Polymers containing anthraquinone units: Polymers from 1,5-diaminoanthraquinone and aralkyldiketones

JOURNAL OF POLYMER SCIENCE: PART A-1 VOL. 9,3337-3347 (1971) Polymers Containing Anthraquinone Units: Polymers from 1,5-Diaminoanthraquinone and Aralkyldiketones ROY M. MORTIER, P. K. DUTT, J. HOEFNAGELS, and C. S. MARVEL, Department of Chemistry, The University of Arizona, Tucsm, Arkma 86721 synopsis SchWs-base polymers have been formed by the condensation of 1,5-diaminoanthra quinone with 1 , 4 and 1,3-diacetylbensene and 2,6diacetylpyridine. These polymers were soluble in methanesulfonic and concentrated sulfuric acids (1,4diacetylbensene polymer) or NJV-dimethylacetamide. The polymer formed from 1,Pdiacetylbenaene was ring-closed in polyphosphoric acid to yield a thermally stable polymer soluble in concentrated sulfuric acid which lost only 10% of its weight at 900°C in a TGA test. INTRODUCTION There are now available many polymeric materials having a high degree of thermal stability. These polymers tend to be of the ladder or partial- ladder type containing polyaromatic heterocyclic units. As a conse- quence of their chemical structure the polymers are usually soluble only in solvents such as methanesulfonic, concentrated sulfuric and polyphosphoric acids. Thus it is hoped that the introduction of anthraquinone units into the polymer will permit solubilization of the polymer by reduction of the quinone group^.^ The reducing agent may be an alkaline solution of sodium hydrosulfite by which means the polymer can be wet-spun into fibers which on treat- ment with acid and air will revert to the ,original anthraquinone structure. This technique has been shown to be viable by Marvel and co-w~rkers.~.~ This paper describes the synthesis of partial-ladder polymers and model compounds built on anthraquinone units. RESULTS AND DISCUSSION Polymerization reactions have been attempted using 1,5diaminoanthra- quinone with 1,3- and 1,4diacetylbensene and 2,6-diacetylpyridine in order to form the Schiff’s-base polymer I and 11. 3337 @ 1971 by John Wiley & Sons, Inc. 3338 MORTIEK ET AL. I II These polymers were then “ring-closed” by treatment with polyphosphoric acid to give poly(benzo [1,2,3-de :4,5,6-d‘e’ ]diquinoline-2,&diyl-p-phenyl- ene) (111) and poly(benzo [1,2,3-de :4,5,6-d’e‘]diquinoline-2,8-diyl-2,6-pj-r- idine) (IV). Iv Model Reactions The Schiff’s-base condensation product of l&diaminoanthraquinone and acetophenone (V) has been prepared in refluxing nitrobenzene using acetic acid as catalyst. The product was isolated and on treatment with poly- phosphoric acid eliminated water to give a closed structure (VI). When an excess of acetophenone and anhydrous zinc chloride as the catalyst were used the closed structure (VI) was obtained directly. O y C H 3 2 + @ 2 +3 6 v VI H,N 0 ex- WCOCH, anhydrous zinc chloride \7m Refluxing nitrobenzene Acetic acid 1 N\ CH3 T A B L E I Po ly co nd en sa tio n R ea ct io ns of I ,. 