U.S. patent application number 14/885706 was filed with the patent office on 2016-09-15 for polyhemiaminal and polyhexahydrotriazine materials from 1,4 conjugate addition reactions.
The applicant listed for this patent is International Business Machines Corporation. Invention is credited to Dylan J. BODAY, Mareva FEVRE, Jeannette M. GARCIA, James L. HEDRICK, Rudy J. WOJTECKI.
Application Number | 20160264744 14/885706 |
Document ID | / |
Family ID | 56886447 |
Filed Date | 2016-09-15 |
United States Patent
Application |
20160264744 |
Kind Code |
A1 |
BODAY; Dylan J. ; et
al. |
September 15, 2016 |
POLYHEMIAMINAL AND POLYHEXAHYDROTRIAZINE MATERIALS FROM 1,4
CONJUGATE ADDITION REACTIONS
Abstract
Polyhemiaminal (PHA) and polyhexahydrotriazine (PHT) materials
are modified by 1,4 conjugate addition chemical reactions to
produce a variety of molecular architectures comprising pendant
groups and bridging segments. The materials are formed by a method
that includes heating a mixture comprising solvent(s),
paraformaldehyde, aromatic amine groups, aliphatic amine Michael
donors, and Michael acceptors, such as acrylates. The reaction
mixtures may be used to prepare polymer pre-impregnated materials
and composites containing PHT matrix resin.
Inventors: |
BODAY; Dylan J.; (Tucson,
AZ) ; FEVRE; Mareva; (San Jose, CA) ; GARCIA;
Jeannette M.; (San Jose, CA) ; HEDRICK; James L.;
(San Jose, CA) ; WOJTECKI; Rudy J.; (San Jose,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
International Business Machines Corporation |
Armonk |
NY |
US |
|
|
Family ID: |
56886447 |
Appl. No.: |
14/885706 |
Filed: |
October 16, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14642920 |
Mar 10, 2015 |
|
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14885706 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09D 5/03 20130101; C09D
161/22 20130101; C08F 12/28 20130101; C08C 19/22 20130101; C08G
16/0231 20130101; C08F 8/32 20130101; C08F 8/28 20130101; C08J
2379/04 20130101; C08G 12/08 20130101; C08G 73/0644 20130101; C09D
179/04 20130101; C08L 79/04 20130101; C08L 61/22 20130101; C08G
73/0638 20130101; C09D 179/04 20130101; C08G 73/0273 20130101; C09D
161/22 20130101; C08G 73/065 20130101 |
International
Class: |
C08J 5/24 20060101
C08J005/24; C09D 161/22 20060101 C09D161/22 |
Claims
1. A method of producing a composite article, comprising: forming a
mixture comprising a solvent, paraformaldehyde, an aromatic amine,
a Michael addition donor, and a Michael addition acceptor; heating
the mixture to a first temperature to produce a mixture of a first
viscosity; coating a work piece with the mixture of the first
viscosity to produce a prepreg; heating the prepreg to a second
temperature to produce a B-stage prepreg of a second viscosity;
cooling the B-stage prepreg; forming an article from the B-stage
prepreg; and heating the article at a temperature from about
150.degree. C. to about 280.degree. C. to form a cured composite
containing polyhexahydrotriazine.
2. The method of claim 1, wherein the mixture of the first
viscosity is produced at a temperature from about 20.degree. C. to
about 40.degree. C.
3. The method of claim 1, wherein the mixture of the first
viscosity comprises covalently bonded Michael addition reaction
products.
4. The method of claim 1, wherein the mixture of the first
viscosity comprises covalently bonded Michael addition reaction
products and PHA oligomers or polymers.
5. The method of claim 2, wherein the second temperature is about
40.degree. C. to about 145.degree. C.
6. The method of claim 5, wherein the B-stage prepreg of the second
viscosity comprises covalently bonded Michael addition reaction
products and PHA oligomers or polymers.
7. The method of claim 1, wherein the composite article comprises
at least an interpenetrating polymer network comprising two or more
polymers.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S. patent
application Ser. No. 14/642,920, filed Mar. 10, 2015. The
aforementioned related patent application is herein incorporated by
reference in its entirety.
FIELD
[0002] The present invention relates to methods of improving the
physical properties of polyhemiaminal (PHA) and
polyhexahydrotriazine (PHT) polymers and networks, and more
specifically to preparing new polyhemiaminals (PHAs) and
polyhexahydrotriazines (PHTs) with tailored macromolecular
architectures for application in the field of composite
materials.
