Preparation and absorption spectrum studies of aromatic and alicyclic poly(amide acid) ammonium salts in water and DMF and in films

Preparation and Absorption Spectrum Studies of Aromaticand Alicyclic Poly(amide acid) Ammonium Salts in Waterand DMF and in Films

QINGHUA LI,1 TAKASHI YAMASHITA,1 KAZUYUKI HORIE,1 HIROSHI YOSHIMOTO,1 TAKAO MIWA,2

YASUNARI MAEKAWA2

1 Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo,Bunkyo-ku, Tokyo 113-8656, Japan

2 Hitachi Research Laboratory, Hitachi Ltd., Omika 7-1-1, Hitachi, Ibaraki 319-12, Japan

Received 9 June 1997; accepted 9 December 1997

ABSTRACT: A series of ammonium salts of poly(amide acid)s (PAS) were preparedfrom various poly(amide acid)s (PAA) with tertiary amines. The solubility of poly-(amide acid) ammonium salts prepared from PAA(PMDA/ODA) in water is related tothe ion concentration of tertiary amines. In order to elucidate the influence of thechemical structures of poly(amide acid)s and poly(amide acid) ammonium salts ontheir absorption spectra, pyromellitic dianhydride (PMDA), 3,3 *,4,4 *-biphenyltetracar-boxylic dianhydride (BPDA), and 3,3 *,4,4 *-benzophenonetetracarboxylic dianhydride(BTDA) were chosen to react with p -phenylenediamine (PDA) and (4,4 *-diaminodi-cyclohexyl)methane (DCHM) to give three kinds of aromatic PAAs and three kinds ofalicyclic PAAs. The corresponding PASs were prepared by the reaction of PAAs withtriethanolamine (TEA). Their ultraviolet–visible (UV–vis) absorption spectra wereinvestigated compared to those of model compounds. A transparent film without absorp-tion above 320 nm was obtained for PAS(PMDA/DCHM). The difference in absorptionspectra of PAS(PMDA/PDA) from that of PAS(PMDA/DCHM) can be related to theexistence of intra- and intermolecular charge transfer (CT) for PAS(PMDA/PDA). Theabsorption spectra of PASs with PDA in films are red shifted compared to those ofcorresponding PAAs in films, while the absorption spectra of PASs in water are blueshifted compared to those of corresponding PAAs in DMF. No differences in the absorp-tion spectra of PAAs and PASs were found in DMF/H2O (9/1) mixed solvent. q 1998John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1329–1340, 1998Keywords: poly(amide acid) ammonium salts; poly(amide acid)s; water-solublepolyimide precursors; UV–vis absorption spectra; charge transfer; solubility

INTRODUCTION crystal displays, because of their superior thermaland mechanical properties and low dielectric con-stants. In general, polyimides (PI) are preparedPolyimides, one of typical high-performance mate-by a two-step process: First, diamines react withrials, have been widely used as electrical insula-dianhydrides in aprotic polar solvents at roomtors, coatings, adhesives, substrates for flexibletemperature to give poly(amide acid)s (PAA), theprinted circuits, and orientating films for liquidprecursor of polyimides. Second, poly(amide acid)sare converted to polyimides by either thermal orCorrespondence to: Q. Li, T. Yamashita, K. Horiechemical imidization. Since poly(amide acid)s are

Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 36, 1329–1340 (1998)q 1998 John Wiley & Sons, Inc. CCC 0887-624X/98/081329-12 not stable during storage, there are efforts to pre-

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8G72 97-102T/ 8g72$$102T 03-23-98 19:31:26 polcas W: Poly Chem

