmospheric pressure in JRF type 1; and Tg (cured material,
°C).
Results were as follows:
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TABLE 2
Dithiol ECHDT DMDS DMDO HDT
Divinyl
Ether
DEG-DVE 145 p (solid) 27 p 24 p
44 Rex 94 Rex 25 Rex 25 Rex
27% 3% 14% 29%
-53 -63 -69 -77
PLURIOL~a 77 p 41 p 59 p 25 p
43 Rex 47 Rex 27 Rex 23 Rex
27% 11 % 18% 30%
-57 -61 -67 -76
BD-DVE" 185 p (solid) (solid) (solid)
42 Rex -- 20 Rex 22 Rex
44% -- 21 % 44%
-59 -- -79 -85
HD-DVE 155 p (solid) (solid) (soft solid)
50 Rex -- 14 Rex 29 Rex
57% -- 27% 68%
-60 -63 -78 -86
Poly-THF 91 p (solid) 27 p --
30 Rex 75 Rex 17 Rex --
64% 29% 37% --
-69 -79 -79 __
°PLURIOL~ E200 divinyl ether
bButanediol divinyl ether
~polytetrahydrofuran divinyl ether
dHexanedithiol
From the foregoing table it is apparent that the following combinations
of divinyl ether and dithiol afford liquid polythioethers having good fuel
resistance and low temperature flexibility when cured: PLURIOL~
E-200/DMDO; and DEG-DVE/DMDO. Other potentially useful combinations
include DEG-DVE/ECHDT; DEG-DVE/HDT; PLURIOL~ E-200/ECHDT;
PLURIOL~ E-200/HDT; and poly-THF/DMDO. PLURIOL~ E-200/DMDS also
has excellent fuel resistance and low temperature flexibility when cured, but
the uncompounded material does not remain in a liquid state for an extended
period of time.
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Example 10 Addition of DMDS to PLURIOLO/DMDO Polymers
Four liquid polythiol ether polymers were prepared as previously
described herein. The polymers had the following compositions (listed values
are molar equivalents):
1 2 3 4
PLURIOL~ E-200 6.6 6.6 6.6 6.6
DMDO 8 6 4.5 4
DMDS 0 2 3.5 4
To each of these polymers was added 0.2 molar equivalents of TAC to
afford a number average molecular weight of about 3000 and a SH
functionality F of 2.2. Each resultant uncompounded polymer was cured as in
Example 9 (15 g of the curing agent composition and 0.30 g of DABCO). For
each polymer, the following properties were measured: Tg (resin, °C);
Tg
(cured, °C); viscosity (p); % swell in JRF type 1; % weight gain in JRF
type 1;
and % weight gain in water. Results are given in Table 3.
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TABLE 3
1 2 3 4
Tg (resin) -67 -66 -64 -63
(cured) -59 -58 -56 -56
Viscosity 59 53 62 80
JRF
Swell 24 21 21 20
Wt Gain 18 15 16 16
H20
Wt Gain 11.8 11.5 7.4 7.5
All of the foregoing polymers displayed excellent fuel resistance.
Polymers 1 and 2 in particular also displayed excellent low temperature
flexibility when tested according to AMS 3267 ~ 4.5.4.7.
Example 11 Addition of ECHDT to PLURIOLO/DMDO Polymers
Four liquid polythiol ether polymers were prepared as previously
described herein. The polymers had the following compositions (listed values
are molar equivalents):
1 2 3 4
PLURIOL~ E-200 6.6 6.6 6.6 6.6
DMDO 8 7 6 5
ECHDT 0 1 2 3
Each of these polymers had a number average molecular weight of
about 3000 and a SH functionality F of 2.2. Each resultant uncompounded
polymer was cured as in Example 10. For each polymer, the following
properties were measured: Tg (resin, °C); Tg (cured, °C);
viscosity (p); % swell
in JRF type 1; % weight gain in JRF type 1; and % weight gain in water.
Results are given in Table 4.
