J. MATER. CHEM., 1991, 1(6), 935-938 Preparation and Characterization of wholly Aromatic para-Linked Copolyamides of Poly(p-phenyleneterephthalamide) Kazuki Suehiro,* Takayuki Tsutsumi, Miyuki Kuramori and Kunio Ide Department of Applied Chemistry, Faculty of Science and Engineering, Saga University, Honjo-machi, Saga, 840 Japan Wholly aromatic para-linked copolyamides of poly( p-phenyleneterephthalamide) have been prepared by direct polycondensation via a phosphorylation reaction using various amounts of p-aminobenzoic acid, toluene-p- diamine or nitroterephthalic acid (NTA) as comonomer. Viscosity number, perhaps degree of polymerization as well, increased with increasing comonomer content, whereas crystallinity of copolymers decreased. In particular, a bulky nitro group decreased crystallinity and the copolymers with NTA content >50 mol% were amorphous and similar to poly (p-pheneylenenitroterephthalamide). Melting point was not greatly changed by copolymeriz- ation.Thermal decomposition temperatures of copolymers containing NTA were lower than those of other copolymers by ca. 100 "C. Keywords: Copolymer; Viscosity ; Polyamide Poly(p-phenyleneterephthalamide)(PPTA) spun in the liquid- phate, terephthalic acid (TA), nitroterephthalic acid (NTA) crystalline state has high mechanical strength and is a high- and p-aminobenzoic acid (ABA), and examined the effect of tensile-modulus fibre. It also has a high melting point and comonomer structures on crystallinity and thermal properties good thermal stability.But PPTA is hard to process and has of copolymers. Note that ABA is a monomer of poly(p- poor solubility in organic solvents. Various methods have benzamide) (PBA), which is another wholly aromatic para- been tried in attempts to circumvent these limitations: intro- linked polyamide having excellent mechanical properties and duction of substituent groups onto the benzene rings,' N-sub- thermal stability. ~titution,~~~ etc. Copolymerization with cop~lymerization,~ meta-linked monomers increases the solubility and lowers the melting point, but the decomposition temperature and the crystallinity decrease^.^ In addition, mechanical properties of Experimentalmeta-linked aramids, such as poly(m-phenylene isophthalam- Materialside), are inferior to those of para-linked PPTA.Therefore, we prepared (Scheme 1) three types of wholly N-Methyl-2-pyrrolidone, pyridine and N,N-dimethylaceta-para-linked PPTA copolymers, with various compositions, mide were purified by vacuum distillation. Commercially from phenylene-p-diamine (PD), toluene-p-diamine (TD) sul- obtained anhydrous LiCl was dried at 130 "C for 24 h in -xH,NoNH2 + xH02COCO2H + (1-2x)HZN 0 C 0 2 H -*12NeNH2 + (1-x)H2NaNH2 + H02CeC02H H2NoNH2 + xH02CeCO2H + (1-4H02C-Scheme 1 (a) PD/TA/ABA copolymer; (b)(PD/TD)-TA copolymer; (c) PD-(TA/NTA) copolymer uucuo. All other chemicals were reagent grade and were used as received. Polymerization Aromatic polyamides, for example PPTA, are usually prepared by the low-temperature solution reaction between tereph- thaloyl chloride and phenylene-p-diamine in amide solvents such as hexamethylphosphoric triamide and N-methyl-2-pyr- rolidone.6 In the present study, we employed a more con- venient direct polycondensation method developed by Yamazaki and Higashi in which the carboxylic groups need not be chlorinated prior to p~lymerization.