soluble, uv-fluorescent polyamides and polyimides containing oligophenyls in the main chain and...

Macromol. Chem. Phys.200,2327–2337 (1999) 2327

Soluble, UV-fluorescent polyamides and polyimides containingoligophenyls in the main chain and highly phenylated side groups

Dedicated to Prof.A. K. Tsolison the occasion of his forthcoming 65th birthday

John A. Mikroyannidis

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

(Received: February 19, 1999; revised April 26, 1999)

SUMMARY: Starting from pyrylium salts four new aromatic diamines were synthesized and used for thepreparation of rigid-rod polyamides and polyimides. The polymers containp-terphenyl orp-quinquephenylmoieties in the backbone and pendent groups, which consist of 1,3,5-triphenylbenzene or triphenylmethanesegments. Most of the polymers show excellent solubility in various common solvents and even in 1,1,2,2-tetrachloroethane. Polyamides with pendent groups of triphenylmethane possess enhanced hydrophilicity.The solutions of all polymers in DMF show UV-fluorescence with emission maxima in the range of 350–367 nm. The polymers are amorphous and theirTg values range from 250 to 3108C. They display an outstan-ding thermal stability, i.e., are stable up to 366–4118C and afford char yields of 64–81% at 8008C in N2.

IntroductionRigid-rod polymers are heat-resistant materials with anattractive combination of chemical, physical and mechan-ical properties, giving easily lyotropic solutions1–4). Onthe other hand, their use in some applications is preventeddue to their poor processability caused by limited solubi-lity in common organic solvents and by high glass-transi-tion or melting temperatures. Thus, considerable researchhas been carried out aimed at developing rigid-rod poly-mers that have better processability while retaining theiroutstanding thermal and mechanical properties. Theintroduction of thermally stable bulky pendent groupsalong the polymer backbone is an approach for improvingthe solubility of these materials. A literature surveyrevealed that various aromatic substituents have beenused to prepare soluble rigid-rod polyamides5–14) andpolyimides15–19).

In this respect, we have synthesized certain rigid-rodpolymers starting from pyrylium salts. In particular, solu-ble rigid-rod polyamides and polyimides have been pre-pared in our laboratory from substituted aromatic dia-mines of p-terphenyl20–22) or biphenyl23). We have alsoprepared blue light-emitting, rigid-rod polyamides andpolyimides from an aromatic diamine ofp-quinquephenylbearing phenyl or 4-biphenylyl side groups24). In addition,we have synthesized soluble phenyl- or alkoxyphenyl-substituted rigid polyamides and polyimides containingm-terphenyls in the main chain25). More recently, we haveprepared rigid-rod polyamides and polyimides carryingp-terphenyl orp-quinquephenyl moieties in backbone aswell as naphthyl pendent groups26).

In the present investigation we report the synthesis andcharacterization of a new series of very soluble rigid-rodpolyamides and polyimides, which were obtained through

pyrylium salts. The synthesized polymers contain oligo-phenyl segments in the main chain and highly phenylatedbulky pendent groups. The enhanced solubility and pro-cessability in combination with the UV-fluorescence andthe outstanding heat-resistance are some attractive andinteresting features for these rigid-rod polymers.

Experimental part

Characterization methods

Melting temperatures were determined on an electrothermalmelting point apparatus IA6304 and are uncorrected. IRspectra were recorded on a Perkin-Elmer 16PC FT-IR spec-trometer with KBr pellets.1H NMR spectra were obtainedusing a Bruker spectrometer (400 MHz).13C NMR(100 MHz) spectra were obtained with a Bruker spectro-meter. The NMR spectra were recorded using DMSO-d6 assolvent. Chemical shifts (d values) are given in parts per mil-lion with tetramethylsilane as an internal standard. UV-visspectra were recorded on a Beckman DU-640 spectrometerwith spectrograde DMF. The emission spectra were meas-ured with a Perkin Elmer LS50B luminence spectrometer ina DMF solution or using films prepared by spin coating onquartz plates. DSC and TGA were performed on a DuPont990 thermal analyzer system. Ground polymer samples ofabout 10 mg each were examined by TGA and isothermalgravimetric analysis (IGA), and the weight loss comparisonswere made between comparable specimens. The DSC ther-mograms were obtained at a heating rate of 108C/min in N2

atmosphere at a flow rate of 60 cm3/min. Dynamic TGAmeasurements were made at a heating rate of 208C/min inatmospheres of N2 or air at a flow rate of 60 cm3/min. Ther-momechanical analysis (TMA) was recorded on a DuPont943 TMA using a loaded penetration probe at a scan rate of108C/min in N2 with a flow rate of 60 cm3/min. The TMA

Macromol. Chem. Phys.200, No. 10 i WILEY-VCH Verlag GmbH, D-69451 Weinheim 1999 1022-1352/99/1010–2327$17.50+.50/0

2328 J.A. Mikroyannidis

experimentswere conductedat least in duplicateto assuretheaccuracyof theresults.TheTMA specimenswerepelletsof 8 mm diameterand2 mm thicknesspreparedby pressingpowderof polymerfor 3 min under5–7 kpsiat ambienttem-perature.The inherentviscositiesof polymerswere deter-minedfor solutionsof 0.5g/100ml in DMAc at 308C usingan Ubbelohdesuspendedlevel viscometer. Elementalana-lyses were carried out with a Hewlett-Packardmodel 185analyzer. The wide-angle X-ray diffraction patternswereobtainedfor powderspecimensonanX-ray PW-1840Philipsdiffractometer.