1330 LI ET AL.

pare other precursors of polyimides, such as poly- absorption spectra, six kinds of both PAAs andPASs from the combination of three kinds of dian-(amide acid) esters,1–5 and poly(amide acid) salts,6,7

which have no storage problem in solution. Also, hydrides with aromatic and alicyclic diamineswere prepared. The UV–vis absorption spectra ofpoly(amide acid)s are soluble only in strongly po-

lar solvents which need careful handling. In our these PAAs and PASs with triethanolamine weremeasured in solutions and in films and are dis-previous study,8,9 it was found that the ammo-

nium salts of poly(amide acid)s are soluble in cussed in comparison with those for model com-pounds.water and that their color is different from that

of the original poly(amide acid)s.It is widely accepted that both inter- and intra-

molecular charge transfer (CT) exist in solid-state EXPERIMENTALaromatic polyimides where the aromatic diaminemoiety in a polyimide acts as an electron donor Materialsand the aromatic imide moiety acts as an electronacceptor.10–12 Kotov et al.13 attributed the color of Pyromellitic dianhydride (PMDA) and 3,3 *,4,4 *-

benzophenonetetracarboxylic dianhydride (BTDA)polyimide (PI) film mainly to the intermolecularCT complexes formed owing to molecular aggrega- were of reagent grade and purified by recrystalliza-

tion in distilled acetic anhydride and dried undertion between PI chains in solid state. Analysisbased on X-ray spectroscopy and ultraviolet spec- vacuum at 1507C for 24 h. Reagent grade 3,3*,4,4*-

biphenyltetracarboxylic dianhydride (BPDA) wastroscopy has provided detailed information on theelectronic states of polyimides in a wide energy dried under vacuum at 1807C for 24 h. Reagent

grade p -phenylenediamine (PDA) and 4,4 *-oxydi-range from the ground state up to excited statesin the ultraviolet region.14–16 Although the com- aniline (ODA) were recrystallized from ethanol

and dried under vacuum at 507C for 24 h. (4,4 *-parison of XPS and SXPS spectra has been givenfor a polyimide, PI(PMDA/ODA), composed of Diaminodicyclohexyl)methane (DCHM) was ob-

tained from Wako Chemical and used without fur-pyromellitic dianhydride (PMDA) and oxydiani-line (ODA) and the corresponding poly(amide ther purification. Phthalic anhydride (PhA) was

recrystallized in distilled acetic anhydride andacid), PAA(PMDA/ODA),17 and absorption spec-tra of diamine moieties of PAAs and PIs were com- dried at 507C under vacuum for 24 h. Aniline (A)

and cyclohexylamine (CHA) were used for the re-pared for the kinetic study of imidization,18–20

there is no other information on the electronic action with PMDA, BPDA, BTDA, and PhA to pre-pare the model compounds of poly(amide acid)s.state of the precursors of polyimides. The forma-

tion of CT in polyimides results in high thermal Tertiary amines and other salt-forming com-pounds such as triethanolamine (TEA), triethyla-mechanical properties of polyimides compared to

the usual polymers; on the other hand, it is the mine (Et3A), N ,N-dimethylbutylamine (DBA),N ,N-dimethylhexylamine (DHA), N ,N-dimeth-formation of CT that results in the coloration of

polyimides and reduces the quantum yields for yloctylamine (DOA), N ,N-dimethyldodecylamine(DDA), N,N,N*,N*-tetramethyl-1,2-diaminoethanethe crosslinking reaction of photosensitive poly-

imides.21 Polyimides prepared with alicyclic di- (TDE), N ,N ,N *,N *-tetramethyl-1,4-diaminobu-tane (TDB), N ,N ,N *,N *-tetramethyl-1,6-diami-amines were reported22–24 and showed that the

quantum yield for the photocrosslinking reaction nohexane (TDH), tributylamine (Bu3A) trihex-ylamine (Hex3A), trioctylamine (Oct3A), pyridineof a polyimide with an alicyclic diamine was 4

times higher than that for aromatic polyimides (Py), methyl sulfide (MS), triphenylphosphine(TPP), 4,4 *-bis(4-hydroxyphenyl)sulfone (HPS),in air.

