Resin systems derived from benzocyclobutene-maleimide compounds

Resins are prepared by Diels-Alder polymerization of compounds of the formula ##STR1## where R is a divalent linking group.

BACKGROUND OF THE INVENTION 
The present invention relates to resins obtained by Diels-Alder 
polymerization, and more particularly, to high temperature resistant 
matrix resins obtained by Diels-Alder polymerization of 
benzocyclobutene-maleimide compounds. 
The Diels-Alder reaction is a cycloaddition reaction in which an 
unsaturated group, which is a dienophile, combines with a 1,3-diene to 
form a six membered ring. The Diels-Alder reaction appears to be favored 
by the presence of the diene's electron-yielding groups, and the 
dienophile's electron-attracting groups. 
Although the Diels-Alder reaction is used extensively in organic chemistry, 
it is less commonly employed in polymer chemistry. Yet, it can be quite 
advantageous. For example, at high temperatures, it is expected that 
Diels-Alder adducts with appropriate activating groups (unsaturated and 
conjugated groups) undergo conversion to other products, such as aromatic 
rings, before the temperature required for the reverse reaction or 
degradation process is reached; consequently, such Diels-Alder polymers 
exhibit high thermal stability. 
In most Diels-Alder polymerizations, a bis-diene reacts with a 
bis-dienophile. For example, in W. J. Bailey et al, "Polymeric Diels-Alder 
Reactions," J. Org. Chem. 27, 3295(1962), 2-vinylbutadiene, a 
bi-functional diene, is reacted with benzoquinone, a dienophile. J. K. 
Stille, "Cycloaddition Polymerization," Die Makromolekulare Chemie 154, 
49(1972), teaches that cyclopentadienones undergo a variety of Diels-Alder 
reactions depending on the ring substitution, dienophile, and reaction 
conditions. To obtain a monoadduct, cyclopentadienone is employed with an 
acetylenic dienophile to obtain an aromatic product. Additionally, R. T. 
Kohl et al, "Diels-Alder Reactions of Phenyl-Substituted 2-Pyrones: 
Direction of Addition with Phenylacetylene," Macromolecules 11, 340(1978) 
shows the Diels-Alder reactions of substituted acetylenes with 2-pyrones. 
J. N. Braham et al, "Polyphenylenes via Bis(2-pyrones) and 
Diethynylbenzenes, "The Effect of m- and p-Phenylene Units in the Chain," 
Macromolecules 11,343(1978) shows the Diels-Alder 4+2 cycloaddition 
reaction of bis(2-pyrone) monomers with diethynylbenzenes. 
In some Diels-Alder polymerizations, the same molecule contains both the 
diene and the dienophile moiety. One class of monomer is capable of 
functioning as both a diene and dienophile. Cyclopentadiene and 
2-vinylbutadiene are two examples. In another class of monomer, the diene 
and dienophile are different. Meek and Argabright, J. Org. Chem. 22, 
1708(1957) prepared 
6-[p-(p-maleimidobenzoyloxy)phenyl]-1,2,3,4-tetrachlorofulvene which 
contains a maleimido group as a dienophile and a perchlorofulvene group as 
a diene. W. J. Bailey, "Diels-Alder Polymerization, " Step-Growth 
Polymerization, Marcel Dekker, New York, 1972, stresses that this type of 
polymerization presents considerable difficulty. 
Benzocyclobutene functions very well in a Diels-Alder reaction. As taught 
by W. Oppolzer, Synthesis 793(1978), under appropriate thermal conditions, 
the benzocyclobutene unit undergoes an electrocyclic ring opening to form 
the more reactive o-xylylene functionality. O-xylylene is a powerful diene 
and, engages in a Diels-Alder reaction in the presence of a suitable 
dienophile. See Boekelheide, Accounts Chem. Res. 13, 65(1980). 
An example of a suitable dienophile is a maleimide. Maleimides are 
well-known as possessing strong dienophilicity. The dienophilic site, 
i.e., the carbon-carbon double bond, is not subjected to the substituent 
effect imposed by the rest of the structure. Thus, a maleimide engages in 
a Diels-Alder polymerization in the presence of a suitable diene such as 
o-xylylene. 
Bis-benzocyclobutenes and polymers derived therefrom are disclosed in U.S. 
Pat. No. 4,540,763. The bis-benzocyclobutenes are connected by direct bond 
or a bridging member such as a cyclic imido group. In general, the 
polymers are obtained by addition polymerization wherein the fused 
cyclobutene rings undergo thermal transformation to o-xylylene moieties 
which can react with one another. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide compounds which are 
polymerizable by Diels-Alder polymerization. 
Another object of the present invention is to provide compounds useful in 
the preparation of high-temperature resistant matrix resins by Diels-Alder 
polymerization. 
A more particular object of the present invention is to provide 
high-temperature resistant matrix resins prepared by Diels-Alder 
polymerization of benzocyclobutene-maleimide compounds. 
Another object of the present invention is to provide high-temperature 
resistant matrix resins which are useful in composite materials in the 
advanced aircraft and aerospace vehicles. 
A further object of the present invention is to provide high-temperature 
resistant matrix resins which can be aromatized at high temperature. 
