Liquid crystal polyester thermosets

The present invention provides (1) curable liquid crystalline polyester monomers represented by the formula: EQU R.sup.1 --A.sup.1 --B.sup.1 --A.sup.2 --B.sup.2 --A.sup.3 --R.sup.2 where R.sup.1 and R.sup.2 are radicals selected from the group consisting of maleimide, substituted maleimide, nadimide, substituted naimide, ethynyl, and (C(R.sup.3).sub.2).sub.2 where R.sup.3 is hydrogen with the proviso that the two carbon atoms of (C(R.sup.3).sub.2).sub.2 are bound on the aromatic ring of A.sup.1 or A.sup.3 to adjacent carbon atoms, A.sup.1 and A.sup.3 are 1,4-phenylene and the same where said group contains one or more substituents selected from the group consisting of halo, e.g., fluoro, chloro, bromo, or iodo, nitro lower alkyl, e.g., methyl, ethyl, or propyl, alkoxy, e.g., methoxy, ethoxy, or propoxy, and fluoroalkyl, e.g., trifluoromethyl, pentafluoroethyl and the like, A.sup.2 is selected from the group consisting of 1,4-phenylene, 4,4'-biphenyl, 2,6-naphthylene and the same where said groups contain one or more substituents selected from the group consisting of halo, e.g., fluoro, chloro, bromo, or iodo, nitro, lower alkyl, e.g., methyl, ethyl, and propyl, lower alkoxy, e.g., methoxy, ethoxy, or propoxy, and fluoroalkyl or fluoroalkoxy, e.g., trifluoromethyl, pentafluoroethyl and the like, and B.sup.1 and B.sup.2 are selected from the group consisting of --C(O)--O-- and --O--C(O)--, (2) thermoset liquid crystalline polyester compositions comprised of heat-cured segments derived from monomers represented by the formula: EQU R.sup.1 --A.sup.1 --B.sup.1 --A.sup.2 --B.sup.2 --A.sup.3 --R.sup.2 as described above, (3) curable blends of at least two of the polyester monomers and (4) processes of preparing the curable liquid crystalline polyester monomers.

FIELD OF THE INVENTION 
The present invention relates to the field of curable liquid crystal 
polyester monomers and to thermoset liquid crystalline polyester 
compositions prepared therefrom. 
BACKGROUND OF THE INVENTION 
Liquid crystal polymers are recognized as having great potential for the 
development of new materials with exceptional physical and mechanical 
properties. In general, liquid crystal polymers consist of polymer chains 
containing anisotropic structural units (mesogenic groups) which may be 
incorporated into the polymer backbone, as pendent groups, or both. The 
mesogenic groups may be rod-like or disc-like in nature. Fibers, films, 
and molded plastics processed from the liquid crystalline state have shown 
outstanding properties. 
Another desirable characteristic of such liquid crystalline polymers would 
be that they be thermosetting. Liquid crystal thermosetting polymers are 
known, e.g., the acrylic-terminated thermoset resins and precursors 
disclosed by Conciatori et al. in U.S. Pat. Nos. 4,440,945, 4,452,993, and 
4,514,553, the epoxy-terminated thermoset resins and precursors disclosed 
by Muller et al. in U.S. Pat. No. 4,764,581, and the various 
difunctionally terminated materials disclosed by Dhein et al. in U.S. Pat. 
No. 4,762,901. 
Another type of thermosetting resins utilizing end groups such as 
maleimide, nadimide and methyl nadimide are described in various patents 
such as U.S. Pat. Nos. 4,225,497, 4,550,177, 4,739,030, 4,661,604, 
4,684,714, 4,851,495, and 4,851,501. 
Accordingly, it is an object of this invention to provide curable liquid 
crystalline polyester materials. 
Another object of this invention is to provide a process of preparing 
curable liquid crystal polyester monomers. 
Yet another object of this invention is to provide liquid crystalline 
blends of polyester materials. 
It is a further object of this invention to provide thermoset liquid 
crystalline polyester compositions. 
It is a still further object of this invention to provide thermoset liquid 
crystalline polyester compositions having a high heat resistance. 