BACKGROUND
[0003] PHAs and PHTs are an emerging class of high strength
engineering thermosetting polymers that have a unique combination
of properties. They have high modulus, solvent resistance, and
resistance to environmental stress cracking, yet they can be easily
recycled by decomposition to monomers in a strong acid.
Unfortunately, some PHAs and PHTs are brittle and have poor impact
resistance, which limits their applications.
[0004] There is a need for new lower cost functional PHA and PHT
materials and composites which may be B-staged, or partially cured,
and also combine the strengths of PHAs and PHTs, but with lower
brittleness, higher impact resistance and a method of producing
such materials and composites.
SUMMARY
[0005] PHA and PHT materials are modified by 1,4-conjugate addition
chemical reactions to produce a variety of molecular architectures
comprising pendant groups and bridging segments. The materials are
formed by a method that includes heating a mixture comprising
solvent(s), paraformaldehyde, aromatic amine groups, aliphatic
amine Michael donors, and Michael acceptors, such as acrylates. The
reaction mixtures may be used to prepare polymer pre-impregnated
materials and composites containing PHT matrix resin. Specifically,
embodiments of the disclosure include a PHT comprising a plurality
of trivalent hexahydrotriazine groups having the structure
##STR00001## [0006] and a plurality of phenyl groups having the
structure
##STR00002##
[0006] wherein each wavy bond site of a given hexahydrotriazine
group is covalently linked at a respective wavy bond site of a
phenyl group, and each wavy bond site of a given phenyl group is
covalently linked at a respective wavy bond site of a
hexahydrotriazine group, and wherein at least one of A, B, C, D,
and E is a chemical group that is a reaction product of a
1,4-conjugate addition chemical reaction, and wherein at least one
of A, B, C, D, and E is a Michael addition reaction product, more
specifically, at least one of A, B, C, D, and E is a chemical group
containing a Michael addition donor reaction product, wherein the
Michael addition donor comprises a material selected from the group
consisting of amines, thiols, sulphides, phosphines, phosphides
carbanions, and alkoxides. The recited PHT comprises at least one
of A, B, C, D, and E chemical groups containing a Michael addition
acceptor reaction product, wherein the Michael addition acceptor is
selected from the group consisting of alpha-beta unsaturated
esters, acrylates, methacrylates, alkyl methacrylates,
cyanoacrylates, acrylonitrile, acrylamides, maleimides, vinyl
sulfones, vinyl sulfoxides, vinyl sulfones, vinyl ketones, nitro
ethylenes, vinyl phosphonates, acrylonitrile, vinyl pyridines, azo
compounds, beta-keto acetylenes and acetylene esters. PHTs of the
disclosure further comprise of less than three Michael addition
reaction products that are covalently bound pendant groups, while
in other embodiments, each Michael addition reaction product
covalently bridges at least one hexahydrotriazine group to another
hexahydrotriazine group. In some embodiments, at least one of A, B,
C, D, and E comprises a Michael addition reaction product having a
polymeric segment selected from the group consisting of
poly(amides), poly(carbonates), poly(esters), poly(ether ketones)
poly(ethers), poly(etherimides), poly(imides), poly(olefins),
poly(siloxanes), poly(sulfones), halogenated polymers,
poly(phenylenes), poly(urethanes) and copolymers thereof, wherein
at least one polymeric segment has a repeating unit of at least
two. In further embodiments, the PHT comprises at least one polymer
interpenetrating network, that includes a non-PHT polymer, and
wherein the non-PHT polymer comprises at least one of the Michael
addition reaction products, that may be a radical-initiated
polymer. Embodiments of the disclosure elucidate a method of
producing a PHT containing composite article, comprising: forming a
mixture comprising a solvent, paraformaldehyde, an aromatic amine,
a Michael addition donor, and a Michael addition acceptor; heating
the mixture to a first temperature to produce a mixture of a first
viscosity; coating a work piece with the mixture of the first
viscosity to produce a prepreg; heating the prepreg to a second
temperature to produce a B-stage prepreg of a second viscosity;
cooling the B-stage prepreg; forming an article from the B-stage
prepreg; and heating the article at a temperature from about
150.degree. C. to about 280.degree. C. to form a cured composite
containing polyhexahydrotriazine. More specifically, in some
embodiments the mixture of the first viscosity is produced at a
temperature from about 20.degree. C. to about 40.degree. C., and
the mixture of the first viscosity comprises covalently bonded
Michael addition reaction products. The mixture of the first
viscosity also may comprise covalently bonded Michael addition
reaction products and PHA oligomers or polymers. The second
temperature is about 40.degree. C. to about 145.degree. C., wherein
the B-stage prepreg of the second viscosity comprises covalently
bonded Michael addition reaction products and PHA oligomers or
polymers. A PHT composite article produced by the method may also
contain at least an interpenetrating polymer network comprising two
or more polymers.
