High performance heterocycle oligomers and blends

Linear or multidimensional, crosslinking, solvent resistant oxazole, thiazole, or imidazole (i.e., heterocycle) oligomers and blends of the crosslinking oligomers and noncrosslinking comparable polymers are described. The oligomers are prepared by reacting tetraamines, diaminodiols, or diaminothiols (i.e. four-functional compounds) with poly-carboxylic acid halides, and crosslinking phenylimide end cap monomers in a suitable solvent under an inert atmosphere.

TECHNICAL FIELD 
The present invention relates to linear or multidimensional, solvent 
resistant, crosslinkable oligomers that include oxazole, thiazole, or 
imidazole linkages along the oligomer backbone between mono- or 
difunctional crosslinking end-cap phenylimides of the general formula: 
##STR1## 
and to their method of manufacture. 
BACKGROUND ART 
Recently, chemists have sought to synthesize oligomers for high performance 
advanced composites suitable for aerospace applications. These composites 
should exhibit solvent resistance, be tough, impact resistant, and strong, 
be easy to process, and be thermoplastic. Oligomers and composites that 
have thermo-oxidative stability, and, accordingly can be used at elevated 
temperatures, are particularly desirable. 
While epoxy-based composites are suitable for many applications, their 
brittle nature and susceptibility to degradation make them inadequate for 
many aerospace applications, especially those applications which require 
thermally stable, tough composites. Accordingly, research has recently 
focused upon polyimide composites to achieve an acceptable balance between 
thermal stability, solvent resistance, and toughness. The maximum use 
temperatures of conventional polyimide composites, such as PMR-15, are 
still only about 600.degree.-625.degree. F., since they have glass 
transition temperatures of about 690.degree. F. 
Linear polysulfone, polyether sulfone, polyester, and polyamide systems are 
also known, but each of these systems fails to provide as high thermal 
stability as is required in some aerospace applications. 
There has been a progression of polyimide sulfone compounds synthesized to 
provide unique properties or combinations of properties. For example, 
Kwiatkowski and Brode synthesized maleic-capped, linear polyarylimides as 
disclosed in U.S. Pat. No. 3,839,287. Holub and Evans synthesized maleic- 
or nadic-capped, imido-substituted polyester compositions as disclosed in 
U.S. Pat. No. 3,729,446. We synthesized thermally stable polysulfone 
oligomers as disclosed in U.S. Pat. No. 4,476,184 or U.S. Pat. No. 
4,536,559, and have continued to make advances with 
polyetherimidesulfones, polybenzoxazolesulfones (i.e., heterocycles), 
polybutadienesulfones, and "star" or "star-burst" multidimensional 
oligomers. We have shown surprisingly high glass transition temperatures 
and desirable physical properties in many of these oligomers and their 
composites, without losing ease of processing. 
Multidimensional oligomers, such as disclosed in our copending applications 
U.S. Ser. Nos. 726,258; 810,817; and 000,605, are easier to process than 
many other advanced composite oligomers since they can be handled at lower 
temperatures. Upon curing, however, the unsaturated phenylimide end caps 
crosslink so that the thermal resistance of the resulting composite is 
markedly increased with only a minor loss of stiffness, matrix stress 
transfer (impact resistance), toughness, elasticity, and other mechanical 
properties. Glass transition temperatures above 950.degree. F. are 
achievable. 
Commercial polyesters, when combined with well-known diluents, such as 
styrene, do not exhibit satisfactory thermal and oxidative resistance to 
be useful for aircraft or aerospace applications. Polyarylesters are 
unsatisfactory, also, since the resins often are semicrystalline which 
makes them insoluble in laminating solvents, intractable in fusion, and 
subject to shrinking or warping during composite fabrication. Those 
polyarylesters that are soluble in conventional laminating solvents remain 
so in composite form, thereby limiting their usefulness in structural 
composites. The high concentration of ester groups contributes to resin 
strength and tenacity, but also makes the resin susceptible to the 
damaging effects of water absorption. High moisture absorption by 
commercial polyesters can lead to distortion of the composite when it is 
loaded at elevated temperature. 
High performance, aerospace, polyester advanced composites, however, can be 
prepared using crosslinkable, end-capped polyester imide ether sulfone 
oligomers that have an acceptable combination of solvent resistance, 
toughness, impact resistance, strength, ease of processing, formability, 
and thermal resistance. By including Schiff base (--CH.dbd.N--), 
imidazole, thiazole, or oxazole linkages in the oligomer chain, the 
linear, advanced composites formed with polyester oligomers of our 
copending application U.S. Ser. No. 726,259 can have semiconductive or 
conductive properties when appropriately doped. 