SUMMARY OF THE INVENTION 
To achieve the foregoing and other objects, and in accordance with the 
purposes of the present invention, as embodied and broadly described 
herein, the present invention provides a curable liquid crystalline 
polyester monomer represented by the formula: 
EQU R.sup.1 --A.sup.1 --B.sup.1 --A.sup.2 --B.sup.2 --A.sup.3 --R.sup.2 
where R.sup.1 and R.sup.2 are radicals selected from the group consisting 
of maleimide, substituted maleimide, nadimide, substituted nadimide, 
ethynyl, and (C(R.sup.3).sub.2).sub.2 where R.sup.3 is hydrogen with the 
proviso that the two carbon atoms of (C(R.sup.3).sub.2).sub.2 are bound on 
the aromatic ring of A.sup.1 or A.sup.3 to adjacent carbon atoms, A.sup.1 
and A.sup.3 are 1,4-phenylene and the same where said group contains one 
or more substituents selected from the group consisting of halo, e.g., 
fluoro, chloro, bromo, or iodo, nitro, lower alkyl, e.g., methyl, ethyl, 
or propyl, lower alkoxy, e.g., methoxy, ethoxy, or propoxy, and 
fluoroalkyl, e.g., trifluoromethyl, pentafluoroethyl and the like, A.sup.2 
is selected from the group consisting of 1,4-phenylene, 4,4'-biphenyl, 
2,6-naphthylene and the same where said groups contain one or more 
substituents selected from the group consisting of halo, e.g., fluoro, 
chloro, bromo, or iodo, nitro, lower alkyl, e.g., methyl, ethyl, and 
propyl, lower alkoxy, e.g., methoxy, ethoxy, or propoxy, and fluoroalkyl 
or fluoroalkoxy, e.g., trifluoromethyl, pentafluoroethyl and the like, and 
B.sup.1 and B.sup.2 are selected from the group consisting of --C(O)--O-- 
and --O--C(O)--. Preferably, R.sup.1 and R.sup.2 are radicals selected 
from the group consisting of maleimide, nadimide, methyl nadimide, and 
ethynyl. 
The present invention further provides a thermoset liquid crystalline 
polyester composition comprised of cured segments derived from monomers 
represented by the formula: 
EQU R.sup.1 --A.sup.1 --B.sup.1 --A.sup.2 --B.sup.2 --A.sup.3 --R.sup.2 
where R.sup.1 and R.sup.2 are radicals selected from the group consisting 
of maleimide, substituted maleimide, nadimide, substituted nadimide, 
ethynyl, and (C(R.sup.3).sub.2).sub.2 where R.sup.3 is hydrogen with the 
proviso that the two carbon atoms of (C(R.sup.3).sub.2).sub.2 are bound on 
the aromatic ring of A.sup.1 or A.sup.3 to adjacent carbon atoms, A.sup.1 
and A.sup.3 are 1,4-phenylene and the same where said group contains one 
or more substituents selected from the group consisting of halo, e.g., 
fluoro, chloro, bromo, or iodo, nitro, lower alkyl, e.g., methyl, ethyl, 
or propyl, lower alkoxy, e.g., methoxy, ethoxy, or propoxy, and 
fluoroalkyl, e.g., trifluoromethyl, pentafluoroethyl and the like, A.sup.2 
is selected from the group consisting of 1,4-phenylene, 4,4'-biphenyl, 
2,6-naphthylene and the same where said groups contain one or more 
substituents selected from the group consisting of halo, e.g., fluoro, 
chloro, bromo, or iodo, nitro, lower alkyl, e.g., methyl, ethyl, and 
propyl, lower alkoxy, e.g., methoxy, ethoxy, or propoxy, and fluoroalkyl 
or fluoroalkoxy, e.g., trifluoromethyl, pentafluoroethyl and the like, and 
B.sup.1 and B.sup.2 are selected from the group consisting of --C(O)--O-- 
and --O--C(O)--. Preferably, R.sup.1 and R.sup.2 are radicals selected 
from the group consisting of maleimide, nadimide, methyl nadimide, and 
ethynyl. 
The present invention also provides curable blends including at least two 
liquid crystalline polyester monomers represented by the formula: 
EQU R.sup.1 --A.sup.1 --B.sup.1 --A.sup.2 --B.sup.2 --A.sup.3 --R.sup.2 
where R.sup.1 and R.sup.2 are radicals selected from the group consisting 
of maleimide, substituted maleimide, nadimide, substituted nadimide, 
ethynyl, and (C(R.sup.3).sub.2).sub.2 where R.sup.3 is hydrogen with the 
proviso that the two carbon atoms of (C(R.sup.3).sub.2).sub.2 are bound on 
the aromatic ring of A.sup.1 or A.sup.3 to adjacent carbon atoms, A.sup.1 
and A.sup.3 are 1,4-phenylene and the same where said group contains one 
or more substituents selected from the group consisting of halo, e.g., 
fluoro, chloro, bromo, or iodo, nitro, lower alkyl, e.g., methyl, ethyl, 
or propyl, lower alkoxy, e.g., methoxy, ethoxy, or propoxy, and 
fluoroalkyl, e.g., trifluoromethyl, pentafluoroethyl and the like, A.sup.2 
is selected from the group consisting of 1,4-phenylene, 4,4'-biphenyl, 
2,6-naphthylene and the same where said groups contain one or more 
substituents selected from the group consisting of fluoro, chloro, bromo, 
iodo, nitro, methyl, ethyl, methoxy, ethoxy or trifluoromethyl, and 
B.sup.1 and B.sup.2 are selected from the group consisting of --C(O)--O-- 
and --O-- C(O)--. 