5- D ia m in oa nt hr aq ui no ne T em pe ra tu re , T im e, So lv en ts fo r IC xp t. C om on om er a So lv en tb OC C at al ys ts hr Pr od uc tb R em ar ks 1 2 3- 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 1, 4D A B 1, ID A B 1, C L )A B 1, 3- D A B 2, G -D A P 1, C D A B 1, 4D A B Se lf- co nd en sa tio n of I & D A B Se lf. co nd en sa tio n of 1 ,S D A A Q 1, 4D A B 1, C D A B 1, 4D A B 1, 4D A B 1, 3- D A B 2, 6- D A P 1, SD A B 2, 6* D A P 18 0 17 0 14 0- 17 0 17 0 16 0 16 0 17 0 16 0 17 0 24 0 20 0 Ir, O 24 0 25 0 Zn C1 2 N on e Zn C lz H O A c H O A c/ A cz O C C la C 02 H C Fa C O zH Zn C ll Zn Cl 2 N on e N on e N on e N on e N on e 6 40 4- 20 48 24 22 90 22 23 '/2 7 20 1 1 - - A ce to ne D M A c - - - D M A c - -1 C on c. H zS O ~ M eS O aH C on c. H 2F Od M eS O aH C on c. H Z S O ~ D M A c (p ar tia lly ) - D M A c In so lu bl e pr od uc t N o re ac tio n Pa rt ia lly c on de ns ed p ro du ct s. 0. 05 5 q in b 5 0. 12 d l/g N o re ac tio n 93 % y ie ld o f 1, 5- di ac et am id o an th ra qu in on e N o re ac tio n U nk no w n pr od uc t Q ua nt ita tiv e re co ve ry of m on om er s PO ly 19 er ; q in h = 0 .4 6 dl /g Po ly m er ; q in h = 0 .2 1 dl /g Po ly m er ; V in h = 0 .2 8 dl /g N o re ac tio n; c om on om ew Po ly co nd en sa tio n to ok p la ce su bl im ed - ~~ ~~ ~~ ~ 8 C om on om er s: d ia ce ty lb en ze ne (D A B ), di ac et yl py ri di ne (D A P) , d ia m in oa nt hr aq ui no ne (D A A Q ). b So lv en ts : X ,X -d im et hy la ce ta m id e (D Pt lA c) . 0 C at al ys ts : gl ac ia l a ce tic a ci d (H O A c) , a ce tic a nh yd ri de ( A cz O ). 3340 MORTIER Er AL. Pol yamdensations Polycondensations were carried out in solution, in the melt and in sealed tubes. Initially 1,4-diacetylbenzene was the comonomer used with 1,5-diaminoanthraquinone. 1,3-Diacetylbenzene and 2,&diacetylpyridine were later introduced in order to try to improve the solubility of the poly- mers. The reactions are summarized in Table I. Reactions in solution using 1,4-diacetylbenzene and 1,5-diaminoan- thraquinone yielded, at best, partially condensed structures of low molec- ular weight. Elemental analyses and infrared epectra indicated that these products contained N-H groups. The inherent viscosities, measured in dimethylacetamide at 30°C were in the range 0.05-0.12 dl/g. Replace- ment of zinc chloride by acetic acid or trichloroacetic acid as catalyst did not yield any polymeric products. Use of an acetic acid-acetic anhydride mixture as catalyst gave a 93% yield of 1,5diacetamido-anthraquinone. As the reaction was catalyzed by acids, noted in the synthesis of the model compounds (V and VI), a stronger acid than those previously used was employed. However, the use of trifluoroacetic acid as catalyst and dimethylacetamide as solvent gave rather ambiguous r a d t s . The in- frared spectrum did not show the sharp doublet at 3305 and 3410 cm-‘ (N-H) which is characteristic of 1,5-diaminoanthraquinone nor the diketone carbonyl peak at 1650 cm-’. The inherent viscosity of the product was POLYMERS CONTAINING ANTHRAQUINONE UNITS 3341 w The experiments are summarized in Table 11. TABLE I1 Treatment of Schiff's Base Polymers with Polyphosphoric Acid Polymer Tempera- Solvents from Sol- ture, Time, for Expt. (Table I) vent? "C hr product 1 expt. 15 PPA 150 5 hr Conc. HSO4 2 expt. 16 PPA 160 6 hr Conc. H2SO4 (partially) 3 expt. 21 PPA 150 5 hr MeSOaH MeS03H Remarks vinh = 0.56 dl/g Product appeared to be cross l ied Unsatisfactory analysis for closed structure a Solvent: polyphosphoric acid (PPA). A successful ring-closing experiment (Table 11, expt. 1) was carried out on the Schiff's-base polymer formed from 1,4-diacetylbenzene and 1'5- diaminoanthraquinone (Table I, expt. 15). The