To determinethe equilibrium water absorption,polymersampleswere previously conditionedat 1208C in an ovenfor 12 h. They were subsequentlyplaced in a desiccatorwhere65%r.h. (relativehumidity) wasmaintainedby meansof anoversaturatedaqueoussolutionof NaNO2 at 208C, andwereperiodicallyweighed.

Reagentsandsolvents

3-Nitrobenzaldehydeand triphenylmethanewere recrystal-lized from ethanol95%. 1,4-Benzenedicarboxaldehydewasrecrystallized from distilled water. Acetyl chloride wasrefluxed with PCl5 for severalhours to remove traces ofacetic acid, and then it was distilled. 4-Nitrophenylaceticacid sodium salt was prepared by reacting equimolaramountsof 4-nitrophenylaceticacid with aqueoussodiumhydroxide. Terephthaloylchloride was recrystallizedfromhexane.Pyromellitic dianhydride (PMDA) and benzophe-none tetracarboxylicdianhydride (BTDA) were recrystal-lized from acetic anhydride. Dimethylacetamide(DMAc)and1,2-dichloroethaneweredried by distillation over CaH2.1,3,5-Triphenylbenzene,acetic anhydride,boron trifluorideetherate,1,4-dioxaneand hydrazinehydrate were used assupplied.

Preparationof startingmaterials(Schemes1 and2)

4-Acetyl-(39,59-diphenyl)biphenyland1-(4-diphenylmethyl)-phenylethanonewerepreparedby acetylationof 1,3,5-triphe-nylbenzene27) andtriphenylmethane28) usingaceticanhydrideandacetylchloride,respectively, accordingto reportedmeth-ods.

4-(3-Nitrophenyl)-2,6-bis[4-(39,59-diphenyl)biphenylyl]pyr-ylium tetrafluoroborate (1a): A flask was charged with amixture of 3-nitrobenzaldehyde(0.26g, 1.75mmol), 4-acetyl-(39,59-diphenyl)biphenyl (1.04g, 3.00mmol), 1,2-dichloroethane(20 mL) andboron trifluoride etherate(0.55mL, 4.38mmol). The mixture wasstirred and refluxed in astreamof N2 for 4 h, and then it was concentratedundervacuum. A mixture of ethyl acetate/ether(1:2 v/v) wasaddedto the residue,and the dark red precipitatewas fil-tered, washedwith ether and dried to afford 1a. It wasrecrystallizedfrom a mixture of 1,4-dioxane/ether(1:2 v/v)(1.18g, 75%,mp 184–1868C).

IR (KBr, cm–1): 1618, 1598, 1494, 1456 (aromaticandpyrylium structure);1528,1348(NO2); 1078(br, BF4

–).1H NMR (DMSO-d6): d = 8.83–8.07 (m, 4H, aromatic

metato O+ andortho to NO2); 7.83–7.14(m, 36H, otheraro-matic).

4-(3-Nitrophenyl)-2,6-bis[4-diphenylmethyl)phenyl]pyry-lium tetrafluoroborate (1b): Compound1b was preparedaccordingto the proceduredescribedfor 1a from the reac-tion of 3-nitrobenzaldehyde(0.50g, 3.31mmol) with 1-(4-diphenylmethyl)phenylethanone (1.89g, 6.62mmol) andboron trifluoride etherate (1.04 mL, 8.27mmol) in 1,2-dichloroethane(20 mL). The reactionmixture was concen-trated under vacuum,and ether was addedto the residue.The yellow precipitatewas filtered, washedwith etheranddriedto afford 1b. It waspurified by recrystallizationfrom amixture of ethyl acetate/ether(1:1 v/v) (1.58g, 62%, mp116–1188C).

IR (KBr, cm–1): 1620, 1599, 1496, 1460 (aromaticandpyrylium structure);1528,1350(NO2); 1082(br, BF4


metato O+ andortho to NO2); 7.80–7.16(m, 30H, otheraro-matic);5.84–5.70(m, 2H, aliphatic).

4,399-Dinitro-29,69-bis[4-(39,59-diphenyl)biphenylyl]-p-ter-phenyl (2a): A mixture of 1a (2.23g, 2.48mmol), 4-nitro-phenylacetic acid sodium salt (1.00g, 4.96mmol), andaceticanhydride(5 mL) wasstirredandrefluxed for 4 h. Itwas cooledat 08C and the precipitatewas filtered, washedwith water, then with methanoland dried to afford 2a as apaleyellow-brownsolid. It wasrecrystallizedfrom a mixtureof chloroform/ether (1:1 v/v) (2.15g, 93%, mp 156–1588C).

