Acetylene terminated matrix and adhesive oligomeric compositions

A composition prepared by mixing a high Tg, acetylene-terminated phenylquinoxaline oligomer with an acetylene-substituted reactive diluent. The presence of the reactive diluent in the mixture effectively lowers the Tg of the oligomer so as to provide the composition with adequate flow for melt processing.

FIELD OF THE INVENTION 
This invention relates to acetylene-terminated phenylquinoxaline resin 
compositions which have adequate flow characteristics necessary for melt 
processing. 
BACKGROUND OF THE INVENTION 
To meet a variety of advanced aircraft and aerospace requirements, there is 
a need for high temperature thermoset resins for matrix and adhesive 
applications. Such resins, because of the complexity of structure, the 
high glass transition temperature needed and high temperature 
thermooxidative stability required, have critical processing difficulties 
when required to conform to the state-of-the-art processing criteria. OSHA 
requirements negate processing such materials from solvent base systems, 
thereby necessitating fabrication of the resins via melt techniques. 
As disclosed in U.S. Pat. Nos. 3,966,729 and 4,147,868, recent advances in 
matrix and adhesive resins have resulted in the discovery of new 
phenylquinoxaline resins terminated by primary acetylene groups. The 
acetylene moiety can be thermally homopolymerized between 200.degree. and 
250.degree. C. to form a moisture insensitive, high temperature resin 
system. Although the materials show excellent resistance to heat and 
environmental surroundings, they lack the necessary flow required for melt 
processing because of their high glass transition temperature (Tg) 
(140.degree.-170.degree. C.). 
It is a principal object of this invention, therefore, to reduce the Tg of 
selected acetylene-terminated phenylquinoxaline oligomers so that they 
have flow characteristics required for melt processing. 
Another object of the invention is to provide a composition containing an 
acetylene-terminated phenylquinoxaline oligomer and, as a reactive 
diluent, an acetylene-substituted aromatic ether. 
A further object of the invention is to provide oligomer-reactive diluent 
materials which co-cure on thermal treatment. 
Other objects and advantages of the invention will become apparent to those 
skilled in the art upon consideration of the ensuing disclosure and the 
drawing which shows graphically the cure rheometry, i.e., variations in 
viscosity with time at certain constant temperatures, of compositions of 
this invention and of oligomers per se. 
SUMMARY OF THE INVENTION 
The present invention resides in a composition consisting essentially of a 
mixture of (1) an acetylene-terminated phenylquinoxaline oligomer and (2) 
an acetylene-substituted reactive diluent. The presence of the reactive 
diluent in the mixture effectively lowers the Tg of the oligomers so as to 
provide the composition with adequate flow for melt processing. As a 
result the compositions are eminently suitable for use in the fabrication 
of structural reinforced composites while meeting rigid OSHA regulations. 
The oligomers used in the composition are high Tg, acetylene-terminated 
phenylquinoxaline resins that can be represented by the following formula: 
##STR1## 
In the above formula, X is a single bond, 
##STR2## 
Z is 
##STR3## 
and Ar is 
##STR4## 
The letter n is an integer indicating the number of recurring units and is 
usually in the range of 1 to 20, inclusive. The oligomers and a process 
for their preparation are disclosed in U.S. Pat. No. 4,147,868, the 
disclosure of which is incorporated herein by reference. 
The acetylene-substituted aromatic compounds used as reactive diluents can 
be represented by the following structural formulas: 
##STR5## 
The reactive diluents are new compounds which are prepared as described 
hereinafter in Examples I and II. Additional details regarding the 
acetylene-substituted aromatic ethers are disclosed in our copending 
patent application Ser. No. 088,505, filed on Oct. 26, 1979, the 
disclosure of which is incorporated herein by reference. 
The reactive diluents are completely compatible with the high Tg oligomers 
and have very low glass transition temperatures (II=-49.degree. C.; 
III=-39.degree. C.). Since the materials are soluble in the same solvents, 
the preferred procedure for mixing the materials is to dissolve the 
materials in a solvent and then remove the solvent under reduced pressure. 
There is thus obtained a homogeneous mixture of the oligomer and reactive 
diluent. Examples of solvents that can be employed include methylene 
chloride, tetrahydrofuran and dioxane. 