In this paper, the solubility in water of poly- and diaminodiphenylsulfone (DDS) were of re-agent grade and used for preparing salts of poly-(amide acid) ammonium salts (PAS) prepared

from PAA(PMDA/ODA) with various tertiary (amide acid)s.The solvent used for the preparation of theamines was examined and it was found that the

solubility of poly(amide acid) ammonium salts poly(amide acid)s and their model compoundswas N ,N-dimethylacetamide (DMAc), which wasprepared from PAA(PMDA/ODA) in water is re-

lated to the ion concentration of tertiary amines. distilled before use and stored with molecularsieves. The spectroscopic grade N ,N-dimethyl-Then, in order to elucidate the influence of the

chemical structures of PAAs and PASs on their formamide (DMF) and water (H2O) were used


POLY(AMIDE ACID) AMMONIUM SALTS 1331

for measuring the UV–vis absorption spectra of Preparation of Poly(amide acid) Ammonium Salts(PASs) and Model Ammonium Salts (MASs)poly(amide acid)s and their ammonium salts, as

well as their model compounds. The ammonium salts of PAAs, PASs, were pre-pared from PAAs (0.16 mmol) and triethanol-amine (0.32 mmol) in water (1 mL). The mixturePreparation of Poly(amide acid)s (PAAs)was kept stirring continuously at room tempera-ture under nitrogen atmosphere until the solutionPoly(amide acid)s (PAA) were prepared with abecame homogeneous and transparent. The reac-usual procedure25 using a 100 mL three-necktion scheme for the formation of PAS(PMDA/round-bottom flask fitted with a mechanical stir-PDA) is given by eq. 1, and the chemical struc-rer, nitrogen inlet, and drying tube. A typical pro-tures of all of the PASs are shown in Table I.cedure is as follows: PDA (0.66 g, 6.1 mmol) was

dissolved in DMAc (18 mL) under nitrogen.PMDA (1.34 g, 6.1 mmol) was then added, andthe mixture was kept stirring for 24 h at roomtemperature to produce a viscous and homoge-neous PAA solution. The PAA was purified by pre-cipitation in water and dried at 507C under vac-uum for 24 h. The other poly(amide acid)s such asPAA(PMDA/ODA), PAA(PMDA/DCHM), PAA-(BPDA/PDA), PAA(BPDA/DCHM), PAA(BTDA/PDA), and PAA(BTDA/DCHM) were preparedas the same procedure as for PAA(PMDA/PDA).The intrinsic viscosities, [h] , of the PAAs, which Model ammonium salts of amide acids, MASs,were measured in DMAc at 307C, are shown in were prepared from MAAs (0.16 mmol) and tri-Table I. ethanolamine (0.32 mmol) in water (1 mL). The

mixture was kept stirring continuously at roomtemperature under nitrogen atmosphere until the

Preparation of Model Amide Acids (MAAs) solution became homogeneous and transparent.

A model bis(amide acid) MAA(PMDA/A) wasMeasurements of UV–Vis Absorption Spectraprepared by reacting PMDA (2.16 g, 9.9 mmol)and IR Spectrawith aniline (A) (1.80 mL, 19.8 mmol) in DMAc

(36 mL) at room temperature under nitrogen at- The UV–vis absorption spectra were measuredmosphere for 5 h. The product was precipitated with a Jasco V-570 UV/vis/NIR spectrophotome-from water and dried under vacuum at 507C for ter. In order to minimize the influence of the sol-24 h. MAA(PMDA/A) was identified by thin layer vent on the absorption spectra of PAAs and PASschromatography (TLC) and its IR spectrum. in DMF and DMF/H2O (9/1) solution, we used aModel bis(amide acid)s such as MAA(PMDA/ 1 mm quartz cell while a usual 10 mm quartzCHA), MAA(BPDA/A), MAA(BPDA/CHA), MAA- cell was used for the measurements of absorption(BTDA/A), and MAA(BTDA/CHA) were pre- spectra of PASs in water. The absorption intensi-pared with the same procedure as for MAA- ties of PAAs and PASs in films were normalized(PMDA/A) and also identified by TLC and IR as to film thickness by measuring with a Talystepspectra. thickness gauge (Rank Taylor Hobson Ltd.) . IR

A model mono(amide acid), MAA(Ph/A), was spectra were recorded with a Jasco IR-700 infra-synthesized from phthalic anhydride (1.84 g, 12.4 red spectrophotometer.mmol) and aniline (1.13 mL, 12.4 mmol) in DMAc(17 mL) at 07C for 3 h under a nitrogen atmo-

RESULTS AND DISCUSSIONsphere. The product was precipitated from waterand dried under vacuum at room temperature for

Preparation of Poly(amide acid) Ammonium Salts24 h. MAA(Ph/A) was identified by TLC and IRand Their Solubility in Waterspectrum. A model mono(amide acid), MAA(Ph/

CHA), was synthesized as MAA(Ph/A) and iden- The solubilities of various salts derived fromPAA(PMDA/ODA) were first examined by thetified by TLC and IR spectrum.