In accordance with the present invention, resins are obtained by the 
Diels-Alder polymerization of compounds which exhibit both diene and 
dienophile functionalities. The present invention provides compounds of 
the general formula (I) 
##STR2## 
wherein R is a divalent linking group. Upon heating these compounds to 
about 200.degree. C., the benzocyclobutene unit undergoes an electrocyclic 
ring-opening to form the more reactive o-xylylene functionality which 
engages in a Diels-Alder polymerization with the maleimide unit of the 
compound to form a six membered ring which conceivably can be converted to 
highly thermally stable structures such as a benzene ring and/or 
benzoquinone structure, at high temperatures. 
The maleimide functionality is ideal as the dienophilic component for a 
Diels-Alder polymerization and offers several advantages over other 
dienophilic components. The starting material for maleimide, i.e., maleic 
anhydride, is fairly inexpensive compared to starting materials required 
for other dienophilic components. The preparation of maleimide does not 
involve the use of an expensive catalyst. Also, the dienophilicity of 
maleimide is known to greatly exceed that of other dienophiles. 
In a more particular embodiment, the compound is represented by the formula 
(II) 
##STR3## 
where R is a divalent linking group. 
To maximize the thermal stability of the resin, in the compound of formulas 
(I) and (II) above, R is selected so as to provide a linking group which 
is as thermooxidatively stable as the Diels-Alder polymerization bond. 
Thus, in a preferred embodiment, R is an aromatic divalent linking group, 
and more particularly, a benzimido group. In other applications where 
thermooxidative stability is not as critical, numerous R groups are useful 
in the compounds of the present invention. 
In one embodiment, R is a direct bond. 
In another embodiment, R is represented by the formula (IV) 
##STR4## 
where X is a divalent linking group. 
In a more particular embodiment, X is selected from the group consisting of 
--C(CF.sub.3).sub.2 --,--C(CH.sub.3).sub.2 --, --CH.sub.2 
--,--O--,--S--,--CO--,--SO.sub.2 --, and a direct bond. 
In another embodiment, X is represented by the formula (V) 
##STR5## 
where Y is selected from the group consisting of --C(CF.sub.3).sub.2 
--,--C(CH.sub.3).sub.2 --,--CH.sub.2 --,--O--,--S--,--CO--,--SO.sub.2 
--and a direct bond. 
In an additional embodiment, X is represented by the formula (VI) 
##STR6## 
where Z is selected from the group consisting of --C(CF.sub.3).sub.2 
--,--C(CH.sub.3).sub.2 --,--CH.sub.2 --,--O--,--S--,--CO--,--SO.sub.2 
--and a direct bond. 
In another embodiment, R is represented by the formula (vII) 
##STR7## 
where p is 0 or 1. 
In a preferred embodiment, R is represented by the formula (III) 
##STR8## 
where n is 0 or 1. In a particularly preferred embodiment, n is 0. 
Some resins with excellent high temperature stability are obtained by 
Diels-Alder polymerization of compounds of the formula (I) above where R 
is represented by the formula (III) above. 
Other objects and advantages of the invention will be apparent from the 
following description, the accompanying drawings and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION 
The following reaction scheme sets forth the synthesis of 
4-aminobenzocyclobutene. 
##STR9## 
Step (A) is explained in Cava and Napier, J. Am. Chem. Soc. 79, 1701 
(1957). Sanders and Giering, J. Org. Chem. 38, 3055 (1973) provides 
details on Step (B). Step (C) is discussed in Lloyd and Ongley, 
Tetrahedron 20, 2185 (1964) while Step (D) is discussed in Horner and 
Schmelzer, Chem Ber 93 1774 (1960). 
To prepare a compound of the formula (II) where R is a direct bond, 
4-aminobenzocyclobutene is reacted with freshly purified maleic anhydride 
in methylene chloride at room temperature to lead to the formation of 
yellow maleamic acid. Subsequent treatment of N-4-benzocyclobutenyl 
maleamic acid with the dehydrating agent, acetic anhydride and in the 
presence of triethylamine and nickel acetate tetrahydrate provides the 
desired maleimide. 
To prepare a compound of the formula (II) wherein R is represented by the 
formula (III) where n is 0, 4-aminobenzocyclobutene and commercially 
available 4-nitrophthalic anhydride are condensed in a mixed solvent of 
acetic acid and toluene under Dean-Stark conditions. The resulting product 
is subsequently subjected to catalytic hydrogenation in the presence of 
10% palladium on carbon and anhydrous magnesium sulfate and using ethyl 
acetate as solvent. Finally, the desired compound is prepared from the 
foregoing amine and maleic anhydride in CH.sub.2 Cl.sub.2/ ethyl acetate 
followed by cyclodehydration of the maleamic acid intermediate using the 
established reagents and solvent (acetic anhydride, triethylamine, nickel 
acetate tetrahydrate and acetone). 