BRIEF DESCRIPTION OF THE FIGURES AND DRAWINGS
[0007] So that the manner in which the above recited features of
the present disclosure can be understood in detail, a more
particular description of the disclosure, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings and in the body of the
specification. It is to be noted, however, that the appended and
embedded drawings illustrate only typical embodiments of this
disclosure and are therefore not to be considered limiting of its
scope, for the disclosure may admit to other equally effective
embodiments.
[0008] FIG. 1 shows exemplary chemical compounds that may be used
according to some embodiments of the disclosure.
[0009] FIG. 2A is a representation of a polymer material structure
according to one embodiment of the disclosure.
[0010] FIG. 2B is a representation of a polymer material structure
according to another embodiment of the disclosure.
[0011] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures and drawings. It is contemplated
that elements disclosed in one embodiment may be beneficially
utilized on other embodiments without specific recitation.
DETAILED DESCRIPTION
[0012] New PHA and PHT materials and their methods of preparation
are disclosed with properties that are useful in the field of
composite materials. In particular, the new PHAs and PHTs may serve
as a matrix resin in a polymer pre-impregnated mat (pre-preg) and
for light-weight and high strength composites in the fields of
electronics, automotive, and aerospace. To that end, Michael
addition chemical reactions, a subset of 1,4 conjugate addition
chemical reactions, are used to prepare modified PHA and PHT
materials with improved properties.
[0013] As illustrated in reaction example 1, PHAs and PHTs may be
prepared by the exemplary reaction of aromatic diamines (ODA),
paraformaldehyde (CH.sub.2O).sub.n in N-methyl-2-pyrrolidone (NMP)
solvent:
Reaction Example 1
##STR00003##
[0015] Per reaction example 1, the PHAs are generally prepared at a
temperature from about 40.degree. C. to about 60.degree. C. The
PHAs form films when cast from a polar aprotic solvents (e.g.,
NMP), and the PHA films are stable at a temperature from about
20.degree. C. to less than about 150.degree. C. The PHT films are
formed by thermally treating a PHA film at a temperature of at
least 150.degree. C., preferably from about 165.degree. C. to about
280.degree. C., more preferably from about 180.degree. C. to about
210.degree. C., and most preferably from about 190.degree. C. to
about 210.degree. C., and for a period of time of about 1 minute to
about 24 hours, and more preferably about 1 hour. The PHT films can
also have a high Young's modulus as measured by nanoindentation
methods. In some instances, the Young's modulus of a PHT film can
have a value in a range of about 8 GPa to about 14 GPa, exceeding
that of bone (9 GPA). However, as mentioned prior, some PHTs suffer
from poor impact resistance and brittleness, so there is a need for
new modified PHTs for wider application.
[0016] The aromatic diamine (ODA), as shown reaction example 1, is
a non-limiting component in the preparation of new modified PHAs
and PHTs produced by Michael addition reactions. In general, the
practitioner may choose any small molecule, oligomer, or polymer
having an aromatic amine group in a PHA and/or PHT synthesis. The
aromatic amine may include mono, di, tri, tetra, or penta amine
functionality. The aromatic amine may be mono or polycyclic, and
may include bridging groups, polymeric segments, and other chemical
functionality, aromatic and/or aliphatic. The aromatic amine may
contain inorganic elements and functionality such as phosphate,
sulfate, and the like. The aromatic amine may have positively
charged quaternary amines, and/or a plurality of plus or minus
charges. The aromatic amine may include chemical functionality that
participates in other chemical reactions, transformations, or
interactions, including, but not restricted to: synthesis,
decomposition, single replacement and double replacement,
oxidation/reduction, acid/base, nucleophilic, electrophilic and
radical substitutions, and addition/elimination reactions. In some
embodiments, the aromatic amine may engage in polymerization
reactions such as condensation, step growth, chain growth and
addition polymerizations.
[0017] The aromatic amine may include one or more aliphatic amines,
which may be primary and/or secondary, or mixtures thereof.