Conductive and semiconductive plastics have been extensively studied (see, 
e.g., U.S. Pat. Nos. 4,375,427; 4,338,222; 3,966,987; 4,344,869; and 
4,344,870), but these polymers do not possess the blend of properties 
which are essential for aerospace applications. That is, the conductive 
polymers do not possess the blend of (1) toughness, (2) stiffness, (3) 
elasticity, (4) ease of processing, (5) impact resistance (and other 
matrix stress transfer capabilities), (6) retention of properties (over a 
broad range of temperatures), and (7) high temperature resistance that is 
desirable on aerospace advanced composites. These prior art composites are 
often too brittle. 
Thermally stable multidimensional oligomers having semiconductive or 
conductive properties when doped with suitable dopants are also known and 
are described in our copending applications (including U.S. Ser. No. 
773,381 to Lubowitz, Sheppard, and Torre). The linear arms of the 
oligomers contain conductive linkages, such as Schiff base (--N.dbd.CH--) 
linkages, between aromatic groups. Sulfone and ether linkages are 
interspersed in the arms. Each arm is terminated with a mono- or 
difunctional end cap (i.e., a radical having one or two crosslinking 
sites) to allow controlled crosslinking upon heat-induced or 
chemically-induced curing. 
Polyamides of this same general type are described in our copending patent 
application U.S. Ser. No. 061,938; polyetherimides, in U.S. Ser. No. 
016,703; and polyamideimides, in U.S. Ser. No. 092,740. 
SUMMARY OF THE INVENTION 
The present invention relates to linear or multidimensional oxazole, 
thiazole, and imidazole (i.e., heterocycle) oligomers, particularly 
benzoxazole, benzothiazole, and benzimidazole oligomers, capped with mono- 
or difunctional end-cap monomers (i.e., monomers having one or two 
crosslinking sites) to achieve superior thermal stability while retaining 
desirable strength and physical properties. 
The oligomers are usually prepared by the condensation of: (a) 2 moles of a 
phenylimide carboxylic acid halide end-cap monomer of the general formula: 
##STR2## 
wherein D=an unsaturated hydrocarbon radical; 
i=1 or 2; and 
.phi.=phenyl 
(b) n moles of a diacid halide particularly an aromatic dicarboxylic acid 
halide having a plurality of aryl groups intermediately linked by 
"sulfone" linkages and terminal carboxylic acid halide functionalities 
attached to the aryl groups; and 
(c) (n+1) moles of four-functional compound of the formula: 
##STR3## 
(such as a diaminodihydroxybenzene) wherein R is an hydrocarbon radical 
(preferably, an aromatic radical, if the highest thermal stability is 
sought); Y=--OH, --NH.sub.2, or --SH; and the amine functionalities 
(--NH.sub.2) are not substituted on the same carbon atom as the Y 
substituents. 
The end-cap monomer preferably is selected from the group consisting of: 
##STR4## 
wherein D= 
##STR5## 
R.sub.1 =lower alkyl, aryl, substituted aryl (including hydroxyl or 
halo-substituents), lower alkoxy, aryloxy, halogen, or mixtures thereof 
(preferably lower alkyl); 
X=halogen, preferably Cl; 
G=--SO.sub.2 --, --S--, --O--, or --CH.sub.2 --; 
i=1 or 2; 
j=0, 1, or 2; 
.phi.=phenyl; 
T=methallyl or allyl; and 
Me=methyl. 
Preferred end-cap monomers are the phenylimide acid halides wherein D 
includes a radical selected from: 
##STR6## 
wherein R" is hydrogen or lower alkyl. 
Blended oligomers are prepared to include the crosslinking oligomers and at 
least one comparable, noncrosslinking polymer. The polymer generally has a 
substantially identical backbone to the oligomer, but is terminated (or 
quenched) with a monomer that is unable to crosslink. Accordingly, the 
comparable polymer is generally prepared by condensing: 
(a) 2 moles of an acid halide end-cap quenching monomer; 
(b) n moles of the diacid halide of the crosslinking oligomer; 
(c) (n+1) moles of the four-functional compound of the crosslinking 
oligomer. 
A suitable monomer for quenching the polymerization reaction for the 
comparable oligomer is benzoic acid halide 
##STR7## 
Of course, the crosslinking oligomers can also be prepared by the 
condensation of: 
(a) 2 moles of a suitable phenylimide amine, phenol, or sulfhydryl (i.e., 
thio) monomer; 
(b) n moles of a four-functional compound; and 
(c) (n+1) moles of a suitable diacid halide. 
The comparable polymer could also include the analogous backbone and could 
be quenched with a phenol or suitable thio- or amino-monomer (such as 
aniline). 