~ Thus, 20 mmol of monomers were heated at 100-105 "C for 3 h under nitro- gen in a mixed solvent of N-methyl-2-pyrrolidone (50 cm3) and pyridine (10 cm3) containing triphenyl phosphite (22 mmol) and LiCl (2.0g).After it had been cooled, the reaction mixture was poured into methanol and the precipitate was washed with water and then methanol, followed by vacuum drying.Measurements Viscosity numbers (q,,/C where qsp=specific viscosity and C =concentration) were measured with an Ostwald viscometer at 30 "C using a 5 g dm-3 solution in concentrated sulphuric acid. Thermogravimetric and differential thermal analyses were done at a heating rate of 10 "C min-' in a nitrogen atmosphere. X-Ray diffraction patterns were obtained with graphite-monochromatized Cu-Ka radiation. Solubility of polymers was observed in N,N-dimethylacetamide containing 5% LiCl at room temperature. Results and Discussion Pale- to dark-yellow polymers were obtained in good yields of over 92% (Table 1). Viscosity numbers of the copolymers in concentrated sulphuric acid solution were generally higher than those of the homopolymers of the constituent Table 1 Effects of composition on characteristics of PPTA cop01 yamides composition yield (%p/C)/ (Oh)(mol%) lo-' dm3 g-' T,"/ "C Tdb/"C (a) PD/TA/ABA copolymers PD/TA/ABA 50/50/0 100 0.48 517 499 40/40/20 100 0.79 525 51 1 30/30/40 20/20/60 100 98 2.24 4.13 530 525 506 515 10/10/80o/o/ loo 97 98 2.70 1.72 522 525 522 485 (b)(PD/TD)-TA copolymers PD/TD 100/0 100 80120 93 0.48 1.27 517 500 499 499 60140 95 1.63 500 494 40160 94 4.80 515 520 20180 93 2.93 510 516 0/100 92 0.93 515 504 (c) Pd-(TA/NTA) copolymers TA/NTAI 0010 100 0.48 517 499 75/25 50150 96 95 1.47 6.19 512 - 443 424 25/75 01100 95 95 5.09 3.52 414 403 " Melting point; temperature of 10% weight loss.J. MATER. CHEM., 1991, VOL. 1 comonomers in the copolymers. All copolymers rich in PPTA content had rather low viscosities. Highly crystalline PPTA had the lowest viscosities, whereas amorphous PD- (TA/NTA) copolymers had especially high viscosities. These copolymers are less crystalline as will be shown later and would be more soluble in the solvent during the polymeriz- ation process, possibly making the chain-growth reaction easier to achieve. All homopolymers and copolymers prepared were soluble in sulphuric acid. The amorphous PD-(TA/NTA) copolymers comprised of more than 50mol% NTA dissolved in N,N-dimethylacetamide containing 5 wt.% LiCI. PBA and poly(me- thyl-p-phenylene terephthalamide) (PMPTA) were also soluble in it, but PPTA and other crystalline copolymers were insol- uble or partially soluble.When a sulphuric acid solution of polymers was smeared on a glass plate and coagulated by soaking in water, thin films could be obtained for all polymers with viscosities higher than 0.127 dm3 g-'. X-Ray diffraction curves of copolymers and corresponding blends are shown in Fig. 1-5. A comparison of Fig. 1 and 3 10 20 30 201° Fig. 1 X-Ray diffraction curves of PD/TA/ABA copolymers PPTA/PBA (PD/TA/ABA) (50/50/0) *.-I89 (10/10/80) 10 20 30 20t0 Fig. 2 X-Ray diffraction curves of blends of poly(p-phenylene tereph- thalamide) (PPTA) and poly( p-benzamide) (PBA) J. MATER. CHEM., 1991, VOL. 1 /fi \oo/o (PPTA) 780120 .-/\ iiz_i; \-o/loo(PMPTA) I I I I 10 20 30 261" Fig.3 X-Ray diffraction curves of (PD/TD)-TA copolymers PPTA /PMPTA (mol %) 10 20 30 26i" Fig. 4 X-Ray diffraction curves of blends of poly(p-phenylene tereph- thalamide) (PPTA) and poly(methy1-p-phenylene terephthalamide) (PM PTA) with Fig. 2 and 4,respectively, shows that crystallinities of these copolymers are apparently lower than those of the homopolymer blends with the corresponding comonomer compositions. Therefore, the copolymerization reaction would appear to proceed practically at random. Since bulky nitro groups on the phenyl rings hinder