final product was soluble only in methanesulfonic and concentrated sulfuric acids. It had an in- herent viscosity of 0.56 dl/g (0.5% in sulfuric acid at 30°C). Thermo- gravimetric analysis in nitrogen at a heating rate of 3OC/min (Fig. 1) showed the polymer to be stable up to 900°C (10% weight loss at this tem- perature). The initial decomposition temperature in air at the same heat- ing rate was 440°C. Treatment of the polymer formed from 2,6-diacetylpyridine and 1'5- diaminoanthraquinone (Table I, expt. 21) with polyphosphoric acid gave a product soluble only in methanesulfonic acid (Table 11, expt. 3). The elemental analysis and infrared spectrum of the product were unsatisfac- tory for the ring-closed polymer. EXPERIMENTAL Monomers 1,5-Diaminoantbraquinoinone. Technical grade material was acetylated followed by hydrolysis and recrystallization from nitrobenzene. The ma- terial was partially freed from solvent by pumping under vacuum and 3342 MOHTIEll ET AL. 100 50 - ',\ \ -___-- - --- --_ - Atmosphere oir - Atmosphere N ---- - AT=3OC./min. I I I I I I I 0 200 400 600 000 Fig. 1. TGA curve for partial ladder polymer from 1,4-diacetylbenzene and 1,6diamino- anthraquinone finally purified by Soxhlet extraction with ethanol for 48 hr. The ma- terial had mp 319320°C (corr). 70.82%; H, 4.14%; N, 11.96%. ANAL. Calcd for CI~HIONIOS: C, 70.58y0; €1, 4.207,; N, 11.77%. Found: C, 1,4-Diacetylbenzene. Commercial material was crystallized twice from ethanol and was further purified by sublimation at 0.25 mm Hg pressure anda temperature of 90°C. The material had mp 114-114.5"C (corr). ANAL. Calcd for CIOHIOOZ: C, 74.08%; H, 6.17%. Found: C, 73.80%; H, 6.31%. 2,6-Diacetylpyridine. Commerical material was recrystallized from ether and sublimed. The purified material had mp 78°C. 1,3-Diacetylbenzene. This material was prepared from isophthaloyl chloride5 by the method of Ruggli and Gassenmeier.6 A mixture of isophthalic acid (40 g), phosphorus pentachloride (200 g), and phosphorus oxychloride (130 g) was heated for 6 hr on a water bath. The phosphorus oxychloride was removed by distillation, and pure iso- phthaloyl chloride was obtained by vacuum distillation. The yield was theoretical and the material had bp 146°C (15 em Hg).5 Freshly prepared sodium ethylacetoacetate (60 g, preparcd from sodium and ethyl acetoace- tate in dry cther) was suspended in dry benztmc (200 ml), and isophthaloyl chloride (40 g) in benzene (160 ml) was added dropwise to the stirred sus- pension. After heating for 4 hr on a water bath, the reaction mixture was filtered and the filtrate evaporated to dryness. The residue waa vacuum- distilled to give product IX, bp 150-158°C (15 mm Hg). POLYMERS CONTAINING ANTHRAQUINONE UNITS 3343 M X A solution of IX in 10% alcoholic ammonia (225 ml) was stirred at 60°C on a water bath for 1 hr. The reaction mixture was cooled, poured into water, acidified with 5% hydrochloric acid, and the resultant solution ex- tracted with ether. The ether layer was washed with water, dried prith anhydrous magnesium sulfate and, after filtering, evaporated to dryness to give product X as the residue. This material (15 g) was heated for 4 hr in 60 ml of 15y0 sulfuric acid on a water bath. The reaction mixture was cooled, extracted with ether, and the ether extract treated with sodium bi- carbonate, washed with water, and