Generally, the four-functional compound is selected from the group 
consisting of: 
dihydroxybenzidine; 
dimercaptobenzidine; 
2,6-diamino-3,5-dihydroxybenzene; 
2,6- diamino-3,5-dimercaptobenzene; or diaminobenzidine. 
Heterocyle oligomers of this general type are easily processed into 
prepregs and composites. The composites (or laminates) are chemically, 
thermally, and dimensionally stable at relatively high temperatures and 
exhibit solvent-resistance. 
Multidimensional oligomers can be prepared by reacting the four-functional 
compounds and phenylimide acid halide end-cap monomers with an aromatic 
hub having 3 or more reactive acid halide functionalities, such as a 
compound of the formula: 
##STR8## 
wherein Ar=an aromatic moiety of valence w, and 
w=an integer greater than or equal to 3, and generally 3 or 4. 
The hub (Ar) may be a residue of cyuranic acid or an imide/acid compound 
formed by reacting, for example, triaminobenzene with phthalic acid 
anhydride or a corresponding acid anhydride. The arms of the 
multidimensional oligomers can be extended by adding diacid halides to the 
reaction mixture, as will be understood. Corresponding ether/acid hubs can 
be prepared by condensing a phenolic hub, like phloroglucinol with 
nitrobenzoic acid or with nitrophthalic acid. Blends of multidimensional 
oligomers and corresponding polymers can also be prepared.

BEST MODE CONTEMPLATED FOR CARRYING OUT THE INVENTION 
The crosslinking oligomers of the present invention are oxazoles, 
thiazoles, or imidazoles (i.e., heterocycles) generally prepared by the 
condensation of: 
(a) 2 moles of a phenylimide carboxylic acid halide end-cap monomer; 
(b) n moles of a diacid halide, particularly an aromatic dicarboxylic acid 
halide having a plurality of aryl groups intermediately linked by 
"sulfone" (i.e., electronegative) linkages and terminal acid halide 
functionalities attached to aryl groups; and 
(c) (n+1) moles of a four-functional compound of the formula: 
##STR9## 
wherein R is a hydrocarbon radical (preferably an aromatic radical), 
Y=--OH, --SH, or --NH.sub.2, and the Y and --NH.sub.2 are on separate 
carbon atoms. Generally, the amine and Y are on adjacent carbon atoms of 
an aromatic ring. The four-functional compound, accordingly, is generally 
selected from the group consisting of: 
dihydroxybenzidine; 
dimercaptobenzidine; 
2,6-diamino-3,5-dihydroxybenzene; 
2,6-diamino-3,5-dimercaptobenzene; or diaminobenzidine. 
The end-cap monomer generally is selected from the group consisting of: 
##STR10## 
wherein D= 
##STR11## 
R.sub.1 =lower alkyl, aryl, substituted aryl (including hydroxyl or 
halo-substituents), lower alkoxy, aryloxy, halogen, or mixtures thereof 
(preferably lower alkyl); 
X=halogen; 
.phi.=phenyl; 
G=--O--, --S--, --SO.sub.2 -- or --CH.sub.2 --; 
i=1 or 2; 
j=0, 1, or 2; 
T=methallyl or allyl; and 
Me=methyl. 
These end-cap monomers have hydrocarbon unsaturation to provide one or two 
crosslinking sites. For the highest thermal stability, D includes a 
radical selected from 
##STR12## 
wherein R" is hydrogen or lower alkyl. 
The reaction is generally carried out at an elevated temperature under an 
inert atmosphere (dry N.sub.2 purge) in a suitable solvent including an 
excess of base (KOH or NaOH) to reduce the possibility of undesirable side 
reactions that might otherwise occur in an acidic solution. Usually about 
10% excess base is added, based upon the molar quantities of the 
reactants. 
The dicarboxylic acid halide (or dicarboxylic acid) may include an aromatic 
chain segment selected from the group consisting of: 
(a) phenyl; 
(b) naphthyl; 
(c) biphenyl; 
(d) a polyaryl "sulfone" divalent radical of the general formula: 
##STR13## 
wherein D=--S--, --O--, --CO--, --SO.sub.2 --, --(CH.sub.3).sub.2 C--, 
--(CF.sub.3).sub.2 C--, or mixtures thereof throughout the chain; or 
(e) a divalent radical having conductive linkages, illustrated by Schiff 
base compounds selected from the group consisting of: 
##STR14## 
wherein R is selected from the group consisting of: phenyl; biphenyl; 
naphthyl; or 
a divalent radical of the general formula: 
##STR15## 
wherein W=--SO.sub.2 -- or --CH.sub.2 --; and q=0-4; or (f) a divalent 
radical of the general formula: 
##STR16## 
where R.sup.1 =a C.sub.2 to C.sub.12 divalent aliphatic, alicyclic, or 
aromatic radical, and, preferably, phenyl (as described in U.S. Pat. No. 
