Synthesis and Properties of New SolubleN-Phenyl–Substituted Aromatic-Aliphatic and All AromaticPolyamides Derived from 4,4*-Dianilinobiphenyl

MEENAKSHI GOYAL, MASA-AKI KAKIMOTO, YOSHIO IMAI

Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Meguro-ku, Tokyo 152, Japan

Received 30 June 1997; accepted 17 November 1997

ABSTRACT: New N-phenylated aromatic-aliphatic and all aromatic polyamides were pre-pared by the high-temperature solution polycondensation of 4,49-dianilinobiphenyl withboth aliphatic (methylene chain lengths of 6–11) and aromatic dicarboxylic acid chlorides.All of the aromatic-aliphatic polyamides and the wholly aromatic polyamides exhibited anamorphous nature and good solubility in amide-type and chlorinated hydrocarbon solvents,except for those aromatic polyamides containing p-oriented phenylene or biphenylylenelinkages in the backbone; the latter were crystalline and insoluble in organic solventsexcept m-cresol. The N-phenylated aromatic-aliphatic polyamides and aromatic poly-amides had glass transition temperatures in the range of 79–116°C and 207–255°C,respectively, and all the polymers were thermally stable with decomposition temperaturesabove 400°C in air. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2193–2200, 1998Keywords: N-phenylated polyamides; 4,49-dianilinobiphenyl; solubility; thermalbehavior

INTRODUCTION

Wholly aromatic polyamides are well establishedas high-performance materials with excellentthermal stability and mechanical properties.1,2

However, most aromatic polyamides are difficultto process due to their limited solubility and highmelt or softening temperatures. Earlier we dem-onstrated approaches for improving the solubilityand processability of these polyamides.3,4 One ofthe effective approaches to this goal is the intro-duction of a bulky pendent phenyl group along thepolymer backbone.3,4

The other promising method of improving thesolubility and processability of aromatic poly-amides is the incorporation of N-alkyl or N-phe-nyl substituent groups on the amide connecting

units, which eliminates intermolecular hydrogenbonding, thereby converting insoluble crystallineand rigid aromatic polyamides into more soluble,less crystalline materials with lower melting tem-perature s (Tm), or glass transition temperatures(Tg).5–9 Greenwood et al. reported that N-methyl–substituted aromatic polyamides were soluble inchlorinated hydrocarbon solvents and had Tg val-ues less than 180°C,5 while we found that theN-phenyl substitution had minimal detrimentaleffect on the thermal stability of aromatic poly-amides.8,9 This is also the case with the N-alkylsubstitution of aliphatic polyamides, which notonly lowered markedly the melting temperaturesbut also destroyed the crystallinity altogether.10

Nevertheless, to our knowledge, the latter type ofN-phenyl–substituted aromatic-aliphatic poly-amides are unknown to date.

The first objective of the present study is tolearn the properties of new N-phenylated aro-matic-aliphatic polyamides derived from 4,49-di-

Correspondence to: Y. ImaiJournal of Polymer Science: Part A: Polymer Chemistry, Vol. 36, 2193–2200 (1998)© 1998 John Wiley & Sons, Inc. CCC 0887-624X/98/132193-08

2193

anilinobiphenyl and various aliphatic dicarboxy-lic acids having methylene chain lengths of 6–11.The second is to get more information on theN-phenyl substitution of aromatic polyamides,and to determine the properties of new N-phenylsubstituted aromatic polyamides from 4,49-diani-linobiphenyl and various aromatic dicarboxylicacids, which could be compared with those of thep-dianilinobenzene-based aromatic polyamidesreported previously8,9 (Scheme 1).

EXPERIMENTAL

Materials

4’-Dianilinobiphenyl (1) was purchased from To-kyo Kasei Co., and purified by recrystallizationfrom toluene, giving white shining flakes; m.p.246–247°C (lit.11 m.p. 247°C).