IR (KBr, cm–1): 1596(aromatic);1524,1346(NO2).1H NMR (DMSO-d6): d = 8.50–8.16 (m, 4H, aromatic

ortho to NO2); 7.82–7.38(m, 40H, otheraromatic).4,399-Dinitro-29,69-bis[1-(4-diphenylmethyl)phenyl]-p-ter-

phenyl (2b): Compound2b was preparedas a pale brownsolid in 86% yield (1.11 g) from the reactionof 1b (1.24g,1.60mmol) with 4-nitrophenylacetic acid sodium salt(0.65 g, 3.20mmol) andaceticanhydride(3.5mL) accordingto theproceduredescribedfor 2a. It wasrecrystallizedfroma mixtureof chloroform/ether(2:1 v/v); mp 120–1228C.

IR (KBr, cm–1): 1598(aromatic);1526,1348(NO2).1H NMR (DMSO-d6): d = 8.58–8.12 (m, 4H, aromatic

ortho to NO2); 7.86–6.98 (m, 34H, other aromatic);5.73–5.54(m, 2H, aliphatic).

4,399-Diamino-29,69-bis[4-(39,59-diphenyl)biphenylyl]-p-ter-phenyl (3a): A flask was charged with a mixture of 2a(1.13 g, 1.22mmol), 1,4-dioxane(15 mL) and a catalyticamountof palladium 10% on activatedcarbon.Hydrazinehydrate(5 mL) wasaddeddropwiseto thestirredmixture at1018C and refluxing was continuedfor 64h. The mixturewas subsequentlyfiltered and the filtrate was poured intowater. The precipitatewas filtered, washedwith water anddried to afford 3a as a light yellow solid. It was recrystal-lized from a mixture of 1,4-dioxane/water(2:1 v/v) (0.90g,85%,mp 193–1958C).

IR (KBr, cm–1): 3415, 3345 (N1H stretching); 1618(N1H deformation); 1594, 1496, 1448 (aromatic); 1280(C1N stretching).

1H NMR (DMSO-d6): d = 7.86–7.42 (m, 37H, aromaticapartfrom thoseortho andmetato NH2); 6.66(m, 3H, aro-matic meta to NH2); 6.51 (m, 4H, aromaticortho to NH2);5.14(br, 4H, NH2).

13C NMR (DMSO-d6): d = 142.54,141.03,131.16,129.81,128.57,128.05,127.18,126.16,125.28,114.91.

Soluble,UV-fluorescentpolyamidesandpolyimidescontaining oligophenyls in themainchain... 2329

C66H48N2 (869.1) Calc. C 91.21 H 5.57 N 3.22Found C 90.92 H 5.63 N 3.18

4,399-Diamino-29,69-bis[1-(4-diphenylmethyl)phenyl]-p-ter-phenyl (3b): Compound3b was preparedas a light brownsolid in 97%yield (0.94g) by catalytichydrogenationof 2b(1.05g, 1.30mmol) utilizing hydrazinehydrate (4 mL) in1,4-dioxane(15 mL) accordingto the proceduredescribedfor 3a. It wasrecrystallizedfrom a mixture of 1,4-dioxane/water(1:1 v/v); mp 155–1578C.

IR (KBr, cm–1): 3420, 3342 (N1H stretching); 1620(N1H deformation);1602, 1492, 1450 (aromatic); 1282(C1N stretching).

The1H NMR and13C NMR spectraareshownin Fig. 2.


4,49-(1,4-Phenylene)bis{2,6-bis[4-(39,59-diphenyl)bipheny-lyl]}pyrylium tetrafluoroborate(4a): A mixture of 1,4-ben-zenedicarboxaldehyde(0.25g, 1.82mmol), 4-acetyl-(39,59-diphenyl)biphenyl (2.53g, 7.28mmol), 1,2-dichloroethane(20 mL) and boron trifluoride etherate(1.2 mL, 9.1mmol)wasstirredandrefluxedin a streamof N2 for 4 h. It wassub-sequentlyconcentratedundervacuumand etherwas addedto the residue. The dark brown precipitate was filtered,washedwith etherand dried to afford 4a. It was recrystal-lized from a mixture of 1,4-dioxane/ether(1:2 v/v) (2.55g,86%,mp 219–2218C).