4,556,697). 
Thiazole, oxazole, or imidazole linkages, especially between aryl groups, 
may also be used in the conductive or semiconductive oligomers, instead of 
the Schiff base linkages. The oligomers being heterocycles, may be 
semiconductive upon doping even without incorporating additional 
conductive linkages. 
The diacid halide preferably is an aromatic dicarboxylic acid selected from 
the group consisting of: 
##STR17## 
wherein q is an electronegative ("sulfone") group, preferably --CO--, 
--S--, --(CF.sub.3).sub.2 C--, or --SO.sub.2, and, generally, --CO--, 
--SO.sub.2 --; and m equals a small integer generally from 1-5. 
Preferred diacid halides include: 
##STR18## 
Schiff base dicarboxylic acids and diacid halides can be prepared by the 
condensation of aldehydes and aminobenzoic acid (or other amine acids) in 
the general reaction scheme: 
##STR19## 
or similar syntheses. 
Other diacid halides that can be used, but that are not preferred, are 
disclosed in U.S. Pat. No. 4,504,632, and include: 
adipylchloride, 
malonyl chloride, 
succinyl chloride, 
glutaryl chloride, 
pimelic acid dichloride, 
suberic acid dichloride, 
azelaic acid dichloride, 
sebacic acid dichloride, 
dodecandioic acid dichloride, 
phthaloyl chloride, 
isophthaloyl chloride, 
terephthaloyl chloride, 
1,4-naphthalene dicarboxylic acid dichloride, and 
4,4'-diphenylether dicarboxylic acid dichloride. 
Polyaryl or aryl diacid halides are preferred to achieve the highest 
thermal stabilities in the resulting oligomers and composites because 
aliphatic bonds are not as thermally stable as aromatic bonds. 
Particularly preferred compounds include intermediate "sulfone" (i.e. 
electronegative) linkages to improve the toughness of the resulting 
oligomers. For purposes of this description, "sulfone" linkages should be 
understood to include --SO.sub.2 --, --S--, --CO--, and --(CF.sub.3).sub.2 
C--, unless clearly limited to only --SO.sub.2 --. 
Suitable diacid halides include compounds made by reacting nitrobenzoic 
acid with a bisphenol (i.e., dihydric phenol, dialcohol, or diol). The 
bisphenol is preferably selected from the group consisting of: 
2,2-bis-(4-hydroxyphenyl)-propane (i.e., bisphenol-A); 
bis-(2-hydroxyphenyl)-methane; 
bis-(4-hydroxyphenyl)-methane; 
1,1-bis-(4-hydroxyphenyl)-ethane; 
1,2-bis-(4-hydroxyphenyl)-ethane; 
1,1-bis-(3-chloro-4-hydroxyphenyl)-ethane; 
1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-ethane; 
2,2-bis-(3-phenyl-4-hydroxyphenyl)-propane; 
2,2-bis-(4-hydroxynaphthyl)-propane 
2,2-bis-(4-hydroxyphenyl)-pentane; 
2,2-bis-(4-hydroxyphenyl)-hexane; 
bis-(4-hydroxyphenyl)-phenylmethane; 
bis-(4-hydroxyphenyl)-cyclohexylmethane; 
1,2-bis-(4-hydroxyphenyl)-1,2-bis-(phenyl)-ethane; 
2,2-bis-(4-hydroxyphenyl)-1-phenylpropane; 
bis-(3-nitro-4-hydrophenyl)-methane; 
bis-(4-hydroxy-2,6-dimethyl-3-methoxyphenyl)-methane; 
2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane; 
2,2-bis-(3-bromo-4-hydroxyphenyl)-propane; or mixtures thereof, as 
disclosed in U.S. Pat. No. 3,262,914. Bisphenols having aromatic character 
(i.e., absence of aliphatic segements), such as bisphenol-A, are 
preferred. 
The bisphenol may be in phenate form, or a corresponding sulfyhydryl can be 
used. Of course, mixtures of bisphenols and disulfhydryls can be used. 
Other suitable bisphenols are described in our copending Application Nos. 
016,703 and 726,258; or in U.S. Pat. Nos. 4,584,364; 4,661,604; 3,262,914, 
or 4,611,048. 
While bisphenol-A is preferred (because of cost and availability), the 
other bisphenols can be used to add rigidity to the oligomer without 
significantly increasing the average formula weight, and therefore, can 
increase the solvent resistance. Random or block copolymers are possible. 
