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AFML-TR-78-
A/DA 0) 63S
SYNTHESIS AND (^) PROPERTIES OF BENZIL END-CAPPED ACETYLENE
TERMINATED PHENYLQUINOXALINES (BATQS)
Polymer Branch
Nonmetallic Materials Division
December 1978
TECHNICAL REPORT AFML-TR-78-
Final Report for Period October 1976 - August 1978
Approved (^) for public release; distribution unlimited.
AIR FORCE (^) MATERIALS LABORATORY
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AIR FORCE SYSTEMS COMMAND BetA albeCopy
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OFFICIAL FILE COPY
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This report has (^) been reviewed by the Information Office (01) and is releasable to the National Technical Information Service (NTIS). At NTIS, it will be avail- able to the general public, including foreign nations.
This technical report has been reviewed and is approved for publication.
C. ARNOLD R. L. VAN DEUSEN, Chief Project Scientist Polymer (^) Branch Nonmetallic Materials Division
FOR THE COMMANDER
6JM Kelble,^ Chief 9onmetallic Materials Division
"If (^) your address has changed, (^) if you wish to (^) be removed from our mailing (^) list, or if the addxessee is no longer employed by your organization please (^) notify AEFMI !Rp ,W-PAFB, OH 45433 to help us maintain a current mailing list".
Copies of this report should not be returned unless return is required by se- curity considerations, contractual obligations, or notice on a specific document. AIR FORCE/56780/6 March 1979 - 141
FOREWORD
This report was prepared by the Polymer Branch, Nonmetallic Materials Division. This work was initiated under Project (^) No. 2419, "Nonmetallic and Composite Materials", Task No. 241904, Work Unit Directive 24190415, "Structural (^) Resins". It was administered under the direction of the Air Force Materials Laboratory, Air Force Systems (^) Command, Wright- Patterson Air Force Base, Ohio, with Dr. F. E. Arnold as Project (^) Scientist. This report (^) describes work conducted from October 1976 to August 1978.
The work described in this report was conducted in the Polymer Branch laboratory by Dr. F. L. Hedberg and Dr. F. E. Arnold of the Air Force Materials Laboratory. (^) The manuscript was released by the authors in August 1978 for publication as a Technical Report.
iii
TABLE OF CONTENTS
SECTION PAGE
I INTRODUCTION 1
II RESULTS^ AND^ DISCUSSION^3
III EXPERIMENTAL^10
REFERENCES 14
This report is concerned with the synthesis of a stable, acetylene-
containing benzil end-capping agent, 4-(3-ethynylphenoxy)benzil, which was
reacted with diamine terminated phenylquinoxalines (BATQ's). The
modification of structure retained the meta-ethynyl orientation thereby
generating amorphous low softening oligomers.
SECTION II
RESULTS AND DISCUSSION
The synthesis of the new end-capping agent 4-(3-ethynylphenoxy)benzil (I) is shown in reaction scheme (1). Hydrolysis^ of^ 3-ethynylphenyl-p- toluenesulfonate followed by nucleophilic displacement of the nitro group on 4-nitrobenzil provided a 47% overall yield of I. The material exhibits excellent shelf-life in contrast to the diaminophenoxyphenyl acetylene (Reference 2) which slowly decomposed even under a nitrogen atmosphere.
HC C - -O-TOS HC C-- o Na (1.)
N02 C-C- H0CO-kJ%- (^) C-C-•
= I
The benzil end-capped oligomers were prepared by the reaction of various aromatic (^) tetraamines with aromatic benzils in 2 to 1 molar ratio of reactants. The ortho diamine end-capped quinoxaline oligomers were then reacted with excess I in m-cresol. All the oligomers prepared were soluble (20-30%) in low-boiling organic solvents such as methylene chloride, chloroform, dioxane, and tetrahydrofuran. Purification of the BATQs were carried by reprecipitation from tetrahydrofuran into methanol. The various structures prepared are shown in Figure 1.
K2)X~ NH2 (^) I I ItI
- R-C'C-Ar-C-C-R H 2 N (^) N
H 2 N
"02 X YN:Ar"F N Q XIg(NH
H 2 N/O n NH (^2) R R C=CH C=CH
(^0 )
00
4 N 0 NN nN R R BATQ
The thermal behavior (^) of the BATQ oligomers was studied by both differential (^) scanning calorimetry (DSC) and thermomechanical analysis (TMA). Samples (^) of each oligomer were then cured at 280% for six hours
under nitrogen and the Tg's after cure were determined. The results (^) of the thermoanalytical measurements (^) are summarized in Table 1.
