Rigid-Rod Polyamides and Polyimides Prepared from 4,3(-Diamino-2*,6*-Di(2-naphthyl)-p-terphenyl and 2*,6*,3-,5--Tetra(2-naphthyl)-4,4(-Diamino-p-quinquephenyl

JOHN A. MIKROYANNIDIS

Chemical Technology Laboratory, Department of Chemistry, University of Patras, GR-26500 Patras, Greece

Received: 12 May 1998; accepted 11 August 1998

ABSTRACT: A series of rigid-rod polyamides and polyimides containing p-terphenyl orp-quinquephenyl moieties in backbone as well as naphthyl pendent groups were syn-thesized from two new aromatic diamines. The polymers were characterized by inher-ent viscosity, elemental analysis, FT-IR, 1H-NMR, 13C-NMR, X-ray, differential scan-ning calorimetry (DSC), thermomechanical analysis (TMA), thermal gravimetric anal-ysis (TGA), isothermal gravimetric analysis, and moisture absorption. All polymerswere amorphous and displayed Tg values at 304–337°C. Polyamides dissolved uponheating in polar aprotic solvents containing LiCl as well as CCl3COOH, whereaspolyimides were partially soluble in these solvents. No weight loss was observed up to377–422°C in N2 and 355–397°C in air. The anaerobic char yields were 57–69% at800°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 15–24, 1999Keywords: polyamides; polyimides; synthesis; rigid-rod polymers; pyrylium; p-ter-phenyl; p-quinquephenyl

INTRODUCTION

Rigid-rod polymers are of particular interest dueto their outstanding heat-resistance and mechan-ical properties.1 Many efforts have been made tosynthesize rigid-rod polymers by incorporatingaromatic rings into the polymer backbone andincreasing the polymer rigidity. However, the in-fusibility and the limited solubility of these ma-terials reduce their processability and restrictfurther applications. Therefore, the interest wasfocused on the preparation of polymers with im-proved processability either by introducing flexi-ble moieties in the main chain thus interruptingthe rigid character or by attachment of pendentsubstituents. The latter may be bulky aromatic orlong aliphatic groups. Aromatic substituents havebeen used extensively to prapare soluble rigid-rodpolyamides2–11 and polyimides.12–16

Recently, new rigid-rod polymers have beensynthesized in our laboratory starting from pyry-lium salts. More particularly, soluble rigid-rodpolyamides and polyimides have been preparedfrom substituted aromatic diamines of p-terphe-nyl17–19 or biphenyl.20 In addition, we have pre-pared blue light-emitting, rigid-rod polyamidesand polyimides from an aromatic diamine of p-quinquephenyl carrying phenyl or 4-biphenylylside groups.21 Finally, we have synthesized solu-ble phenyl- or alkoxyphenyl-substituted rigidpolyamides and polyimides containing m-terphe-nyls in the main chain.22

The present investigation deals with the syn-thesis and characterization of rigid-rod poly-amides and polyimides containing p-terphenyl orp-quinquephenyl units in the main chain as wellas 2-naphthyl pendent groups. The kind of thelateral substituent may influence the rigidity ofpolymers and therefore their general properties.Specifically, the compact and stiff 2-naphthylpendent groups are expected to increase the chain

Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 37, 15–24 (1999)© 1999 John Wiley & Sons, Inc. CCC 0887-624X/99/010015-10

15

rigidity and therefore the Tg transitions. In addi-tion, these bulky pendent groups should affect thesolubility of polymers. Owing to their wholly aro-matic structure, the synthesized polymers shoulddisplay an excellent thermal stability.