Aromatic amines typically exhibit more preference for
hexahydrotriazine formation compared to an aliphatic amine, and the
aromatic amine typically does not interfere with a Michael addition
reaction performed in its presence. For example, an aliphatic amine
group may undergo an aza-Michael addition chemical reaction when in
contact with an unsaturated hydrocarbon moiety (e.g., C.dbd.C
double bond), that is in proximity of an electron withdrawing group
such as carbonyl, cyano, or nitro. Specifically, the Michael
addition is a reaction between nucleophiles and activated olefin
and alkyne functionalities, wherein the nucleophile adds across a
carbon-carbon multiple bond that is adjacent to an electron
withdrawing and resonance stabilizing activating group, such as a
carbonyl group. The Michael addition nucleophile is known as the
"Michael donor", the activated electrophilic olefin is known as the
"Michael acceptor", and reaction product of the two components is
known as the "Michael adduct". Examples of Michael donors include,
but are not restricted to: amines, thiols, phosphines, carbanions,
and alkoxides. Examples of Michael acceptors include, but are not
restricted to: acrylate esters, alkyl methacrylates, acrylonitrile,
acrylamides, maleimides, cyanoacrylates and vinyl sulfones, vinyl
ketones, nitro ethylenes, a,b-unsaturated aldehydes, vinyl
phosphonates, acrylonitrile, vinyl pyridines, azo compounds,
beta-keto acetylenes and acetylene esters. FIG. 1 shows a group of
exemplary Michael donors 101 and a group of exemplary Michael
acceptors 102.
[0018] One such non-limiting example of a Michael addition reaction
is shown below in reaction example 2, where
4-(2-aminomethyl)aniline (a Michael donor) is first reacted with
lauryl acrylate (a Michael acceptor) to form the Michael adduct,
and then is further reacted to form a PHT network with lauryl ester
groups outboard. In other embodiments, a diamine such as ODA may be
added to link the hexahydrotriazine moieties, and thus producing a
hybrid macromolecular architecture that contains both
hexahydrotriazine-lauryl ester pendant groups and hexahydrotriazine
linking segments. FIG. 2A generally illustrates such a PHT network,
comprising hexahydrotriazine moieties/domains 200, pendant groups
201, and linking segments 202, which may be polymeric. We note that
the wavy lines attached to the hexahydrotriazine nitrogen atoms on
this and further examples serves as an abbreviation and may
represent pendant chemical groups or linking chemical segments.
Reaction Example 2
##STR00004##
[0020] This embodiment and others, as generally illustrated in FIG.
2A, may form a toughened network comprising "soft" aliphatic
domains of pendant Michael adducts and "hard" segments of PHT. In
other embodiments, the Michael acceptor may be even larger or more
bulky than a lauryl group, which may lead to more free volume
within the PHA and/or PHT matrix, and may further define or
delineate discrete domains. For example, the domains formed by
pendant groups and linking segments may include crystallites and/or
amorphous regions, and thus may serve as a means to modify the
modulus of the bulk PHA/PHT material, or a composite material with
PHT as the matrix resin. The domains may also exhibit specific melt
and or glass transitions.
[0021] In other embodiments, hydrophilic/lipophilic balance of the
pendant group(s) or linking group(s), may be modified for certain
properties, such as modulus, adhesion to a substrate, or water
repulsion/adsorption. The pendant group may be charged, like a
phosphate group, and may engage in ionic interactions with a polar
component in a composite material, such as a reinforcing fiber or
mineral filler. In another embodiment, the pendant group may be a
hydrogen bonding group, such as hydroxyl, which may engage in
hydrogen bonding with a polar component. Interactions of these
types may lead to increased adhesion of the PHA and/or PHT to the
reinforcing fiber or mineral filler and may result in less cracking
or delamination.
[0022] In another embodiment, as illustrated in reaction example 3,
a star-like PHT material may be formed with covalently bound
Michael adducts that are positively charged, for example the
reaction product of 4-(aminomethyl)aniline and
[2-(acryloyloxy)ethyl] trimethylammonium chloride, thus yielding a
star-like structure(s). In other embodiments, a diamine such as ODA
may be added to link the hexahydrotriazine moieties, thus producing
a hybrid macromolecular architecture that contains both
hexahydrotriazine pendant groups and hexahydrotriazine linking
segments.
Reaction Example 3
##STR00005##
[0024] In some cases, after the formation of a PHA or a PHT network
or polymer, the pendant or other matrix functionality may undergo
further chemical reactions, as initiated by heat, light, or other
means such as nucleophilic or electrophilic attack, or by free
radical mechanisms of bond formation. For example, a PHT network
may contain a Michael adduct comprising epoxy, vinyl, sulfone, or
anhydride functionality, that is useful for a second chemical
reaction that may form more covalent bonds.
