Polymer Journal, Vol. 24, No. 12, pp 1429-1436 (1992) Synthesis and Properties of Novel p-Aramid Including Pyrazine Ring Shigeyuki UETA, Yoshihiro FuKUDA, Keiko KoGA*, and Motowo TAKAYANAGI Department of Industrial Chemistry, Faculty of Engineering, and *Advanced Instruments Center, Kyushu Sangyo University, Matsukadai 2-3-1, Higashi-ku, Fukuoka 813, Japan (Received June 8, 1992) ABSTRACT: Poly[p-phenylene(2,5-di-p-carbonylphenylpyrazine)amide] (PPPA) was synthe­ sized by the polycondensation of 2,5-di-p-chloroformylphenylpyrazine with p-phenylenediamine. Dicarboxylic acid was prepared by dimerization of p-cyanophenacyl bromide. Molecular characterization was carried out by IR and NMR. PPPA is soluble in sulfuric acid, forming liquid crystals. The temperature at the lOwt% loss in TGA was 54SOC. The fiber spinning was difficult due to the strong tendency to crystallization and rapid relaxation from liquid crystalline state. From the X-ray diffraction pattern ofuniplanar oriented film ofPPPA, approximate lattice constant was evaluated as a=7.94A, b=5.23A, and c=20.6A (fiber axis). Fiber period agreed with the identity period for all trans conformation of PPPA. Tensile modulus along the molecular axis was estimated as 21(}--220 GPa by referring to the theoretical moduli of poly(p-phenylenetere­ phthalamide) and poly(p-phenylene). KEY WORDS Poly[p-phenylene(2,5-di-p-carbonylphenylpyrazine)amide] I p-Aramid I Pyrazine Ring I Decomposition Temperature I X-ray Crystal Structure I Tensile Modulus I Poly(p-phenyleneterephthalamide) (PPT A) PPTA was found to make the polymers is a rigid rod-like molecule and gives Kevlar insoluble in sulfuric acid. fiber with ultrahigh modulus and strength Bizzarri and others1 •2 reported the solid state through liquid crystal spinning of a sulfuric polymerization of 4-amino-4' -carboxy-p-ter­ acid solution of PPTA. For improvement of phenylene and its thermal stability. Li and the functions of Kevlar fiber, new types of others3 synthesized novel aramids by low p-aramid have been explored in various ways. temperature polycondensation of p-terphenyl­ For example, to introduce p-polyphenyls such ene diamine and its dicarboxylic acid chlorides asp-biphenyl or p-terphenyl group in the main and reported their properties. According to chain of p-aramid is expected to exceed PPTA them, increase in the number of p-phenylene in the stiffness and heat endurance. The in the main chain lowered the solubility in increase of the fraction of poly(p-phenylene) sulfuric acid and the spinning of fiber from segments in the fiber period of the p-aramid sulfuric acid was impossible. Thus, so far there increases the tensile modulus along the has been no successful synthesis of p-aramids molecular axis compared with that of PPTA, composed of bi- or terphenyl groups, which since the stiffness of poly(p-phenylene) is are soluble in sulfuric acid. It is necessary to higher than that of PPTA as mentioned in later find out a new p-aramid, which includes part. In spite of these expectations, the p-terphenyl group as a stiffening component, introduction of wholly aromatic p-biphenyl or but at the same time soluble in sulfuric acid terphenyl group into the molecular skeleton of for processing. 1429 S. UETA et al. In this paper, 4,4"-dicarboxy-p-terphenyl p-Cyanophenacyl bromide (1) was synthe­ including pyrazine ring was synthesized, with sized by bromination of 4-acetylbenzonitrile. which the p-aramid prepared by polycondensa­ Bromination was carried out in a mixed tion with p-phenylenediamine was obtained. solution of dichloromethane and methanol The pyrazine ring has aromaticity in addition (10: 1) and white plate-like crystals were to a tertiary amine nature. Replacement of the obtained. mp 92°C, yield 98%. IR (KBr): 3100 aromatic ring by pyrazine ring will bring no (vCH,), 2230 (vcN), 1710 em - 1 (vc=o). 1H NMR effect on the molecular stiffness of the p-aramid. (CDC1 3) () 4.45 (s, 2, CH2), and 7.95 ppm ( q, Nitrogen atoms in pyrazine rings have 4, benzene ring). nucleophilic properties for sulfuric acid, which 2,5-Di-p-cyanophenylpyrazine (2) was syn­ are expected to make new aramid molecules thesized by dimerization of 1. N,N-Dimethyl­ soluble in sulfuric acid. The aramid composed acetamide (DMAc) was cooled to -10°C and of p-terphenyl, one of which rings is pyrazine, saturated with ammonia, to which a solution has been found soluble in sulfuric acid as of 1 in DMAc was added dropwise to dimerize. expected. The spinning of fiber using this The solution was left overnight, heated at 90oC aramid was difficult at present due to rapid for 6 h, to which hydrogen peroxide and crystallization and orientation relaxation from sodium