EXPERIMENTAL

Characterization Methods

Melting temperatures were determined on anelectrothermal melting point apparatus IA6304and are uncorrected. IR spectra were recorded ona Perkin-Elmer 16PC FT-IR spectrometer withKBr pellets. 1H-NMR spectra were obtained usinga Brucker spectrometer (400 MHz) and a VarianT60A spectrometer (60 MHz). 13C-NMR (100MHz) spectra were obtained with a Brucker spec-trometer.The NMR spectra were recorded usingDMSO-d

6as solvent. Chemical shifts (d values)

are given in parts per million with tetramethylsi-lane as an internal standard. DSC and TGA wereperformed on a DuPont 990 thermal analyzer sys-tem. Ground polymer samples of about 10 mgeach were examined by TGA and isothermalgravimetric analysis (IGA), and the weight losscomparisons were made between comparablespecimens. The DSC thermograms were obtainedat a heating rate of 20°C/min in N2 atmosphere ata flow rate of 60 cm3/min. Dynamic TGA measure-ments were made at a heating rate of 20°C/min inatmospheres of N2 or air at a flow rate of 60cm3/min. Thermomechanical analysis (TMA) wasrecorded on a DuPont 943 TMA using a loadedpenetration probe at a scan rate of 20°C/min in N2with a flow rate of 60 cm3/min. The TMA experi-ments were conducted at least in duplicate toassure the accuracy of the results. The TMA spec-imens were pellets of 8 mm diameter and 2 mmthickness prepared by pressing powder of poly-mer for 3 min under 5–7 kpsi at ambient temper-ature. The inherent viscosities of polymers weredetermined for solutions of 0.5 g/100 ml inCCl3COOH or DMAc at 30°C using an Ubbelohdesuspended level viscometer. Elemental analyseswere carried out with a Hewlett-Packard model185 analyzer. The wide-angle X-ray diffractionpatterns were obtained for powder specimens onan X-ray PW-1840 Philips diffractometer.

To determine the equilibrium water absorp-tion, polymer samples were previously condi-tioned at 120°C in an oven for 12 h. They weresubsequently placed in a desiccator where 65%

r.h. (relative humidity) was maintained by meansof an oversaturated aqueous solution of NaNO2 at20°C, and were periodically weighed.

Reagents and Solvents

3-Nitrobenzaldehyde and 2-acetylnaphthalenewere recrystallized from ethanol 95%. 1,4-Ben-zenedicarboxaldehyde was recrystallized fromdistilled water. 4-Nitrophenylacetic acid so-dium salt was prepared by reacting equimolaramounts of 4-nitrophenylacetic acid with aque-ous sodium hydroxide. Terephthaloyl chloridewas recrystallized from n-hexane. Pyromelliticdianhydride (PMDA) and benzophenone tetra-carboxylic dianhydride (BTDA) were recrystal-lized from acetic anhydride. Dimethylacetamide(DMAc) and 1,2-dichloroethane were dried bydistillation over CaH2. Triethylamine was driedby distillation over KOH. Boron trifluorideetherate, acetic anhydride, 1,4-dioxane, pyri-dine, and hydrazine hydrate were used as sup-plied.

Preparation of Starting Materials

4-(3-Nitrophenyl)-2,6-di(2-naphthyl)pyryliumtetrafluoroborate (1)

A flask was charged with a solution of 3-nitroben-zaldehyde (1.21 g, 8.00 mmol) and 2-acetylnaph-thalene (2.72 g, 16.00 mmol) in 1,2-dichloroeth-ane (15 ml). Boron trifluoride etherate (2.5 ml,20.00 mmol) diluted with 1,2-dichloroethane (5ml) was added dropwise to the stirred solution atroom temperature. The mixture was subse-quently refluxed for 5 h under N2. Next, it wasconcentrated under vacuum and ether was addedto the residue. The dark brown solid obtained wasfiltered, washed with ether, and dried to afford 1(2.40 g, 55%). It was purified by recrystallizationfrom a mixture of chloroform/ether (1:1 v / v). Mp119–121°C.

Anal. calcd. for C31H20NO3BF4: C, 68.79%; H,3.72%; N, 2.59%. Found: C, 68.58%; H, 3.76%; N,2.53%. IR (KBr) cm21: 1,616; 1,604; 1,496; 1,452(aromatic and pyrylium structure); 1,528; 1,350(NO2); 1,084 (br, BF4

2). 1H-NMR (DMSO-d6)ppm: 8.87–8.16 (m, 2H, aromatic meta to O1 and2H, aromatic ortho to NO2); 8.06–7.21 (m, 16H.other aromatic).