[0025] In other embodiments, additional synergists and initiating
chemistries may be added to the mixture to react the pendant or
integrated matrix functionality. For example, excess or left over
starting materials may be further reacted or consumed by addition
of a free radical initiator to the reaction mixture before, during
or after PHA and/or PHT matrix formation. For example, and in
reference to reaction example 2, 4-(2-aminomethyl)aniline (Michael
donor) is reacted with lauryl acrylate (Michael acceptor) to form
the Michael adduct. The adduct may be further reacted with
paraformaldehyde to form a PHT matrix under conditions similar to
reaction example 1. However, because of possible steric constraints
imposed by the desired functional group, and the limits of
diffusion, some acrylate material may remain unreacted and trapped
as a liquid within the hardened PHT matrix, and thus may be further
chemically reacted or polymerized as needed. In related
embodiments, the Michael acceptor and/or donor may be in excess of
a theoretical stoichiometric value, and may also serve as the
reaction solvent. To chemically react or consume the aforementioned
excess material, such as an acrylate, the practitioner may choose
to add a photoinitiator to the reaction mixture, such as an
Irgacure.RTM. product manufactured by BASF of Ludwigshafen,
Germany, and then after PHA or PHT film formation, irradiate the
film with an appropriate wavelength of ultraviolet (UV) light to
effect a final cure, or post-cure, which may produce an
interpenetrating acrylic network within the PHA or PHT host.
Generally, photoinitiators for UV cured coatings and adhesives are
compounds that, under absorption of light, such as that from a
mercury lamp at a specific wavelength, undergo a photoreaction,
producing reactive species that are capable of initiating the
polymerization of the unsaturated constituents in a
formulation.
[0026] In other embodiments, a thermally activated free radical
initiator may be used to react acrylic and other unsaturated
chemistry within a PHA or PHT matrix to form an interpenetrating
polymer network and/or to build viscosity. Examples of suitable
free radical initiators generally include azo, and the inorganic
and organic peroxides. Those skilled in the art may choose a
suitable initiator wherein half the mass of the molecule decomposes
to free radical species over a time period (half-life) and at a
suitable temperature. In one embodiment, the Michael addition
reaction occurs at a first temperature, for example about
25.degree. C., and during a first time, about 0.5 hour, and then
reaches completion. Excess acrylate may then be consumed by a free
radical initiator at a second temperature at which the free
radicals are generated by initiator decomposition. In this fashion,
acrylate oligomers and/or polymers are produced in the reaction
mixture. One example of an azo initiator is
1,1'-azobis(cyclohexane-1-carbonitrile), an azo initiator soluble
in NMP and having high temperature decomposition (10 hour
half-life, 88.degree. C.), available from WAKO Chemicals, USA. In
one example, after the Michael reaction has reached completion, an
azo initiator in the amount of about 1% to about 5% by weight of
acrylate, is added to the reaction mixture to react or polymerize a
predetermined amount of over stoichiometric acrylate moieties, and
wherein the acrylate may also serve as a reaction solvent or impart
solvency for the reaction mixture components. Further heating of
the reaction mixture will thus produce a polymer produced by
free-radical chemistry, then PHA, and then finally PHT. In another
example, azo initiator in the amount of about 2% by weight of
acrylate is added to the reaction mixture to react unreacted
acrylate that is not in great excess or used as a solvent. In these
and similar embodiments, the modulus and strength of the material
may be modified by this technique, and/or viscosity of the reaction
mixture may be increased to aid further processing, such as a
coating step, where the mixture is applied to a fiberglass mat
substrate. It should also be appreciated that an article comprising
an interpenetrating network, such as an olefinic polymer within a
PHT matrix, may produce a material that is plasticized by the
olefinic component and therefore may exhibit less brittleness and
more flexibility.
[0027] One may choose to add a variety of reactive elements,
molecular building blocks, and initiating chemistries to a reaction
vessel prior to and during the synthesis of a PHA or PHT, to effect
further cure of the reactive matrix components, and thus form
cross-links, and/or interpenetrating network(s) comprising PHA
and/or PHT, and one or more additional curable and/or polymeric
components, some derived from a Michael addition reaction. As
discussed prior, while photo and thermal free radical initiators
may be used to effect a cure during and after PHA and/or PHT matrix
formation, other methods may be available, including heat or light
induced ring closure, such as a Diels-Alder (DA) reaction or other
annulations or cycloadditions. A DA reaction is a
[4+2]-cycloaddition of a conjugated diene and a dienophile.
Advantageously, a Michael acceptor molecule such as an acrylate is
a useful dienophile in a DA type reaction, and may be used to
covalently attach to a PHA and or PHT network that contains a
conjugated diene moiety, such a cyclopentadiene (CP) group. In one
example, a DA reaction may occur during the formation of a PHT
network from about 150.degree. C. to about at about 200.degree. C.,
wherein a CP group reacts with an acrylate group and thus forms a
cyclic cross-link and/or a branch.