The present invention still further provides a process of preparing a 
curable liquid crystalline polyester monomer represented by the formula: 
EQU R.sup.1 --A.sup.1 --B.sup.1 --A.sup.2 --B.sup.2 --A.sup.3 --R.sup.2 
where R.sup.1 and R.sup.2 are radicals selected from the group consisting 
of maleimide, substituted maleimide, nadimide, substituted nadimide, 
ethynyl, and (C(R.sup.3).sub.2).sub.2 where R.sup.3 is hydrogen with the 
proviso that the two carbon atoms of (C(R.sup.3).sub.2).sub.2 are bound on 
the aromatic ring of A.sup.1 or A.sup.3 to adjacent carbon atoms, A.sup.1 
and A.sup.3 are 1,4-phenylene and the same where said group contains one 
or more substituents selected from the group consisting of halo, e.g., 
fluoro, chloro, bromo, or iodo, nitro, lower alkyl, e.g., methyl, ethyl, 
or propyl, lower alkoxy, e.g., methoxy, ethoxy, or propoxy, and 
fluoroalkyl, e.g., trifluoromethyl, pentafluoroethyl and the like, A.sup.2 
is selected from the group consisting of 1,4-phenylene, 4,4'-biphenyl, 
2,6-naphthylene and the same where said groups contain one or more 
substituents selected from the group consisting of halo, e.g., fluoro, 
chloro, bromo, or iodo, nitro, lower alkyl, e.g., methyl, ethyl, and 
propyl, lower alkoxy, e.g., methoxy, ethoxy, or propoxy, and fluoroalkyl 
or fluoroalkoxy, e.g., trifluoromethyl, pentafluoroethyl and the like, and 
B.sup.1 and B.sup.2 are selected from the group consisting of --C(O)--O-- 
and --O--C(O)--, said process comprising: reacting a difunctional compound 
represented by the formula B.sup.3 --A.sup.2 --B.sup.4 wherein B.sup.3 and 
B.sup.4 are --OH, and A.sup.2 is selected from the group consisting of 
1,4-phenylene, 4,4'-biphenyl, 2,6-naphthylene and the same where said 
groups contain one or more substituents selected from the group consisting 
of halo, e.g., fluoro, chloro, bromo, or iodo, nitro, lower alkyl, e.g., 
methyl, ethyl, and propyl, lower alkoxy, e.g., methoxy, ethoxy, or 
propoxy, and fluoroalkyl or fluoroalkoxy, e.g., trifluoromethyl, 
pentafluoroethyl and the like, with an acid chloride represented by the 
formula: Cl--C(O)--A.sup.1 --R.sup.1 wherein A.sup.1 is 1,4-phenylene and 
the same containing one or more substitutes selected from the group 
consisting of halo, e.g., fluoro, chloro, bromo, or iodo, nitro, lower 
alkyl, e.g., methyl, ethyl, and propyl, lower alkoxy, e.g., methoxy, 
ethoxy, or propoxy, and fluoroalkyl or fluoroalkoxy, e.g., 
trifluoromethyl, pentafluoroethyl and the like, and R.sup.1 is a radical 
selected from the group consisting of maleimide, substituted maleimide, 
nadimide, substituted nadimide, ethynyl, and (C(R.sup.3).sub.2).sub.2 
where R.sup.3 is hydrogen with the proviso that the two carbon atoms of 
(C(R.sup.3).sub.2).sub.2 are bound on the aromatic ring of A.sup.1 or 
A.sup.3 to adjacent carbon atoms. Preferably, R.sup.1 and R.sup.2 are 
radicals selected from the group consisting of maleimide, nadimide, methyl 
nadimide, and ethynyl.