As can be seen, the softening behavior is similar for all of the oligomers, except for BATQ-S which is-higher and (^) BATQ-0,P which is substantially (^) lower. The flexibility inherent in the BATQ-0,P structure is probably responsible for the lower softening point, a desirable feature, but the same flexibility also apparently (^) prevents the Tg after cure from reaching the cure temperature, placing undesirable restrictions on the use temperature. A similar anomalously low Tg after cure can be seen for BATQ-P. The remaining BATQ's exhibit cure temperatures and Tg
after cure temperatures analogous to the ATQ system. The differential
between the temperature ranges for softening and cure should afford
a sufficient "window" to prevent premature cure before softening is
complete.
TABLE 1
THERMOANALYTICAL DATA ON BATQ'S
Softening Max Rate Cure Max. Rate Tg After Oligomer Ons^ et^ a^ Softeninga^ Onsetb^ Cureb^ Cureb,^ c BATQ-O 145 0 C 1720C 215 0 C 2760C 3100C BATQ-M 1450C 175 0 C 215 0 C 274 0 C 311 0 C BATQ-S 1600C 1800C 215CC 2730C 3090C BATQ-P 1450C 1620C 210 0 C 2830C 2750C BATQ-H 1500C 170 0 C 200 0 C 280°C 322 0 C BATQ-O,O 1450C 1700C 2100C 2800C 298 0 C BATQ-O,M 1450C 167 0 C 200 0 C 285 0 C 2900C BATQ-O, P 125 0 C 140 0 C 195 0 C 2930C 257 0 C a. Determined by TMA at 200C per minute under nitrogen. b. Determined by DSC at 200C per minute under nitrogen. C. Cured^ at^280 0 C^ for^ six^ hours^ under^ nitrogen.
The material which was selected for further development as a matrix
resin for fiber reinforced composites was BATQ-H. Selection was based
on its low softening range for potential melt prepregability, as well as,
the ecomonics resulting from the simplified synthetic routes to the new
end-capping agent (I)and aromatic benzil, 1,4-(4-benziloxy) benzene
(Reference 6). Cost projection of the BATQ-H oligomer is $25-$30 per
pound based on raw materials costs, and scale-up procedures. This cost
is dependent on a long-term commitment to the BATQ-H resin as a com-
mercial product with a market base of 100,000 lb/yr. Further cost
reductions are anticipated from a current laboratory effort on low-cost
synthetic procedures for m-hydroxyphenyl acetylene, a key intermediate
in the system.
Analysis by TMA of the n=l-3 oligomer (^) mixture of BATQ-M from column chromatography (^) revealed an initiation of softening at 15 0 °C, only slightly higher than for unchromatographed (^) BATQ-M. The softening rate of the chromatographed BATQ-M did not (^) maximize until 2000 C, however, significantly higher than (^) the 175 0 C obtained for the unchromatographed material. It (^) is thus apparent that the presence of the BA-DAB-BA and the oligomers of n>3 exerts a great influence upon (^) softening rate even at the 12% concentration level. The DSC trace of (^) the cure exotherm was virtually identical for both the (^) chromatographed and unchromatographed material, (^) commencing around 200 0 C and maximizing at 274 0 C (^) with a slight shoulder at 2200 C. In view of its low softening point, (^) its standard BATQ-like curing behavior, and its high Tg after cure, the use (^) of BA-DAB-BA by itself would afford the best combination of processing and (^) cure characteristics of any of the BATQ's. Its disadvantages (^) are the greater amount of 4-(3-ethynylphenoxy)benzil (^) required for its preparation and its (^) lower molecular weight between crosslinks after cure. (^) The fact that its presence in a mixture with a BATQ substantially improves (^) the softening behavior (^) suggests the addition of BA-DAB-BA as a reactive diluent (^) to BATQ systems (^) to afford a preselected choice of initial Tg. (^) This would be particularly advantageous if the bulk viscosity (^) of the softened BATQ does (^) not afford a sufficient "window" for cure. The most effective reactive diluent for the ATQ and (^) BATQ systems would be one (^) of minimum molecular weight between reaction sites, thereby providing the lowest possible Tg, yet have (^) a molecular structure which would be compatible with the oligomers. Reaction of I (^) with 3-(3,4-diamino- phenoxy)-phenylacetylene (^) provided 6-(3-ethynylphenoxy)-3-(4-3-ethynyl- phenoxy)-2-phenylquinoxaline (AA-BA) which exhibited (^) a softening range of (^) 20-25 0 C by TMA. DSC (20°C/min) revealed an onset of (^) the cure exotherm at 150%C with a maximum at 258 0 C. It was found that (^) (AA-BA) was completely miscible (^) and compatible with the BATQ-H oligomer as evidenced by (^) a single Tg of mixtures of the two components. (^) For example, a mixture of 20% (AB-BA) and 80% BATQ-H exhibited a Tg of 1160C which (^) after cure at 280%C (^) increased to 305°C.