The amount of reactive diluent contained in the composition usually ranges 
from about 1 to 40 weight percent, preferably about 5 to 30 weight 
percent, based upon the total weight of the composition. The oligomers and 
the reactive diluents co-cure on thermal treatment. Thus, the composition 
can be readily cured by heating in an inert or oxidative atmosphere at a 
temperature ranging from about 250.degree. to 300.degree. C. for about 2 
to 8 hours.

A more complete understanding of the invention can be obtained by referring 
to the following illustrative examples which are not intended, however, to 
be unduly limitative of the invention. 
EXAMPLE I 
1-Phenoxy-3-(m-ethynylphenoxy)benzene (II) 
A solution of 24.6 g (0.726 mol) of 1-phenoxy-3-(m-bromophenoxy)benzene, 
6.31 g (75.0 mmol) of 2-methyl-3-butyn-2-ol and 0.36 g triphenylphosphine 
in 200 ml triethylamine was degassed with nitrogen for 20 minutes. To the 
degassed solution was added 0.036 g (0.0508 mmol) of 
bis-triphenylphosphine palladium II dichloride and 0.14 g (0.755 mmol) 
cuprous iodide. The mixture was heated to reflux for 24 hours, cooled to 
room temperature and the triethylamine removed under reduced pressure. The 
resulting yellow-green oil was dissolved in methylene chloride, dried over 
MgSO.sub.4, filtered and chromatographed on silica gel using 1:1 methylene 
chloride-hexane as the eluent. After solvent was removed under reduced 
pressure, 24.0 g (96%) of an orange oil was recovered. 
Analysis Calc'd for C.sub.23 H.sub.19 O.sub.3 : C,80.21; H,5.56; Found: 
C,79.85; H,5.39. 
A solution of 24.0 g (0.0697 mol) of the butynol adduct, a mixture of 0.75 
g of potassium hydroxide dissolved in 20 ml of methanol, and 100 ml of 
toluene was heated to reflux under nitrogen. During the course of two 
hours the methanol and 60 ml of toluene were removed by distillation. The 
remaining toluene was removed under reduced pressure. The resulting dark 
oil was chromatographed on silica gel using 3:1 hexane-methylene chloride 
as the eluent. The solvent was removed under reduced pressure to give 
17.10 g (81.7%) of a light yellow, viscous oil. 
Analysis Calc'd for C.sub.20 H.sub.13 O.sub.2 : C,83.90; H,4.58; Found: 
C,83.30; H,4.62. 
EXAMPLE II 
1,3-Bis-(m-ethynylphenoxy)benzene (III) 
A mixture of 12.60 g (0.03 mole) of 1,3-bis-(m-bromophenoxy)benzene and 
6.03 g (0.072 mole) of 2-methyl-3-butyn-2-ol and 100 ml of triethylamine 
was degassed by passing nitrogen through the solution for 20 minutes. To 
the reaction mixture was then added 0.03 g (0.042 mmol) of 
bis-triphenylphosphine palladium II dichloride, 0.13 g (0.624 mmol) of 
cuprous iodide and 0.30 g (1.14 mmol) of triphenylphosphine. The 
temperature of the reaction mixture was raised to 80.degree. C. and 
maintained there for 24 hours. The reaction was then cooled to room 
temperature and the triethylamine removed under reduced pressure. The 
resulting yellow-red oil was chromatographed on a 5 cm.times.60 cm dry 
silica gel column (quartz) using 1:1 hexane-ether as the eluent. The 
second fluorescent band was collected (appears yellow on the column). The 
solvent was removed under reduced pressure to yield 10.6 g (83%) of a dark 
viscous oil. The product was used in the next step of the reaction 
sequence without further purification. 
A mixture of 10.6 g of the bis-butynol adduct and 0.75 g of KOH in 20 ml of 
anhydrous methanol were added to 100 ml of toluene and heated to reflux 
under nitrogen. The methanol and 40 ml of the toluene were then removed by 
distillation over a period of two hours. The reaction was monitored by TLC 
on silica gel plates containing fluorescent indicator using 3:1 
hexane-methylene chloride as the developing solvent. The product appeared 
as the first spot to be eluted. The reaction was judged to be complete 
when no starting material appeared at the origin of the TLC plate after 
developement. After a total reaction time of two hours, the reaction 
mixture was cooled, and the toluene removed at 35.degree. C. under reduced 
pressure. The red viscous residue was chromatographed on a dry 5 
cm.times.60 cm column (quartz) of silica gel using 3:1 hexane-methylene 
chloride. The first large fluorescent band was collected and the solvent 
removed at 50.degree. C. under high vacuum. The last traces of hexane were 
removed by pumping on the yellow oil for 18 hours at 0.2 mm pressure. The 
yield of pure product was 6.1 g (79%). 