[0028] Reaction example 4 illustrates an embodiment wherein a
difunctional Michael acceptor is used to create a novel PHA and/or
PHT material, which may have PHA and/or PHT domains covalently
bridged by segments comprising the Michael adducts.
Reaction Example 4
##STR00006##
[0030] As shown in reaction example 4, the difunctional Michael
acceptor comprises bridging molecular structure or segments "R",
which may be aliphatic, aromatic, or both, and may contain chemical
functionality that may engage in other chemical reactions,
transformations, or interactions, including, but not restricted to:
synthesis, decomposition, single replacement and double
replacement, oxidation/reduction, acid/base, nucleophilic,
electrophilic and radical substitutions, and addition/elimination
reactions. In some embodiments, the R bridging segment may also
engage in polymerization reactions such as condensation, step
growth, chain growth and addition polymerizations. The various R
groups may be the same or different.
[0031] In one non-limiting example, R=is a methylene group,
--CH.sub.2--. In other embodiments, R may be an oligomeric or
polymeric moiety, with no lower or upper limit on molecular weight.
For example, R may be a poly(ether) segment
--(CH.sub.2CH.sub.2O).sub.n--. Other non-limiting examples of
oligomeric and/or polymeric R groups include poly(amide),
poly(carbonate), poly(ester), poly(ether ketone), poly(ether),
poly(etherimide), poly(imide), poly(olefin), poly(siloxane),
poly(sulfone), halogenated polymers, poly(phenylene),
poly(urethane) and their copolymers. A representation of such a
toughened and less brittle PHT network is generally illustrated in
FIG. 2B, which includes hexahydrotriazine moieties/domains 203, and
linking R groups or segments 204.
[0032] In other embodiments a first polymer bridging group R may be
a first polymer, while a second polymer bridging group R is a
second polymer different from the first polymer. In some
embodiments, the first polymer and the second polymer may be the
same polymer, but may have different molecular weights. In this
way, a PHT or a PHA matrix may display multiple polymer melt
transitions and/or glass transition temperatures as a function of
the R linking groups or segments. It is further noted that any
number of different Michael acceptors and/or mixtures may be used
in these methods and compositions. For example, the Michael
acceptor may be mono, di, tri, and tetra functional, and each group
R may have different molecular weights, chain lengths, and
molecular structures. Of further note and benefit, the oligomeric
and/or polymeric R groups may adhere to or wet out composite
fillers such as fibers and mineral fillers, thus further
strengthening a composite product and decreasing brittleness.
[0033] In another embodiment, a non-limiting acrylic elastomer is
used to produce a PHT network with some flexibility and some
elongation, as represented by reaction example 5. Herein, the
aromatic amine may include two aliphatic amine Michael donors and
one aromatic amine for hexahydrotriazine formation, and the
aliphatic Michael donor contains at least two primary or secondary
aliphatic amine groups that may be reacted with a diacrylate
acceptor, such as poly(butadiene) diacrylate. This may be termed a
Michael addition polymerization, resulting in a macromolecular
architecture comprising PHA or PHT domains bridged by soft
rubber-like domains, as generally illustrated in FIG. 2B.
Reaction Example 5
##STR00007##
[0035] In other embodiments, the residual double bonds in the
poly(butadiene) segment (x,y) are further reacted to create
cross-links which may lead to reversible elastomeric properties.
The segments x and y may be at least 1 segment or repeating unit.
Examples of some cross-linking chemistries include sulfur
vulcanization and peroxide, such as tert-butyl perbenzoate, dicumyl
peroxide, benzoyl peroxide, di-tert-butyl peroxide and the like. In
other embodiments, the modified PHT polymer, for example a rubber
modified PHT polymer, may be recycled for other uses by exposure to
an acidic solution at a pH of about 3 or less. The acidic solution
may selectively depolymerize the hexahydrotriazine moieties to
Michael adduct precursors, and the degree of depolymerization may
be controlled by selecting the pH and depolymerization time. In
this way a modified PHT polymer may be softened, and viscosity may
be reduced as desired.
[0036] The polymer bridging groups derived from the Michael adducts
impart some molecular-scale flexibility to the PHT or PHA polymer
network owing to the reduced cross-link density, resulting in
increased toughness and impact resistance to the material, which
are useful properties in composite applications. A narrow
distribution of molecule sizes in the polymer bridging groups
provides maximum efficiency of adding impact resistance per mole of
polymer bridging groups added. When the Tg is below room
temperature (.about.23.degree. C.), longer polymer chains added to
the polymer network may provide more toughness than shorter chains,
so in a broad molecular weight distribution of polymer bridging
groups, the short chains may have less effect on impact resistance
and toughness than the longer chains.