HC=-C
AA-BA A preliminary evaluation of (AA-BA) material was carried out to determine its potential as a matrix resin for high temperature graphite composites, since it exhibited excellent physical characteristics for processing. The material could be melt prepreged at 174°F and exhibited good tack and drape. Graphite laminates were fabricated at 350'F for 30 minutes under 200 psi and then postcured overnight in a circulating air oven at 500 0 F. Short beam shear strengths of around 8,500 psi were achieved at room temperature with good retention of mechanical properties at 450°F (90%) and at 500°F (74%).
- 4-(3-Ethynylphenoxy)benzil (I)
To a solution of 3-ethynylphenol (4.75 g,^ 0.0403^ mole)^ in dimethysulfoxide (50^ ml)^ under^ nitrogen^ was^ added^ sodium^ methoxide (2.17 g,^ 0.0402^ mole).^ The^ mixture^ was^ stirred^ for^30 minutes^ at^ 23°C, transferred to an addition funnel under nitrogen, and added over^ a 20-minute period^ to^ a^ solution^ of^ 4-nitrobenzil^ (9.30^ g,^ 0.0365^ mole) in dimethylsulfoxide (100^ ml)^ stirred^ at^90 0 C^ under^ nitrogen.^ When addition was complete, the reaction mixture^ was^ stirred^ overnight at 230 C and^ poured^ into^ a^ solution^ of^ sodium^ hydroxide^ (50^ g)^ in^ ice water (I liter). Extraction with toluene^ (3x50^ ml)^ followed^ by^ chroma- tography on silica gel with benzene as eluent afforded 5.80 g (49%) of 4-(3-ethynylphenoxy)benzil as^ a^ yellow^ oil^ which^ solidified^ upon^ standing at 23 0 C overnight to a pale yellow solid, m.p.^ 79-81^0 C.
Anal. Calcd. for C2 2 H1 4 03 :^ C,^ 80.97;^ H,^ 4.32;^ mol.^ wt.,^326
Found: C, 80.40; H, 3.86; mol. wt., 325 (by mass spectrometry)
- GENERAL OLIGOMER^ PREPARATION A solution of bis-benzil (2 moles) in m-cresol was^ added^ dropwise^ to a solution of tetraamine (1 mole) in m-cresol at 90-I00°C under^ nitrogen. After addition, the^ reaction^ mixture^ was^ stirred^ for^ two^ hours^ at 90-100%C and then a solution of 4-(3-ethynylphenoxy)benzil (2.2 moles) in chloroform was added. The chloroform was removed by distillation, and the reaction mixture heated an additional hour at 90-100%C and then precipitated into^ a^ solution^ of^ 10%^ sodium^ hydroxide^ (sufficient quantity to neutralize the m-cresol) in methanol. Purification was accomplished by^ two^ reprecipitations^ from^ tetrahydrofuran^ into^ methanol.