Bisphenols of the type described are commercially available. Some may be 
easily synthesized by reacting dihalogen intermediate with bis-phenates, 
such as the reaction of 4,4'-dichlorophenyl-sulfone with bis(disodium 
biphenolate). Preferred dihalogens in this circumstance are selected from 
the group consisting of: 
##STR20## 
wherein X=halogen, preferably chlorine; and 
q=--S--, --SO.sub.2 --, --CO--, --(CH.sub.3).sub.2 C--, and 
--(CF.sub.3).sub.2 C--, and preferably either --SO.sub.2 -- or --CO--. 
The heterocycle oligomers of the present invention can also be prepared by 
the condensation of: 
(a) 2 moles of a crosslinking phenylimide amine, phenol, or sulfhydryl 
end-cap monomer; 
(b) n moles of the four functional compound; and 
(c) (n+1) moles of a suitable diacid halide. 
In this case, the end-cap monomer generally has the formula: 
##STR21## 
wherein D, i, and .phi. are as previously defined and Y=--OH, --SH, or 
--NH.sub.2. 
Blends can improve impact resistance of composites without causing a 
significant loss of solvent resistance. The blends comprise mixtures of 
one or more crosslinkable oligomer and one or more polymer that is 
incapable of crosslinking. Generally, the blends comprise substantially 
equimolar amounts of one polymer and one oligomer having substantially 
identical backbones. The crosslinkable oligomer and comparable polymer can 
be blended together by mixing mutually soluble solutions of each. While 
the blend is preferably equimolar in the oligomer and polymer, the ratio 
of the oligomer and polymer can be adjusted to achieve the desired 
physical properties. 
Although the polymer in such a blend usually has the same length backbone 
as the oligomer, the properties of the composite formed from the blend can 
be adjusted by altering the ratio of formula weights for the polymer and 
oligomer. The oligomer and polymer generally have substantially identical 
repeating units, but the oligomer and polymer merely need be compatible in 
the solution prior to sweeping out as a prepreg. Of course, if the polymer 
and oligomer have identical backbones, compatibility in the blend is 
likely to occur. Blends that comprise relatively long polymers and 
relatively short oligomers (i.e., polymers having higher average formula 
weights than the oligomers) prior to curing are preferred, since, upon 
curing, the oligomers will effectively increase in MW by crosslinking. 
In synthesizing the comparable polymers, quenching end caps can be 
employed, if desired, to regulate the polymerization of the comparable 
polymer, so that it has an average formula weight substantially identical 
with the crosslinkable oligomer. For thermal stability, an aromatic 
compound, such as aniline or benzoic acid chloride is preferred to quench 
the synthesis. 
Solvent resistance may decrease markedly if the comparable polymer is 
provided in large excess to the crosslinkable oligomer in the blend. 
The blends will generally comprise a mixture of a heterocycle oligomer and 
the same heterocycle polymer (i.e., oxazole oligomer and oxazole polymer). 
The polymer may, however, be a different heterocycle, such as an imide, 
imidazole, or thiazole. The mixture may include several types of oligomers 
or several types of polymers, such as a three component mixture of an 
oxazole oligomer, a thiazole oligomer, and an imidazole polymer. 
The blends may be semi-interpenetrating networks of the general type 
described by Egli et al. "Semi-Interpenetrating Networks of LARC-TPI" 
available from NASA-Langley Research Center. 
Because the oligomers synthesized in accordance with this invention 
generally have appreciable molecular weight between the reactive 
(crosslinking) groups, the oligomers will retain sufficient plasticity to 
be processible during fabrication prior to crosslinking of the end caps to 
thermoset composites. If possible, thermoplastic formulations with high 
molecular weights should be synthesized so long as the oligomers retain 
the necessary solubility. The oligomers preferably have MWs (i.e., average 
formula weights) between about 5000-40,000, and, more preferably, between 
about 15,000-25,000. Thermosetting heterocycle oligomers of the present 
invention generally will have average formula weights of between about 
500-5000. Mixtures of oligomers having molecular weights within these 
ranges may also be used, for example, a mixture of an oligomer having a 
molecular weight of about 1,000 with an oligomer having a molecular weight 
of about 20,000, or a mixture of an oligomer with a molecular weight of 
about 5,000 with an oligomer having a molecular weight of about 10,000 or 
about 20,000. Within the described ranges, the oligomers can be 
crosslinked to form solvent resistant composites of high thermal stability 
suitable for many aerospace applications. The oligomers, however, are 
relatively soluble, and, therefore, may be easily processed into prepregs 
by conventional steps. 
Solubility of the oligomers becomes an increasing problem as chain length 
increases. Therefore, shorter chains are preferred, if the resulting 
oligomers remain processible. That is, the chains should be long enough to 
yield thermoplastic characteristics to the oligomers but short enough to 
keep the oligomers soluble during the reaction sequence. 