1332 LI ET AL.

Table I. Summary of the Preparation of PASs and PAAs

Structure [h] (dL/g)

Sample PAA PAS PAAa PASb

PMDA/PDA HO{R1{OH N/ 0O{R1{O0 /N 1.71 1.73PMDA/DCHM HO{R2{OH N/ 0O{R2{O0 /N 0.40 0.42BPDA/PDA HO{R3{OH N/ 0O{R3{O0 /N 1.93 1.97BPDA/DCHM HO{R4{OH N/ 0O{R4{O0 /N 0.41 0.41BTDA/PDA HO{R5{OH N/ 0O{R5{O0 /N 1.80 1.85BTDA/DCHM HO{R6{OH N/ 0O{R6{O0 /N 0.34 0.37

a In DMF, 307C.b In water, 307C.

present authors. An amine or other salt-forming than 25% water. PAS with Et3A is soluble in thewhole range of water/NMP ratios. PAS with Bu3Acompound, 0.52 mmol in the case of a solid and

0.5 mL in the case of a liquid, was added into a 1 is soluble in 15–50% water content, while PASswith Hex3A and Oct3A are insoluble in the wholemL DMF solution of 10 wt % PAA(PMDA/ODA),

and then 1 mL of water was added. The solubility range of water/NMP mixed solvents.A solubility difference between the PASs withof PAS(PMDA/ODA) at these two steps is sum-

marized in Table II. Ammonium salts prepared Et3A and Py shows that the solubility depends onthe basicity of amines. However, the solubility offrom N ,N-dimethylalkylamine are soluble in wa-

ter when the number n of methylene group is various alkylamines in Table I shows the effect ofthe alkyl chain length. Considering these results,smaller than 7, while they become insoluble in

water for n ú 7. Ammonium salts prepared from we can conclude that the solubility of PAS is con-trolled by the ion concentration. This interpreta-tetramethyl(methylene)ndiamine show a bound-

ary of solubility at n Å 6. When the other salt- tion explains the fact that some PASs become sol-uble with excess amounts of amines.forming compounds, i.e., methyl sulfide, triphe-

nylphosphine, 4,4 *-bis(4-hydroxyphenyl)sulfone, Six kinds of PASs were prepared from the reac-tion of PAA(PMDA/PDA), PAA(PMDA/DCHM),and diaminodiphenylsulfone, were added to DMF

solutions of PAA(PMDA/ODA), the solutions re- PAA(BPDA/PDA), PAA(BPDA/DCHM), PAA-(BTDA/PDA), and PAA(BTDA/DCHM) with tri-mained homogeneous, but when water was added,

the solutions became gelled. Figure 1 shows the ethanolamine in water. As the tertiary ammo-nium salts of PAAs were prepared in water duringsolubility of PAA(BPDA/PDA) and PAS(BPDA/

PDA)26 prepared from equimolar amounts of stirring at room temperature, the initially-hetero-geneous reaction systems changed to homoge-Et3A, Bu3A, Hex3A, Oct3A, and Py added to the

carboxylic acid in water/N-methylpyrrolidone neous and transparent solutions. From the IRspectra of PAS films, the characteristic band of(NMP) mixed solvents. PAA is soluble in NMP,

while it is insoluble in solvent containing more {COOH at 1720 cm01 disappeared and a band



Table II. Solubility of Poly(amide acid) Salts of PAA(PMDA/ODA) with Various Tertiary Aminesand Other Salt-Forming Compounds

Tertiary Amine and Other Salt-Forming Addition of Salt-Forming Compds. Further AdditionCompds. to PAA/DMF Solutiona of Waterb