A series of aliphatic dicarboxylic acid chlorides2a–2c, and 2e (m 5 6–8, and 10), isophthaloylchloride (3a), and terephthaloyl chloride (3b),

were obtained commercially; they were purifiedby vacuum distillation before use. Undecanedioylchloride (2d, m 5 9), tridecanedioyl chloride (2f,m 5 11), and aromatic dicarboxylic acid chlorides3c–3f were prepared by the reaction of the corre-sponding dicarboxylic acids with thionyl chloride,and purified by distillation under vacuum or bysublimation.

All the solvents used were purified by vacuumdistillation.

Polymerization

Aliphatic-Aromatic Polyamide 4c from 1 and 2c

A mixture of 2.150 g (6.4 mmol) of diamine 1,1.152 g (6.4 mmol) of sebacoyl chloride (2c), and7.0 mL of o-dichlorobenzene was placed in athree-necked flask equipped with a nitrogen inlet,a mechanical stirrer, and a drying tube. The re-action mixture was heated with stirring at 160°Cfor 7 h under a slow stream of nitrogen. At aninitial stage of the reaction, the evolution of hy-drogen chloride gas was rapid and later on itslowed down. The viscous polymer solution wasdiluted with 30 mL of chloroform and poured into300 mL of hexane to precipitate the polymer. Thepolymer obtained was filtered, washed thoroughlywith hot methanol, and dried in a vacuum oven.The yield of the polymer was 3.15 g (98%). Theinherent viscosity was 1.24 dL/g, measured at aconcentration of 0.5g/dL in sym-tetrachloroeth-ane at 30°C. The IR spectrum (film) exhibited anabsorption band at 1674 cm21 (CAO).

ANAL. Calcd for (C34H34N2O2)n: C, 81.24%; H,6.77%; N, 5.57%. Found: C, 80.12%; H, 6.77%; N,5.32%.

The other aromatic-aliphatic polyamides weresynthesized by a similar procedure.

Aromatic Polyamide 5a from 1 and 3a

A mixture of 1.176 g (3.5 mmol) of diamine 1,0.71 g (3.5 mmol) of isophthaloyl chloride (3a),and 5.0 mL of tetramethylene sulfone was placedin a three-necked flask, and the reaction mixturewas heated with stirring at 160°C for 24 h undernitrogen. The polymer was isolated by pouringthe solution into 300 mL of methanol, giving aprecipitate. The polymer was collected by filtra-tion, washed thoroughly with hot methanol, anddried under vacuum. The yield of the polymer was1.55 g (95%), and the inherent viscosity was 1.03dL/g in sym-tetrachloroethane. The IR spectrumScheme 1.

2194 GOYAL, KAKIMOTO, AND IMAI

(film) exhibited an absorption at 1662 cm21

(CAO).ANAL. Calcd for (C32H22N2O2)n: C, 82.38%, H,

4.75%; N, 6.00%. Found: C, 81.39%; H, 4.53%; N,5.76%.

The other aromatic polyamides were synthe-sized by an analogous procedure.

Measurements

FTIR spectra were recorded on a JASCO FT/IR5000 Fourier transform spectrophotometer. Num-ber average molecular weight (Mn) and weightaverage molecular weight (Mw) were determinedby means of gel permeation chromatography(GPC) using a light-scattering detector and dim-ethylformamide (DMF) as the eluent on the basisof polystyrene calibration. Differential scanningcalorimetery (DSC) and thermogravimetery (TG)were performed with Shimadzu thermal analyz-ers DSC-40M and TGA-40M, respectively, at aheating rate of 10°C/min in air or nitrogen. Wide-angle X-ray diffraction measurements were per-formed on a Rigakudenki XG X-ray diffractionapparatus using nickel-filtered CuKa radiation(35 kV, 20 mA). Mechanical properties of the filmswere determined from stress–strain curves ob-tained from a Toyo Baldwin Tensilon UTM-II-20(specimen length 30 mm, width 10 mm andthickness about 10 mm) at an elongation rateof 2 mm/min.