Linear heterocycle oligomers preferably are synthesized using a diacid 
halide selected from the group consisting of: 
##STR22## 
wherein q is selected from the group consisting of --(CF.sub.3).sub.2 C--, 
--SO.sub.2 --, --S--, or --CO--; X.sub.1 is selected from the group 
consisting of --O-- or --SO.sub.2 --; E, E.sub.1, E.sub.2 and E.sub.3 each 
represent substituent groups selected from the group consisting of 
halogen, alkyl groups having 1 to 4 carbon atoms, and alkoxy groups having 
1 to 4 carbon atoms, and "a," "b," "c," and "d" are all integers having 
values from 0 to 4. 
The compound: 
##STR23## 
is particularly preferred, especially if the end-cap monomer is either: 
##STR24## 
Multidimensional oligomers may be synthesized using an aromatic hub, such 
as cyuranic acid (or its acid halide), the four functional compounds, and 
the acid halide end-cap monomers. The oligomers have the general formula: 
##STR25## 
wherein Ar=the aromatic hub residue; 
M=a monovalent radical having at least one heterocyclic (oxazole, thiazole, 
or imidazole) linkage and at least one, terminal, crosslinking 
functionality; and 
w=an integer greater than or equal to 3, and preferably 3 or 4. 
The chains within each arm (M) can be extended by including diacid halides 
in the reaction mixture. 
In multidimensional oligomers, an aromatic hub includes a plurality of rays 
or spokes radiating from the hub in the nature of a star to provide 
multidimensional crosslinking through suitable terminal groups with a 
greater number (i.e. higher density) of crosslinking bonds than linear 
arrays provide. Usually the hub will have three radiating chains to form a 
"Y" pattern. In some cases, four chains may be used. Including more chains 
leads to steric hindrance as the hub is too small to accommodate the 
radiating chains. A trisubstituted phenyl hub is highly preferred with the 
chains being symmetrically placed about the hub. Biphenyl, naphthyl, or 
azaline (e.g., melamine) may also be used as the hub radical along with 
other aromatic moieties, if desired. 
Triazine derivatives can be used as the hub. These derivatives are 
described in U.S. Pat. No. 4,574,154 and have the general formula: 
##STR26## 
wherein R.sub.2 is a divalent hydrocarbon residue containing 1-12 carbon 
atoms (and, preferably, ethylene) by reacting the amine functionalities 
with phthalic acid anhydride to form arms that include imide linkages and 
terminal acid functionalities (that can be converted to acid halides, if 
desired). The triazine derivatives of U.S. Pat. No. 4,617,390 (or the acid 
halides) can also be used as the hub. 
Hubs suitable for making multidimensional, heterocycle oligomers of the 
present invention can be made by reacting polyol aromatic hubs, such as 
phloroglucinol, with nitrobenzoic acid or nitrophthalic acid to form ether 
linkages and active, terminal carboxylic acid functionalities The 
nitrobenzoic acid products would have three active sites while the 
nitrophthalic acid products would have six; each having the respective 
formula: 
EQU .phi.--[--O--.phi.-COOH].sub.3 or .phi.--[--O--O--(COOH).sub.2 ].sub.3 
wherein .phi.=phenyl. Of course other nitro/acids can be used. 
Hubs can also be formed by reacting the corresponding halo-hub (such a 
tribromobenzene) with aminophenol to form triamine compounds represented 
by the formula: 
##STR27## 
which can then be reacted with an acid anhydride to form a polycarboxylic 
acid of the formula: 
##STR28## 
wherein .phi.=phenyl; the hub being characterized by an intermediate ether 
and imide linkage connecting aromatic groups. Thio-analogs are also 
contemplated, in accordance with U.S. Pat. No. 3,933,862. 
Phenoxyphenyl sulfone arms radiating from a hub with either an amine or 
carboxylic acid are also precursors for making multidimensional 
heterocycle oligomers of the present invention. 
The best results are likely to occur when the hub is cyuranic acid, and 
when a four-functional compound and end-cap monomer are reacted with the 
hub to form a short armed oligomer having three or six crosslinking sites. 
These compounds are the simplest multidimensional oligomers and are 
relatively inexpensive to synthesize. 
Blends of the multidimensional oligomers, comparable to the blends of 
linear oligomers, can also be prepared, as will be understood. 
The oligomers can be synthesized in a homogeneous reaction scheme wherein 
all the reactants are mixed at one time, or in a stepwise reaction scheme 
wherein the radiating chains are affixed to the hub and the product of the 
first reaction is subsequently reacted with the end cap groups. Of course, 
the hub may be reacted with end-capped arms that include one reactive, 
terminal functionality for linking the arm to the hub. Homogeneous 
reaction is Preferred, resulting undoubtedly in a mixture of oligomers 
because of the complexity of the reactions. The products of the processes 
(even without distillation or isolation of individual species) are 
preferred oligomer mixtures which can be used without further separation 
to form the desired advanced composites. 