dried with calcium chloride. After filtration, the ether was removed by distillation and the residue was dis- tilled at 15 mm Hg pressure to give 1,3-diacetylbenzene. The material had by 150-155"C/15 mm Hg; mp 31-32°C. Model Compounds (V and VI) 1,5-Diaminoanthraquinone (0.238 g) was mixed with acetophenone (3 mi) and nitrobenzene (25 q l ) con- taining glacial acetic acid (2 ml) and the mixture refluxed for 16 hr. The product was filtered off, dried, and extracted with ethanol, giving a %yo yield of V which was soluble in dimethylacetamide. ANAL. Calcd. for CIHBN~O~: C, 81.5'35; H, 5.00/,; N, 6.3%. Found: C, 81.8%; H, 5.2%; N, 6.5%. The above product was treated with polyphosphoric acid (10 g) a t 1443°C for 2 hr. The cooled reaction mixture was precipitated into water, filtered and the product extracted with water to render it acid free. The product VI was insoluble in dimethylacetamide but soluble in concentrated sul- furic acid. 4.6%; N, 7.0%. Reaction Catalyzed by Acetic Acid. ANAL. Calcd for CSIHI~N~: C, 88.6%; H, 4.4%; N, 6.9%. Found: C, 87.8%; H, Reaction Catalyzed by Zinc Chloride. A mixture of 1,5-diaminoanthra- quinone (0.238 g) and anhydrous zinc chloride (0.10 g) in an excess of acetophenone was heated at 170°C under nitrogen for 31/2 hr. The reac- tion mixture was cooled, and the precipitated product separated, extracted with ethanol, and dried. ANAL. Calcd for CIHI~N~: C, 88.6%; H, 4.4%; N, 6.9%. (Product VI) Found: C, 87.3%; H, 4.5%; N, 7.1%. 3344 MORTIER ET AL. Polycondensations in Solution Polymer from 1,4-Diacetylbenzene and 1,5-Diaminoanthraquinone (Table I, Expt. 7). Equimolar quantities of 1,5diaminoanthraquinone (0.955 g, 0.004 mole) and 1,4-diacetylbenzene (0.650 g, 0.004 mole) were added to a 100 ml three-necked flask fitted with a nitrogen inlet, sealed stirrer, and air condenser. Nitrobenzene (40 ml) and anhydrous zinc chloride (0.55 g, 0.004 mole) were added and the mixture heated at 160- 170°C for 4 hr and then 140-150°C for 16 hr. After cooling, the reaction mixture was added to ethanol (200 ml) and the resultant mixture filtered. The precipitate was collected, washed with water, and dried under vacuum (0.35 g, 25% yield). The product was a red-brown powder soluble in dimethylacetamide with qinh = 0.12 dl/g (0.5% solution at 30°C). The material softened at 285°C but did not melt. The infrared spectrum showed a broad doublet a t 3305 and 3410 cm-' (N-H), although the intensity was much reduced compared with the doublet found in the spectrum of 1,5-diaminoanthraquinone. ANAL. Calcd for CMHI~NZO, (polymer): C, 79.1%; H, 4.4%; N, 7.7%. Found: C, 74.54%; H,4.36%; N, 8.48%. 1,4-Diacetylbenzene, Acetic Acid-Catalyzed (Table I, Expt. 10). A mixture of 1,5-diaminoanthraquinone (2.38 g, 0.01 mole), 1,4-diacetyl- benzene (1.62 g, 0.01 mole), glacial acetic acid (1.0 ml), acetic anhydride (4.0 ml), and nitrobenzene (50 ml) were heated at 160°C for 24 hr under nitrogen in a 100 ml three-necked flask. After cooling, the reaction mixture was poured into petroleum ether (40/600; 300 ml) to yield a brown precipitate. The precipitate was filtered off and dried under vacuum (3.0 g). The analysis, melting point, and infrared spectrum showed the product to be 1,5-diacetamidoanthraquinone (93% yield). The mp was 316°C with decomposition. ANAL. Calcd for ClsH14N204: C, 67.2%; H, 4.3%; N, 8.7%. Found: C, 67.3%; H, 4.4%; N, 8.6%. Self-Condensation of Monomers (Table I, Exph. 13 and 14). 