Electrically conducting polymers and complexes

Electrically conducting polymer complexes, prepared from N-substituted carbazoles, p-acetoxylbenzaldehyde, and protic acids, are soluble in polar organic solvents giving conductive polymer solutions processable to stable conductive films, coatings, and sponges.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to environmentally stable organic polymers 
and, more particularly, to processible polymers synthesized from 
N-alkylsubstitued carbazole and p-acetoxybenzaldehyde which are highly 
conducting as synthesized. The term polymer as used herein also includes 
oligomers where indicated. 
2. Related Art 
Organic materials that behave as metals or semiconductors provide the 
advantages of these materials together with additional advantages of being 
soluble in organic solvents or having low melting points and glass 
transition temperatures. This minimizes the cost of processing and permits 
composites to be made with thermally sensitive materials such as doped Si 
or GaAs, for example. The enormous molecular design flexibility of organic 
chemistry enables precise tailoring of properties to fill a wide range of 
applications as enumerated above. In addition, the high strength and 
conductivity-to-weight ratios lend the advantage of fabrication of many 
electrical devices of much lower weight than conventional materials. 
Theoretically, conductivity takes place both along the polymer chain and 
between adjacent chains. The active charge carrier, at least in the 
aromatic materials, is believed to be a bipolaron that is delocalized over 
several polymer repeating units. The mobility of such a species along the 
polymer chain is reduced by conformational disorder, necessitating a rigid 
highly crystalline chain structure for maximum intrachain conductivity. 
Various mechanisms such as "hopping" and "interchain exchange" are thought 
to be responsible for the interchain part of the conductivity. 
Unfortunately, all of the most highly crystalline polymers of high 
conductivity are insoluble and infusible. Therefore other materials have 
been sought. 
Successful environmentally stable doped conducting polymers are described 
in U.S. Pat. No. 4,452,725 to S. T. Wellinghoff, S. A. Jenekhe (an 
inventor in the present application) and T. J. Kedrowski and has a common 
assignee with the present application. That patent concerns conducting 
polymers of N-alkyl 3,6' carbazolyl chemically doped with charge transfer 
acceptor dopants such as halogens. Environmentally stable polymer 
complexes of processible poly (3,6-N-alkylcarbazolyl alkenes) which also 
become highly conductive upon doping with charge transfer acceptors such 
as iodine are described in U.S. Pat. Nos. 4,548,738 and 4,598,139 also to 
the same S. A. Jenekhe and one B. J. Fure and commonly assigned with the 
present application. Organic polymers synthesized from carbazole or 
N-substituted carbazoles and benzaldehyde or certain substituted 
benzaldehydes also made conductive by virtue of doping with charge 
transfer acceptors are disclosed in yet another commonly assigned S. A. 
Jenekhe invention in U.S. Pat. No. 4,624,999. 
SUMMARY OF THE INVENTION 
The present invention provides new thermoplastic organic heterocyclic 
linear condensation polymeric materials and complexes which are solution 
and/or melt processible to films, fibers and other shapes, which 
intrinsically, as prepared, exhibit controllable high p-type conductivity 
in the range characteristic of semiconductors. The polymers are products 
of condensation polymerization of an N-alkyl substituted carbazole with 
p-acetoxybenzaldehyde. The genus has the following basic polymer protic 
acid complex structure: 
##STR1## 
Where 
X is a protic acid ion 
0&lt;y&lt;2 
R is an alkyl group having from 1 to 5 carbon atoms; and 
n is an integer having a value from 2 to about 500. 
The protic acid complexes of poly (3,6-N alkylcarbazolyl 
p-acetoxybenzylidene) normally are prepared by simultaneous polymerization 
and doping in a solution containing the protic acid. This forms 
electrically conductive heterocyclic polymer complexes which are also 
soluble in polar solvents. The preferred complex is poly 
(3,6-N-methylcarbazolyl p-acetoxybenzylidene) bisulfate. This complex is 
normally prepared by, the condensation of N-methylcarbazole with 
p-acetoxybenzaldehyde catalyzed by sulfuric acid. The sulfuric acid also 
complexes with the resulting polymer in solution and produces the 
bisulfate complex. The structural formula of the bisulfate complex may be 
represented by: 
##STR2## 
Where 
0&lt;y&lt;2 
R is an alkyl group having from 1 to 5 carbon atoms; and 
n is an integer having a value from 2 to about 500. 
The conductive polymers of the present invention require no further dopant 
or doping step in their preparation other than that introduced by the 
protic acid catalyst during polymerization. 
Introduction of the polar acetoxy group as a side group affects remarkable 
changes in properties compared to even poly (3,6-N-methylcarbazolyl 
benzylidene) (PMCZB), structure with phenyl as the substitute group, for 
example, solubility in polar solvents to give electrically conducting 
polymer solutions is greatly enhanced.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
For use in the polymerization an N-alkyl carbazole in the form of 
n-methylcarbazole was prepared according to procedure next described 
N-methyl-carbazole prepared in this manner was used in the polymerization 
of Examples 1 through 3. 