DETAILED DESCRIPTION 
The present invention is concerned with curable or thermosettable liquid 
crystalline polyester compounds represented by the formula 
EQU R.sup.1 --A.sup.1 --B.sup.1 --A.sup.2 --B.sup.2 --A.sup.3 --R.sup.2 
where R.sup.1 and R.sup.2 are radicals selected from the group consisting 
of maleimide, substituted maleimide, nadimide, substituted nadimide, 
ethynyl, and (C(R.sup.3).sub.2).sub.2 where R.sup.3 is hydrogen with the 
proviso that the two carbon atoms of (C(R.sup.3).sub.2).sub.2 are bound on 
the aromatic ring of A.sup.1 or A.sup.3 to adjacent carbon atoms, A.sup.1 
and A.sup.3 are 1,4-phenylene and the same where said group contains one 
or more substituents selected from the group consisting of halo, e.g., 
fluoro, chloro, bromo, or iodo, nitro, lower alkyl, e.g., methyl, ethyl, 
or propyl, lower alkoxy, e.g., methoxy, ethoxy, or propoxy, and 
fluoroalkyl, e.g., trifluoromethyl, pentafluoroethyl and the like, A.sup.2 
is selected from the group consisting of 1,4-phenylene, 4,4'-biphenyl, 
2,6-naphthylene and the same where said groups contain one or more 
substituents selected from the group consisting of halo, e.g., fluoro, 
chloro, bromo, or iodo, nitro, lower alkyl, e.g., methyl, ethyl, and 
propyl, lower alkoxy, e.g., methoxy, ethoxy, or propoxy, and fluoroalkyl 
or fluoroalkoxy, e.g., trifluoromethyl, pentafluoroethyl and the like, and 
B.sup.1 and B.sup.2 are selected from the group consisting of --C(O)--O-- 
and --O-- C(O)--. Where R.sup.1 and R.sup.2 are substituted maleimide or 
substituted nadimide, the substituents can include one or two groups 
selected from among lower alkyl, lower alkoxy, aryl, aryloxy, halogen, 
substituted alkyl, or substituted alkoxy upon the ring. Also, the bridging 
methylene group in nadimide may be replaced by groups such as oxo, thio, 
or sulfone. Preferably, R.sup.1 and R.sup.2 are radicals selected from the 
group consisting of maleimide, nadimide, methyl nadimide, and ethynyl. 
Throughout the present description, where A.sup.1 or A.sup.3 are bound to a 
(C(R.sup.3).sub.2).sub.2 moiety, the combination of such can be referred 
to as a benzocyclobutene group. FIG. 1(o) illustrates, e.g., the 
hydroquinone benzocyclobutene ester monomer. 
Such curable liquid crystalline polyester compounds or monomers can be 
prepared by a process including reacting a difunctional compound, i.e., a 
diol represented by the formula B.sup.3 --A.sup.2 --B.sup.4 wherein 
B.sup.3 and B.sup.4 are --OH, and A.sup.2 is selected from the group 
consisting of 1,4-phenylene, 4,4'-biphenyl, 2,6-naphthylene and the same 
where said groups contain one or more substituents selected from the group 
consisting of halo, e.g., fluoro, chloro, bromo, or iodo, nitro, lower 
alkyl, e.g., methyl, ethyl, and propyl, lower alkoxy, e.g., methoxy, 
ethoxy, or propoxy, and fluoroalkyl or fluoroalkoxy, e.g., 
trifluoromethyl, pentafluoroethyl and the like, with an acid chloride 
represented by the formula 
EQU Cl--C(O)--A.sup.(1 or 3) --R.sup.(1 or 2) 
wherein A.sup.(1 or 3) is 1,4-phenylene and the same where said group 
contains one or more substituents selected from the group consisting of 
halo, e.g., fluoro, chloro, bromo, or iodo, nitro, lower alkyl, e.g., 
methyl, ethyl, or propyl, lower alkoxy, e.g., methoxy, ethoxy, or propoxy, 
and fluoroalkyl, e.g., trifluoromethyl, pentafluoroethyl and the like, and 
either R.sup.(1 or 2) is a radical selected from the group consisting of 
maleimide, substituted maleimide, nadimide, substituted nadimide, ethynyl, 
and (C(R.sup.3).sub.2).sub.2 where R.sup.3 is hydrogen with the proviso 
that the two carbon atoms of (C(R.sup.3).sub.2).sub.2 are bound on the 
aromatic ring of A.sup.1 or A.sup.3 to adjacent carbon atoms. Preferably, 
R.sup.1 and R.sup.2 are radicals selected from the group consisting of 
maleimide, nadimide, methyl nadimide, and ethynyl. In this process, i.e., 
the reaction of the diol with the acid chloride containing the end-capped 
groups, the result is a liquid crystalline polyester compound or monomer 
wherein the carbonyl of B.sup.1 and B.sup.2 are adjacent to A.sup.1 or 
A.sup.3. To obtain to preferred products the diol is reacted with the acid 
chloride in a ratio of diol:acid chloride of 1:2. An acid scavenger such 
as triethylamine or the like can be added to the reaction mixture. In a 
similar manner, the reaction of a diacid chloride with a phenol containing 
the end-capped groups may yield a liquid crystalline polyester compound or 
monomer wherein the carbonyl of B.sup.1 and B.sup.2 are adjacent to 
A.sup.2. Such end-capped phenol compounds are described in U.S. Pat. No. 