RESULTS AND DISCUSSION

Polymer Synthesis

It has been known that the high-temperature so-lution polycondensation method was particularlyuseful for polyamide synthesis from weakly basicdiamines like 1.6–8 Therefore, the solution poly-condensation of diamine 1 with aliphatic diacidchloride 2c at an elevated temperature was inves-tigated as a model to optimize the reaction condi-tions.

Figure 1 shows the effect of monomer concen-tration on the inherent viscosity of the polymerformed during the polycondensation in o-dichlo-robenzene at 160°C for 7 h. A remarkable in-crease in the viscosity value of the polymer wasobserved as the monomer concentration in-creased, and the inherent viscosity reached ashigh as 1.24 dL/g at the monomer concentration of0.91 mol/L. Any increase in the monomer concen-tration beyond 0.91 mol/L led to a decrease in theinherent viscosity of the polymer.

Figure 2 depicts the course of the polyconden-sation in terms of inherent viscosity of the result-ing polymer with respect to the reaction time. Thepolymerization proceeded rapidly at 160°C withevolution of hydrogen chloride gas, and was al-most complete within 5 h.

The solvent effect on the polycondensation isshown in Table I. Five solvents with high boiling

Figure 1. Effect of monomer concentration on inher-ent viscosity ofpolyamide 4c formed by the polyconden-sation of 4,4′-dianilinobiphenyl with sebacoylchloride in o-dichlorobenzene at 160°C for 7 h.

Figure 2. Effect of reaction time on inherent viscos-ity of polyamide 4c formed by the polycondensation of4,49-dianilinobiphenyl with sebacoyl chloride in o-di-chlorobenzene at 160°C.

N-PHENYL–SUBSTITUTED POLYAMIDES 2195

point above 140°C were selected for the high-temperature solution polycondensation. Althoughthese solvents were found to be almost equallyeffective for the preparation of N-phenylated ar-omatic polyamides with high inherent viscosi-ties,8 in the present case, o-dichlorobenzene wasthe most effective among the solvents, giving apolyamide with the highest viscosity around 1.2dL/g. When solvents such as anisole and nitroben-zene were employed as the reaction media, thepolymerizations also proceeded rapidly, but thepolymer solution started forming a gel within 30min, which actually limited polyamide formationwith a high viscosity value. In the case of solventssuch as sym-tetrachloroethane and sulfolane, theviscosity values of the polymer were low, despitethe fact that the polymerizations progressed inhomogeneous solution. Nevertheless, the poly-merization in the mixture of nitrobenzene andsym-tetrachloroethane (1:2) afforded polyamideswith moderate inherent viscosity. In these poly-merizations, the dielectric constant of the reac-tion media had no influence on the attained vis-cosity values of the polyamide.

Next, the high-temperature solution polycon-densation of diamine 1 was carried out with aseries of aliphatic diacid chlorides 2a–2f havingmethylene chain lengths of 6–11 under the opti-mum reaction conditions, that is, the monomersolution at the concentration of 0.91 mol/L in o-dichlorobenzene at 160°C for 7 h. The results ofthe synthesis of a series of aromatic-aliphaticpolyamides 4a–4f are summarized in Table II.The polyamides having high molecular weights

were successfully obtained by the polymeriza-tions. The inherent viscosities were in the rangeof 0.6–2.2 dL/g, and the number-average molecu-lar weights (Mn) and weight-average molecularweights (Mw) were 20,000–170,000 and 27,000–280,000, respectively, with molecular weight dis-tributions (Mw/Mn) of 1.2–1.7.