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TABLE 4
1 2 3 4
T9 (resin) -67 -66 -65 -64
(cured) -59 -59 -58 -56
Viscosity 59 36 44 50
JRF type
1
Swell 24 21 28 29
Wt Gain 18 18 19 19
H20
Wt Gain 11.8 10.8 8.3 7.8
All of the foregoing polymers displayed good fuel resistance and low
temperature flexibility.
Example 12
In a 250 mL 3-neck flask equipped with a stirrer, thermometer and
condenser, 87.7 g (0.554 mol) of DEG-DVE and 112.3 g (0.616 mol) of
DMDO are mixed and heated to 77°C (about 170°F). To the
mixture is added
0.8 g (4.2 mmol) of VAZO~ 67 catalyst. The reaction mixture is reacted at
82°C (about 180°F) for about 6 hours to afford 200 g (0.06 mol,
yield 100%) of
a low viscosity liquid polythioether resin having a thiol equivalent weight of
1625 and a SH functionality F of 2Ø
Example 13
In a 250 mL 3-neck flask equipped with a stirrer, thermometer and
condenser, 26.7 g (0.107 mol) of TAC, 56.4 g (0.357 mol) of DEG-DVE and
117.0 g (0.642 mol) of DMDO are mixed and heated to 77°C (about
170°F).
To the mixture is added 0.8 g (4.2 mmol) of VAZO 67 catalyst. The reaction
mixture is reacted at 82°C (about 180°F) for about 6 hours to
afford 200 g
(0.07 mol, yield 100%) of a high viscosity liquid polythioether resin having
an
equivalent weight of 800 and a SH functionality F of about 3.5.
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Example 14 Sealant Composition
A sealant composition including the DMDO/DEG-DVE polythioether
polymer of Example 1 was compounded as follows (amounts in parts by
weight):
DMDO/DEG-DVE Polythioether 100
Calcium carbonate 60
Magnesium oxide 1
Phenolic resin3 1
DMP-30 1
Isopropyl alcohol 3
The compounded polymer was mixed intimately with the epoxy resin
curing agent of Examples 9-11 above, in the weight ratio of 10:1 and cured at
ambient temperature and humidity. Tensile strength and elongation were
evaluated according to ASTM 3269 and AMS 3276. The die used to prepare
the test samples is described in ASTM D 412. The die used to prepare test
samples for tear strength testing is described in ASTM D1004. The following
physical properties were obtained for the cured composition:
Cure hardness at 25°C 60 Shore A
Tensile strength at break 550 psi
Elongation at break 600%
Notched tear strength 100 p/i
Low-temperature flexibility Passed
(AMS 3267 ~4.5.4.7)
Example 15 Sealant Composition
A sealant composition including the ECHDT/DEG-DVE polythioether
polymer of Example 9 was compounded as follows (amounts in parts by
weight):
3 METHYLON 75108 phenolic resin available from Occidental Chemical.
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ECHDT/DEG-DVE Polythioether 100
Calcium carbonate 54
Hydrated aluminum oxide 20
Magnesium oxide 1
Phenolic resin of Example 1
14
Hydrogenated terphenyl plasticizer6
DM P-30 1
Isopropyl alcohol 3
The compounded polymer was mixed intimately with an epoxy resin
curing agent of Examples 9-12 above in the weight ratio of 10:1 and cured at
ambient temperature and humidity. The following physical properties were
obtained for the cured composition:
Cure hardness at 25°C 72 Shore A
Tensile strength at break 550 psi
Elongation at break 450%
Notched tear strength 85 p/i
Low-temperature flexibility Passed
Example 16 OH-Terminated Capped Polythioether
In a 500 ml flask, 275.9 g (1.09 mol) PLURIOLO E-200 divinyl ether,
174.7 g (0.95 mol) DMDO, 28.7 g (0.30 mol) 3-mercaptopropanol and 1.83 g
(7.3 mmol) TAC were mixed. The mixture was heated to 70°C, and 2.3 g
(12
mmol) VAZO~ 67 were added slowly. The reaction mixture was stirred and
heated at 85-90°C for 4 hours to afford 480 g (0.15 mol, yield 100%) of
a
polymer having an OH equivalent weight of 1670 (number average molecular
weight = 3200, OH functionality F=2.05).