4,661,604. 
The acid chlorides can be represented by the formula 
EQU Cl--C(O)--A.sup.(1 or 3) --R.sup.(1 or 2) 
wherein A.sup.(1 or 3) is selected from the group consisting of 
1,4-phenylene and the same where said group contains one or more 
substituents selected from the group consisting of halo, e.g., fluoro, 
chloro, bromo, or iodo, nitro, lower alkyl, e.g., methyl, ethyl, and 
propyl, lower alkoxy, e.g., methoxy, ethoxy, or propoxy, and fluoroalkyl 
or fluoroalkoxy, e.g., trifluoromethyl, pentafluoroethyl and the like, and 
either R.sup.(1 or 2) is a radical selected from the group consisting of 
maleimide, substituted maleimide, nadimide, or substituted nadimide, can 
be prepared by reacting para-aminobenzoic acid with the respective 
anhydride to obtain the respective amic acid, cyclodehydrating the amic 
acid with a mixture of acetic anhydride and sodium acetate to obtain an 
intermediate product, and finally reacting the intermediate product with 
oxalyl chloride to obtain the acid chloride. 
Curable blends of the liquid crystalline polyester compounds are also 
provided by this invention. Such blends can allow the tailoring of 
properties such as melting points and which may lower the processing 
temperature of these materials. For example, by blending two or more of 
the polyester monomers the melting point of the blend can be depressed 
beneath that of the individual monomers while retaining the liquid 
crystallinity of the monomers. The liquid crystalline polyester monomers 
or compounds are represented by the formula 
EQU R.sup.1 --A.sup.1 --B.sup.1 --A.sup.2 --B.sup.2 --A.sup.3 --R.sup.2 
where R.sup.1, R.sup.2, A.sup.1, A.sup.2, A.sup.3, B.sup.1 and B.sup.2 are 
as previously described. 
The liquid crystalline polyester monomers can be polymerized by heat alone, 
or by the action of free radical initiators, or by the addition of 
aromatic polyamines as bridging agents, or by the presence of a catalytic 
amount of an alkali metal salt of a Bronsted acid. Preferably, with 
monomers including the end groups of ethynyl and benzocyclobutene, such 
monomers are polymerized by heat. 
In addition to homopolymerization, the liquid crystalline polyester 
monomers can be polymerized with various vinyl monomers such as styrene, 
acrylonitrile, acrylates and methacrylates, or with other type maleimide 
capped compounds. Such copolymerizations can be initiated by free radical 
generating materials such as peroxides, azo compounds, etc. as well known 
to one skilled in the art of polymerization. 
The end-capped compounds or monomers of the present invention can be used 
in forming prepregs or composites as is standard in the art. Crosslinking 
with the end-capped compounds generally can occur with heat alone upon 
heating the compounds to from about 170.degree. C. to about 370.degree. 
C., preferably from about 200.degree. C. to about 340.degree. C. 
Prepregs of the end-capped compounds or monomers can be prepared by 
conventional techniques. While woven fabrics are the typical 
reinforcement, the fibers can be continuous or discontinuous, i.e., in 
chopped or whisker form, and may be ceramic, organic, glass, or carbon, 
i.e., graphite, as is desired for the particular application. 
Composites can be formed by curing the end-capped compounds or prepregs in 
conventional vacuum bag techniques. The end-capped compounds may also be 
used as adhesives, varnishes, films, or coatings. 
The present invention is more particularly described in the following 
examples which are intended as illustrative only, since numerous 
modifications and variations will be apparent to those skilled in the art. 
EXAMPLE A 
N-(para-carboxyphenyl)maleimide was prepared as follows. Maleic anhydride 
(45.2 grams (g)) was dissolved in from 300-400 milliliters (ml) of 
acetone. To this solution, an equimolar amount of para-aminobenzoic acid 
(63.2 g) was added with rapid stirring. The reaction mixture solidified 
within a few seconds. Excess solvent was removed by evaporation to yield 
the amic acid intermediate which was then dried overnight at 65.degree. C. 
under vacuum. 
The dried intermediate material was then dissolved in 200 ml of dimethyl 
formamide and heated to 45.degree. C. Acetic anhydride (72 ml) and 
anhydrous sodium acetate (3.6 g) were then added with stirring. The 
reaction was allowed to proceed at 45.degree. C. for two hours after which 
the mixture was poured into one liter of water slightly acidified by 
addition of 10 ml of concentrated HCl. The resultant yellow product was 
collected by suction filtration, washed with water and dried at 80.degree. 
C. under vacuum. 
EXAMPLE B 
N-(para-carboxyphenyl)nadimide was prepared as follows. 