Triethanolamine (TEA) Insoluble SolubleTriethylamine (Et3A) Insoluble SolubleN,N-Dimethylbutylamine (DBA) Soluble SolubleN,N-Dimethylhexylamine (DHA) Soluble SolubleN,N-Dimethyloctylamine (DOA) Soluble TurbidN,N-Dimethyldodecylamine (DDA) Soluble GelationN,N,N*,N*-Tetramethyl-1,2-diaminoethane (TDE) Gelation SolubleN,N,N*,N*-Tetramethyl-1,4-diaminobutane (TDB) Gelation SolubleN,N,N*,N*-Tetramethyl-1,6-diaminohexane Gelation Insoluble(TDH)Methyl sulfide (MS) Soluble GelationTriphenylphosphine (TPP) Soluble Gelation4,4*-Bis(4-hydroxyphenyl)sulfone (HPS) Soluble GelationDiaminodiphenylsulfone (DDS) Soluble Gelation

a Addition of 0.52 mmol of solid amine or 0.5 mL of liquid amine into a 1 mL DMF solution of 10 wt % PAA.b Further addition of 1 mL of water.

at 1570 cm01 appeared which is characteristic of UV–Vis Absorption Spectra in Solutioncarboxylate groups. This suggests all carboxylic Figure 2 shows the UV–vis absorption spectra ofacid groups have changed to carboxylate anions PAAs in 1.60 1 1004M DMF solution and of PASsin PASs. The aqueous solutions of PASs are more in 1.60 1 1005M water solution. Since the poly-viscous than the corresponding solutions of PAAs (amide acid)s were not soluble in water, and poly-in DMAc at the same concentration, and the in- (amide acid) ammonium salts were not solubletrinsic viscosities of PASs in water are little in DMF, we measured their UV–vis absorptiongreater than the corresponding PAAs in DMF. All spectra in different solvents, i.e., for PAAs in DMFthe films of PASs cast from water and PAAs cast and for PASs in water. DMF has absorption bandfrom DMAc on glass plates are flexible. The chem- below 270 nm, which will cover the absorption ofical structures of PAAs and PASs and their intrin- the targets. So we used a 1 mm quartz cell and asic viscosity data are summarized in Table I. reference for the measurements in DMF to cut

the absorption of DMF to some degree. Thus, theabsorption spectra from 200 to 265 nm measuredin DMF solution are meaningless due to the sol-vent absorption.

PASs in water show an absorption peak atabout 260–280 nm, except for PAS(PMDA/DCHM). In the PMDA series, PAS(PMDA/PDA)shows a peak at 262 nm, while PAS(PMDA/DCHM) shows no peak, as are shown in Figure2. We could presume that the absorption peak at262 nm of PAS(PMDA/PDA) is the absorption ofintramolecular charge transfer (CT).15,16 In theBPDA and BTDA series, both aromatic PASs andalicyclic PASs show absorption peaks at about270–280 nm. The absorptions in alicyclic PASsFigure 1. Solubility of PAA(BPDA/PDA) and PAS-would be mainly due to the absorption of amide(BPDA/PDA) in mixed solvents of water/NMP. Theacid salts of BPDA or BTDA itself, because, indark parts in the graph correspond to soluble composi-

tions. the series of PASs with DCHM, the occurrence


1334 LI ET AL.

Figure 2. UV absorption spectra of PASs in H2O (1.60 1 1005M ) ( ) and PAAsin DMF (1.60 1 1004M , 1 mm cell) (rrr) : a1 , PMDA/PDA; a2 , PMDA/DCHM; b1 ,BPDA/PDA; b2 , BPDA/DCHM; c1 , BTDA/PDA; c2 , BTDA/DCHM.

of intramolecular CT is not suggested. Thus, we DMF becomes difficult to be distinguished and theappearance of the blue shift for PASs could bewould assign the absorption of aromatic PASs to

the absorption of the biphenyltetracarboxylic or hardly observed for the polymers (Fig. 2, c1) , butthe blue shift in band tailing was observed forbenzophenonetetracarboxylic moiety overlapped

with that of the intramolecular CT. The absorp- the model compounds (Fig. 4, c1) . The absorptionpeak intensities, 1max, and wavelength, lmax, oftion of PAS * (BTDA/PDA) prepared from PAA-