Example 17 OH-Terminated Capped Polythioether
In a 250 ml flask, 104.72 g (0.57 mol) DMDO, 80.73 g (0.51 mol) DEG-
DVE and 14.96 g (0.13 mol) butanediol monovinyl ether were mixed and
heated to 75°C. To the heated mixture 0.60 g (3 mmol) VAZOO 67 were
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added slowly. The reaction mixture was stirred and heated at 75-85°C
for 6
hours to afford 200 g (0.064 mol, yield 100%) of a clear, nearly colorless
polymer with very iow odor and a viscosity of 79 poise at 20°C. The OH
equivalent weight was 1570 (number average molecular weight = 3200, OH
functionality F = 2.00).
Example 18 Sealant Composition
A sealant composition including the DMDOIDEG-DVE polythioether
polymer of Example 1 was compounded as follows (amounts in weight
percent):
BASE COMPOSITION:
Wt. % Component
0.277 Tung oil
1.053 triethylene diamine, diazabicyclo
(2,2,2) octane4
55.466 Polythioether polymer of Example
1
0.831 Phenolic resin adhesion promoters
0.554 Phenolic/polysulfide adhesion promoters
0.277 Titanate'
1.108 Amino functional silane8
0.222 Fumed silica
0.554 Titanium dioxide
0.831 Amorphous silica
8.320 Aluminum hydroxide
30.506 precipitated calcium carbonate
4 DABCO triethyl amine, diazabicyclo (2,2,2) octane available from Air
Products & Chemicals.
5 METHYLON 75108 phenolic resin available from Occidental Chemical.
6 The phenolic/polysulfide adhesion promoter was prepared by reacting about
31% VARCUM
29202 phenolic resin, 66% Thiokol LP-3 polysulfide and 3% of a polymer
prepared according
to Example 4 of U.S. Patent No. 4,623,711 (at a ratio of 1 mole dithiol to 1
mole polysulfide)
(incorporated by reference herein) at a temperature of about 150°F
(65°C) for 45 mins, then
heated to 230°F (110°C) over a 45-60 minute period, then heated
at 230°F (110°C) for 165
mins.
' TYZOR TBT titanate available from E.I. duPont de Nemours Company.
8 A-1100 amino functional silane available from OSi Specialities, Inc.
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ACCELERATOR:
Wt. % Component
26.525 Bisphenol A di~lycidyl
ethers
17.684 Epoxy novolac
10.699 Plasticizes"
42.440 Calcium carbonate
0.221 Carbon black
0.088 Carbamate salt'2
2.247 Epoxy functional silane'3
0.085 Deionized water
0.011 Diphenylguanidine
Each of the components of the Base Composition was mixed
sequentially in the order listed. In a separate container, each of the
components of the Accelerator was mixed sequentially in the order listed. A
sealant formulation according to the present invention was prepared by mixing
100 grams of the Base Composition with 18.5 grams of the Accelerator.
The compositions of the present invention are useful in aerospace
applications such as aerospace sealants and linings for fuel tanks; and as
electrical potting or encapsulant compounds. An aerospace sealant material
according to the present invention can exhibit properties including extreme
temperature performance, fuel resistance and flexural strength. The
formulations detailed herein are well suited for use as potting compounds to
encapsulate electrical and electronic components that can experience
temperature extremes, chemically harsh environments and mechanical
vibrations.
The foregoing description is illustrative of particular embodiments of the
invention, but is not meant to be a limitation upon the practice thereof. The
following claims, including all equivalents thereof, are intended to define
the
scope of the invention.
9 EPON 828 bisphenol A diglycidyl ether available from Shell Chemical.
'° DEN 431 epoxy novolac available from Dow Chemical.
11 Hg_40 plasticizes available from Monsanto Co.
'2 Ferbam 76% WDG carbamate salt available from Cabot Corp.
'3 A-187 epoxy functional silane available from OSi Specialities, Inc.
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