If the linear or multidimensional oligomers include Schiff base or other 
conductive linkages, the composites may be conductive or semiconductive 
when suitably doped. The dopants are preferably selected from compounds 
commonly used to dope other polymers, namely, (1) dispersions of alkali 
metals (for high activity) or (2) strong chemical oxidizers, particularly 
alkali perchlorates (for lower activity). Arsenic compounds and elemental 
halogens, while active dopants, are too dangerous for general usage, and 
are not recommended. 
The dopants apparently react with the oligomers or polymers to form charge 
transfer complexes. N-type semiconductors result from doping with alkali 
metal dispersions. P-type semiconductors result from doping with elemental 
iodine or perchlorates. Dopant should be added to the oligomer or blend 
prior to forming the prepreg. 
While research into conductive or semiconductive polymers has been active, 
the resulting compounds (mainly polyacetylenes, polyphenylenes, and 
polyvinylacetylenes) are unsatisfactory for aerospace applications because 
the polymers are: 
(a) unstable in air; 
(b) unstable at high temperatures; 
(c) brittle after doping; 
(d) toxic because of the dopants; or 
(e) intractable. 
These problems are overcome or significantly reduced with the conductive 
oligomers of the present invention. 
While conventional theory holds that semiconductive polymers should have 
(1) low ionization potentials, (2) long conjugation lengths, and (3) 
planar backbones, there is an inherent trade-off between conductivity and 
toughness or processibility, if these constraints are followed. To 
overcome the processing and toughness shortcomings common with Schiff 
base, oxazole, imidazole, or thiazole polymers, the oligomers of the 
present invention generally include "sulfone" linkages interspersed along 
the backbone providing a mechanical swivel for the rigid, conductive 
segments of the arms. 
Because the heterocycle (oxazole, thiazole, or imidazole) linkages are 
themselves within the family of conductive or semiconductive linkages, it 
may be unnecessary to include Schiff base linkages to achieve conductive 
or semiconductive properties upon doping. That is, conductive or 
semiconductive properties might be achieved simply be doping the oxazole, 
thiazole, or imidazole oligomers. 
Linear or multidimensional oligomers can be synthesized from a mixture of 
four or more reactants so that extended chains may be formed. Adding 
components to the reaction mixture, however, adds to the complexity of the 
reaction and of its control. Undesirable competitive reactions may result 
or complex mixtures of macromolecules having widely different properties 
may be formed, because the chain extenders and chain terminators are 
mixed, and compete with one another. 
All reactions should be conducted under an inert atmosphere and at elevated 
temperatures, if the reaction rate needs to be increased. The reaction 
mixture should be well stirred throughout the synthesis. Chilling the 
reaction mixture can slow the reaction rate and can assist in controlling 
the oligomeric product. 
While para isomerization is shown for all of the reactants, other isomers 
are possible. Furthermore, the aryl groups can have substituents, if 
desired, such as halogen, lower alkyl up to about 4 carbon atoms, lower 
alkoxy up to about 4 carbon atoms, or aryl. Substituents may create steric 
hindrance problems in synthesizing the oligomers or in crosslinking the 
oligomers into the final composites. 
The following examples are presented to illustrate various features of the 
invention. 
EXAMPLE I 
Synthesis of bis(3-methylphenoxyphenyl) sulfone 
##STR29## 
A one liter bottle fitted with a stirrer, thermometer, Barrett trap, 
condenser, and nitrogen inlet tube was charged with 88.3 grams (0.82 
moles) of m-cresol, 286.6 grams of dimethyl sulfoxide (DMSO), 134.8 grams 
of toluene, and 65.3 grams of a 50% NaOH solution. The mixture was heated 
to 127.degree. C. and the water was removed. The mixture was then heated 
to 165.degree. C. to remove the toluene, and was cooled to 110.degree. C. 
before adding 111.7 grams (0.39 moles) of dichlorodiphenylsulfone. The 
mixture was heated for 4 hours at 141.degree. C., before the mixture was 
poured into 3 liters of water to crystallize an intermediate. The water 
was decanted, and 1 liter of 2-propanol was added. This mixture was heated 
until the majority of the product dissolved. The product was 
recrystallized, recovered by filtration, washed with 3 liters of water 
followed by 500 ml of -propanol, and dried. 167.4 grams of a 
bis(2-methyl-phenoxyphenyl) sulfone product resulted. The melting point 
ranged from 83.degree.-85.degree. C. 