To prepare a compound of the formula (II) wherein R is represented by the 
formula (IV) and X is --C(CF.sub.3).sub.2 --, a heterogeneous mixture of 
2,2'-bis(phthalimido)hexafluoropropane and 3-nitroaniline is stirred in 
toluene under a nitrogen atmosphere at room temperature for four days. The 
stoichiometry of the dianhydride and the amine is 1:1.1 and the reaction 
is monitored by thin-layer chromatography. The mono-amic acid with some 
contamination of the diamic acid and the starting dianhydride is collected 
by filtration. It is then heated in a large beaker in an oven set at 
170.degree.-175.degree. C. for one hour. The solid is then dissolved in 
minimal amount of methylene chloride. The resulting solution is then 
purified by column chromatography. The isolated imide-anhydride, 
2-(4-phthalic anhydrido)-2'-(4-N-3-nitrophenyl phthalic imido) 
hexafluoropropane is then treated with 4-aminobenzocyclobutene in dimethyl 
acetamide at room temperature followed by dehydrating agents, acetic 
anhydride/pyridine. The asymmetric diimide, 2-(N-4-benzocyclobutenyl 
phthalimido)-2'-(4-N-3-nitrophenyl phthalic imido)hexafluoropropane is 
subsequently catalytically hydrogenated using 10% palladium on carbon, a 
mixed solvent of ethyl acetate and methanol and ammonium formate as a 
hydrogen source. The isolated amine, 2-(N-4-benzocyclobutenyl phthalic 
imido)-2'-(4-N-3-aminophenyl phthalic imido)hexafluoropropane is reacted 
with maleic anhydride to form the intermediate maleamic acid which upon 
cyclodehydration using established reagents and solvent yields the desired 
maleimide, 2-(N-4-benzocyclobutenyl phthalic 
imido)-2'-[4-N-(3-maleimido-phenyl) phthalic imido] hexafluoropropane. 
To prepare a compound of the formula (II) wherein R is represented by the 
formula (VII) where p is 0 and the isomer is meta, Friedel-Crafts reaction 
of benzocyclobutene and 3-nitrobenzoyl chloride in methylene chloride 
using antimony pentachloride as the catalyst and at low temperature leads 
to the formation of 4-benzocyclobutenyl-3-aminophenyl ketone. Catalytic 
transfer hydrogenation of the foregoing nitro-compound in methanol using 
10% palladium on carbon and ammonium formate as the source of hydrogen 
atoms is the next step. The desired maleimide is prepared by the reaction 
of 4-benzocyclobutenyl-3-aminophenyl ketone with maleic anhydride under 
established conditions. 
The para-isomer is prepared via the same synthetic route. 
To prepare a compound of the formula (II) wherein R is represented by the 
formula (VII) where p is 1, the initial amic acid is prepared from 
4-nitrophthalic anhydride and 3-aminophenyl-4-benzocyclobutenyl ketone in 
dimethyl acetamide at room temperature under nitrogen. The 
cyclodehydration of the amic acid leads to the corresponding imide using 
acetic anhydride and pyridine. Catalytic transfer hydrogenation of the 
foregoing nitro-compound using 10% palladium on carbon, methanol and ethyl 
acetate as co-solvents and ammonium formate as the hydrogen source results 
in the isolation of the corresponding amine. Reaction with maleic 
anhydride under established conditions affords the desired maleimide. 
The preferred methods of preparation of certain benzocyclobutene-maleimide 
compounds useful in the present invention are described in the Examples 
below. 
In general, the resins of the present invention are prepared by Diels-Alder 
polymerization of the particular compounds used. Upon heating the 
compounds to about 200.degree. C., Diels-Alder polymerization occurs. 
Also, homopolymerization of both the maleimide and the benzocyclobutene 
functionality can occur simultaneously with the Diels-Alder 
polymerization. These potential polymerization reactions are set forth in 
the following scheme. 
##STR10## 
In the Diels-Alder polymerization, the benzocyclobutene undergoes an 
electrocyclic ring-opening to form the more reactive o-xylylene 
functionality wherein the o-xylylene functionality undergoes cycloaddition 
with a maleimide functionaliry. In the homopolymerization of the 
maleimide, the maleimide functionality undergoes cycloaddition with 
another maleimide functionality. In the homopolymerization of 
benzocyclobutene, the benzocyclobutene reacts with another 
benzocyclobutene by one of at least two possible pathways: (1) 
cycloaddition and (2) linear addition. (1) Following the cycloaddition 
mode, a polymer with an eight membered ring is believed to form. (2) 
Following the linear addition mode, a polymeric structure with a double 
strand of poly (o-xylylene) connected by aromatic bridging groups is 
believed to result. The terms "cycloaddition" and "linear addition" are 
used to describe the structures and do not implicate the mechanisms from 
which they arise. 
In preparing the resins of the present invention, the Diels-Alder 
polymerization occurs at a substantially greater rate than the 
homopolymerization of the maleimide or the benzocyclobutene functionality 
in order to maximize the thermal stability of the resins. Thus, the 
resulting product has minimal homopolymerization product and maximum 
Diels-Alder polymerization product. In general, Diels-Alder polymerization 
occurs at a temperature of about 200.degree.-250.degree. C. while 
homopolymerization occurs at a temperature of about 
185.degree.-240.degree. C. 
An example of a Diels-Alder polymerization scheme is set forth below for 
N-(4-benzocyclobutenyl)-4(N-maleimido)phthalimide. 