[0037] General reaction conditions and procedures for PHA and PHT
polymers including covalently bound Michael adducts and/or
interpenetrating networks comprised of one or more oligomeric or
polymeric components are as follows:
[0038] (1) The solvent can be any suitable solvent. Useful solvents
include dipolar aprotic solvents such as, for example,
N-methyl-2-pyrrolidone (NMP), dimethylsulfoxide (DMSO),
N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), propylene
carbonate (PC), and propylene glycol methyl ether acetate (PGMEA).
Alternatively, the Michael acceptor, such as an acrylate, may serve
as the solvent, and the solvent may be polymerized before, during,
or after other steps in the process, such as PHA and/or PHT
formation.
[0039] (2) Under inert dry conditions, the Michael donor (aliphatic
amine) may be added to the above solvent, containing the Michael
acceptor in a 1:1 molar ratio (1 mole of aliphatic amine:1 mole of
double bond). In such a reaction, a temperature may range from
about 20.degree. C. to about 30.degree. C., and over a time period
from about 15 minutes to 5 hours. One such example is reaction
example 6, shown below, wherein the Michael donor, ethanolamine,
smoothly reacts with the trifunctional Michael acceptor,
1,3,5-triacryloylhexahydro-1,3,5-hexahydrotriazine to form the
star-like Michael adduct:
Reaction Example 6
##STR00008##
[0041] Alternatively, the molar ratio may be adjusted so that there
is a "limiting reagent" or one reagent is in excess. As in (1)
above, the acrylate or Michael acceptor may be in excess and serve
as the solvent. Excess acrylate and/or other sites of unsaturation
may be reacted in later steps using free radical or other
chemistries initiated by heat or light.
[0042] (3) The reaction mixture of (2) may comprise a mixture of
aromatic amines for hexahydrotriazine formation, and/or other
amines, both aromatic and aliphatic, in some combination. In one
non-limiting example, the mixture may contain multiple Michael
donors, for example, a difunctional aliphatic diamine such as
piperazine and a difunctional aromatic amine such as
4-(2-aminomethyl)aniline. In this example, reaction example 7,
piperazine (difunctional Michael donor) chemically reacts with
1,4-butanediol diacrylate (difunctional Michael acceptor) to form
an amino functionalized poly(amino ester) in a Michael addition
polymerization. The amino functionalized poly(amino ester) thus
produced contains aromatic amine end groups that are available for
further reaction with formaldehyde for production of PHA, PHT, or
mixtures thereof.
Reaction Example 7
##STR00009##
[0044] Experimental details for the preparation of the poly(amino
ester) of reaction example 7 are as follows: piperazine (0.1 g,
1.16 mmol) and 1,4-butanediol diacrylate (0.236 g, 1.19 mmol) were
stirred at 50.degree. C. in 0.4 mL N-methylpyrrolidone (NMP) for 3
hours. 4-aminobenzylamine (0.02 g, 0.16 mmol) was added next, and
the mixture was kept at 50.degree. C. for 1 hour.
[0045] As mentioned prior, the poly(amino ester) product reaction
of example 7 contains aromatic amine end groups that may be used
for production of a PHT in a subsequent step. Non-limiting
experimental details for the preparation of a PHT from the
poly(amino ester) of reaction example 7 and the bridging diamine,
4,4'-oxydianiline (ODA), are as follows: ODA (0.2 g, 1 mmol) and
paraformaldehyde (0.1 g, 3.33 mmol) were stirred at 50.degree. C.
in 1.5 mL NMP until the solution became clear (.about.15 minutes).
Then 0.2 g of the poly(amino ester) mixture (.about.32 wt % of
poly(amino ester) vs. ODA) was added, and the solution was stirred
at 50.degree. C. for 1 minute. The solution was then deposited on a
glass microscope slide with aluminum tape (80 .mu.m thickness)
boundaries using a glass Pasteur pipette. The following thermal
treatment was used to drive off the solvent and cure the film:
50.degree. C. for 1 hour, 50.degree. C. to 110.degree. C. over 1
hour, 110.degree. C. for 1 hour, 110.degree. C. to 200.degree. C.
over 1 hour, and then 200.degree. C. for 1 hour, after which time
the film was allowed to cool to .about.23.degree. C. The aluminum
tape was carefully peeled off the slide and the PHT film was
floated from the glass plate by soaking in deionized water. A
differential scanning calorimetry experiment revealed a T.sub.g of
149.degree. C.
