Synthesis and Properties of Novel P-Aramid Including Pyrazine Ring
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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.