(BTDA/PDA) and triethylamine has almost thesame absorption peak and absorption intensityas the absorption of PAS(BTDA/PDA) preparedfrom triethanolamine, as is shown in Figure 3.This means that different tertiary amines wouldnot affect the absorption of ammonium salts.Model compounds, MAAs and MASs, correspond-ing to each structure unit of the PAAs and PASsshow the same appearance, as shown in Figure 4.If the absorption spectra of PASs in water arecompared with those of PAAs in DMF, a largedifference is shown in the PMDA/PDA series. Theabsorption band of PAS(PMDA/PDA) is blueshifted compared with PAA(PMDA/PDA), andthere is an increase in the molar extinction coeffi-cient, 1, of the absorption peak. Furthermore, theband tailing of PAS(PMDA/PDA) in water is cutcompared with the band tailing of PAA(PMDA/PDA) in DMF solution. The same phenomenon is Figure 3. UV absorption of PAS(BTDA/PDA) ( )found in the series of BPDA compounds. In the and PAS * (BTDA/PDA) prepared from triethylamine

(rrr) in H2O (1.60 1 1005M ) .BTDA series, the absorption peak of PAAs in



Figure 4. UV absorption spectra of MASs in H2O (1.60 1 1005M ) ( ) and MAAsin DMF (1.60 1 1004M , 1 mm cell) (rrr): a1, PMDA/A; a2 , PMDA/CHA; b1, BPDA/A;b2 , BPDA/CHA; c1 , BTDA/A; c2 , BTDA/CHA.

PAAs and PASs, MAAs, and MASs are summa- PMDA, BPDA, and BTDA in dichloromethane(CH2Cl2) solution. As it is shown in Figure 5a, therized in Tables III and IV. The blue shift of PASs

compared to PAAs could be explained to be due to absorption spectra of PAS(PMDA/DCHM) agreewith that of PMDA very well, although they werethe different solute–solvent interactions between

PAS–H2O and PAA–DMF. As it is well-known, measured in different solvents. Alicyclic polyim-ides are considered to form no charge transferhydrogen bonds are easily formed in water, which

would change the stabilization energy for conjuga- complex (CTC), inter- or intramolecularly,22–24 sowe could assign the absorption band of PAS-tion of the structural moiety of PASs, resulting in

the blue shift of absorption of PASs in water. (PMDA/DCHM) to be the structural absorptionband of the pyromellitic ring. Accordingly, the ab-Figure 5 shows the UV–vis absorption spectra

of PASs in water and the source compounds sorption peak at 262 nm of PAS(PMDA/PDA) in

Table III. Summary of UV Spectra of Poly(amide acid)s and Their Ammonium Salts in Solution

PDA DCHM

PAAa PASb PAAa PASb

lmax 1max lmax 1max lmax 1max lmax 1max

(nm) (M01 cm01) (nm) (M01 cm01) (nm) (M01 cm01) (nm) (M01 cm01)

PMDA (307.1) (1.34 1 104) 262.0 3.30 1 104

BPDA 284.6 2.81 1 104 281.0 3.18 1 104 277.0 2.68 1 104 273.0 2.38 1 104

BTDA 282.0 2.81 1 104 278.0 3.25 1 104 (274.1) (1.56 1 104) 271.0 2.09 1 104

a Measured in DMF.b Measured in water.Data in parentheses are not so obvious.


1336 LI ET AL.

Table IV. Summary of UV Spectra of Model Amide Acids and Their Ammonium Salts in Solution

A CHA

MAAa MASb MAAa MASb

lmax 1max lmax 1max lmax 1max lmax 1max

(nm) (M01 cm01) (nm) (M01 cm01) (nm) (M01 cm01) (nm) (M01 cm01)

PMDA 303.2 1.37 1 104 259.0 5.57 1 104

BPDA 276.7 3.37 1 104 269.0 5.22 1 104 278.8 2.35 1 104 270.0 3.96 1 104

BTDA 267.0 4.98 1 104 267.5 4.21 1 104

a Measured in DMF.b Measured in water.

