CA1341107C - Self-doped polymers - Google Patents

Abstract

A self-doped conducting polymer having along its backbone a .pi.-electron conjugated system which comprises a plurality of p-phenylenevinylene monomer units, between about 0.01 and 100 mole % of the units having covalently linked thereto air least one Bronsted acid group. The conductive zwitterionic polymer is also provided, as are monomers useful in the preparation of the polymer and electrodes comprising the polymer.

Description

13411p7 SELF-DOPED POLYMERS
Description Technical Field This invention relates generally to the field of conducting polymers. More particularly the invention relates to self-doped conjugated polymers in which Bronsted acid groups are covalently bound to the backbone of the polymer.
Background Art The requirements for conductive polymers used in the electronic anti other industries are becoming more and more stringent. There is also an increasing need for materials which permit reduction in the size and weight of electronic parts and which themselves exhibit long-term stability and superior performance.
In order to satisfy these demands, active efforts have been made in recent years to develop new conductive macromolecular or palymeric materials. A number of proposals have also been made regarding the potential uses of such new compounds. Far example, P.J. Nigrey et al. in Chem. Comm.
pp. 591 et seg. (1979) have disclosed the use of polyacetylenes as secondary battery electrodes. Similarly, in the J. Electro Chem. Soc., p. 1651 et s_,eg. (1651) and in ~-7 / , J

-lA-Japanese Patent Applications Laid Open Publication Number & Date 1. No. 136469/1981 58-37290 / March1983;