IR (KBr, cm–1): 1622, 1596, 1492, 1458 (aromaticandpyrylium structure);1082(br, BF4


metato O+); 8.22–7.42(m, 72H, otheraromatic).4,49-(1,4-Phenylene)bis{2,6-bis[1-(4-diphenylmethyl)phe-

nyl]}pyrylium tetrafluoroborate (4b): Compound4b waspreparedaccordingto the proceduredescribedfor 4a fromthe reaction of 1,4-benzenedicarboxaldehyde(0.27 g,2.05mmol) with 1-(4-diphenylmethyl)phenylethanone(2.34g, 8.18mmol) and boron trifluoride etherate(1.3 mL,10.23mmol) in 1,2-dichloroethane(20 mL). The reactionmixture was concentratedunder vacuumand ethyl acetatewasaddedto the residue.The yellow-brownprecipitatewasfiltered, washedwith ethyl acetateanddried to afford 4b. Itwas recrystallizedfrom a mixture of chloroform/ether (2:1v/v) (1.89g, 67%,mp 241–2438C).

IR (KBr, cm–1): 1623, 1598, 1492, 1450 (aromaticandpyrylium structure);1081,1060(BF4

–).1H NMR (DMSO-d6): d = 8.51 (s, 4H, aromaticmeta to

O+); 7.68–6.79 (m, 60H, other aromatic); 5.88–5.57 (m,4H, aliphatic)

29,69,39995999-Tetrakis[4-(39,59-diphenyl)biphenylyl]-4,4999-di-nitro-p-quinquephenyl(5a): A mixture of 4a (1.20g,0.74mmol), 4-nitrophenylaceticacid sodium salt (0.60g,2.95mmol) andpropionicanhydride(2 mL) wasstirredandrefluxedfor 4 h. It wascooledat 08C andtheprecipitatewasfiltered, washedwith water, thenwith methanolanddried toafford 5a asa light yellow-brownsolid. It wasrecrystallizedfrom a mixture of chloroform/ether(2:1 v/v) (1.17g, 94%,mp 166–1688C).

IR (KBr, cm–1): 1596(aromatic);1518,1344(NO2).

1H NMR (DMSO-d6): d = 8.70–8.53 (m, 4H, aromaticortho to NO2); 7.79–7.12(m, 80H, otheraromatic).

29,69,3999,5999-Tetrakis[1-(4-diphenylmethyl)phenyl]-4,4999-di-nitro-p-quinquephenyl(5b): Compound5b waspreparedasa brown solid in 91% yield (2.84g) from the reactionof 4b(2.99 g, 2.17mmol) with 4-nitrophenylaceticacid sodiumsalt(1.76g, 8.67mmol) andaceticanhydride(5 mL) accord-ing to the proceduredescribedfor 5a. It was recrystallizedfrom a mixture of chloroform/ether(2:1 v/v); mp 152–1548C.

IR (KBr, cm–1): 1598(aromatic);1520,1346(NO2).1H NMR (DMSO-d6): d = 8.12 (m, 4H, aromaticortho to

NO2); 7.86–6.70 (m, 68H, other aromatic);5.60–5.53 (m,4H, aliphatic).

29,69,3999,5999-Tetrakis[4-(39,59-diphenyl)biphenylyl]-4,4999-di-amino-p-quinquephenyl (6a): A flask was charged with amixtureof 5a (1.41g, 0.83mmol), 1,4-dioxane(15 mL) anda catalytic amountof palladium 10% on activatedcarbon.Hydrazine hydrate(4 mL) wasaddeddropwiseto thestirredmixture at 1018C andrefluxing wascontinuedfor 64 h. Themixture wassubsequentlyfiltered, and the filtrate wascon-centratedundervacuum.Waterwasaddedto theresidue,and6a wasobtainedasa palebrown solid. It wasrecrystallizedfrom a mixture of 1,4-dioxane/water(2:1 v/v) (1.31g, 97%,mp 208–2108C).

IR (KBr, cm–1): 3450, 3375 (N1H stretching); 1620(N1H deformation); 1594, 1512, 1450 (aromatic); 1280(C1N stretching).

1H NMR (DMSO-d6): d = 7.83–7.40 (m, 76H, aromaticapartfrom thoseortho andmetato NH2); 6.61(m, 4H, aro-matic meta to NH2); 6.53 (m, 4H, aromaticortho to NH2);5.17–5.09(br, 4H, NH2).

13C NMR (DMSO-d6): d = 143.46,142.56,141.91,140.98,139.58, 132.98, 130.55, 128.82, 127.26, 125.81, 125.34,124.27,115.38.


29,69,3999,5999-Tetrakis[1-(4-diphenylmethyl)phenyl]-4,4999-di-amino-p-quinquephenyl(6b): Compound6b was preparedas a light yellow solid in 92% yield (2.99g) by catalytichydrogenationof 5b (3.39g, 2.35mmol) utilizing hydrazinehydrate(8 mL) in 1,4-dioxane(30 mL) accordingto thepro-ceduredescribedfor 6a. It wasrecrystallizedfrom a mixtureof 1,4-dioxane/water(2:1 v/v); mp 172–1748C.

IR (KBr, cm–1): 3453, 3370 (N1H stretching); 1620(N1H deformation);1600, 1512, 1492, 1448 (aromatic);1280(C1N stretching).