In the case of the synthesis of aromatic poly-amides 5a–5f, o-dichlorobenzene was not found tobe a good reaction medium, because the polymerstarted precipitating during the reaction. Aftertesting various solvents, tetramethylene sulfoneappeared to be the best choice. Hence, the poly-condensation of diamine 1 with various aromaticdiacid chlorides 3a–3f was carried out in tetram-ethylene sulfone at an elevated temperature of160 or 200°C. The aromatic polyamides 5a, 5e,and 5f remained soluble throughout the polymer-ization at 160°C, while the other three polymers5b–5d precipitated out of the polymerization mix-ture during the reaction. Therefore, the polymer-izations in the latter three cases were conductedat the high temperature of 200°C. Table III sum-marizes the results of synthesis of the aromaticpolyamides. These polymers were obtained withinherent viscosities of 0.2–1.0 dL/g, indicative ofmoderate to high molecular weights, which weredependent on the aromatic diacid chlorides used.

The structures of these polymers were con-firmed to be polyamides by means of IR spectros-copy and elemental analysis. The IR spectra of allthe N-phenylated polyamides exhibited an ab-sorption band characteristic of amide carbonyl atabout 1650 cm21. The elemental analysis values

Table I. Solvent Effect of Synthesis of N-Phenylated Aliphatic-Aromatic Polyamide 4c

Polymerizationa Polymer

SolventDielectricConstant

Temperature(°C) Remarksb

Yield(%)

hinhc

(dL/g)

Anisole 4.3 155 G 95 0.51sym-Tetrachloroethane 7.9 140 S 96 0.31o-Dichlorobenzene 9.9 160 S 98 1.24Nitrobenzene 35 160 G 95 0.58Sulfolaned 43 160 S 94 0.19NB 1 TCEe — 140 S 93 0.55

a Polymerization was carried out with 3.2 mmol of each monomer (1 and 2c) in 3.5 mL of the solvent for 7 h.b Appearance of the polymerization mixture: S, homogeneous solution throughout the reaction; and G, gelation during the

reaction.c Measured at a concentration of 0.5 g/dL in sym-tetrachloroethane at 30°C.d Tetramethylene sulfone.e The 1 : 2 mixture of nitrobenzene and sym-tetrachloroethane.

2196 GOYAL, KAKIMOTO, AND IMAI

of the polymers generally agreed fairly well withthe calculated values for the proposed structures.

Polymer Properties

All of the N-phenylated aromatic-aliphatic poly-amides 4a–4f and the aromatic polyamides, ex-cept for 5b and 5d, which were crystalline, werefound to show amorphous patterns by wide-angleX-ray diffraction diagrams. The high crystallinityof conventional polyamides and aromatic poly-amides mostly disappeared by the introduction ofbulky pendent phenyl substituent upon the N-position in amide connecting groups. The amor-phous nature of these N-phenylated polyamideswas reflected also in their good solubility dis-cussed below.

The solubility of aromatic-aliphatic polyamides4a–4f and aromatic polyamides 5a–5f is listed inTable IV. All of the aromatic-aliphatic polyamidesand aromatic polyamides 5a, 5e, and 5f werereadily soluble in m-cresol, chlorinated hydrocar-bon solvents such as chloroform and sym-tetra-chloroethane, and amide-type solvents such asDMF. This behavior is in accordance with theearlier reports on the solubility behavior of p-dianilinobenzene-based aromatic polyamides.8,9

The good solubility can be attributed to the bulkypendent phenyl group in the polymer backbone.In the aromatic-aliphatic polyamides, the solubil-ity in common organic solvents increased with theincrease in aliphatic chain length from 6 in 4a to11 in 4f. For example, polymers 4a–4c were in-soluble in tetrahydrofuran, while polymers 4d–4f

Table II. Synthesis of N-Phenylated Aromatic-Aliphatic Polyamidesa

DiacidChloride

Polymer

CodeYield(%) hinh

bMn

c

(31024)Mw

c

(31024) Mw/Mn

2a 4a 98 1.40 7.9 9.7 1.22b 4b 96 1.95 15.0 26.0 1.72c 4c 98 1.24 6.6 9.1 1.42d 4d 93 2.21 17.0 28.0 1.62e 4e 95 1.70 9.0 13.7 1.52f 4f 97 0.63 2.0 2.7 1.4

a Polymerization was carried out with 3.2 mmol of each monomer (1 and 2) in 3.5 mL ofo-dichlorobenzene at 160°C for 7 h.

b Measured at a concentration of 0.5 g/dL in sym-tetrachloroethane at 30°C.c Determined by GPC on the basis of polystyrene calibration using DMF as the eluent.