2. No. 12116E~/1981 58-21889 / Feb. 1983;

3. No. 3870/1.984 60-147885 / Aug. 1985;

4. No. 3872/1984 60-148184 / Aug. 1985;

5. No. 3873/1984 60-147877 / Aug. 1985;

6. No. 196566/1984 61-75307 / April1986;

7. No. 196573/1984 61-75428 / April1986;

8. No. 203368/1984 61-79765 / April1986;

9. No. 203369/1984 61-79766 / April1986:

a _2-have also disclosed the use of polyacetylenes, Schiff base-containing quinazone polymers, polyarylene quinones, poly-p-phenylenes, poly-2,5-thienylenes and other polymericrmaterials as electrode materials for secondary batteries.
The use of polymeric materials in electrochromic applications has also been suggested, in, e.g., A.F. Diaz et al., J. Electroanal. Chem. 111: 111 _et seq. (1980), Yoneyama et al., J. Electroanal. Chem. 161, p. 419 (1984) (polyaniline), A.F.Diaz et al., J. Electroanal. Chem. 149:
101 (1983) (poly,pyrrole), M.A. Druy et al., Journal de Physique 44: C3-595 (June 1983), and Kaneto et al., Ja an Journal of Applied Physics 22(7): L412 (1983) (polythiophene).
These :highly conductive polymers known in the art are typically rendered conductive through the process of doping with acceptors or donors. In acceptor doping, the backbone of 'the acceptor-doped polymer is oxidized, thereby introducing positive charges into the polymer chain. Similarly, in donor doping, the polymer is reduced, so that negative charges are introduced into the polymer chain. It is these mobile positive or negative charges which are externally introduced into the polymer chains that are :responsible for the electrical conductiv-ity of the doped polymers. In addition, such "p-type"
(oxidation) or ":n-type" (reduction) doping is responsible for substantially all the changes in electronic structure which occur after doping, including, for example, changes ''0 in the optical a:nd infrared absorption spectra.
Thus, in all previous methods of doping the counterions are derived from an external acceptor or donor functionality. lDuring electrochemical cycling between neutral and ionic states, then, the counterions must migrate in and out of the bulk of the polymer. This solid state diffusion of externally introduced counterions is often the rate-limiting step in the cycling process. It is thus desirable to overcome this limitation and thereby increase the response time in electrochemical or electrochromic doping and undoping operations. It has been found that the response time can be shortened if the period required for migration of counterions can be curtailed. The present invention is predicated upon this :L 0 discovery.
Disclosure of the Invention The present invention provides conducting polymers that can be rapidly doped and undoped, and which are capable of maintaining a stable, doped state for long L5 periods of time relative to conducting polymers of the prior art. The superior properties of the polymers of the present invention result from the discovery that conduct-ing polmers can be made in a "self-doped" form; i.e., the counterion that provides conductivity can be covalently :ZO linked to the polymer itself. In contrast to the polymers of the prior art, therefore, the need for externally introduced counterions is obviated, and the rate-limiting diffusion step alluded. to above is eliminated as well.
The polymers of the invention can display '~5 conductivities of on the order of at least about 1 S/cm.
The self-doped polymers may be used as electrodes in electrochemical cells, as conductive layers in electrochromic displays, field effective transistors, Schottky diodes and the like, or in any number of applica-:30 Lions where a highly conductive polymer which exhibits rapid doping kinetics is desirable.
In its broadest aspect, the present invention is directed to a conducting self-doped polymer having along its backbone a p-electron conjugated system which :35 comprises a plurality of monomer units, between about 0.01 and 100 mole ~ of said units having covalently linked 4 a3411p7 thereto at least one Bronsted acid group. The present invention also encompasses the zwitterionic form of such polymers.
In commonly assigned Canadian application No.
520,452, filed 1~4 October 1986, certain self-doped polymers are disclosed which contain a recurring structure selected from th~s following structures (I) or (II):
1. 0 R-x-M
(I) , ~ ~E J
1. 5 l i~-x-M
v ( I I ) -~'~I ~ N N --2. 5 In Formula I: Ht is a heterogroup; Y1 is selected from the group consisting of hydrogen and -R-X-M; M is an atom or group which when oxidized yields a positive monovalent counterion; X is a Bronsted acid anion; and R is a linear or branched alkyl, ether, ester or amide moiety having between 1 and about 10 carbon atoms. In Formula II, Y2, Y3 and Y4 are independently selected from the group consisting of hydrogen and -R-X-M, wherein R, X and M are as given for Formula I.
?~ 5 The present application is directed to a new class of self-doped polymers, polyp-phenylenevinylenes), which contain the recurring structure (III):
oY~ o_R_x_M
J. 0 ( I I I ) ~/ 1 CK = C Et J. 5 In Formula III, Y2, R, X and M are as defined for Formula II.
A prefE~rred subset of the polyp-phenylene-vinylenes) given by Formula III may be represented by structure III-1, as follows:
M, a5 i o '~
(III-1) O
R, In Formula III-1,, M is as defined earlier, n is an integer in the range of :L to 10 inclusive, and R' is -(CH2)nS03 M+, alkyl (1-lOC), or aryl. In the latter '~5 case, R' is typically monocyclic, and may or may not be substituted with one or more alkyl (1-lOC) groups.

134110~
In yet another preferred embodiment of the invention, a conductive polymer is provided containing a recurring zwitterionic structure (IIIa):
CG
~x cu=-cu=_~-.
(IIIa) GI2X~
wherein R and X are as defined above.
The imrention is also directed to monomers use-ful in making thE~ above self-doped polymers, methods of synthesizing the polymers, and devices employing the polymers.
Brief Description of the Figures Figures 1 and 2 are infrared spectra of polyp-phenylenevinylene) polymers, as prepared herein, taken at a range of pH values.
Modes for Carrying Out the Invention The terms "conducting" or "conductive" indicate the ability to transmit electric charge by the passage of ionized atoms or electrons. "Conducting" or "conductive"
compounds includE~ compounds which embody or incorporate mobile ions or electrons as well as compounds which may be oxidized so as to embody or incorporate mobile ions or electrons.
The term "self-doping" means that a material may be rendered conducting or conductive without external introduction of :LOns by conventional doping techniques.
In the self-doping polymers disclosed herein, potential counterions are c:ovalently bound to the polymer backbone.

~,,~1 10~
The term "Bronsted acid" is used to refer to a chemical species which can act as a source of one or more protons, i.e. as a proton-donor. See, e.g., the McGraw-Hill Dictionary of Scientific and Technical Terms (3rd Ed.
1984) at page 220. Examples of Bronsted acids thus include carboxylic, sulfonic and phosphoric acids.
The term "Bronsted acid group" as used herein means Bronsted acids as defined above, anions of Bronsted acids (i.e. where the protons have been removed), and salts of Bronsted acids, in which a Bronsted acid anion is associated with a monovalent cationic counterion.
"Monomer units" as used herein refer to the recurring structural units of a polymer. The individual monomer units of a particular polymer may be identical, as in a homopolymer, or different, as in a copolymer.
The polymers of the present invention, which may be copolymers or homopolymers, have a backbone structure that provides a p-electron conjugated system. The recur-ring structure (III) may constitute anywhere from about 0.01 to about 100 mole ~ monomers substituted with one or more "-R-X-M" functionalities. In applications requiring high conductivity, usually at least about 10 mole $ of the monomer units are substituted, typically about 50 to 100 mole ~. In semiconductor applications, it is usually less than about 10 mole $ of the monomer units that are substituted, sometimes as little as about 0.1 or about 0.01 mole $.
The polyp-phenylenevinylene) monomer units represented by Formulae III and IIIa include monomer units which are substituted with 1 or 2 "-R-X-M" substitutents.
Copolymers encompassing these monomer units are envisioned by the present invention as well. In both the homopolymers and copolymers of the present invention, between about 0.01 and 100 mole $ of the polymer should be provided with Bronsted acid groups.