4,3(-Dinitro-2*,6*-di(2-naphthyl)-p-terphenyl (2)

A mixture of 1 (1.20 g, 2.22 mmol), 4-nitropheny-lacetic acid sodium salt (0.90 g, 4.44 mmol) and

16 MIKROYANNIDIS

acetic anhydride (4.5 ml) was refluxed for 6 h. Itwas cooled at about 210°C overnight, and thelight brown precipitate was filtered, washed withwater, and dried to afford 2 (0.66 g, 52 %). It wasrecrystallized from acetonitrile. Mp 106–108°C.

Anal. calcd. for C38H24N2O4: C, 79.71%; H,4.22%; N, 4.89%. Found: C, 79.60%; H, 4.19%; N,4.95%. IR (KBr) cm21: 1,598 (aromatic); 1,520;1,346 (NO2). 1H-NMR (DMSO-d6) ppm: 8.84–8.17(m, 4H, aromatic ortho to NO2); 7.97–7.22 (m,20H, other aromatic).

4,3(-Diamino-2*,6*-di(2-naphthyl)-p-terphenyl (3)

A flask was charged with a mixture of 2 (2.22 g,3.88 mmol), 1,4-dioxane (25 ml) and a catalyticamount of palladium 10% on activated carbon.Hydrazine hydrate (10 ml) was added dropwise tothe stirred mixture at the boiling temperatureand refluxing was continued for 24 h. The mixturewas filtered and the filtrate was concentrated un-der vacuum. Water was added to the residue andthe pale brown precipitate was filtered, washedwith water, and dried to afford 3 (1.54 g, 77%). Itwas recrystallized from a mixture of tetrahydro-furane/petroleum ether (1:1 v / v). Mp 169–171°C.

Anal. calcd. for C38H28N2: C, 89.03%; H, 5.51%;N, 5.46%. Found: C, 88.86%; H, 5.48%; N, 5.53%.IR (KBr) cm21: 3,338; 3,208 (N-H stretching);1,618 (N-H deformation); 1,604; 1,514; 1,452 (ar-omatic); 1,278 (C-N stretching). 1H-NMR (DMSO-d6) ppm: 7.89–7.30 (m, 20H, aromatic apart fromthose ortho to NH2); 6.56 (m, 4H, aromatic orthoto NH2); 4.80 (br, 4H, NH2).

4,4*-(1,4-Phenylene)bis[2,6-di(2-naphthyl)pyryliumtetrafluoroborate] (4)

A flask was charged with a solution of 1,4-ben-zenedicarboxaldehyde (0.96 g, 7.00 mmol) and2-acetylnaphthalene (4.81 g, 28.00 mmol) in 1,2-dichloroethane (20 ml). Boron trifluoride etherate(4.4 ml, 35 mmol) diluted with 1,2-dichloroethane(5 ml) was added dropwise to the stirred solutionat room temperature. The mixture was subse-quently refluxed for 5 h under N2. It was concen-trated under vacuum and ethyl acetate was addedto the residue. After cooling at 0°C for ca. 1 h, thebrown-red precipitate was filtered, washed withethyl acetate, and dried to afford 4 (4.62 g, 72%).It was recrystallized from a mixture of chloro-form/ether (2:1 v / v). Mp 144–146°C.

Anal. calcd. for C56H36O2B2F8: C, 73.55%; H,3.97%. Found: C, 73.26%; H, 4.05%.

IR (KBr) cm21: 1,618; 1,596; 1,494; 1,452 (aro-matic and pyrylium structure); 1084 (BF4

2). 1H-NMR (DMSO-d6) ppm: 8.84 (s, 4H, aromatic orthoto O1); 7.92–7.25 (m, 32H, other aromatic).

2*,6*,3(,5--Tetra(2-naphthyl)-4,4--dinitro-p-quinquephenyl (5)

A mixture 4 (1.99 g, 2.18 mmol), 4-nitrophenyla-cetic acid sodium salt (1.77 g, 8.72 mmol) andacetic anhydride (4.4 ml) was refluxed for 6 h. Itwas cooled at 210°C overnight, and the palebrown precipitate was filtered, washed with wa-ter, then with methanol, and dried to afford 5(1.96 g, 92%). It was recrystallized from ni-tromethane. Mp 139–141°C.