1H NMR (DMSO-d6): d = 7.76–7.07 (m, 64 H, aromaticapartfrom thoseortho andmetato NH2); 6.67(m, 4 H, aro-matic meta to NH2); 6.51 (m, 4 H, aromaticortho to NH2);5.67–5.59(m, 4 H, aliphatic);5.06(br, 4H, NH2).

13C NMR (DMSO-d6): d = 145.46,144.47,142.57,142.27,141.54, 141.06, 139.09, 138.44, 133.10, 130.56, 129.97,128.77, 128.28, 126.25, 125.82, 124.86, 124.07, 122.61,121.91,115.80,114.71,114.22,55.61.

C106H80N2 (1381.8) Calc. C 92.14H 5.84 N 2.03Found C 91.82H 5.87 N 2.08


Preparationof polymers

PolyamidesM1a, M1b, M2a and M2b(Chart 1): The pre-paration of M1a is given as a generalprocedurefor thesynthesisof polyamides:A flask waschargedwith a solutionof 3a (1.0500g, 1.21mmol) in DMAc (15 mL) containing5wt.-% LiCl. To the mixture 0.5 mL of propyleneoxide wasadded.Terephthaloylchloride (0.2453g, 1.21mmol), dis-solvedin DMAc (5 mL), wasaddeddropwiseto the stirredsolutionat –108C underN2. Stirring of themixturewascon-tinuedat this temperaturefor 5 h andthenat room tempera-ture overnight in a streamof N2. It was pouredinto water,and the pale yellow precipitatewas filtered, washedfirstlywith water, then with hot acetoneand dried to afford M1a(1.03g, 85%).

PolyimidesP1b, B1b, P2bandB2b (Chart2): As a typicalprocedurefor thepreparationof polyimides,thesynthesisofP1b is given: PMDA (0.1171g, 0.54mmol) was addedatonce to a stirred solution of 3b (0.4000g, 0.54mmol) inDMAc (15 mL) at 08C. Themixture wasstirredat that tem-peraturefor 2 h andthenat room temperaturefor 6 h underN2. Acetic anhydride (5 mL) and pyridine (2 mL) wereaddedto the stirred solution, and it was heatedat 1008Covernight. It was subsequentlypoured into water, and thebrown precipitatewas filtered, washedfirstly with water,thenwith hot acetoneanddried into a vacuumovenat about1508C to afford P1b (0.47g, 95%).

The reactionyields, the inherentviscositiesand the ele-mentalanalysesfor all polymersaregivenin Tab.1.

Resultsand discussion

Synthesisandcharacterizationof monomers

Thesubstitutedaromaticdiamines3 and6 were preparedaccording to the synthetic route depicted in Schemes1

and 2. Their synthesiswas achieved through pyryliumsalts obtainedby reacting aromatic aldehydeswith substi-tutedacetophenones29). Thepyrylium saltsreactedwith 4-nitrophenylacetic acid sodiumsalt in aceticanhydride toafford substituted oligophenyls30). The monomerswerecharacterizedusing elementalanalysis, FT-IR as well as1H and13C NMR spectroscopy.

The properties of the synthesized polymers areundoubtedly influenceduponthestructuralcharacteristicsof the parentdiamines3 and6. They contain p-terphenylor p-quinquephenylsegments as well as bulky pendentgroupspossessing thestructureof 1,3,5-triphenylbenzeneor triphenylmethane. In addition,diamines3 carry meta-linkageswhich usually lead to a significant increaseinchain flexibility and thus solubility and may also affectthe electronic properties of polymers. Furthermore, dia-mines3 are non-symmetric, leadingto the possibility ofdifferent constitutional regularities of polyamides pre-pared6).

To estimate the structuralcharacteristicsof diamines,their geometrieswere calculatedby means of a modelingsystem. Fig. 1 presentsthe optimized geometriesof 6aand 6b, which were calculated by the CS Chem3DProversion 3.5 modelingsystem.It seemsthat in both dia-minesthethreecentralringsof p-quinquephenylsegmentare almost coplanar. In contrast,due to the interactionscausedby thebulky sidesubstituents beingat ortho posi-tion, the two terminal ringsof p-quinquephenyl aremoretwisted. The pendentgroups deviate significantly fromthe coplanar conformation, especially in the case of 6b.The three rings of the triphenylmethanemoiety can befreely rotated around their bonds, thus increasing themolecule disorder. Obviously, 6a is more coplanar than

Scheme1:


6b because the factor of deviation from plane (FDP) is0.870and1.808,respectively. Note that thevalueof FDPis zerofor anabsolutely planar structure.