120 g of carbazole was dissolved in 600 ml acetone/180 ml dimethyl sulfate 
(CH.sub.3).sub.2 SO.sub.4 in a reaction flask. Next, 120 g NaOH pellets 
was added to the reaction solution. Distilled water was dripped slowly 
into the reaction flask with stirring. The flask was allowed to reflux for 
three (3) hours, and then cooled for 20 minutes. The reaction mixture was 
quenched in cold distilled water and off-white crystals precipitated. The 
precipitate was recrystallized in distilled water to yield white crystals. 
The melting point of 91.1.degree. C., compared favorably with the 
literature value of 87-88.degree. C. for N-methylcarbazole. 
In accordance with the invention, examples 1 and 2 are directed to an 
intrinsically conducting polymeric material, poly (N-alkylcarbazolyl 
p-acetoxybenzylidene) in the form using the methyl substituted carbazole 
(PMCZAB), which is highly conducting as synthesized, and thus requires no 
external dopant. Structure II shows the polymer structure and composition 
for the generic bisulfate embodiment. 
EXAMPLE 1: (PMCZAB-1) 
10.949 g (0.0667 mole) para-acetoxybenzaldehyde (Fairfield Chemical Co.) 
and 1.23 ml H.sub.2 SO.sub.4 were added to 150 ml dioxane solvent in a 
reaction vessel with flowing argon. 12.083 g (0.0667 mole) 
N-methylcarbazole in 100 ml dioxane was next added. Additional 4 ml of 
H.sub.2 SO.sub.4 was added within 1 hour. The mechanical stirrer was 
rotated at 100 rpm. The reaction vessel was thermostated in an oil bath 
held at 92.degree. C. After 51 hr. reaction time, the reaction mixture was 
quenched into 1,500 ml methanol. The resulting suspension was evaporated 
on a hot plate till about 100 ml with methanol (acetone: methanol=3:1), 
evaporated until dry. A metallic copper-brown solid represented by 
structure II was obtained. 
EXAMPLE 2: (PMCZAB-2) 
The same procedure as in Example 1 was used except that 5.23 ml conc. 
H.sub.2 SO.sub.4 was added at once, the reaction temperature was 
93.degree. C., and the polymerization time was 51 hr. 46 min. 
As synthesized poly (N-methylcarbazolyl p-acetoxybenzylidene) PMCZAB-1 and 
PMCZAB-2 were highly conducting (about 10.sup.-1 ohm.sup.-1 cm.sup.-1) 
metallic copper-colored polymers. The polymers are stable in air and 
processible by solvent casting from solutions in dimethylformamide (DMF) 
and other solvents. The preferred alkyl substitute is methyl. 
Main advantages includce the excellent environmental stability of the 
polymeric conductor and the one-step process of making it, requiring no 
further external doping. As a consequence, ready fabrication of articles 
from the material is possible. Also, the material, unlike many prior 
carbazole derivatives, does not require doping with such agents as 
Br.sub.2 and I.sub.2, which might corrode metals in electronic 
applications. 
The direct synthesis of complexed poly (3,6-N-methylcarbazolyl 
p-acetoxybenzlidene) (PMCZAB) and its properties are next addressed. 
EXAMPLE 3 
The following is a typical polymerization procedure for poly 
(3,6-N-methylcarbazolyl p-acetoxybenzylidene). 10.949 g (66.7 nmol) 
para-acetoxybenzaldehyde and 5.23 ml (94.2 mmol) H.sub.2 SO.sub.4 were 
added to 150 ml dioxane solvent in a reaction flask and followed with 
12.083 g (66.7 mmol) N-methylcarbazole in 100 ml dioxane. The reaction 
vessel was thermostated in an oil bath held at 92.degree. C. The reaction 
mixture was stirred with a mechanical stirrer at 100 rpm under argon 
atmosphere After 75 hr. reaction time, the mixture was quenched into 100 
ml of methanol. The resulting solution suspension was evaporated on a hot 
plate until about 200 ml remained at which time about 600 ml acetone was 
added. The resulting solution was stirred and evaporated until dry. A 
metallic copper-brown colored solid was collected. Elemental analysis 
calculated for the repeating unit [(C.sub.22 H.sub.16 NO.sub.2).sup.y+ 
(HSO.sub.4.sup.31 )y].sub.n for y=1.3:%C=58.39, %H=3.85, %N=3.09, 
%O=25.45, %S=9.20; found:%C=58.24, %H=5.12, %N=2.98, %O=24.48, %S=9.12. 
The compound may be represented by the structure II with y=1.3. 