_g_ i3411p7 In a preferred embodiment, the present invention encompasses electrically neutral polymers given by Formula III. In order to render the polymers conductive, they must be oxidized so as to remove the M moiety and yield a polymer containing a recurring zwitterionic structure ac-cording to IIIa. In the preferred embodiment, for example, M may b~e H, Na, Li or K; X may be C02, S03 or HP03; and R is a straight chain alkyl or ether group (i.e., -(CH2)x- or -(CH2)y0(CH2)z-, where x and (y+z) are from 1 to about 10). In a particularly preferred embodiment, M is H, Li or Na; X is C02 or S03; R is a linear alkyl having from 2 to about 4 carbon atoms; and the substituted monomers of the polymers are either mono-:L5 or di-substituted with -R-X-M groups.
In order to "undope" the zwitterionic form of the polymers, an electric charge may be supplied in the direction contrary to that used in doping (alternatively, a mild reducing agent may be used as discussed below).
The M moiety is ~~aused to migrate into the polymer and neutralize the X counterion. The undoping process is thus as rapid as the doping process.
Scheme I represents the oxidation and reduction of polymers containing the recurring structure (III), i.e.
'~5 the transition between the electrically neutral and conductive zwitt~erionic forms:
:3 0 OY1 ~~? X M ~ \ 0,~ o~ XO
Scheme I 1 -M ~Oxtda~i~~
-Cd=CN~ ~ ~~1~-=CN CN =~w t ~~ CfZedu~~w., :35 _g_ Where X is C02, the above electrochemical conversion is strongly pH-dependent in the pH range of 1-6. Where X is S03, on the other hand, the above electrochemical reaction is pH-independent over the much larger pH range of about 1-14 (the pKa for X=S03 and M=H in Formula III is about 1). The sulfonic acid derivative is thus charged at virtually any pH, while the carboxylic acid derivative is charged at only higher pH. By varying the pH of the polymer solution, then, it is easier to control the conductivity of the carboxylic acid derivatives than that of the corresponding sulfonic acid derivatives. The particular Bronsted acid moiety selected will thus depend on the particular application.
These self-doped polymers typically have conductivities of at least about 1 S/cm and chain lengths of about several hundred monomer units. Chain lengths normally range from about 100 to about 500 monomer units;
higher molecular weights within this range are preferred, however.
In the practice of the present invention, a Bronsted acid group is introduced into the polymer to make it self-doping. The Bronsted acid may be introduced into a monomer, followed by polymerization or copolymerization.
One may also prepare a polymer or copolymer of the unsubstituted monomers of Formula III and then introduce the Bronsted acid into the polymer backbone.
Covalently linking a Bronsted acid to a monomer or polymer is within the skill of the art. See, e.g., _J.
per. Chem. Soc. 70:1556 (1948). By way of illustration, an alkyl group on a monomer or polymer backbone can be concatenated to an alkyl halide using N-bromo succinimide (NBS) as shown in Scheme II:
3 5 C X13 / C u,, ~3 ,~
\ N-~ / \
Scheme II

_lo_ 1 3 4 1 1 0 7 The halide can then be treated with sodium cyanide/sodium hydroxide or sodium sulfite followed by~hydrolysis to give a carboxylic or sulfonic Bronsted acid, respectively, as shown in Scheme III:
.L 0 c Uy c.c~o N
N4c r~
~~ g~ ~, Scheme III
us ~- cup so;N
~3 Ll~ c, y Another example ahowing the addition of a Bronsted acid with an ether linking group is shown in Scheme IV:
~G11L3~