Anal. calcd. for C70H44N2O4: C, 86.04%; H,4.54%; N, 2.87%. Found: C, 85.87%; H, 4.50%; N,2.93%. IR (KBr) cm21: 1,598 (aromatic); 1,518;1,344 (NO2). 1H-NMR (DMSO-d6) ppm: 8.50 (s,4H, aromatic ortho to NO2); 7.93-7.26 (m, 40H,other aromatic).

2*,6*,3-,5--Tetra(2-naphthyl)-4,4--diamino-p-quinquephenyl (6)

A flask was charged with a mixture of 5 (2.07 g,2.12 mmol), 1,4-dioxane (25 ml) and a catalyticamount of palladium 10% on activated carbon.Hydrazine hydrate (8 ml) was added dropwise tothe stirred mixture at the boiling temperatureand refluxing was continued for 24 h. The mixturewas filtered and the filtrate was concentrated un-der vacuum. Water was added to the residue andthe pale brown precipitate was filtered, washedwith water, and dried to afford 6 (1.71 g, 88%). Itwas recrystallized from a mixture of 1,2-dichloro-ethane/ether (1:1 v / v). Mp 176–178°C.

Anal. calcd. for C70H48N2: C, 91.67%; H, 5.28%;N, 3.05%. Found: C, 91.42%; H, 5.33%; N, 2.94%.IR (KBr) cm21: 3,444; 3,378 (N-H stretching);1,620 (N-H deformation); 1,603; 1,514; 1,448 (ar-omatic); 1,272 (C-N stretching). 1H-NMR (DMSO-d6) ppm: 7.81–7.28 (m, 40H, aromatic apart fromthose ortho to NH2); 6.57 (s, 4H, aromatic ortho toNH2); 4.70 (br, 4H, NH2).

Preparation of Polymers

Polyamides PA1 and PA2

As a typical example, the preparation of poly-amide PA2 is given: A flask was charged with asolution of 6 (0.80 g, 0.87 mmol) in DMAc (15 ml)containing 5 wt % LiCl. Triethylamine (0.18 g,

RIGID-ROD POLYAMIDES 17

1.74 mmol) was added to the solution. Terephtha-loyl chloride (0.18 g, 0.87 mmol), dissolved inDMAc (5 ml), was added dropwise to the stirredsolution at 210°C. Stirring of the mixture wascontinued at this temperature for 5 h and then atroom temperature overnight in a stream of N2. Itwas poured into water, and the pale yellow-brownprecipitate was filtered, extracted for approxi-mately 2 h with 1,4-dioxane, and dried to affordPA2 (0.81 g, 88%).

Polyimides PIP1, PIB1, PIP2, and PIB2

As a typical procedure for the preparation of poly-imides, the synthesis of PIP2 is given: PMDA(0.14 g, 0.65 mmol) was added to the stirred so-lution of 6 (0.60 g, 0.65 mmol) in DMAc (20 ml)containing 5 wt % LiCl at 0°C. The solution be-came viscous, and stirring was continued at roomtemperature for 5 h and then at 100°C for 1 hunder N2. Acetic anhydride (5 ml) and pyridine (1ml) were added to the solution, and it was heatedat 100°C overnight. It was poured into water, andthe brown precipitate was filtered, extracted forabout 2 h with 1,4-dioxane, and dried to affordPIP2 (0.70 g, 97%).

The reaction yields, the inherent viscosities,and the elemental analyses for all polymers arelisted in Table I.

RESULTS AND DISCUSSION

Schemes 1 and 2 outline the synthesis of two newaromatic diamines 3 and 6, which are derivatives

of p-terphenyl and p-quinquephenyl respectively.More particularly, 3-nitrobenzaldehyde reactedwith 2-acetylnaphthalene in the presence of borontrifluoride etherate to afford pyrylium salt 1. Thelatter reacted with 4-nitrophenylacetic acid anhy-dride, which is generated in situ from 4-nitrophe-nylacetic acid sodium salt and excess of aceticanhydride, to yield compound 2 (Reference 23).Finally, the catalytic hydrogenation of 2 to thecorresponding diamine 3 was carried out bymeans of hydrazine hydrate. Diamine 6 was sim-ilarly synthesized starting from 1,4-benzenedi-carboxaldehyde.