##STR11## 
A Differential Scanning Calorimetric (DSC) study indicates the endothermic 
or exothermic nature of a reaction as the temperature increases. 
Typically, the reaction temperature is plotted on the abscissa while the 
heat flow is plotted on the ordinate. The DSC study is useful in the 
present invention because it indicates the exotherms for a given compound. 
For example, when R is represented by formula (III) where n equals 0 in 
the compound of formula (II) above, the DSC is represented by FIG. 1. FIG. 
1 shows a T.sub.poly onset (beginning polymerization temperature) of about 
221.degree. C. The T.sub.m (melting temperature) is about 230.degree. C. 
FIG. 1 shows a T.sub.poly max (temperature at which polymerization reaches 
its maximum) of about 256.degree. C. Rescanning the sample after heating 
to 450.degree. C. shows a Tg.sub.(cure) (glass transition temperature of 
the polymer) of about 328.degree. C. 
The T.sub.poly and T.sub.m valves were obtained by subjecting a compound 
sample to DSC measurements, which indicate the amounts of heat absorbed 
(endothermic) or evolved (exothermic) with respect to a reference 
temperature point or range when the sample undergoes either chemical 
chnges (T.sub.poly)or physical changes (T.sub.m). T.sub.g(cure) was 
determined both by DSC and thermomechanical analyses which employ a 
sensitive probe to detect the softening point of the sample at its 
surface. 
Table 1 sets forth thermal characteristics of compounds of formula (II). 
TABLE 1 
______________________________________ 
THERMAL CHARACTERISTICS OF COMPOUNDS 
OF FORMULA (II) 
T poly 
Example 
Tg(ini) Tm Onset Max Tg(cure) 
Tdec T10% 
______________________________________ 
5 -20.degree. 
77.degree. 
228.degree..sup.a 
259.degree..sup.a 
287.degree. 
--.sup.b 
--.sup.b 
8(meta) 
3.degree. 
93.degree. 
224.degree. 
261.degree. 
249.degree. 
431.degree. 
470.degree. 
8(para) 
-- -- 188.degree. 
248.degree. 
-- 353.degree. 
400.degree. 
3 86.degree. 
230.degree. 
231.degree. 
256.degree. 
328.degree. 
484.degree. 
498.degree. 
11 44.degree. 
-- 198.degree. 
257.degree. 
258.degree. 
403.degree. 
452.degree. 
______________________________________ 
All Table 1 temperatures are expressed in .degree.C. Example numbers 
correspond to the Examples given below. T.sub.g (ini) is the initial glass 
transition temperature and was determined from the rescan of a sample 
previously heated just past the melting temperature, T.sub.m. Tpoly onset 
is the beginning polymerization temperature while Tpoly max is the 
temperature at which polymerization reaches its maximum. T.sub.g (cure) is 
the final glass transition temperature and was determined from the rescan 
of the sample previously heated to 450.degree. C. T.sub.dec is the 
temperature at which major decomposition or weight loss occurs as observed 
by TGA. Both TGA and DSC runs were conducted at 10.degree. C./min. TGA was 
run under air and DSC was run under N.sub.2. T.sub.10% is the temperature 
at which 10% of the original weight of the sample is lost during the TGA 
run. Values a were determined under a N.sub.2 pressure of 500 psi. For 
values b, when a sample was run under atmospheric pressure, volatilization 
of the compound began at 148.degree. C.; about 71% of the original weight 
was lost between 200.degree.-238.degree. C. 
FIG. 2 represents a composite thermogram of the thermogravimetic analysis 
(TGA) of compounds of formula (II). The extrapolated values at which the 
major decompositions began (T.sub.dec) are indicated. 
It is believed that the resultant resin can be aromatized at 
high-temperature in the presence of air (O.sub.2) to enhance the 
thermodynamic stability of the final polymeric structure. Although gaseous 
H.sub.2 O will be produced as volatiles in the aromatization process, such 
process will take place primarily on the surface of the thermosets and 
will have minimal formation of voids. 
The Diels-Alder polymerization of the compounds has a significant impact on 
the nature and properties of the resins prepared. In a particularly 
preferred embodiment, resins prepared by the Diels-Alder polymerization of 
compounds of the formula (II) above where R is represented by formula 
(III) where n is 0 are high temperature resistant matrix resins useful in 
composite materials in the advanced aircraft and aerospace vehicles. 
The present invention is illustrated in more detail by the following 
non-limiting examples. 
EXAMPLE 1 
Preparation of N-4-Benzocyclobutenyl 4-nitro phthalimide. 
A mixture of 4-nitro phthalic anhydride (3.57 g, 18.5 mmol) and freshly 
prepared 4-aminobenzocyclobutene 2.20 g (18.5 mmol) was heated to reflux 
in acetic acid (100 ml) and toluene (100 ml) under nitrogen. The water of 
condensation was removed continuously and azeotropically using a 
Dean-Stark trap. After about 17 hrs, the dark but homogeneous reaction 
mixture was allowed to cool to room temperature and poured into 600 ml 
water. The mixture was then extracted with ethyl acetate (100 ml, then 4 
.times.50 ml). The organic extract was washed with aq. NaHCO.sub.3 and 
then H.sub.2 O, and finally dried over MgSO.sub.4. Immediately after the 
removal of hydrated MgSO.sub.4 by filtration, the filtrate was subjected 
to rotary evaporation to provide slightly tacky yellow-green crude 
product, which was redissolved in CH.sub.2 Cl.sub.2. The resultant 
solution was filtered through a bed of silica gel (approximately 20 g) and 
washed with CH.sub.2 Cl.sub.2 until the filtrate was colorless. The 
combined filtrate was again stripped on a rotary evaporator to afford 
yellow plates, which was collected on a fitted filter funnel, washed with 
petroleum ether and dried in oven under vacuum at 80.degree. C. overnight. 