Cis-5-norbornene-endo-2,3-dicarboxylic anhydride (19.14 g) was gently 
heated in 70 ml of acetone until it dissolved. To this solution, an 
equimolar amount of para-aminobenzoic acid (16.05 g) was added with rapid 
stirring. The reaction mixture turned the color white with a slight tinge 
of pink. Heating was stopped after five minutes and stirring maintained 
for about 20 minutes to ensure complete reaction. The amic acid 
intermediate which was then dried overnight at 65.degree. C. under vacuum. 
The dried intermediate material was then suspended in 65 ml of dimethyl 
formamide and heated to 45.degree. C. Acetic anhydride (30 ml) and 
anhydrous sodium acetate (1.27 g) were then added with stirring. The 
reaction was allowed to proceed at 45.degree. C. for two hours after which 
the mixture was poured into one liter of water slightly acidified by 
addition of 10 ml of concentrated HCl. The resultant white product was 
collected by suction filtration, washed with water and dried at 80.degree. 
C. under vacuum. 
EXAMPLE C 
N-(para-carboxyphenyl)methyl nadimide was prepared as follows. 
Methyl-5-norbornene-2,3-dicarboxylic anhydride (18.48 g) was dissolved in 
45 ml of acetone. To this solution, an equimolar amount of 
para-aminobenzoic acid (14.2 g) was added with rapid stirring. The 
reaction mixture turned the color yellow. Stirring was maintained for 
about 20 minutes to ensure complete reaction. The yellow intermediate 
material was then dried overnight at 65.degree. C. under vacuum. 
A cyclodehydration reaction was then performed on the dried intermediate 
material in the manner of Examples A and B. The resultant white product 
was collected by suction filtration, washed with water and dried at 
80.degree. C. under vacuum. 
EXAMPLE D 
Para-maleimidobenzoyl chloride was prepared in accordance with the 
procedure described by Adams et al. in J. Am. Chem. Soc., 42, 599 (1920). 
The N-(para-carboxyphenyl) maleimide (15 g) was suspended in about 80 ml 
of benzene with stirring. To this mixture was added 15 ml (a 2.5:1 molar 
excess) of oxalyl chloride, whereupon some gas was evolved. The mixture 
was then heated slowly to reflux and maintained at reflux for two hours. 
Excess oxalyl chloride was removed by distillation. The reaction mixture 
was then cooled and the yellow product recovered by suction filtration. 
The resultant product was washed with hexane and dried under vacuum at 
room temperature. 
EXAMPLE E 
Para-nadimidobenzoyl chloride and para-(methyl nadimido)benzoyl chloride 
were prepared from the products of Examples B and C in the same manner as 
Example D. 
EXAMPLE 1 
Preparation of hydroquinone bismaleimide ester monomer, shown in FIG. 1(a), 
was as follows. Hydroquinone (1.086 g, 0.0099 moles) was suspended in 25 
ml diethyl ether and 3.3 ml of triethylamine. The solution was cooled in 
an ice bath and the acid chloride (4.64 g) from Example D was carefully 
added with stirring. Stirring was continued for about 30 minutes to ensure 
complete reaction. The mixture was heated to evaporate the solvent and the 
resultant product recrystallized from a 60/40 (v/v) phenol/trichloroethane 
mixture and dried at 80.degree. C. under vacuum. The hydroquinone 
bismaleimide ester monomer had a crystalline to nematic phase transition 
of 282.degree. C. as determined from differential scanning calorimetry and 
polarized optical microscopy. 
EXAMPLE 2 
Preparation of hydroquinone bisnadimide ester monomer, shown in FIG. 1(b), 
was as follows. Hydroquinone (0.365 g, 0.0033 moles) was suspended in 10 
ml diethyl ether and 0.93 ml of triethylamine. The solution was cooled in 
an ice bath and 2.0 g of the para-nadimidobenzoyl chloride from Example E 
was carefully added with stirring. The reaction was exothermic. Stirring 
was continued for about 30 minutes to ensure complete reaction. The 
mixture was heated to evaporate the solvent and the resultant product 
recrystallized from a mixture of trichloroethane/hexane and dried at 
80.degree. C. under vacuum. The hydroquinone bisnadimide ester monomer had 
a crystalline to nematic phase transition of 307.degree. C. as determined 
from differential scanning calorimetry and polarized optical microscopy. 
EXAMPLE 3 
Preparation of hydroquinone bis(methyl nadimide) ester monomer, shown in 
FIG. 1(c), was as follows. Hydroquinone (0.349 g) was suspended in 10 ml 
diethyl ether with 0.89 ml of triethylamine. The solution was cooled in an 
ice bath and 2.0 g of the para-(methyl nadimido)benzoyl chloride from 
Example E was carefully added with stirring. The reaction was exothermic. 