The monomers were characterized by elemen-tal analyses as well as IR, 1H-NMR and 13C-NMRspectroscopy. Figures 1 and 2 present typical 13C-NMR spectra of compounds 3 and 5 in DMSO-d6

solution. Assignments of peaks for both spectraare given in the figures. Most of the carbon nuclei,and especially those of the naphthyl groups, hadcomparable shifts and appeared in the region of120–130 ppm in both spectra.

The structural configuration of diamines 3 and 6was studied from their optimized geometries, ascalculated by means of CS Chem3D Pro version 3.5modeling system. In the case of diamine 6, the mid-dle ring of the p-quenquephenyl segment is almostcoplanar with the two adjacent phenyls. In contrast,due to the interactions caused by the bulky naph-thyl substituents, the two terminal rings of p-quen-quephenyl are more twisted. The pendent naphthylis essentially planar. An analogous configurationwas observed for diamine 3. The fact that the pen-dent naphthyl groups are planar constitutes a

Table I. Yields, Inherent Viscosities, and Elemental Analyses of Polymers

PolymerYield(%)

ninh

(dl/g)EmpiricalFormula

Elemental Analyses

C (%) H (%) N (%)

PA1 86 0.97a (C46H30N2O2)n Calcd. 85.96 4.70 4.36Found 85.83 4.73 4.32

PA2 88 1.12a (C78H50N2O2)n Calcd. 89.46 4.81 2.67Found 89.11 4.78 2.73

PIP1 93 1.34b (C48H26N2O4)n Calcd. 82.98 3.77 4.03Found 82.63 3.81 4.07

PIB1 98 1.26b (C55H30N2O5)n Calcd. 82.69 3.79 3.51Found 82.35 3.85 3.46

PIP2 97 1.41b (C80H46N2O4)n Calcd. 87.41 4.22 2.55Found 87.17 4.28 2.46

PIB2 92 1.32b (C87H50N2O5)n Calcd. 86.84 4.19 2.33Found 86.72 4.11 2.38

a Inherent viscosity in CCl3COOH (0.5 g/dl) at 30°C.b Inherent viscosity of intermediate poly(amic acids) in DMAc (0.5 g/dl) at 30°C.

18 MIKROYANNIDIS

drawback from the aspect of the polymer solubility,since it is well established that the presence of non-planar lateral substituents along the polymer back-bone increases the solubility.

Rigid-rod polyamides and polyimides bearingnaphthyl pendent groups were synthesized, thestructures of which are shown in Charts 1 and 2.Polyamides PA1 and PA2 were prepared by re-

Scheme 1.

Scheme 2.

RIGID-ROD POLYAMIDES 19

acting terephthaloyl chloride with diamines 3 and6 respectively. Polyimides PIP and PIB were pre-pared from the reactions of these diamines withPMDA and BTDA. The yields of the preparationreactions were 86–88% for polyamides and 92–98% for polyimides (Table I). The inherent viscos-ities (ninh) of polymers ranged from 0.97–1.41dl/g. In the case of polyimides, the ninh of theintermediate poly(amic acids) were determined,because the polyimides were partially solubleeven in polar aprotic solvents and CCl3COOH. It

seems that polyamides showed a somewhat lowerdegree of polymerization than polyimides. In ad-dition, the polymers containing p-quenquephe-nyls in the main chain displayed higher ninh val-ues than the corresponding ones bearing p-ter-phenyls.

No optimization of the conditions utilized inthe preparation reactions of polymers was made.It is well known that the addition of tertiaryamines in the synthesis of aromatic polyamidesreduces the molecular weights of the obtainedpolymers, whereas temperatures below 210°Care favorable. Furthermore, the synthesis of poly-imides in m-cresol gives usually higher molecularweights than in DMF/Ac2O.

Figure 3. FT-IR spectra of polymers PA1 and PIP2.

Figure 1. 13C-NMR spectrum of compound 3 inDMSO-d6 solution.