Yield 3.85 g (71%). Calc. for C.sub.16 H.sub.10 N.sub.2 O.sub.4 :65.30% C; 
3.42% H; 9.52% N. Found: 64.17% C; 3.29% H; 9.54% N. Mass Spectroscopy: 
M.sup.+ (294, 100%). 
EXAMPLE 2 
Preparation of N-4-Benzocyclobutenyl-4-aminophthalimide. 
1.50 g (5.10 mmol) of N-4 benzocyclobutenyl-4-nitrophthalimide, 1.70 g of 
MgSO.sub.4, 0.2 g of 10% Pd/C and 60 ml of ethyl acetate were placed in a 
pressure bottle and the mixture was then rocked on a hydrogenator under 
initial hydrogen pressure of 60 psi for about 17 hrs. The resultant 
reaction mixture, which was yellow-green, was filtered through celite and 
the solid residue was washed with acetone until the filtrate was 
colorless. The combined yellow-green filtrate was stripped to dryness to 
provide greenish yellow product, which was collected on a fritted filter 
funnel, washed with petroleum ether and dried in vacuo overnight. Yield: 
1.20 g (88.9%). The product was used in the subsequent reaction without 
further purification. Mass Spectroscopy: M.sup.+ (264 100%). IR (KBr 
plate): .nu.(NH.sub.2):3290 m, 3390 m cm.sup.-1 ; .nu.(CH.sub.2) 2860 w, 
2940 m; .nu.(imide): 1773 ms, 1690 vs cm.sup.-1, .delta.(imide) 744 ms, 
.sup.1 HNMR (acetone): 2.93 ppm (s, broad 2H); 3.23 ppm (5.4 H): 7.45 
(center, complex, 6 H). 
EXAMPLE 3 
Preparation of N-(4-benzocyclobutenyl)-4(N-maleimido) phthalimide. 
1.60 g (6.05 mmol) of N-(4-benzocyclobutenyl)-4-amino phthalimide and 0.60 
g (6.08 mmol) of maleic anhydride were placed in a 250 ml round-bottomed 
flask. 150 ml of CH.sub.2 Cl.sub.2 was added and the resultant suspension 
was heated to reflux. After 2 hrs, there was no indication that the amine 
was dissolving in refluxing CH.sub.2 Cl.sub.2. Therefore, about 40 ml of 
ethyl acetate was added to dissolve some of the amine and the reaction 
mixture was refluxed overnight. The following morning found the reaction 
mixture was containing a lot of light yellow precipitates. Hence, it was 
allowed to cool to r.t. and solvent was removed completely by rotary 
evaporation. To the resultant maleic amic acid was added 200 ml acetone, 
0.25 g Ni(OAc).sub.2 .multidot.4H.sub.2 O, and a solution of 1 ml 
NEt.sub.3 and 2 ml of acetic anhydride when NEt.sub.3/ Ac.sub.2 O was 
added, the reaction mixture turned completely clear (but still yellow). It 
was heated to gentle reflux and maintained at reflux for 6 hrs. After the 
reaction mixture had been allowed to cool to r.t., it was stripped 
completely to afford light yellow solid as crude product. Dissolving the 
crude product in CH.sub.2 Cl.sub.2, treating the resultant solution with 
solid NaHCO.sub.3 and finally filtering it through a bed of silica gel, 
bright yellow powder was obtained after removal of the solvent from the 
filtrate by rotary evaporation. Yield: 1.85 g (88.9%). (The product was 
soluble in CH.sub.2 Cl.sub.2 but insoluble in CHCl.sub.3 and acetone). 
Calc. for C.sub.20 H.sub.12 O.sub.4 N.sub.2 : 69.76% C; 3.51% H; 8.14% N. 
Found: 68.05% C; 3.50% H; 8.50% N. Mass Spectroscopy: M.sup.+ (344, 100%). 
IR (KBr): .nu.(alicyclic CH.sub.2) 2975 w, 2962 w, 2934 m; .nu.(aromatic 
imide) 1772 m, 1715 vs; .delta.(aromatic imide): 705 m. 
EXAMPLE 4 
Preparation of N-phenyl-maleamic acid. 
2.80 g (28.55 mmole) of maleic anhydride was dissolved completely in about 
60 ml of methylene chloride. To this solution was added the freshly 
prepared 4-aminobenzocyclobutene (3.35 g., 28.11 mmole). Immmediately, 
bright yellow precipitates formed quantitatively. The reaction was quite 
exothermic as evidenced by the self-refluxing of methylene chloride. 