In subsequent polymerizations, the amount of initial sulfuric acid was 
varied and the value of y determined by elemental analysis was found to be 
1.2-1.7. Attempts to reduce the oxidized polymer in structure II, by 
reactions with NaHCO.sub.3 or sodium dithionite were not successful. 
The as-synthesized polymer bisulfate complexes exhibit a high d.c. 
conductivity (.about.10.sup.-2 to 0.1 ohm.sup.-1 cm.sup.-1) without 
further doping and are found to contain up to 1.2-1.7 moles of the 
bisulfate counterion per polymer repeating unit. The copper colored 
polymer complex is largely amorphous but exhibits a melting point of about 
234.degree. C. probably due to the bisulfate counterion. The observed 
optical absorption maxima at .about.604-636 nm are attributed to charge 
transfer bands. The polymer complex can be processed into dense continuous 
films of sponge-like morphology from conductive solutions. 
With respect to the complex of Example 3, polymer molecular weight 
distribution was characterized using a Waters Model 150C gel permeation 
chromatograph (GPC) at 100.degree. C. in dimethylformamide (DMF). The GPC 
was packed with 10.sup.5, 10.sup.4, 10.sup.3, and 500 Angstrom 
ultrastyrogel columns in DMF and operated at a flow rate of 1 mL/min. 
UV-Visible-near IR spectra were obtained using thin films cast on sapphire 
wafers and a Perkin-Elmer Model Lambda 9 UV-Vis-NIR spectrophotometer in 
the wavelength range 185-3,200 nm. 
Fourier transform infrared (FTIR) spectra of thin films of the bisulfate 
complex of PMCZAB cast on KC1 plates were obtained using a Digilab Model 
FTS-14 spectrometer. Films were cast from DMF solutions. 
Thermal analysis, including differential scanning calorimetry (DSC) and 
thermogravimetric analysis (TGA), was done using a DuPont Model 1090B 
thermal analyzer equipped with a DSC cell module and a Model 991 TGA 
module. Samples were sealed in DSC cells and run from 25-600.degree. C. at 
10.degree. C./min; TGA runs were likewise performed at 10.degree. C./min 
in air or nitrogen atmospheres. 
X-ray diffraction patterns of the polymer samples were obtained using a 
Rigaku powder x-ray diffractometer with a sealed tube CuK.alpha.x-ray 
radiation at 1.540562 Angstrom wavelength. The 20 scans were from 
3-90.degree., step size of 0.02.degree. and 1-second counting time per 
step. 
The morphology of the fracture surfaces of PMCZAB complexes was observed 
with a Cambridge SR-4 scanning electron microscope (SEM). The d.c. 
conductivity measurements were made on films cast on glass slides using 
principally a two-point technique but also a standard four-point probe 
instrument. 
The 3,6-carbazolyl structure II was assigned based on knowledge of similar 
carbazobe/aldehyde condensation polymers. Calculated and observed 
elemental analyses were in reasonable agreement. EDAX of the sample 
observed in the SEM showed a strong sulfur peak and no other elements. The 
EDAX mapping of sulfur in the samples revealed a uniform distribution. 
Also, the ESCA spectra of the surface and sputtered surface (-50 A) gave 
the expected qualitative composition. The mole ratio of the dopant 
counterion (HSO.sub.4.sup.-) to the polymer repeating unit, y, was found 
to be always greater than 1 (1.2-1.7) in four polymerizations. Although 
the hydrogen analysis was higher than calculated, loss of the methine 
hydrogen was inferred from the high conductivity of the polymer complex 
and previous work on related polymers. 
The simultaneous polymerization and doping in solution using a Bronsted 
acid catalyst (H.sub.2 SO.sub.4) is noteworthy. This result shows that 
similar polymerization and doping in solution may be reasonably predicted 
using other protic acids HX, such as HClO.sub.4, HBF.sub.4, CH.sub.3 
SO.sub.3 H, etc. The polymer complex PMCZAB.sup.y+ (HSO.sub.4.sup.-).sub.y 
is soluble in several organic polar solvents, including methanol, ethanol, 
DMF, N-methyl-2-pyrrolidone (NMP) and partially in water, acetone, and 
acetonitrile. The purple colored solutions which are conductive have been 
used to produce conductive films by solvent casting on substrates. This 
adds to the few known conducting polymer solutions: polycarbazoles in 
liquid iodine and poly(p-phenylene sulfide) in liquid AsF.sub.5 
/AsF.sub.3. By use of other protic acids (HX) in the polymerization, a 
system of conducting polymer solutions of PMCZAB.sup.y+ (X.sup.-)y with 
different anions could be prepared for various uses. 