Stirring was continued for about 1.5 hours to ensure complete reaction. 
The mixture was heated to evaporate the solvent and the resultant product 
recrystallized from hexane and dried at 80.degree. C. under vacuum. The 
hydroquinone bis(methyl nadimide) ester monomer had a crystalline to 
nematic phase transition of 288.degree. C. as determined from differential 
scanning calorimetry and polarized optical microscopy. 
EXAMPLE 4 
Preparation of methylhydroquinone bismaleimide ester monomer, shown in FIG. 
1(d), was as follows. Methylhydroquinone (0.527 g) was dissolved in 15 ml 
diethyl ether with 1.2 ml of triethylamine. The solution was cooled in an 
ice bath and 2.0 g of the acid chloride from Example D was carefully added 
with stirring. Stirring was continued for about 45 minutes to ensure 
complete reaction. The mixture was heated to evaporate the solvent and the 
resultant product recrystallized from a mixture of 
1,2-dichloroethane/hexane and dried at 80.degree. C. under vacuum. The 
methylhydroquinone bismaleimide ester monomer had a crystalline to nematic 
phase transition of 245.degree. C. as determined from differential 
scanning calorimetry and polarized optical microscopy. 
EXAMPLE 5 
Preparation of methylhydroquinone bisnadimide ester monomer, shown in FIG. 
1(e), was as follows. Methylhydroquinone (0.412 g) was dissolved in 15 ml 
diethyl ether with 0.9 ml of triethylamine. The solution was cooled in an 
ice bath and 2.0 g of the para-nadimidobenzoyl chloride from Example E was 
carefully added with stirring. Stirring was continued for about 30 minutes 
to ensure complete reaction. The mixture was heated to evaporate the 
solvent and the resultant product recrystallized from 
1,2-dichloroethane/hexane and dried at 80.degree. C. under vacuum. The 
methylhydroquinone bisnadimide ester monomer had a crystalline to nematic 
phase transition of 271.degree. C. as determined from differential 
scanning calorimetry and polarized optical microscopy. 
EXAMPLE 6 
Preparation of methylhydroquinone bis(methyl nadimide) ester monomer, shown 
in FIG. 1(f), was as follows. Methylhydroquinone (0.197 g, 0.00158 moles) 
was dissolved in 12 ml diethyl ether with 0.45 ml of triethylamine. The 
solution was cooled in an ice bath and 1 g of the para-(methyl 
nadimido)benzoyl chloride from Example E was carefully added with 
stirring. Stirring was continued for about 30 minutes to ensure complete 
reaction. The mixture was heated to evaporate the solvent and the 
resultant product recrystallized from a mixture of toluene/hexane and 
dried at 80.degree. C. under vacuum. The methylhydroquinone bis(methyl 
nadimide) ester monomer had a crystalline to nematic phase transition of 
211.degree. C. as determined from differential scanning calorimetry and 
polarized optical microscopy. 
EXAMPLE 7 
Preparation of chlorohydroquinone bismaleimide ester monomer, shown in FIG. 
1(g), was as follows. Chlorohydroquinone (0.613 g, 0.0042 moles) was 
dissolved in 15 ml diethyl ether with 1.2 ml of triethylamine. The 
solution was cooled in an ice bath and 2.0 g of the acid chloride from 
Example D was carefully added with stirring. Stirring was continued for 
about 1 hour to ensure complete reaction. The mixture was heated to 
evaporate the solvent and the resultant product recrystallized from a 
mixture of methylene chloride/hexane and dried at 80.degree. C. under 
vacuum. The chlorohydroquinone bismaleimide ester monomer had a 
crystalline to nematic phase transition of 215.degree. C. as determined 
from differential scanning calorimetry and polarized optical microscopy. 
EXAMPLE 8 
Preparation of chlorohydroquinone bisnadimide ester monomer, shown in FIG. 
1(h), was as follows. Chlorohydroquinone (0.479 g, 0.0033 moles) was 
dissolved in 15 ml diethyl ether with 0.45 ml of triethylamine. The 
solution was cooled in an ice bath and 2.0 g of the para-nadimidobenzoyl 
chloride from Example E was carefully added with stirring. Stirring was 
continued for about 1 hour to ensure complete reaction. The mixture was 
heated to evaporate the solvent and the resultant product recrystallized 
from a mixture of 1,1,2-trichloroethane/hexane and dried at 80.degree. C. 
under vacuum. The chlorohydroquinone bisnadimide ester monomer had a 
crystalline to nematic phase transition of 271.degree. C. as determined 
from differential scanning calorimetry and polarized optical microscopy. 