[0046] (4) Per reaction example 7, PHT formation may occur in a
separate step or addition as described, while in other embodiments
the reaction mixture may contain all the necessary components to
perform a "one-pot" synthesis of a PHA and/or PHT polymer
comprising covalent groups produced from Michael addition
reactions. For example, all the components of reaction example 7
may be all combined in one reaction vessel with ODA and
paraformaldehyde to produce a PHT. Those schooled in the art will
appreciate that the temperature(s) of the reaction vessel will need
to be controlled as each component is reacted. In another example,
a reaction vessel padded with nitrogen may be charged with a dry
and degassed solvent, paraformaldehyde (PF), lauryl acrylate, and
4-(2-aminomethyl)aniline. In some embodiments, the acrylate may
serve as the solvent, or may be co-solvent. The mole ratio of
aliphatic amine to acrylate may be about 1.0:1.2, or wherein the
acrylate is in some excess, and the moles of PF are sufficient to
form PHA/PHT hexahydrotriazine structures (ex. 0.5 mole aromatic
amine:1.25 mole PF). The above mixture may warmed to between about
20.degree. C. and about 30.degree. C. to effect the Michael
addition reaction, which may concurrently build mixture viscosity,
and in some cases may not substantially initiate the reaction of
the aromatic amine with the PF. Then, over a time period from about
0.5 hours and about 1 hour, the mixture may be further heated to
between about 30.degree. C. and about 50.degree. C. to cause the
reaction of the aromatic amine with PF, and thus produce a PHA
material over a time period from about 1 hour to about 24 hours. In
this embodiment and others, the PF serves as a "thermal latent
curing agent", that is, it does not undergo reaction with the
aromatic amine to form hexahydrotriazine structures until heated to
a higher temperature.
[0047] In other embodiments the PHA material may be converted
directly to a PHT product without isolating the PHA material. To
that end, the reaction mixture may heated from about 190.degree. C.
to about 210.degree. C. for a period of time of about 1 minute to
about 24 hours, for example about 1 hour. In summary of conditions
1-4 above, in a "one-pot" preparation of PHA and/or PHT, the
Michael addition may occur first under more mild conditions, and
then after further heating, the PF will react with the aromatic
amine to form a PHA and/or PHT material.
[0048] In one embodiment, a composite article may be produced using
the reaction mixture and method(s) as described. Here, the Michael
addition reaction is first performed from about 20.degree. C. to
about 30.degree. C. for a period of time of about 1 hour to build
viscosity for the application of the mixture to a fiberglass or
carbon fiber mat. Alternatively, a reaction mixture may be produced
comprising the reaction products of both Michael addition and PHA
formation, by heating the mixture from about 30.degree. C. to about
60.degree. C. for a time period until a desired working viscosity
is obtained. The mixture may be then applied to the fiber mat, and
thus impregnate the fiber mat with the partially cured mixture. The
fiber mat thus produced may be known as a polymer pre-impregnated
mat (pre-preg). At this juncture, excess partially cured resin and
other components may be removed from the prepreg by a squeegee, and
then the prepreg may be subjected to further heat to achieve a
certain desired stage of cure, followed by cooling (quench) to stop
the chemical reaction(s), and so that the material may be handled
for later steps in the composite preparation process. This
composite precursor article may be termed a "B-stage" pre-preg,
wherein the resin mixture is partially cured, maintains some
flexibility, and may be handled for further transport and/or
processing. The B-stage pre-preg may comprise of Michael adducts,
PF, PHA oligomers and polymers and other reaction components. At
this stage the B-stage pre-preg may be used to create a composite
article in a mold. The fully cured article may be produced by
heating to about 200.degree. C. in a vacuum autoclave to complete
the reaction of the amine components with the thermal latent PF in
the mixture, remove solvent, and thereby produce a composite with
PHT matrix resin.
[0049] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" and/or "comprising," when used in this
specification, specify the presence of stated features, integers,
steps, operations, elements, and/or components, but do not preclude
the presence or addition of one or more other features, integers,
steps, operations, elements, components, and/or groups thereof.
When a range is used to express a possible value using two
numerical limits X and Y (e.g., a concentration of X ppm to Y ppm),
unless otherwise stated the value can be X, Y, or any number
between X and Y.
[0050] The description of the present invention has been presented
for purposes of illustration and description, but is not intended
to be exhaustive or limited to the invention in the form disclosed.
Many modifications and variations will be apparent to those of
ordinary skill in the art without departing from the scope and
spirit of the invention. The embodiments were chosen and described
in order to best explain the principles of the invention and their
practical application, and to enable others of ordinary skill in
the art to understand the invention.
* * * * *