1,5-Di- aminoanthraquinone (1.0 g, 0.0042 mole) and zinc chloride (0.75 g, 0.0055 m) were added to a 100-ml three-necked flask fitted with a nitrogen inlet, sealed stirrer and air condenser. Nitrobenzene (50 ml) was added and the mixture heated at 170°C for 23 hr under a slow stream of nitrogen. After cooling, the reaction mixture was added to petroleum ether (40/60; 500 ml). Water (100 ml) was added and the mixture stirred for 12 hr. The insoluble material was filtered off and air-dried overhight. It had mp 320"C, and its infrared spectrum was identical with that of 1,Bdiamino- anthraquinone. The yield was quantitative. ANAL. Calcd for C I ~ H I ~ N Z O ~ : C, 70.6%; H', 4.2%; N, 11.8%. Found: C, 69.8%; 1,4-Diacetylbenzene was treated similarly. The reaction mixture was allowed to cool and then added to a large excew of petroleum ether. A H, 4.270; N, 11.6%. POLYMERS CONTAINING ANTHRAQUINONE UNITS 3345 white precipitate of 1,4-diacetylbenzene was formed, and the monomer (infrared, mp 114°C) was recovered quantitatively. Melt Polyeondensations Polymer from 1 ,QDiacetylbenzene and 1,5-Diaminoanthraquinone (Table 1, Expt. 15). The Schiff's base polymer (VII) was prepared by the melt condensation of 1,Pdiacetylbenzene (0.324 g, 0.002 mole) and 1,5-diaminoanthraquinone (0.476 g. 0.002 mole). The reactants were ground together, and the intimate mixture was placed in a polymerization tube of the type described by Foster and Marvel.' The system was purged with nitrogen and quickly placed in a metal bath at 240"C, this temperature being maintained for '/z hr. Sublimation of both monomers was observed. The product was cooled under nitrogen, crushed, and ex- tracted with ethanol and dimethylacetamide. The yield of polymer was S9% and it had an inherent viscosity in concentrated sulfuric acid at 30°C of 0.46 (0.4S% solution). ANAL. Calcd for C ~ ~ H I ~ ~ O Z : C, 79.1%; H, 4.4%; N, 7.7%. Found: C, 78.8%; H, 4.2%; N, 7.5%. When this reaction was repeated at a lower temperature (Table I, expt. IS), the reaction was stopped intermittently in order to collect the sublimate and regrind the reactants. The product from this reaction, a black brittle material was obtained in S9% yield. The material was par- tially soluble in methanesulfonic and concentrated sulfuric acids (72%). The inherent viscosity of the product was 0.21 dl/g. The infrared spec- trum showed the absence of both the sharp NH2 doublet at 3305 and 3410 cm-' characteristic of 1,5-diaminoanthraquinone and the broad diacetyl- benzene carbonyl peak at 1650 cm-'. The product did not soften below 500"C, but there was a small amount of white sublimate a t 300°C. (closed): C, 87.8%; H, 3.7%; N, 8.5%. Found: C, 81.4%; H, 4.0%; N, 8.5%. ANAL. Calcd for polymer (open): C, 79.1%; H, 4.4%; N, 7.7%. Calcd for polymer Polyeondensations in Sealed Tubes 1 f-Diacetylbenzene and 2,6-Diaeetylpyridine (Table 1, Expts. 20 and 21). 