crystallization, the PD- (TA/NTA) copolymers whose NTA content is more than 50mol% are amorphous. On the other hand, since a methyl group is not as bulky as a nitro group, the (PD/TD)-TA copolymers are somewhat crystalline.The X-ray diffraction patterns of the PD/TA/ABA and (PD/TD)-TA copolymers changed gradually with increasing content of another comono- mer. Consequently, the crystal structures of these copolymers would also undergo a gradual change. A minor comonomer TA/NTA 10 20 30 261" Fig. 5 X-Ray diffraction curves of PD-(TA/NTA) copolymers sequence might be relatively easily excluded from the crystal of the major component in the case of a copolymer composed of a flexible chain such as an aliphatic copolyamide. In contrast, rejection of the rigid comonomer unit is difficult in the course of crystallization of the wholly aromatic para- linked copolyamides and the resulting crystal has the charac- teristics of a mixed crystal.Although melting points of the PD/TA/ABA copolymers were slightly higher than those of the (PD/TD)-TA copoly- mers with pendant methyl groups, the melting points of these copolymers were in the vicinity of 500 "C which is similar to those of PPTA and other homopolymers (Table 1). Lowering of the melting points is usually observed for aliphatic copoly- amide~.*.~However, the present aromatic copolyamides did not show a distinct melting-point depression, eutectic behav- iour. This is because, as previously mentioned, the crystal structures of the copolymers are gradually transformed from that of one homopolymer to that of another with the change in the comonomer composition, namely, having an isomorph- ous tendency.The temperatures of the 10% weight loss for the original weights were used as a measure of thermal stability and are listed in Table 1. The corresponding temperatures of the crystalline copolymers are also only slightly affected by the composition similar to the melting points. The decomposition temperature of the amorphous PD-(TA/NTA) copolymers was nearly 400 "C and evidently lower than those of the crystalline copolymers. The 10% weight loss temperatures of terephthalic acid and nitroterephthalic acid were 3 13 and 269 "C, respectively. Therefore, low decomposition tempera- tures of poly(p-phenylene nitroterephthalamide) (PPNTA) and PD-(TA/NTA) copolymers are attributable to the thermal instability of nitroterephthalic acid.In conclusion, the crystallinity of PPTA decreases gradually but the melting point and decomposition temperature are not changed markedly by the copolymerization with ABA or TD. However, NTA having a bulky nitro group decreases the crystallinity significantly and lowers the thermal stability. References 1 R. Takatsuka, K. Uno, F. Toda and Y. Iwakura, J. Polym. Sci., Polym. Chem. Ed., 1977, 15, 1905. 2 M. Takayanagi and T. Katayose, J. Polym. Sci.,Polym. Chem. Ed., 1981, 19, 1133. 938 J. MATER. CHEM., 1991, VOL. 1 3 4 5 6 M. Takayanagi and T. Katayose, J. Polym. Sci., Polym. Chem. Ed., 1983, 21, 31. Y. Imai, N. Hamaoka and M. Kakimoto, J. Polym. Sci., Polym. Chem. Ed., 1984, 22, 1291. T. Kiyotsukuri and K.Tsujimoto, Sen-i Gakkaishi (J. SOC.Fiber Sci. Tech. Jpn.), 1978, 35, T-13. T. I. Bair, P. W. Morgan and F. L. Killian, Macromolecules, 1977, 10, 1396. 7 8 9 N. Yamazaki, M. Matsumoto and F. Higashi, J. Polym. Sci., Polym. Chem. Ed., 1975, 13, 1373. W. Mokudai, M. Ishihara, C. Morishita and R. Oda, Rikagaku-kenkyusho Iho (Bull. Inst. Phys. Chem. Res.), 1940, 19, 1448. K. Suehiro, T. Egashira, K. Imamura and Y. Nagano, Acta Polym., 1989, 40,4. Paper 1/01526E;Received 2nd April, 1991