Table III. Synthesis of N-Phenylated Aromatic Polyamides

DiacidChloride

Polymerizationa Polymer

Temperature (°C) Remarksb Code Yield (%) hinhc (dL/g)

3a 160 S 5a 1.03 (A)3b 200 P 5b 0.54 (B)3c 200 P 5c 0.30 (B)3d 200 P 5d 0.36 (B)3e 160 S 5e 0.20 (A)3f 160 S 5f 0.51 (A)

a Polymerization was carried out with 3.5 mmol of each monomer (1 and 3) in 5.0 mL oftetramethylene sulfone for 7 h.

b Appearance of the polymerization mixture: S, homogeneous solution throughout the reaction;and P, polymer precipitation during the reaction.

c Measured at a concentration of 0.5 g/dL in sym-tetrachloroethane (A) or in concentratedsulfuric acid (B) at 30°C.

N-PHENYL–SUBSTITUTED POLYAMIDES 2197

dissolved in this solvent at room temperature. Inthe case of aromatic polyamides 5b–5d, they werecompletely insoluble in organic solvents except form-cresol. This behavior can be attributed to rigidp-phenylene, naphthalene-2,6-diyl, or biphenyl-4,49-diyl linkages in these polymers. The solubil-ity behavior of the N-phenylated aromatic poly-amides was similar to that of the p-dianilinoben-zene-based aromatic polyamides reportedpreviously.9

All of the aromatic-aliphatic polymers and ar-omatic polyamide 5a gave colorless transparentfilms by casting from 7% chloroform solutions. Itwas impossible to prepare films for the other ar-omatic polyamides mainly due to their insolubil-ity or poor solubility in chloroform. The tensileproperties of films of typical aromatic-aliphaticpolyamides 4a and 4e are listed in Table V. As thealiphatic chain length increased from 6 in 4a to 10

in 4e, the tensile strength decreased from 49 to 27MPa and the tensile modulus from 1.5 to 1.3 GPa,while a significant increase in the elongation atbreak from 9.3 to 58% was observed, which im-plies an increase in the flexibility of the poly-amide backbone. Aromatic polyamide 5a gave afilm having rather inferior tensile properties,compared with the aromatic-aliphatic poly-amides.

The thermal behavior of the N-phenylatedpolyamides was evaluated by means of DSC andTG. The TG curves of typical polyamides 4a and5a are shown in Figures 3 and 4, respectively, andthe thermal properties are summarized in TableVI. The aromatic-aliphatic polyamides had glasstransition temperatures (Tg) in the range of 79–116°C. As expected on the basis of the chemicalstructures, the Tg values decreased monotoniclywith increase in the aliphatic chain length. Atwo-step degradation was observed on the TGcurves in air with the decomposition startingaround 400°C, and the decomposition tempera-tures at 10% weight loss for all the aromatic-aliphatic polymers in nitrogen ranged from 420 to435°C.

The DSC curves of aromatic polyamides 5b and5d were found to be different from those of theother aromatic polyamides, and exhibited endo-therms due to melting temperatures at 408°C for5b and at 439°C for 5d. The observation of melt-ing temperatures only for these polymers wasconsistent with the above-mentioned crystallinenature. All the aromatic polyamides except 5d

Table IV. Solubility of N-Phenylated Polyamidesa

Solvent

Polymer

4a,4b 4c

4d,4e 4f

5a,5e

5b, 5c,5d 5f

Sulfuric acid 11 11 11 11 11 11 11m-Cresol 11 11 11 11 11 11 11Chloroform 11 11 11 11 11 2 1sym-Tetrachloroethane 11 11 11 11 11 2 1Dimethylformamide 11 11 11 11 11 2 1Tetrahydrofuran 2 2 11 11 2 2 2Methanol 2 6 6 6 2 2 2Benzene 2 2 6 6 2 2 2Acetone 2 2 2 6 2 2 2Hexane 2 2 2 2 2 2 2

a Solubility: 11, soluble at room temperature; 1, soluble at lower concentration; 6, swelling; and 2, insoluble.