Additional 30 ml of methylene chloride was added to moderate the reaction 
temperature. Finally, the resultant bright yellow heterogeneous mixture 
was stirred overnight at room temperature. The reaction mixture was 
filtered and the yellow solid product collected was washed with methylene 
chloride (3 .times.25 ml) and air-dried. Yield: 5.03 g (82.4%). Anal Calc. 
for C.sub.12 H.sub.11 NO.sub.3 : C, 66.35; H, 5.10; N, 6.45. Found: C, 
66.66; H, 5.27; N, 6.34. 
EXAMPLE 5 
Preparation of N-4-benzocyclobutenyl maleimide. 
N-phenyl-maleamic acid (6.00 g, 27.62 mmol) was partially dissolved in 
about 100 ml of acetone in a 250 ml round-bottomed flask. To this stirred 
heterogeneous mixture was added solid nickel acetate tetrahydrate (0.25 
g), followed by the mixture of acetic anhydride (6.27 g. 61.42 mmol) and 
triethylamine (1.82 g, 23.0 mmol). Gradually, almost all the solids 
dissolved and the resultant reaction mixture was stirred at room 
temperature for two days. After all the solvent had been removed by rotary 
evaporation, the residual oil (smell of acetic acid) was mixed with a 
small amount of methylene chloride. The solution was passed through a 
small column containing silica gel saturated with hexane. The column was 
eluted with hexane until the yellow band developed reached its bottom. 
Then, it was eluted with methylene chloride. The second yellow fraction 
collected was then subjected to rotary evaporation and hexane was then 
added slowly to the concentrated solution to precipitate the product as a 
yellow solid. The product was collected, washed with hexane and air-dried 
overnight. Yield: 4.34 g (78.9%). Anal Calc. for C.sub.12 H.sub.9 NO.sub.2 
: C, 72.35; H, 4.55; N, 7.03. Found: C, 71.84; H, 4.54; N, 6.90. Mass 
Spectroscopy: M.sup.+ , 199 (100%). Proton NMR (CDCl.sub.3),.delta.(ppm): 
3.23 (singlet, 4H, alicyclic protons); 6.87 (singlet, 2H, olefinic 
protons); 7.03-7.33 (complex, 3H, aromatic protons). IR (KBr): 
.nu.(maleimide): 1710 cm.sup.-1, vs; 1772 cm.sup.-1, W. 
EXAMPLE 6 
Preparation of 4-benzocyclobutenyl-3-nitrophenyl ketone. 
8.91 g (48.0 mmol) of 3-nitrobenzoyl chloride was placed in a 500 ml 3 
necked round-bottomed flask equipped with a mechanical stirrer, a 
thermometer and an addition funnel capped with a nitrogen inlet-adaptor. 
About 200 ml of methylene chloride was added and the resultant colorless 
solution was subsequently chilled to about -15.degree. C. under nitrogen. 
A methylene chloride (20 ml) solution of antimony pentachloride (11.05 g, 
48.25 mmol) was then added dropwise over a period of 20 minutes. The 
yellow and homogeneous reaction mixture was allowed to warm up to about 
0.degree. C., at which temperature it was continuously stirred for another 
30 minutes. Then, it was chilled again to about -20.degree. C. and a 
methylene chloride (30 ml) solution of benzocyclobutene (5.00 g, 48.0 
mmol) was delivered via the addition funnel over a period of about 15 
minutes. The reaction mixture slowly became dark and then bright yellow 
precipitates formed. At the end of the addition, the yellow reaction 
mixture was stirred at -20.degree. C. for another hour and then allowed to 
warm up to room temperature on its own. Upon reaching room temperature, 
the reaction mixture was green and heterogeneous. It was stirred at room 
temperature overnight. The green reaction mixture was poured into a 
2-liter beaker containing about 1000 g of ice cubes. The mixture was then 
stirred vigorously until all the ice melted. Two layers appeared; the 
methylene chloride layer was dark green and the aqueous layer was white 
and opaque. The methylene chloride solution was separated from the aqueous 
layer via a separatory funnel. The aqueous phase was subsequently 
extracted with two portions (30 ml) of methylene chloride. The combined 
extract was dried over anhydrous magnesium sulfate. After the removal of 
the drying agent by suction/filtration, the filtrate was concentrated to 
about 30 ml and passed through a small chromatography column containing 
about 50 g of silica gel saturated with hexane. The column was then eluted 
with 1:1 methylene chloride/hexane. Upon removal of the solvent from the 
first fractions, the desired product was isolated as a yellow solid. 
Yield: 11.0 g (90%). Anal Calc. for C.sub.15 H.sub.11 NO.sub.3 ;C, 71.13; 
H, 4.38; N, 5.53. Found: C, 70.67; H, 4.51; N, 5.52. IR(KBr pellet): 
.nu.(CO) at 1646 cm.sup.-1 vs; .nu.(NO.sub.2) at 1534 cm.sup.-1 and 1350 
cm.sup.-1 vs. Proton NMR (CDCl.sub.3, .delta. in ppm): 3.30 (singlet, 
alicyclic protons, 4H); 7.17-7.32, 7.57-7.89, 8.14-8.65 (multiplet, 
aromatic protons, 7H). 