Figure 2. 13C-NMR spectrum of compound 5 inDMSO-d6 solution.

Chart 1.

20 MIKROYANNIDIS

Structural characterization of polymers wasaccomplished by elemental analyses, FT-IR, 1H-NMR, and 13C-NMR spectroscopy as well as X-rayanalysis. Figure 3 presents typical FT-IR spectraof polymers PA1 and PIP2. Polyamide PA1showed characteristic absorptions at 3,280 (N-Hstretching), 1,655 (C5O), 1,600 (aromatic), 1,516(N-H deformation and aromatic), and 1,318 cm21

(C-N stretching). Polyimide PIP2 displayed ab-sorptions at 1,776; 1,726; 1,368; and 1,094 cm21

assigned to the imide structure.The 1H-NMR spectrum of polyamide PA1 in

DMSO-d6 solution showed peaks at 9.91 (br, 2H,NHCO), 7.97 (s, 4H, aromatic of terephthalic acidsegment), and 7.82–6.62 (m, 24H, aromatic ofdiamine segment). On the other hand, the 13C-NMR spectrum of PA1 in DMSO-d6 solution dis-played a characteristic upfield peak at 164 ppmassigned to the -NHCO- moiety.

The crystallinity of polymers was attempted tobe evaluated by X-ray diffractograms. All poly-

mers were generally amorphous due to the pres-ence of the voluminous and rigid pendent groups,which increased considerably the disorder inchains. In addition, the p-terphenyl as well as thep-quenquephenyl moieties of backbone deviatesignificantly from the coplanar conformation, as itwas shown by the modeling system, and conse-quently disrupted a dense chain packing. Finally,the polymers derived from diamine 3 possessedpara and meta orientation, which contributed totheir amorphous character. However, upon com-paring the curves of polyamides with those ofpolyimides, it seems that the former indicated alow level ordering, since they displayed weak dif-fraction peaks especially at the region of 40–50°.The stiff and rigid imide structure should causeless dense chain packing.

The hydrophilicity of polyamides PA1 and PA2was estimated by determination of their isother-mal water absorption (Figure 4). They showedwater uptake 4.69 and 3.29%, respectively, fol-lowing exposure for 50 h. The corresponding num-bers of moles of absorbed water per amide equiv-alent weight (NMAW) were 0.84 and 0.96. Thepresent polyamides showed higher hydrophilicitythan our previously synthesized analogous rigid-rod polyamides carrying phenyl or 4-biphenylylpendent groups, the NMAW values of which were0.15–0.57 (References 18,21). Such a behaviorwas attributed to the bulkier naphthyl pendentgroups, which formed larger openings in thechain packing that increased the water accessi-bility.

Table II summarizes the solubilities of poly-mers.Polyamides dissolved upon heating in polaraprotic solvents (DMF, NMP, DMAc) containingLiCl. In addition, they dissolved in hot CCl3COOH,

Chart 2.

Figure 4. Water absorption vs. time for polyamidesPA1 and PA2.

RIGID-ROD POLYAMIDES 21

while were insoluble in other less efficient solvents.The solutions of polyamides in CCl3COOH did notform gel or precipitate on cooling. Polyimides werepartially soluble only in polar aprotic solvents andCCl3COOH. Undoubtedly, the present polymersdisplayed lower solubility than our analogous poly-mers containing phenyl or 4-biphenylyl pendentgroups.18,21

No fluorescence was observed, when the solu-tions of polyamides PA1 and PA2 in DMF wereexposed to a UV lamp. It has been reported thatother analogous polyamides derived from 4,40-diamino-3,5,30,50-tetraphenyl-p-terphenyl,17

4-amino-40-carboxy-29,69-diphenyl-p-terphenyl18

and 29,69,3-,5--tetraphenyl- or tetra(4-biphen-ylyl)-4,400-diamino-p-quinquephenyl21 were fluo-

rescent. Since the rodlike oligophenyl moietyshould be the chromophore unit, the reasons forwhich the present polyamides did not exhibit flu-orescence are unknown and need further investi-gation. The absence of fluorescence can be causedby ion separation during the excitation proce-dure.24–27 In addition, when the solutions of poly-amides in CCl3COOH were examined under po-larization microscope, they did not display lyo-tropic behavior.