Table V. Tensile Properties of Films of N-Phenylated Aromatic-Aliphatic Polyamides

Polymer

4a 4e

Inherent viscositya (dL/g) 1.40 1.70Tensile strength (MPa) 49 27Elongation at break (%) 9.3 58Tensile modulus (GPa) 1.5 1.3

a Measured at a concentration of 0.5 g/dL in sym-tetrachlo-roethane at 30°C.

2198 GOYAL, KAKIMOTO, AND IMAI

had glass transition temperatures between 207and 255°C, depending on the aromatic diacid com-ponents. The Tg values of the N-phenylated aro-matic polyamides were a little higher than thoseof the p-dianilinobenzene-based ones reportedpreviously.9

These aromatic polyamides were stable up totemperatures as high as 400°C both in air and innitrogen. The temperatures of 10% weight losswere above 460°C for all the aromatic polyamidesin air as well as in nitrogen, showing their highthermal stability, inspite of the presence of N-

phenylated amide linkage. The thermal stabilitywas almost comparable to that of the p-dianilino-benzene–based aromatic polyamides.9

CONCLUSIONS

New N-phenylated aromatic-aliphatic polyamidesand aromatic polyamides having high molecularweights were successfully synthesized by thehigh-temperature solution polycondensation of4,49-dianilinobiphenyl with both aliphatic and ar-omatic dicarboxylic acid chlorides. The resultingpolyamides had characteristics of good solubilityand high thermal stability, and some polymerscould give transparent, creasable, and flexiblefilms, that would be promising for high tempera-ture applications.

REFERENCES AND NOTES

1. P. E. Cassidy, Thermally Stable Polymers, Dekker,New York, 1980.

Table VI. Thermal Behavior of N-PhenylatedPolyamides

PolymerGlass Transition

Temperaturea (°C)

DecompositionTemperatureb (°C)

In Air In Nitrogen

4a 116 410 4254b 111 410 4304c 99 410 4354d 95 410 4204e 89 415 4354f 79 410 4255a 235 500 4955b 253 (408) 500 5005c 240 475 4655d — (439) 505 5255e 207 475 4605f 255 505 500

a Determined by DSC at a heating rate of 10°C/min innitrogen. The value in parentheses is the polymer meltingtemperature.

b Temperature of 10% weight loss determined by TG at aheating rate of 10°C/min.

Figure 3. TG curves of polyamide 4f: (A) in air, and(B) in nitrogen at a heating rate of 10°C/min.

Figure 4. TG curves of polyamide 5d: (A) in air and(B) in nitrogen at a heating rate of 10°C/min.

N-PHENYL–SUBSTITUTED POLYAMIDES 2199

2. H. H. Yang, Aromatic High-Strength Fibers, Wiley,New York, 1989.

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St.Clair, and N. J. Johnston, J. Polym. Sci., Polym.Chem. Ed., 18, 1047 (1980).

6. M. Matzner, R. Barclay, Jr., and C. N. Merriam,J. Appl. Polym. Sci., 9, 3337 (1965).

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Sci., Polym. Chem. Ed., 22, 1291 (1984).9. Y. Oishi, M. Kakimoto, and Y. Imai, J. Polym. Sci.,

Polym. Chem. Ed., 25, 2493 (1987).10. R. Hill and E. E. Walker, J. Polym. Sci., 3, 609

(1948).11. CRC Handbook of Chemistry and Physics, 76th ed.,

CRC Press, Boca Raton, FL, 1995, p.3–85.

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