EXAMPLE 7 
Preparation of 4-benzocyclobutenyl-3-aminophenyl ketone. 
4-benzocyclobutenyl-3-nitrophenyl ketone (11.0 g, 43.4 mmol) was partially 
dissolved in a mixed solvent (30 ml of ethyl acetate and 70 ml of methanol 
in a 300 ml round-bottomed flask). To the suspension was added 0.95 g of 
10% Pd/C followed by the addition of 13.0 g (206 mmol) of ammonium 
formate. The black reaction mixture was then stirred magnetically under an 
atmosphere of nitrogen at room temperature for about 3 hrs. The reaction 
mixture was then filtered through a bed of Celite and the solid residue 
was washed with methanol until the filtrate was colorless. The 
yellow-green filtrate was subsequently subjected to rotary evaporation. 
The resultant viscous amber liquid was mixed with about 50 ml of methylene 
chloride and the solution formed was washed with 2 portions (100 ml) of 
H.sub.2 O. Finally, the methylene chloride extract was dried over 
anhydrous magnesium sulfate. After the removal of the drying agent and the 
solvent, a very viscous and amber liquid was isolated. Despite drying in 
the vacuum (70.degree. C.) for more than 24 hours, it never solidified. 
Yield: 8.0 g. It was used in the subsequent synthesis without further 
purification. Mass Spectroscopy: M.sup.+, m/e= 223, 100%. IR(KBr pellet). 
.nu.(NH.sub.2) at 3365 vs and 3460s; .nu.(CO) at 1646 vs. Proton NMR 
(CDCl.sub.3, .delta. in ppm): 3.21 (singlet, 4H, alicyclic protons); 3.83 
(singlet, 2H, NH.sub.2); 6.73-7.77 (multiplet, 7H, aromatic protons). 
EXAMPLE 8 
Preparation of 4-benzocyclobutenyl-3-(N-maleimido)phenyl ketone. 
1.98 g (8.87 mmol) of 4-benzocyclobutenyl-3-aminophenyl ketone was 
dissolved in about 35 ml of dimethyl acetamide and the resultant solution 
was stirred at about 10.degree. C. under nitrogen for about 20 minutes. 
Then, freshly purified maleic anhydride (0.87 g, 8.87 mmol) was added in 
one portion. The bright yellow solution was stirred at 10.degree. C. for 
30 minutes and then at room temperature for another 5 hours. A mixture of 
triethylamine (1.0 ml) and acetic anhydride (4.0 ml) was added to the 
reaction mixture, which turned dark slowly. After the reaction mixture had 
been stirred under nitrogen at room temperature overnight, it was poured 
into a 1-liter beaker containing about 600 ml of cold aqueous sodium 
chloride (30 g). The dark brown solid precipitate was collected on a 
fritted filter funnel and washed with a copious amount of water. After it 
had been air-dried (with suction) for about 2 hours, the dark brown crude 
solid was extracted with methylene chloride. The methylene chloride 
extract was dried over anhydrous magnesium sulfate. After the removal of 
the drying agent, the methylene chloride solution was concentrated and 
passed through a coarse fritted funnel containing a bed of SiO.sub.2 
(approximately 20 g). Methylene chloride was used as the eluent. The 
yellow filtrate collected was subjected to rotary evaporation. Dark amber 
oil was isolated and upon standing at room temperature for several days, 
it solidified. Yield: 1.66 g (62%). Anal. Calc. for C.sub.19 H.sub.13 
NO.sub.3 : C, 75.24; H, 4.32; N, 4.62. Found: C, 74.70; H, 4.52; N, 4.58 . 
Mass Spectroscopy: M.sup.+, m/e=303, 100%. Proton NMR (CDl.sub.3, .delta. 
in ppm): 3.30 (singlet, 4H, alicyclic protons); 6.92 (singlet, 2H, 
olefinic protons); 7.14-7.27, 7.61-7.88 (multiplet, 7H, aromatic protons). 
IR (KBr pellet): .nu.(alicyclic C--H) at 2928 W; .nu.(maleimide) at 1750 
VW and 1718 vs; .nu.(keto-carbonyl) at 1653 ms. 
EXAMPLE 9 
Preparation of 3-(N-4-nitrophthalimid)phenyl-(4-benzocyclobutenyl) ketone. 
4-benzocyclobutenyl-3-aminophenyl ketone (2.00 g, 8.96 mmol) was dissolved 
in about 50 ml of dimethyl acetamide. To the resultant yellow-orange 
solution was added 4-nitrophthalimide (1.73 g, 8.96 mmol). The dark amber 
reaction mixture was then stirred at room temperature under nitrogen for 
about 5 hours. After a mixture of acetic anhydride (4.0 ml) and pyridine 
(3 ml) had been delivered, the reaction mixture was stirred at room 
temperature under nitrogen overnight. The dark reaction mixture was poured 
into a 1-liter beaker containing about 600 ml of chilled aqueous sodium 
chloride (30 g) solution. The light yellow precipitates were collected on 
a fritted filter funnel and washed with a copious amount of water. It was 
then air-dried, with suction overnight. The dried crude product was 
extracted with methylene chloride. The resultant methylene chloride 
solution was dried over anhydrous magnesium sulfate. The methylene 
chloride solution was then concentrated to about 30-40 ml and hexane was 
then added slowly to precipitate out off-white solid product, which was 
subsequently collected on a fritted filter funnel, washed with hexane and 
air-dried overnight. Yield: 2.80 (71%). Anal. Calc. for C.sub.23 H.sub.14 
N.sub.2 O.sub.5 : C, 69.32; H, 3.54; N, 7.03. Found: C, 68.23; H, 3.58; N, 
6.82. Mass Spectroscopy: M.sup.+, 398. 71.6%. Infra spectroscopy (KBr 
pellet): 1786 m and 1730 vs assignable to the asymmetric and symmetric 
stretches of the imide group; 1654 vs, assignable to the keto-carbonyl 
group; 15345 and 1345 s, assignable to the asymmetric and symmetric 
stretches of the nitro group. 