hydroxide were added. The precipitate the liquid crystalline state, but useful informa­ was recrystallized with N,N -dimethylform­ tion on this polymer was obtained from amide and white needle like crystals were uniaxially oriented film. The X-ray crystal obtained. mp 385°C, yield 22%. IR (KBr): 2230 structure of the oriented film revealed that the (vcN), 1480 em - 1 (pyrazine ring). molecular conformation in crystal was all 2,5-Di-p-carboxyphenylpyrazine (3) was pre­ trans-conformation as found in the PPTA pared by refluxing 2 in a mixed solution of crystal. This information made evaluation of H 2 SOcH2 0-CH3COOH (5: 5: 4) at 110- tensile modulus of this new polymer possible, 120oC. White crystal powder was obtained. mp which suggested higher modulus value than 480°C, yield 98%. IR (KBr): 3500 (v0H), 1690 PPTA. Other properties such as heat endurance (vc=o), 1480 em - 1 (pyrazine ring). 1H NMR and phase diagram of liquid crystal are also (D2 S04 ) () 7.96 (q, 8, benzene ring), 9.48 (s, 2, reported here. pyrazine ring), and 10.32 ppm (s, 2, COOH). 2,5-Di-p-chloroformylphenylpyrazine (4) EXPERIMENTAL was prepared by dissolving 3 in thionylchloride, adding pyridine as a catalyst and refluxing Synthesis of Aramid Monomers upon heating. White needle like crystal was Scheme 1 shows the route of synthesis. obtained. mp 295°C, yield 98%. IR (KBr): 1710 Bromination Dimerization NC--o-Q-0-cN Br2 NH3 /DIIAc 1 2 Hydrolysis Chloroformylation --o-Q-0-c HOOC --o-Q-0-cDOH _....:_..:._:__:._:_:..c..:.:.:., C I OC OC I H+ SOCI2 3 4 _L_o_w _T_em..:..p_. _P_o ...:.1y_me_r_i z_a_t _i _LH._t=\ ..H Q F\ fr=\ F\ HMPA/LiCiz, -lO"C 5 Scheme 1. 1430 Polym. 1., Vol. 24, No. 12, 1992 p-Aramid Including Pyrazine Ring (vc=o), 1480 em - 1 (pyrazine ring). RESULTS AND DISCUSSION Preparation of p-Aramid Results of Characterization of P P P A p-Aramid was prepared by the method of Figure 1 shows IR absorption spectra of Bair and others.4 p-Phenylenediamine was PPP A and PPTA. The N-H stretching band dissolved in a solution of hexamethylphos­ of 3350 em- 1 is found in common for both phoric triamide (HMPA) and lithium chloride PPPA and PPT A. Amide I, II, and III are in a nitrogen atmosphere, to which a solution found at 1650, 1550, and 1310 cm- 1 , acid chloride solution 4 was added at - lOoC respectively. The wave number of 850 em - 1 is with stirring. Then it was warmed to 50°C by the absorption of p-substituted phenylene. The taking 30 min. After washing the polymerizate absorption of pyrazine ring is found at 1480 with water, ethanol and acetone, and drying in em- 1 only for PPPA. vacuum, a yellow powder of poly[p-phenyl­ Figure 2 shows 13C NMR spectrum of PPPA ene(2,5-di-p-carbonylphenylpyrazine)amide] in deuterized sulfuric acid. Two absorptions (PPPA) (5) was obtained. The method of Akzo 5 was also tried. Characterization Methods ofp-Aramid(PPPA) Inherent viscosity was measured by dissolv­ ing 0.5 g dl- 1 of p-aramid in 98% sulfuric acid Q) (.) and using a Ubbelohde viscometer at 25°C. c .....ctl Infrared absorption spectrum was measured on ..... a Nihonbunko A-202 infrared spectrometer by E (/) use of KBr method. A Rigaku DSC-8230 c ctl.... Differential Scanning Calorimeter was used t- with a nitrogen purge. Thermogravimetric analysis was carried out on the instrument of the same company, Model TG-8110, with 4000 2000 1500 1000 500 heating rate of lOaC min - 1 to the temperature as high as 600°C in nitrogen atmosphere. A Wave number /cm- 1 Rigaku Geiger Flex RAD-III A X-ray dif­ Figure 1. Infrared spectra of (a) PPPA and (b) PPTA. fractometer was employed for recording the diffraction intensity curves. An X-ray photo­ graph was taken using a Rigakudenki X-ray H a H c b d<z.s-J b c generator CN-2013 with Cu-Ka beam with 6(3.6-) b Laue camera, with accelerating voltage of 40kV and tube current of 20mA. The NMR spectrum was taken using a a Hitachi R-90H high resolution Fourier­ e c transforming NMR spectrometer. p-Aramid was dissolved in deuterized sulfuric acid (D2 S04 ). Chemical shifts were measured with tetramethylsilane as a reference. 180 160 140 120 13 C Chemical shift 5/ppm Figure 2. 13C NMR spectrum of PPPA in D 2 S04 . Po1ym. J., Vol. 24, No. 12, 1992 1431 S. UETA et a/. around 130 ppm are the carbon atoms in Figure 4 shows the phase diagram as a benzene ring. A comparison with the NMR function of temperature and concentration for spectrum ofPPTA and the absorption intensity PPPA in 97% sulfuric acid prepared by confirmed that the aromatic ring bonded to the observing the birefringent image under polar­ nitrogen atom of amide group denoted by (a) ization optical microscope under crossed is located at 126.9 ppm and the aromatic ring polars.