TheIR andNMR spectraof thesynthesizedmonomerswere consistent with their structures.Fig. 2 presents the1H NMR and 13C NMR spectraof diamine 3b. The 1HNMR spectrum showed peaks at ppm 7.53–6.80 (m,31H, aromaticapart from thoseortho andmetato NH2);6.61 (m, 3H, aromatic meta to NH2); 6.50 (m, 4H, aro-matic ortho to NH2); 5.68–5.58 (m, 2H, aliphatic) and4.97 (br, 4H, NH2). Assignments of peaksfor the 13CNMR spectrum are given in the figure. In this spectrumthe aliphatic protons displayed a downfield peak at56 ppm.

Synthesisandstructuralcharacterizationof polymers

A seriesof rigid-rod polyamides and polyimides wereprepared,the structuresof which are shown in Charts1and 2. Polyamides M1 and M2 were synthesized fromthe reactions of 3 and6, respectively, with terephthaloylchloride by the low-temperature solution polycondensa-tion in the presenceof propyleneoxideasanacid accep-tor. All the polycondensations proceededhomogeneouslygiving viscous polyamide solutions. Polyimides P1 andP2werepreparedby reacting3 or 6 with PMDA, whereasB1 and B2 from the reactionsof thesediamineswithBTDA using the two-step procedure. Cyclodehydrationwascarriedoutby acombinationof chemical andthermal

Scheme2:

Fig. 1. Optimized geometriesfor diamines6a (upper) and6b(lower) (CS Chem3Dpro MolecularModeling System,Version3.5,1995;CambridgeSoft Corporation,1995)


means,andthe reaction mixture gelled only for P2b andB2b. The yieldsof the preparation reactions for all poly-merswerealmostquantitative (81–96%)andtheir inher-entviscositiesrangedfrom 1.10to1.72dL/g (Tab.1).

Structural characterization of polymers was accom-plishedby elementalanalyses,FT-IR as well as 13C and1H NMR spectroscopy. Fig. 3 presentstypical FT-IR spec-tra of polymersM1a and P1b. Polyamide M1a showedcharacteristic absorptions at 3418 (N1H stretching),1672 (C=O), 1594 (aromatic), 1514 (N1H deformation)and 1315, 1250 cm–1 (C1N stretching). Polyimide P1bdisplayed absorptions at 1776, 1726, 1368 and 1114cm–1 associated with the imide structure. The 1H NMRspectrum of polyamide M2a in a DMSO-d6 solutionshowedpeaksat ppm 10.29(NHCO), 7.96 (aromaticofterephthalic acid segment) and 7.88–6.90 (other aro-matic). Fig. 4 presentsthe 13C NMR spectrum of M2a

Fig. 2. 1H NMR (upper)and 13C NMR (lower) spectra of diamine3b in a DMSO-d6

solution

Fig. 3. FT-IR spectraof polymersM1 a andP1b


with most probableassignments of peaks. The upfieldpeakat 164ppmwasassigned to theamidecarbonyl.

Crystallinity, hydrophilicity andsolubility of polymers

The crystallinity of polymers wasevaluatedby means ofX-ray diffractograms.Fig. 5 presentsthe X-ray diffracto-gramsof the synthesized polyamides.As expected,bothpolyamidesand polyimides were amorphous, with some

low-level ordering.Theamorphouscharacterof polymerswas evidently attributed to the bulky pendentgroups,which created poor packing and high free volume. Inaddition, thepolymersderivedfrom diamines3 possessa

Tab.1. Yields,inherentviscositiesandelemental analysesof polymers

Polymer Yieldin %

ginh

dL=gEmpirical formula Elementalanalyses(in %)

C H N

M1 a 85 1.26a) (C74H49N2O2)n (998.2)n Calc. 89.04 4.95 2.81Found 88.90 4.98 2.74

M1 b 86 1.10a) (C64H45N2O2)n (874.1)n Calc. 87.95 5.19 3.20Found 87.63 5.22 3.16

M2 a 89 1.53a) (C134H90N2O2)n (1760.2)n Calc. 91.44 5.15 1.59Found 91.12 5.19 1.53

M2 b 81 1.45a) (C114H82N2O2)n (1511.9)n Calc. 90.56 5.47 1.85Found 90.38 5.43 1.87

P1b 95 1.64b) (C66H42N2O4)n (927.1)n Calc. 85.51 4.57 3.02Found 85.18 4.61 3.07

B1b 92 1.57b) (C73H46N2O5)n (1031.2)n Calc. 85.03 4.50 2.72Found 84.87 4.43 2.79

P2b 94 1.72b) (C116H78N2O4)n (1563.9)n Calc. 89.09 5.03 1.79Found 88.95 5.08 1.72

B2b 96 1.67b) (C123H82N2O5)n (1668.0)n Calc. 88.57 4.96 1.68Found 88.31 4.93 1.72

a) Inherent viscosityin DMAc (0.5g/dL) at 308C.b Inherent viscosityof intermediate poly(amicacids)in DMAc (0.5g/dL) at 308C.