EXAMPLE 10 
Preparation of 3-(N-4-aminophthalimid)phenyl-(4-benzocyclobutenyl) ketone. 
3-(N-4-nitrophthalimid)phenyl-(4-benzocyclobutenyl) ketone (2.18 g, 5.47 
mmol) was dissolved in about 20 ml of ethyl acetate, followed by the 
addition of 0.1 g of palladium on carbon (10%) and about 30 ml of 
methanol. To the resultant black mixture was added ammonium formate (2.00 
g, 31.7 mmol) in one portion. The reaction mixture was subsequently 
stirred under nitrogen for about 4 hrs, at which time the thin-layer 
chromatogram of the reaction mixture indicated all the starting 
nitro-compound had been consumed. Hence, the olive-green reaction mixture 
was filtered through a bed of Celite and the solid residues were extracted 
with ethyl acetate. The yellow-green filtrate was then subjected to rotary 
evaporation to afford yellow waxy solid, which was taken up in a mixture 
of methylene chloride and water. The methylene chloride layer was 
separated and dried over anhydrous magnesium sulfate. After the removal of 
the drying agent and the solvent, about 1.60 g of amber solid product was 
obtained and used in the subsequent synthesis without further treatment. 
IR(KBr pellet): .nu.(NH.sub.2) at 3364 and 3222 cm.sup.-1 ; .nu.(aliphatic 
C-H) at 2970 and 2930 cm.sup.-1 ; .nu.(imide) at 1765 and 1714 cm.sup.-1 ; 
.nu.(keto-carbonyl) at 1652 cm.sup.-1. Mass Spectroscopy: M.sup.+, 
m/e=368, 100%. 
EXAMPLE 11 
Preparation of 3-(N-4-maleimido-phthalimid)phenyl-(4-benzocyclobutenyl) 
ketone. 
The crude 3-(N-4-aminophthalimid)phenyl-(4-benzocyclobutenyl) ketone (1.50, 
ca. 4.07 mmol) was completely dissolved in about 80 ml of methylene 
chloride and maleic anhydride (0.40 g, 4.08 mmol) was added neat. The 
resultant reaction mixture was stirred under nitrogen overnight. It 
remained dark brown and homogeneous throughout the period. After methylene 
chloride had been removed by rotary evaporation, about 80 ml of acetone 
was added, followed by the addition of 0.1 g of nickel acetate 
tetrahydrate, and a mixture of triethylamine (0.5 ml) and acetic anhydride 
(2.5 ml). The reaction mixture was stirred at room temperature under 
nitrogen for another 17 hours. After the solvent had been removed via 
rotary evaporation, the residual dark oil was treated with about 50 ml of 
methylene chloride. The resultant solution was then poured into about 180 
ml of H.sub.2 O in a separatory funnel. The methylene chloride layer was 
drained off and the aqueous phase was extracted with 2 portions (20 ml) of 
methylene chloride. The combined organic solution was dried over anhydrous 
magnesium sulfate. After the removal of the drying agent by filtration, 
the filtrate was concentrated and added to a small chromatographic column 
containing abut 50 g of SiO.sub.2, saturated with hexane. The column was 
then eluted with 1:1 hexane/CH.sub.2 Cl.sub.2. About 1.20 g of 
peach-colored solid was isolated from the first fractions. Yield: 67%. 
Anal. Calc. for C.sub.27 H.sub.16 N.sub.2 O.sub.5 : C, 72.31; H, 3.60; N, 
6.25. Found: C, 71.97; H, 3.48; N, 6.10. Mass Spectroscopy: M.sup.+, 
m/e=368, 100%. IR(KBr pellet): .nu.(aromatic and olefinic C--H) at 3099 W; 
.nu.(alicyclic C--H) at 2970 W and 2930 W; .nu.(imide) at 1774 m and 1720 
vs; .nu.(keto-carbonyl) at 1653 ms. Proton NMR (CDCl.sub.3, .delta. values 
in ppm): 3.27 (s, alicyclic protons); 6.98 (s, olefinic protons ); 
7.16-7.26 (m, aromatic protons associated with benzocyclobutene moiety); 
7.61-8.13 (m, aromatic protons associated with other aryl groups). 
Having described the invention in detail and by reference to preferred 
embodiments thereof, it will be apparent that modifications and variations 
are possible without departing from the scope of the invention defined in 
the appended claims.