water solution can be attributed to the absorption compounds MAS(PMDA/A), MAS(PMDA/CHA),MAS(Ph/A), and MAS(Ph/CHA).due to the intramolecular CT transition. Exten-

sive conjugation exists between the carbonyl In Figure 5b, the absorption of PAS(BPDA/DCHM) is bigger than that of BPDA but isgroup and the nitrogen atom, resulting in the par-

tial contribution of enolization, as shown in eq. 2. smaller than that of PAS(BPDA/PDA). The samephenomenon is shown in Figure 5c. Hasegawa etal. compared the UV–vis absorption spectra ofmodel phthalimide compounds of M(PhA/A) withM(PhA/CHA)27 and those of benzophenonebis-(imide)s of M(BTDA/3-EA), M(BTDA/2,4-DMA),and M(BTDA/2,6-DEA) with M(BTDA/MCHA)28

(3-EA, 3-ethylaniline; 2,4-DMA, 2,4-dimethylani-line; 2,6-DEA, 2,6-diethylaniline; MCHA, 2-meth-ylcyclohexylamine) (M: model compounds of poly-imides) and concluded that the conjugation be-tween the phthalimide plane and the N-aryl groupwas very small. So we would assign the absorptionof PAS(BPDA/PDA) or PAS(BTDA/PDA) to theoverlap of the absorption of the biphenyltetracar-boxylic or benzophenonetetracarboxylic moiety it-self and the absorption of the weak intramolecularDue to the contribution of enolization, the conju-charge transfer, which results in the small in-gation between the tetracarboxylic moiety and thecrease of molar extinction coefficients and thediamine moiety as well as the formation of chargesmall red shift of aromatic PAS compared to thetransfer between them increases. Lafemina etalicyclic PAS.al.15 simulated the absorption spectrum of model

compounds of PI(PMDA/ODA) with the CNDO/S3 computational model, and by comparing the UV–Vis Absorption Spectra in a Mixed Solventcomputational spectra with experimental spectra,they reached the conclusion that the absorption Since water and DMF have different polarities,

the solvent effect would affect the absorption spec-peak at 4.4 eV (282 nm) was due to the formationof an intramolecular charge transfer complex. tra of PASs and PAAs. In order to compare the

absorption spectra of PAAs and PASs in the sameKan et al.16 studied the UV–vis absorption spec-tra of PI(PMDA/ODA) with different curing his- solvent and to eliminate the effect of solvents, we

found a mixed solvent of DMF and water withtories and assigned the absorption peak at 4.35 eV(285 nm) to be an intramolecular charge transfer the volume ratio of 9/1 DMF/H2O, which could

dissolve both PAAs and PASs. The UV–vis ab-transition. The same feature is found in Figure6, which shows the absorption spectra of model sorption spectra of PAAs and PASs were mea-



sured in this mixed solvent with the concentra-tions of 1.60 1 1004M , in 1 mm quartz cells.Figure 7 shows that almost no difference was ob-served for the absorption spectra of PASs andthose of the corresponding PAAs. These resultssuggest that the effect of the change in the substit-uent from electron-attracting carboxylic acid toless attracting carboxylate anion on the absorp-tion spectra is not so marked as long as the solventis mainly composed of DMF.

Figure 6. UV absorption spectra of dimer and monomodel compounds of PAS(PMDA/PDA) and PAS-(PMDA/DCHM) in H2O (1.60 1 1005M ) : a: MAS-(PMDA/A) ( ) , MAS(PMDA/CHA) (rrr) ; b, MAS-(PhA/A) ( ) , MAS(PhA/CHA) (rrr) .

The absorption profiles for PAS(PMDA/PDA)and PAA(PMDA/PDA) in DMF/H2O (9/1) mixedsolvent in Figure 7 a1 agree rather well with theabsorption profile for PAA(PMDA/PDA) in DMFwith a moderate tailing at 300–400 nm in Figure2 a1 . This phenomenon of moderate tailing inDMF would be attributed to the selective solva-tion of the electron-attracting pyromellitic moiety29

by the aprotic polar solvent (DMF) and its influ-ence on the electronic state of intramolecular CT.