Analysis Calc'd for C.sub.22 H.sub.14 O.sub.2 : C,85.07; H,4.54; Found: 
C,84.72; H,4.23. 
EXAMPLE III 
Samples of the reactive diluents prepared in Examples I and II were mixed 
in various percentages with an acetylene-terminated phenylquinoxaline 
oligomer described above wherein X=single bond, 
##STR6## 
and Ar= 
##STR7## 
The oligomer had a Tg of 165.degree. C. Various amounts of the oligomer 
and reactive diluents were dissolved in methylene chloride after which the 
solvent was removed under reduced pressure. 
Small samples of the various mixtures were placed in test tubes. The tubes 
were heated at 280.degree. C. for 6 hours, removed and allowed to cool to 
room temperature. Thermal mechanical analysis (TMA) or differential 
scanning calorimetry (DSC) was determined on the non-cured and co-cured 
mixtures to determine the reduction in Tg or the effective lowering of Tg 
for fabrication. The data obtained are shown below in the table. 
TABLE 
______________________________________ 
% % Tg.degree. C..sup.(1) 
Tg.degree. C..sup.(2) 
Reduction.sup.(3) 
Diluent 
Oligomer Uncured Co-cured.sup.(4) 
Tg.degree. C. 
______________________________________ 
100(II) 
0 -49.degree. C. 
100(III) 
0 -39.degree. C. 
0 100 165.degree. C. 
20(II) 80 91.degree. C. 
223.degree. C. 
74.degree. C. 
30(II) 70 70.degree. C. 
184.degree. C. 
95.degree. C. 
10(III) 
90 106.degree. C. 
311.degree. C. 
59.degree. C. 
20(III) 
80 72.degree. C. 
306.degree. C. 
93.degree. C. 
30(III) 
70 58.degree. C. 
314.degree. C. 
107.degree. C. 
______________________________________ 
.sup.(1) Determined by DSC at a heating rate of 20.degree. C./min. 
.sup.(2) Determined by TMA at a heating rate of 20.degree. C./min. 
.sup.(3) Reduction in Tg of oligomer resulting from reactive diluent. 
.sup.(4) Mixture cocured at 280.degree. C. for 6 hours. 
EXAMPLE IV 
Samples of the oligomer described in Example III and reactive diluent III, 
as prepared in Example II, were dissolved in tetrahydrofuran and 
precipitated into water to provide a finely divided powder which was dried 
under vacuum (30 mm Hg) at 60.degree. C. Specimens were prepared by 
pressing the uncured powder mixture at 40,000 psi into 12 mm diameter by 2 
mm thick pellets. Pellets were also prepared in a similar manner for the 
oligomer alone. 
In a series of runs, the pellets were placed between preheated parallel 
plates in Rheometrics RMS-7200 Mechanical Spectrometer. The pellets were 
subjected to low frequency (160 mHz) sinusoidal shear rate viscocity 
measurements at constant temperatures. The results of the runs are shown 
graphically in the drawing together with the temperatures used. 
As seen from the graphs shown in the drawing, the processing window for the 
composition of this invention is greatly expanded over that of the 
oligomer alone. For example, the amount of time allowed for processing the 
present composition over the oligomer alone is increased 12 minutes at 
195.degree. C. and 41 minutes at 176.degree. C. for the ideal fabricating 
viscosity of 10.sup.4 poise. Furthermore, the presence of the reactive 
diluent permits processing at the lower temperature of 154.degree. C. with 
times greater than one hour whereas the oligomer alone exhibits no flow 
below 180.degree. C. 
From the foregoing, it is seen that by mixing the acetylene-substituted 
reactive diluent with the high Tg, acetylene-terminated phenylquinoxaline 
oligomer, a composition is obtained that has a decreased glass transition 
temperature. As a result of lowering of the Tg, the composition flows for 
a longer period of time at a lower temperature. The composition can be 
advantageously utilized, therefore, in the fabrication of composite 
structures via melt techniques. 
As will be evident to those skilled in the art, modifications of the 
present invention can be made in view of the foregoing disclosure without 
departing from the spirit and scope of the invention.