The thermal properties of polymers were inves-tigated by DSC and TMA. The DSC thermogramsof polymers at the first heating showed a broadendothermic peak in the range of 80–100°C,which should be attributed to the evaporation ofwater traces. In contrast, the DSC traces at thesecond heating did not display any distinct tran-sition up to 300°C. The glass transition (Tg) tem-peratures of polymers were determined by the

Figure 5. TMA thermograms of polymers. Condi-tions: N2 flow, 60 cm3/min; heating rate, 20°C/min.

Figure 6. TGA thermograms in N2 and air of poly-mers PA2, PIP1, and PIB2. Conditions: Gas flow, 60cm3/min; heating rate, 20°C/min.

Table II. Solubilities of Polymersa

Polymer

Solventsb

DMF NMP DMAc CCl3COOH H2SO4 TCE DCB CH

PA1 1c 1c,d 1c 1 12 2 2 2PA2 1c 1c 1c 1 12 2 2 2PIP1 12 12 12 12 2 2 2 2PIB1 12 12 12 12 2 2 2 2PIP2 12 12 12 12 2 2 2 2PIB2 12 12 12 12 2 2 2 2

a Solubility: 1, soluble in hot solvent; 12, partially soluble; 2, insoluble.b DMF, N,N-dimethylformamide; NMP, N-methylpyrrolidone; DMAc, dimethylacetamide; TCE, 1,1,2,2-tetrachloroethane;

DCB, 1,2-dichlorobenzene; CH, cyclohexanone.c Solvent containing 5% wt / wt LiCl.d Gel is formed on cooling.

22 MIKROYANNIDIS

TMA method using a loaded penetration probe.They were obtained from the onset temperaturesof these transitions recorded at the second heat-ing (Figure 5). Polymers PA1, PA2, PIP1, PIP2,PIB1, and PIB2 showed Tgs at 304, 310, 316,325, 307, and 337°C, respectively. It seems thatthe polymers derived from diamine 6 displayedhigher Tgs than the corresponding ones preparedfrom diamine 3, owing to their longer rodlike seg-ment of backbone. On the other hand, all poly-mers did not show melting as it was confirmed byboth DSC and TMA.

The thermal stability of polymers was ascer-tained by TGA and IGA. Figure 6 presents typicalTGA traces of polymers PA2, PIP1 and PIB2 inN2 and air. The initial decomposition tempera-ture (IDT), the polymer decomposition tempera-ture (PDT), and the maximum polymer decompo-sition temperature (PDTmax) in both N2 and air aswell as the anaerobic char yield (Yc) at 800°C forall polymers are listed in Table III. IDT and PDTwere determined for the temperature at which 0.5and 10% weight losses were observed, respec-tively. PDTmax corresponds to the temperature atwhich the maximum rate of weight loss occurred.

The polymers were stable up to 377–422°C inN2 and 355–397°C in air and afforded anaerobicchar yields of 57–69% at 800°C. The polymerscontaining p-quinquephenyl segments were morethermally stable than the corresponding ones car-rying p-terphenyl segments, since they showednot only higher IDT both in N2 and air but alsohigher Yc. Among the synthesized polymers,PIP2 seemed to be the most thermally stable,since it displayed the highest values of IDT and

Yc. Finally, the polymers showed weight losses of7.9–17.1%, after 20 h isothermal aging at 300°Cin static air (Table III).

CONCLUSIONS

A simple and convenient method, which proceedsthrough pyrylium salts, was applied for the syn-thesis of two new aromatic diamines 3 and 6.Rigid-rod polyamides and polyimides were pre-pared from them. All polymers were amorphous.Polyamides, which showed an enhanced hydro-philicity, dissolved upon heating in polar aproticsolvents containing LiCl as well as CCl3COOH.Their solutions were not fluorescent and did notdisplay lyotropic behavior. All polymers exhibitedTgs at high temperatures (304–337°C). The poly-mers bearing p-quinquephenyl segments in themain chain showed higher Tgs as well as thermalstability than the corresponding ones containingp-terphenyl segments. No weight loss was ob-served up to 377–422°C in N2, and the anaerobicchar yields were 57–69% at 800°C.