EXAMPLE 9 
Preparation of chlorohydroquinone bis(methyl nadimide) ester monomer, shown 
in FIG. 1(i), was as follows. Chlorohydroquinone (0.458 g) was dissolved 
in 15 ml diethyl ether with 0.9 ml of triethylamine. The solution was 
cooled in an ice bath and 2.0 g of the para-(methyl nadimido)benzoyl 
chloride from Example E was carefully added with stirring. The reaction 
was exothermic. Stirring was continued for about 1 hour to ensure complete 
reaction. The mixture was heated to evaporate the solvent and the 
resultant product recrystallized from acetone/water and dried at 
80.degree. C. under vacuum. The chlorohydroquinone bis(methyl nadimide) 
ester monomer had a crystalline to nematic phase transition of 255.degree. 
C. as determined from differential scanning calorimetry and polarized 
optical microscopy. 
EXAMPLE 10 
Preparation of biphenyl bismaleimide ester monomer, shown in FIG. 1(j), was 
as follows. Biphenol (0.792 g, 0.0043 moles) was suspended in 10 ml 
diethyl ether and 1.4 ml of triethylamine. The solution was cooled in an 
ice bath and 2.0 g of the acid chloride from Example D was carefully added 
with stirring. Stirring was continued for about 90 minutes to ensure 
complete reaction. The resultant product was collected by suction 
filtration, washed with chloroform and dried at 20.degree. C. under 
vacuum. The biphenyl bismaleimide ester monomer had a crystalline to 
nematic phase transition of 299.degree. C. as determined from differential 
scanning calorimetry and polarized optical microscopy. 
EXAMPLE 11 
Preparation of naphthyl bismaleimide ester monomer, shown in FIG. 1(k), was 
as follows. 2,6-dihydroxynaphthalene (0.681 g, 0.0043 moles) was suspended 
in 10 ml diethyl ether and 1.4 ml of triethylamine. The solution was 
cooled in an ice bath and 2.0 g of the acid chloride from Example D was 
carefully added with stirring. Stirring was continued for about 90 minutes 
to ensure complete reaction. The resultant product was collected by 
suction filtration, washed with chloroform and dried at 20.degree. C. 
under vacuum. The naphthyl bismaleimide ester monomer had a crystalline to 
nematic phase transition of 287.degree. C. as determined from differential 
scanning calorimetry and polarized optical microscopy. 
EXAMPLE 12 
Preparation of hydroquinone bis(ethynyl) ester monomer, shown in FIG. 1(l), 
was as follows. Hydroquinone (0.67 g) was suspended in 15 ml diethyl ether 
with 1.7 ml of triethylamine. The solution was cooled in an ice bath and 
4-ethynylbenzoyl chloride (2.0 g) was carefully added with stirring. The 
tan product solidified almost immediately. The product was recrystallized 
from 1,1,2,2-tetrachloroethane and dried. 
EXAMPLE 13 
Preparation of methylhydroquinone bis(ethynyl) ester monomer, shown in FIG. 
1(m), was as follows. Methylhydroquinone (0.756 g) was dissolved in 15 ml 
diethyl ether. The solution was cooled in an ice bath and 4-ethynylbenzoyl 
chloride (2.0 g) was carefully added with stirring. To this mixture was 
added 1.7 ml of triethylamine. A large exotherm was observed. The product 
was recrystallized from acetonitrile and dried. The methylhydroquinone 
bis(ethynyl) ester monomer had a crystalline to nematic phase transition 
of 173.degree. C. as determined from differential scanning calorimetry. 
EXAMPLE 14 
Preparation of chlorohydroquinone bis(ethynyl) ester monomer, shown in FIG. 
1(n), was as follows. Chlorohydroquinone (0.88 g) was dissolved in 15 ml 
diethyl ether. The solution was cooled in an ice bath and 4-ethynylbenzoyl 
chloride (2.0 g) was carefully added with stirring. To this mixture was 
added 1.7 ml of triethylamine. A large exotherm was observed. The product 
was recrystallized from a mixture of 1,1,2,2-tetrachloroethane and 
acetonitrile and then dried at 125.degree. C. under vacuum. The 
chlorohydroquinone bis(ethynyl) ester monomer had a crystalline to nematic 
phase transition of 187.degree. C. as determined from differential 
scanning calorimetry. 
EXAMPLE 15 
Approximately equal amounts of the crystalline powders from Examples 10 and 
11 were mixed on a glass plate and gradually heated. The blend melted to a 
nematic phase at 268.degree. C. and crosslinked with continued heating. In 
comparison, the monomer from Example 10 had a melting point of 299.degree. 
C. and the monomer from Example 11 had a melting point of 287.degree. C. 
While the present invention has been described with reference to specific 
details, it is not intended that such details should be regarded as 
limitations upon the scope of the invention, except as and to the extent 
that they are included in the accompanying claims.