EXAMPLE II 
Synthesis of bis(3-carboxyphenoxyphenyl) sulfone 
##STR30## 
A reaction flask fitted with a stirrer, condenser, thermometer, and N.sub.2 
purge was charged with 100 grams of the product of Example I, 775 grams of 
pyridine, and 155 grams of water. The mixture was refluxed and oxidized 
with 49 grams of KMnO.sub.4, filtered to recover the intermediate to which 
775 grams of 1.8 N NaOH solution was added. The mixture was refluxed, 
oxidized, and filtered again The oxidation steps were repeated 5 times. 
The resulting final product had a melting point ranging from about 
213.5.degree. to 219.degree. C. 
EXAMPLE III 
Synthesis of the Acid Chloride of the Product Obtained in Example II 
##STR31## 
Twenty grams of the product of Example II was mixed with 61.2 grams of 
SO.sub.2 Cl in a reaction flask, fitted with a stirrer, condenser, 
thermometer, and dry N.sub.2 purge. The mixture was refluxed for 2 hours 
and the SO.sub.2 Cl was distilled off. Two hundred ml of benzene was added 
and the mixture was refluxed, cooled, and filtered to recover the raw 
product which was recrystallized to a powder. The powder was mixed with 
200 ml of benzene, refluxed, and cooled to form a precipitate that had a 
melting range of about 115.degree. to 118.degree. C. 
EXAMPLE IV 
Synthesis of Nadic Dicapped Polybenzoxazole 
Formula Weight Approximately 4,000 
##STR32## 
5.62 grams (10.66 moles) of the acid chloride terminated sulfone of Example 
III was combined with 2.47 grams (5.3 mmoles) of nadic dicapped acid 
chloride in CH.sub.2 Cl.sub.2. The mixture of acid chlorides was added 
using an addition funnel to a stirred slurry of 2.88 grams (13.3 mmoles) 
of 3,3'-dihydroxybenzidine in dimethylacidamide (DMAC). The mixture was 
stirred for 3 hours at room temperature, and then sat under N.sub.2 for 48 
hours in the atmosphere. The product was recrystallized from CH.sub.2 
Cl.sub.2 using petroleum ether, was washed with petroleum ether, and 
washed again with methanol. The product yield was 82%, and the product had 
a melting range of 220.degree.-245.degree. C. 
EXAMPLE V 
Synthesis of Nadic Dicapped Polybenzoxazole 
Formula Weight Approximately 2,410 
##STR33## 
12.53 grams (23.76 m-moles) of the acid chloride terminated sulfone in 
Example III was combined with 7.71 grams (35.65 m-moles) of 
3,3'-dihydroxybenzidine in pyridine. The mixture was stirred under 
nitrogen in an ice water bath. 11.00 grams (23.76 m-moles) of nadic 
dicapped acid chloride in CH.sub.2 Cl.sub.2 was added over a 30-minute 
period, and the mixture was stirred 3 hours at room temperature. 
The product was precipitated in a blender with water, recovered with 
filtration, washed with water, and then washed again with methanol. The 
product was dried under nitrogen, and had a melting point of about 
245.degree. C. 
EXAMPLE VI 
General Method of Preparation of Composites for Oligomer of Example IV 
The resulting oligomers were impregnated on epoxy-sized T300/graphite 
fabric style (Union Carbide 35 million modulus fiber 24.times.24 weave). 
The solution obtained in each Example was coated onto the dry graphite 
fabric so that 38% by weight of the resulting prepreg would be the 
oligomer. The prepreg was allowed to dry under ambient conditions to less 
than 1% volatile content. The prepreg was then cut into 6x6-inch pieces 
and stacked to obtain a consolidated composite of approximately 
0.062-inch. The stack of prepreg was then vacuum bagged and consolidated 
under a bag pressure of 200 psi for 3 hours at 650.degree. F. and for two 
hours thereafter in an autoclave. 
EXAMPLE VII 
A polybenzoxazole oligomer was made using the procedure described in 
Examples IV and V. Composite panels were fabricated as described in 
Example VI, and the mechanical properties of each panel were determined. 
Table I illustrates the mechanical properties. 
TABLE I 
______________________________________ 
Summary Mechanical Properties 
of Polybenzoxazole Oligomers 
Shear Strength 
Panel Resin psi (1) at: 
Example No. 
FMW Cure T .degree.F. 
RT 450.degree. F. 
650.degree. F. 
______________________________________ 
Example IV 
4000 650 3460 -- -- 
Example V 2500 650 4720 4090 2680 
______________________________________ 
(1) Short beam shear test method 
While preferred embodiments have been described, those skilled in the art 
will recognize alterations, variations, or modifications that might be 
made to the embodiments without departing from the inventive concept. The 
description and examples, accordingly, are meant to illustrate the 
invention. The claims should be interpreted liberally in view of the 
description, and should be limited only as is necessary in view of the 
pertinent prior art.