Chart1: Chart2:


para-metaorientationthatcontributed to their amorphousnature.Thus,thelow degreeof crystallinity of thesepoly-mers was reflected in their enhanced solubility (see

below). PolyamidesM1a andM2a, ascomparedto M1band M2b, displayed a stronger and sharperreflectionpeak approximately at 2H = 208, indicating a slightlyhigher packing density31). This behaviour is reasonablebecause,asit wasshown by themodeling system, the lat-eral substituents of triphenylmethaneare less coplanarandcausesignificantly higherdisorder in chains thanthesubstituentsof 1,3,5-triphenylbenzene.

The equilibrium water absorption of polyamideswasdetermined andcorrelatedwith their hydrophilicity. Fol-lowing an exposure time of 100h, polyamides M1a,M1b and M2a, M2b displayed an isothermal wateruptake of 1.97, 6.83, 1.71 and 4.49%,respectively. Thecorresponding numbersof moles of absorbedwater peramide equivalentweight (NMAW) were0.55,1.66, 0.84and 1.89.The remarkably higher hydrophilicity of poly-amidesM1b andM2b, carryingpendentgroupsof triphe-nylmethane,was assumedto be due to the formation oflarger openings in the chain packing that increasedthewater accessibility. Generally, thesepolyamides showedhigher hydrophilicity than our previously synthesizedanalogousrigid-rod polyamideswith phenyl or 4-biphe-nylyl pendentgroups21,24) as well as with naphthyl pen-dent groups26), the NMAW valuesof which were 0.15–0.57and0.84–0.96, respectively.

The bulky pendent groups of polymerspreventedalsostrong interactionsthusimproving their solubility, despite

Fig. 4. 13C NMR spectrum of polyamideM2 a in a DMSO-d6 solution

Fig. 5. Wide-angleX-ray scatteringcurvesfor polyamides


the fact that the polymerscontained rodlike segmentsofp-terphenyl or p-quinquephenylin themain chain.Tab.2summarizes the qualitative solubility of polymers. It isnoteworthy that all polymers, except P2b and B2b,showedanexcellent solubility, beingsolublein all testedsolventsat room temperatureor upon heating. They dis-solvednot only in polarorganic solventslike DMF, NMP,DMAc without the addition of inorganicsaltsbut alsoinhalogenated aliphatic solventssuchas1,1,2,2-tetrachlor-oethane.However, P2b andB2b exhibited poor solubilityowing to the combination of the longer rodlike segmentandthemorerigid imide structure.

Optical propertiesof polymers

Theoptical propertiesof polymerswerealsoinvestigated.The UV-visible spectraof polyamidesin a DMF solutionshowedmaxima in the rangeof 270–310nm. All poly-merswereUV-fluorescent in bothsolutionandsolidstate.Theemissionspectraof films preparedby spincoatingonquartz substratewere almost identical with those in aDMF solution. Fig. 6 presentstypical emission spectra ofpolyamidesM1a andM2a aswell asof polyimides B2band P2b in a DMF solution. They showed maxima at360, 366, 367 and364nm, respectively, whenexcitedat270nm. The emission intensity of polyimides wasremarkably lower thanthatof polyamides.This behaviourconformswith cetainliterature data32) andwasattributedto a possible luminescencequenching in polyimides byan energy transfer mechanism33). All spectradisplayedemission tail at longer wavelength, indicating strongintramolecular interactions among the oligophenyl andthe carboxylic acid moiety and/or the side groups.Theemissionspectrawere independent of the wavelength ofthe excitation. Upon irradiation at 270nm, the solutionsin DMF of polyamidesM1b andM2b aswell asof poly-imidesB1b andP1b displayedemissionmaximaat 350,

360, 365,351nm, respectively. The striking similarity ofthe electronic propertiesof thesepolymers indicatesthatthesemolecular propertiesare predominantly governedby therigid-rod andhighly conjugatedpolymerbackboneandarenot influencedby the natureof the attached sidechains.Theemissionmaxima of thestudiedpolymersarein goodagreement with thoseof our analogousrigid-rodpolyamides24), which appeared in the region of 364–404nm.

Thermalandthermomechanicalpropertiesof polymers

The thermal and thermomechanicalproperties of poly-merswere determined by DSC,TMA, TGA andisother-mal gravimetric analysis (IGA). The DSC curves,which

Tab.2. Solubilities of polymersa)

Polymer Solventsb)

DMF NMP DMAc CCl3COOH H2SO4 Pyridine m-Cresol TCE CH

M1a + ++ ++ ++ ++ ++ ++ + +M1b + ++ ++ ++ ++ ++ ++ + +M2a +c) ++ ++ ++ + ++ + + +M2b + ++ ++ ++ + ++ + + +P1b + ++ ++ ++ + + + + +B1b + ++ ++ ++ + + + + +P2b +– +– +– +– +– +– +– +– +–B2b +– +– +– +– +– +– +– +– +–

a) Solubility; ++, solubleat roomtemperature;+, solublein hot solvent;+-, partially soluble.b) DMF, N,N-dimethylformamide;NMP, N-methyl-2-pyrrolidone; DMAc, dimethylacetamide;TCE, 1,1,2,2-tetrachloroethane;CH,

cyclohexanone.c) Gel is formedoncooling.