1,5-diaminoanthraquinone (0.002 mole) was ground together with 1,3-diacetylbenzene (0.002 mole) and 2,6-diacetylpyridine (0.002 mole). The intimate mixtures were introduced into medium-walled pyrex tubes which were flushed with nitrogen. After sealing, the tubes were placed in a metal bath and heated for 1 hr a t 250°C. After cooling, the products were removed from the tubes, crushed extracted with ethanol and dried under vacuum at 70°C. H, 4.11%; N, 8.41%. H, 4.0%; N, 11.3%; residue, 1.2%. ANAL. Calcd for CUHENZOZ: C, 79.1%; H, 4.4%; N, 7.7%. Found: C, 75.4%; ANAL. Calcd for CtaH~sOaNa: C, 75.6%; H, 4.1%; N, 11.5%. Found: C, 76.6%; 3346 MORTIER ET AL. Ring Closures Polymer from 1,4-Diacetylbenzene (Table 11, Expt. 1). The Schiif’s- base polymer (VII; Table I, expt. 15) (0.50 g) was mixed with polyphos- phoric acid (10 g) in a 100-ml three-necked flask fitted with a mechanical stirrer and nitrogen inlet. The mixture was heated at 150°C for 5 hr with stirring. After cooling, the reaction mixture was added to water and the precipitated polymer filtered off, extracted with water and alcohol and finally dried under vacuum at 60°C. The inherent viscosity of the polymer in concentrated sulfuric acid at 30°C was 0.56 dl/g (0.50% solution). A thermo- gravimetric analysis under nitrogen at a heating rate of 3”C/min showed only 10% weight loss at 900°C. The initial decomposition temperature in air a t the same heating rate was 440°C (Fig. 1). ANAL. Calcd for CwHteN2: C, 87.8%; H, 3.7%; N, 8.5%. Found: C, 86.4%; H, 3.6%; N, 8.4%; Residue, 0.9%. SUMMARY Aralkyldiketones have been polymerized with 1,5-diaminoanthraquinone by various means to form Schiff’s-base polymers. These polymers have been treated with polyphosphoric acid in attempts to produce totally ring- closed polymers having a partial-ladder type structure. Melt polymeriza- tions have been successful for 1,4-diacetylbenzene but when 2,Gdiacetyl- pyridine or 1,3-diacetylbenzene were used no polymers were formed due to sublimation of these monomers. They were polymerized with 1,5di- aminoanthraquinone when the reactions were done in sealed tubes. Only low molecular weight polymers (qinh I 0.12 dl/g) were formed when the reactions were carried out in solution. The use of zinc chloride as catalyst may have limited the growth of the polymer as it is known that it can complex with ketones:8 Also, it is possible that, due to the long reaction times and high tempera- tures required to effect polycondensation, a solvent decomposition product or the solvent itself may have caused side reactions to take place. It should be noted that self-condensation of the comonomers did not appear to interfere in the polycondensations (Table I, expts. 13 and 14). We are indebted to Dr. Kurt L. Loening, Chemical Abstracts Service, for the name of our polymers. We are indebted to Dr. G. F. L. Ehlers, Air Force Materials Laboratory, WrighLPatterson Air Force Base, for the thermogravimetric curves. This work was supported by the Air Force Materials Laboratory, Air Force Systems Command, Wright-Patterson Air Force Base, Ohio. POLYMERS CONTAINING ANTHRAQUINONE UNITS 3347 References 1. A. H. Frazer, High Temperature Resistant Polymers, Interscience, New York, pp. 2. E. Grandmougin, Chem. Ber., 39, 3.563 (1906). 3. W. Bracke and C. S. Marvel, J . Polym. Sci. A-l,8,3177 (1970). 4. J. Szita, L. H. Brannigan, and C. S. Marvel, J . Polym. Sei. A-1, 9, 691 (1971). 5. J. Schreder, Chem. Ber., 7,708 (1874). 6. P. Ruggli and E. Gassenmeier, Helv. Chim. Acta, 22,496 (1939). 7. R. T. Foster and C. S. Marvel, J . Polym. Sci. AI , 3, 417 (1967). 8. P. K. Dutt and S. R. Palit, J . Polym. Sci. B., 3, 801 (1965). 138-210. R.eceived July 22, 1971