REFERENCES AND NOTES

1. Jr. Jackson, J. W. Br Polym J 1980, 12, 54.2. Kricheldorf, H. R.; Burger, R. J Polym Sci Part A

Polym Chem 1994, 32, 355.3. Meyer, W. R.; Gentile, F. T.; Suter, U. W. Macro-

molecules 1991, 24, 642.4. Aharoni, S. M. Polym Adv Techn 1995, 6, 373.

Table III. Thermal Stabilities of Polymers

Polymer

In N2 In Air

wt Losse

(%)IDTa

(°C)PDTb

(°C)PDTmax

c

(°C)Ycd

(%)IDT(°C)

PDT(°C)

PDTmax

(°C)

PA1 377 489 519 57 355 456 437 17.1PA2 381 493 521 60 359 433 452 13.4PIP1 400 545 608 62 368 437 453 15.0PIB1 404 533 586 59 370 456 437 10.0PIP2 422 563 619 69 397 461 493 12.3PIB2 415 549 604 68 385 441 460 7.9

a Initial decomposition temperature.b Polymer decomposition temperature.c Maximum polymer decomposition temperature.d Char yield at 800°C.e Weight loss after 20 h isothermal ageing at 300°C in static air.

RIGID-ROD POLYAMIDES 23

5. Hatke, W.; Schmidt, H. W.; Heitz, W. J Polym SciPart A Polym Chem 1991, 29, 1387.

6. Morgan, P. W. Macromolecules 1977, 10, 1381.7. Jadhav, J. Y.; Preston, J.; Krigbaum, W. R. J Polym

Sci Part A Polym Chem 1989, 27, 1175.8. Jadhav, J. Y.; Preston, J.; Krigbaum, W. R. Macro-

molecules 1988, 21, 540.9. Hatke, W.; Land, H. L.; Schmidt, H. W.; Heitz, W.

Makromol Chem Rapid Communn 1991, 12, 235.10. Kricheldorf, H. R.; Schmidt, B. Macromolecules

1992, 25, 5471.11. Kricheldorf, H. R.; Schmidt, B.; Burger, R. Macro-

molecules 1992, 25, 5465.12. Schmitz, L.; Rehahn, M. Macromolecules 1993, 26,

4413.13. Cheng, S. Z. D.; Arnold, F. E.; Zhang, A.; Hsu,

S. L. C.; Harris, F.W. Macromolecules 1991, 24,5856.

14. Schmitz, L.; Rehahn, M.; Ballauff, M. Polymer1993, 34, 646.

15. Brandelik, D.; Field, W. A.; Arnold, F. E. PolymPrepr 1987, 28(1), 88.

16. Harris, F. W.; Lin, S. H.; Li, F.; Cheng, S. Z. D.Polymer 1996, 37, 5049.

17. Spiliopoulos, I. K.; Mikroyannidis, J. A. Macromol-ecules 1996, 29, 5313.

18. Spiliopoulos, I. K.; Mikroyannidis, J. A. Macromol-ecules 1998, 31, 522.

19. Mikroyannidis, J. A. Polymer, in press.20. Spiliopoulos, I. K.; Mikroyannidis, J. A. Polymer

1997, 38, 2733.21. Spiliopoulos, I. K.; Mikroyannidis, J. A. Macromol-

ecules 1998, 31, 515.22. Spiliopoulos, I. K.; Mikroyannidis, J. A. Macromol-

ecules 1998, 31, 1236.23. Zimmermann, T.; Fischer, G. W. J Prakt Chem

1987, 329(6), 975; Chem Abstr 988, 109, 169929q.24. Czarnick, A. W. Acc Chem Res 1994, 27, 302.25. de Silva, A. P.; Guanarante, H. Q. N.; McCoy, C. P.

J Chem Soc Chem Commun 1996, 2399.26. de Silva, A. P.; Guanarante, H. Q. N. Nature 1993,

364, 42.27. Huston, M. E.; Haider, K. W.; Czarnick, A. W. J Am

Chem Soc 1988, 110, 4460.

24 MIKROYANNIDIS