UV–Vis Absorption of PASs and PAAs in Films

Figure 8 shows the UV–vis absorption spectra ofFigure 5. UV absorption spectra of PASs in H2O PASs and PAAs in films with a thickness of ca.(1.60 1 1005M ) and PMDA, BPDA, and BTDA in

0.60 mm. As can be seen, PASs with PDA are redCH2Cl2 (1.60 1 1005M ) : a, PAS(PMDA/PDA) ( ) ,shifted compared with the corresponding PAAsPAS(PMDA/DCHM) (rrr) , PMDA (---) ; b, PAS-with PDA, in contrast to the UV–vis absorption(BPDA/PDA) ( ) , PAS(BPDA/DCHM) (rrr) ,in solution in Figure 2. Especially in the case ofBPDA (---) ; c, PAS(BTDA/PDA) ( ) , PAS(BTDA/

DCHM) (rrr) , BTDA (---) . PAS(PMDA/PDA), a shoulder between 250 and


1338 LI ET AL.

Figure 7. UV absorption spectra of PASs ( ) and PAAs (rrr) in DMF/H2O (9/1)mixed solution with 1 mm cell: a1 , PMDA/PDA; a2 , PMDA/DCHM; b1 , BPDA/PDA;b2 , BPDA/DCHM; c1 , BTDA/PDA; c2 , BTDA/DCHM.

400 nm appears and becomes broader and more and strong absorption bands, which can be attrib-uted to the intermolecular charge transfer transi-marked than that for PAA(PMDA/PDA). Ontion from the highest occupied molecular orbitalthe other hand, the absorption of PAS(PMDA/(HOMO) located around the N-phenylene moietyDCHM) agrees with that of PAA(PMDA/DCHM),to the lowest unoccupied molecular orbitalincluding a very small absorption shoulder at 300(LUMO) located around the pyromellitic moiety.nm. It is widely accepted that intermolecular

Furthermore, the absorption band of PAS-charge transfer complexes are formed in aromatic(PMDA/PDA) is stronger than that of PAA(PMDA/polyimide films.10–12 Intermolecular charge trans-PDA), which probably suggests that the intermo-fer could be correlated to the electronic affinity oflecular charge transfer in PASs can be more easilythe dianhydrides and the ionic potential of theformed than in PAAs. The explanation could bediamines which form the polyimides.10,30 Intermo-that, when PAS is formed, the polar environmentlecular charge transfer results in coloration ofdue to negative and positive charges around thepolyimides.12,30 The values of electronic affinity forpyromellitic moiety emerges, which would en-PMDA, BPDA, and BTDA are 1.90, 1.38, and 1.55hance the close packing of the intermoleculareV,30 respectively, which show that PMDA hascharge transfer complex. A similar tendency isthe greatest electronic affinity within these sourcefound in other PASs and PAAs with aromatic di-compounds and is supposed to generate intermo-amines. With the increase in polarity of micro-lecular charge transfer in the PI film most easilyenvironments, the energy for intermolecularand strongly. Hence PASs and PAAs, precursorscharge transfer transition would shift to longerof polyimides, which also have the dianhydridewavelengths.20 So we can conclude that, in films ofmoiety in their polymer chains, are presumed toPASs, intermolecular charge transfer interactionsform intermolecular charge transfer complexes inwould be stronger than in PAAs films.film. It is suggested from Figure 8 that by compar-

ing the absorption band of PAS(PMDA/PDA)CONCLUSIONwith PAS(PMDA/DCHM) and that of PAA-

(PMDA/PDA) with PAA(PMDA/DCHM), PAS- We prepared a series of poly(amide acid) ammo-nium salts, using different kinds of tertiary(PMDA/PDA) and PAA(PMDA/PDA) have broad



Figure 8. UV absorption spectra of PASs ( ) and PAAs (rrr) in films with athickness of ca. 0.60 mm: a1 , PMDA/PDA; a2 , PMDA/DCHM; b1 , BPDA/PDA; b2 ,BPDA/DCHM; c1 , BTDA/PDA; c2 , BTDA/DCHM.

amines and various poly(amide acid)s. The solu- REFERENCES AND NOTESbility of poly(amide acid) ammonium salts pre-pared from PAA(PMDA/ODA) in water is related

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Preparation and absorption spectrum studies of aromatic and alicyclic poly(amide acid) ammonium salts in water and DMF and in films