FIG. 1 shows the GPC traces of the molecular weight distribution in two 
polymerizations. Curves 1 and 2 correspond to a short (.about.48 hr.) and 
long (75 hr.) polymerization time, respectively. In addition, the relative 
amount of initial acid catalyst is three times less in the polymerization 
of curve 1 compared to curve 2. It is interesting that both a small high 
molecular weight fraction and a large low molecular weight fraction are 
present in the product of curve 1. However, the polymer sample from the 
longer polymerization time and larger amount of acid catalyst gave a 
predominantly high molecular weight polymer with a broad molecular weight 
distribution. The discrete peaks marked as a, b, c, etc. in curve 1 of 
FIG. 3 were identified as corresponding to oligomers n=1, 2, 3, etc. of 
the polymer II without the counterion. An excellent linear fit of the 
molecular weight M.sub.n =328.4 n+181.24 plotted against the elution 
volume was obtained for n&gt;2 and used to estimate M.sub.n and DP.sub.n for 
the high molecular weight fractions. The high molecular weight fraction in 
curve 2 gave M.sub.n .about.8,500-80,000 or DP.sub.n .about.26-244. 
FIG. 2 shows the DSC thermogram of the polymer complex. indicating a large 
endothermic peak at 234.degree. C. which is interpreted as melting. The 
polymer complex decomposes above 260-280.degree. C., as indicated by the 
continuously increasing DSC curve. The weight loss characteristic of the 
complex revealed by TGA which shows onset of initial decomposition at 
.about.200.degree. C. resulting in ca 20% weight loss at 425.degree. C. is 
attributed to volatilization of the bisulfate anion; this is to be 
compared to .about.26-33% HSO.sub.4.sup.- found in samples of the polymer 
complex by elemental analysis for y=1.2-1.7. Other members of the neutral 
polymers of structure I had onset of thermal decomposition at 
.about.420-450.degree. C. 
X-ray powder diffraction patterns of the polymer complex are shown in FIG. 
3. Two broad peaks with Bragg d-spacing at .about.4.90 and .about.3.75 
Angstrom are evident. The x-ray diffraction (XRD) patterns indicate that 
the degree of crystallinity is not very high or that the crystallite sizes 
are very small compared to the spatial resolution of XRD. 
The typical morphology of the fracture surface of a bulk sample of 
conductive PMCZAB/HSO.sub.4.sup.- complex was a dense continuous 
morphology characteristic of bulk or thin film samples prepared from 
solutions under slow solvent evaporation rate. Rapid evaporation of 
solvent from a highly viscous solution of the polymer complex resulted in 
a porous or sponge-like morphology in bulk samples or films. 
The measured room temperature d.c. conductivity of 
(PMCZAB.sup.y+)(HSO.sub.4.sup.-)y films for four different y values in the 
range 1.2-1.7 was .about.0.01 to 0.10 ohm.sup.-1 cm.sup.-1. This 
conductivity of samples stored in air has remained stable for over two 
years. Quantitative study of the conductivity of the electrically 
conducting solutions of the polymer complex has not been made. Also, the 
photoelectronic properties of PMCZAB complex have not yet been studied. 
FIG. 4 shows the electronic absorption spectra of PMCZAB.sup.y+ 
(HSO.sub.4.sup.-)y thin films for three different polymerizations 
(y=1.2-1.7). The optical absorption maximum (.lambda..sub.max) is located 
at 604-636 nm with a shoulder band maximum at 537-564 nm. This electronic 
absorption maximum is attributed to the charge transfer (CT) band commonly 
observed in carbazole-containing polymer charge transfer complexes. The 
two CT bands are also observed in complexes of carbazole monomers: 
carbazole (CZ)/Chloranil (540 nm; 504 nm); N-ethylcarbazole/Chloranil 
(600.+-.5 nm; 506.+-.2 nm). The characteristic assymmetry of the CT bands 
of carbazoles has been attributed to the two superposed bands which 
originate from transitions from the two highest occupied molecular 
orbitals (HOMO 1, HOMO 2) of carbazole moiety to the lowest unoccupied 
molecular orbital (LUMO) of the acceptor: HOMO 1 - LUMO and HOMO 2 - LUMO. 
The two HOMOs that are separated by .about.0.4-0.5 eV thus give rise to 
the two observed CT bands separated by a similar energy. The CT bands of 
FIG. 4 can be similarly explained. However, the two CT bands of FIG. 4 are 
separated by only -0.25-0.28 eV. Also, the low energy band is the more 
intense of the two CT bands in FIG. 4 in contrast to PVK complexes. The 
smaller energy difference between the two CT bands of 
PMCZAB/HSO.sub.4.sup.- complex compared to .about.0.4-0.5 eV typically 
found in PVK complexes thus suggests that the difference between the first 
and second ionizati,on potentials of PMCZAB is smaller than in PVK. 
The related electronic absorption in the UV which are shown in part in FIG. 
4 revealed bands characteristic of the carbazole moiety with 
.lambda..sub.max at 336-340 nm and 298-302 nm.