- 3,3'-Bis(4-3-ethynylphenoxy phenyl)-2,2'-diphenyl-6,6'-biquinoxaline (BA-DAB-BA)
To 200 ml of tetrahydrofuran stirred at 230 C under nitrogen was added 11.00 g (0.0337 mole) of I followed by 3.44 g (0.0161 mole) of 3,3'-diaminobenzidine. After one minute of stirring to permit complete solution, 4 ml of glacial acetic acid was added. The reaction mixture was then stirred overnight (20 hours total) at 230 C and poured, with
stirring, into 1200 ml of water. The resultant orange suspension was ,extracted 2 x 100 ml with dichloromethane, and the combined organic layers were extracted (^) once with 400 ml of 5% Na 2 CO 3 and 2 x 400 ml with water. The dichloromethane layer was concentrated (^) to 100 ml, diluted with 100 ml of ethyl acetate and poured, with stirring, (^) into one liter of methanol. (^) The precipitate which formed was collected (11.3 g, 88%), redissolved (^) in 100 ml of dichloromethane, diluted with 100 ml of ethyl acetate, and (^) reprecipitated with one liter of methanol to afford 10.3 g (81%) after drying overnight at 23 0 C (^) under reduced pressure. Anal. Calcd. for C5 6 H3 4 N 4 0 2 : C, 84.63; H, 4.28; N, 7.04. Found: C, 84.42, 84.57; H, 4.19, 4.24; (^) N, 6.96, 6.
- 6-(3-Ethynylphenoxy)-3-(4-[3-ethynylphenoxy]phenyl)-2-phenylquinoxaline (AA-BA) A mixture of 15.0 (^) g (0.0528 mole of 3-(3,4-dinitrophenoxy)- phenylacetylene (^) and 600 ml of methanol was heated at reflux until solution was complete (^) (Solution A). A mixture of 368 g (2.11 mole) of sodium dithionite and 1200 ml of water was heated at 60%C (^) until solution was complete at which (^) point a solution of 41.6 g (2.11 mole) of sodium hydroxide in 400 ml of water was added immediately (^) followed by Solution A. A deep purple color formed during (^) the addition and quickly faded to afford a milky yellow solution. An (^) additional 200 ml of methanol was added causing a lightening of the color, and the (^) reaction mixture was stirred for 30 minutes and then extracted 3 x 250 ml with chloroform. (^) The combined (^) chloroform extracts were washed .3 x 250 ml with water and then added to a solution of 7.91 g (0.0243 (^) mole) of 4-(3-ethynylphenoxy)benzil in 150 ml of m-cresol stirred under nitrogen. The reaction mixture (^) was stirred overnight (16 hours), (^) the chloroform was removed by distillation and the remaining solution was poured into a mixture of (^500) ml of 20% NaOH (^) solution and 500 g of ice and then extracted 3 x 250 ml with chloroform. The (^) combined chloroform extracts were extracted 3 x 250 ml with water and distilled to dryness on a rotary evaporator. (^) The oily residue was dissolved in 500 ml of carbon (^) tetrachloride and chromato- graphed on a column of silica gel (2" x 2'). The column was (^) first eluded with one liter of carbon tetrachloride (^) to remove high Rf impurities
REFERENCES
1. F. L. Hedberg, R. F. Kovar, and F. E. Arnold in Contemporary (^) Topics In Polymer Science Vol. 2, ed. Eli M. Pearce, (^) Plenum Publishing Corp., New York, (^235) (1977).
- R. F. Kovar, (^) G. F. L. Ehlers, and F. E. Arnold, J. Polym. Sci., Polym. Chem. Ed., 15, (^1081) (1977).
- M. G. Maximovich, (^) S. C. Lockerby, R. F. Kovar, and F. E. Arnold, Adhesives Age, 11, 40 (1977).
- R. F. Kovar and F. E. Arnold, Sci. Adv. Mat's and (^) Process Eng. Series (^) 8, 106 (1976).
- P. M. Hergenrother, Am. Chem. Soc. Div. Coatings (^) and Plastics Chem. Prepr. 36 (2), 264 (1976).
- H. M. Relles, C. M. Orlando, D. R. Heath, R. W. Schluenz, J. S. Manello, and S. Hoff, J. Polym. Sci., Polym. Chem. (^) Ed. 15, 2441 (1977).
- P. M. Hergenrother, (^) Macromolecules, Vol. 7, 575 (1974).
- C. B. Delano, J. D. Dodson, and R. J. Milligan, (^) High Temperature Resins for Composites, (^) AFML-TR-77-188, PT II (1978).
*U.S.Government PrIntIng Office: 1979 - (^) 657-002/