Fig. 6. Emissionspectraof polyamidesM1 a andM2 a aswellas of polyimides B2b and P2b in a DMF solution (kex =270nm)


wererecordedat thefirst aswell asthesecondheatingofpolymers, did not show a distinct Tg and meltingendothermup to 3008C. TheTg’s of polymerswere deter-minedfrom the TMA methodusing a loadedpenetrationprobeandobtainedfrom the onsettemperaturesof thesetransitions during the second heating (Fig. 7). The Tg

valueswere 250–2688C for polyamidesand275–3108Cfor polyimides. Polyamides M2 displayed higher Tg’s

thanM1 owing to the longer rodlike segment. SincetheTg’s for polyamideswere of the order M1a A M1b andM2a A M2b, the side groups of 1,3,5-triphenylbenzenegave stiffer structuresthan those of triphenylmethane.Finally, PMDA afforded more rigid polyimides thanBTDA did. The polymers of the presentinvestigation, ascomparedto the correspondingrigid-rod polymerscarry-ing phenyl or 4-biphenylyl pendentgroups21,24), showedcomparable Tg values. However, the presentpolymersshowed significantly lower Tg’s thanthe analogouspoly-mersbearingthemorecompact2-naphthyl sidegroups26).

Fig. 8 illustratestypical TGA curvesfor therepresenta-tive polymers M1a, M2b and B2b in N2 and air. Theinitial decomposition temperature (IDT), the polymerdecomposition temperature (PDT), and the maximumpolymer decomposition temperature (PDTmax) in both N2

andair, aswell astheanaerobic charyield (Yc) at 8008C,for all polymers are listed in Tab.3. IDT and PDT weredetermined for the temperature at which 0.5 and 10%weight losseswereobserved, respectively. PDTmax corre-sponds to the temperatureat which the maximum rateofweight loss occurred. Since the polymers were almostwholly aromatic, theyshowedanexcellent thermal stabi-lity being stableup to 389–4528C in N2 and336–4118Cin air. Theyaffordedanaerobic charyieldsof 64–81%at8008C. Therelatively lower thermalstability of thepoly-merswith sidegroupsof triphenylmethanewasattributedto the aliphatic methenylsegment.Following 20h iso-thermal aging at 3008C in static air, the polymers dis-playedweightlossof 4.0–15.4%(Tab.3).

ConclusionsSubstituteddiamines weresynthesizedthroughpyryliumsalts andusedasstarting materials for the preparation ofrigid-rod polyamidesandpolyimides. It wasshownusing

Fig. 7. TMA tracesof polymers.Conditions:N2 flow 60 cm3/min; heatingrate208C/min

Fig. 8. TGA curvesin N2 and air of polymersM1 a, M2 b and B2b. Condi-tions:Gasflow 60cm/min;heating rate208C/min


a modeling systemthat the diamines,which carriedpen-dent groupswith triphenylmethanesegments,were lesscoplanarandpresentedhigherdisorder in thesidegroupsthan the other synthesizeddiamines. All polymersweregenerally amorphous and dissolved not only in polaraprotic solvents without the addition of inorganic salts,but also in halogenated aliphatic solvents as well as invarious common solvents. Polyamides with pendentgroupsof triphenylmethanedisplayed a relatively highequilibrium water absorption indicating an enhancedhydrophilicity. The solutions in DMF of all polymerswere UV-fluorescent.The kind of their side substituentsdid not influenceconsiderablytheemission maxima. Thepolymersshowed Tg’s in the region of 250–3108C. Noweight loss was observedup to 366–4118C in N2, andtheanaerobic charyieldswere64–81%at 8008C.

Acknowledgement: The author is indebted to chemist D.Vachliotis (Center of Instrumental Analysis, University ofPatras,Greece)for recordingtheNMR spectra.

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Tab.3. Thermal stabilitiesof polymers

Polymer In N2 In Air Wt. losse)

in %IDT in 8Ca) PDTin 8Cb) PDTmax in 8Cc) Yc in %d) IDT in 8C PDTin 8C PDTmax in 8C

M1 a 404 549 571 66 400 478 489 5.3M1 b 389 514 543 64 336 426 408 16.2M2 a 437 646 649 81 411 469 480 4.0M2 b 422 597 582 74 351 424 433 15.4P1b 400 549 574 68 347 415 411 14.8B1b 422 563 582 72 359 422 512 12.3P2b 407 541 578 73 355 467 498 9.6B2b 452 574 609 73 377 486 519 5.8

a) Initial decompositiontemperature.b) Polymer decompositiontemperature.c) Maximum polymerdecompositiontemperature.d) Charyield at 8008C.e) Weight lossafter20h isothermal ageingat 3008C in staticair.

soluble, uv-fluorescent polyamides and polyimides containing oligophenyls in the main chain and...

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