~> -~ N0.ocL~tcuZ~-ocNZcN3 Scheme IV

Ii CUL ocuZ~~lZ ~ -dC~l2 c~1 ~
I y :30 ~, N a d CIaZ OCI~~ C (~IZ CUO ~I
:35 134110~
The polymers of the present invention may be synthesized by the electrochemical methods set forth in, e.g., S. Hotta et al., Synth. Metals _9:381 (1984), or by chemical coupling methods such as those described in Wudl et al., J. Org. Chem. 49:3382 (1984), Wudl et al., Mol.
Cryst. Liq. Cryst. 118:199 (1985) and M. Kobayashi et al., Synth. Metals. 9:77 (1984).
The po.ly(p-phenylenevinylenes) of Formulae III
.l0 and IIIa are preferably synthesized as follows:
or. x - .M
~Eu-to~NcQ. c»z c~
_~ 5 I ~ -~ ~ ~ I
CQ uJL
Scheme V
c~'( z.
20 CNz_ SIZz ~a S /
(Z~5 - C u~ 0 t~X- fL/
'~ 5 Pad y me.; tx ~y In Sch~ame V, Y2, R, X and M are as defined above.
Copolymerization of the monomers of Formula III
may be effected according to the same procedures outlined in the above-cited references. In a preferred embodiment, the majority of monomers are at least mono-substituted with an -R-X-M group as described.
';5 Composites of the polymers of Formula III may be prepared in conjunction with water-soluble polymers such 134110~
as polyvinyl alcohol and the polysaccharides. Because the polymers of the present invention may be fairly brittle, preparation of composites using additional polymeric materials provides polymers which are more flexible and less brittle. Films may be cast from aqueous solutions of polymers given by Formula III also containing a pre-determined amount of one or more additional water-soluble polymers. Since the key procedural criterion in this step :LO is dissolving two or more polymers in water, the only practical limitation on the additional polymers is that they be water-soluble.
The polymers of the present invention offer a specific advantage over conventional conducting polymers for use as electrodes in electrochemical cells. Because the counterions are covalently bound to the polymer, the cell capacity is not limited by electrolyte concentration and solubility. This means that in optimized cells, the total amount of electrolyte and solvent can be reduced :? 0 considerably, thus enhancing the energy density of the resulting battery. The facile kinetics of ion transport provided by the novel self-doping mechanism leads to rapid charge and discharge as well as to faster electrochromic switching. Electrodes fabricated using the polymers of ''S the invention may be fabricated entirely from these polymers or from conventional substrates coated with these polymers. Conventional substrates may include, for example, indium tin oxide coated glass, platinum, nickel, palladium or any other suitable anode materials. When 30 used as an electrode, the internal self-doping of the polymer effects the transition represented by Scheme I.
The self-doped conducting polymers of the inven-tion also offer specific advantages over conventional conducting polymers for use in a variety of device ap-:35 plications where long term performance requires that the dopant ions not be continuously mobile. Examples of such uses include fabrication of Schottky diodes, field effec-tive transistors, etc. Because the dopant ion is covalently bound to the polymer chain in self-doped polymers, the problem of diffusion of the ion (e.g., in the vicinity of a junction or interface) is solved.
Examples LO It is to be understood that while the invention has been described in conjunction with the preferred specific embodiment thereof, that the foregoing descrip-tion as well as the examples which follow are intended to illustrate and not limit the scope of the claimed inven-Lion. Other aspects, advantages and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains.
:Z 0 :Z 5 :30 .35 The following examples are directed to the dynthesis of a poly (p-phenylen~winyle:ne) (PPV) according to Scheme VI:
OH OOH O~~OMe ~ 1)NaOMe _ _ I ~~ MsC'1 / 2)CL~'~ OH / py OMe OMe OMe (A) (B) pal O~'~SO3Na NaI I ~ NazSOj ~~ DMF/SOC12 --a acetone / /
OMe OMe CC) (D) O ~~SOZCI O~SOzCI O
HCHO/Bf.1 ~ CHpCI CH SCI-I ~ ~S+/
_-~ 3 r3 _\
CIHZC I ~ S+-OMe OMe CI OMe (E) (p) O~SOZCI
Y'n S~
~ Cl_ OMe (I) fY
O /~SOZCI NaOMe HZO O~S03HPy ~ /~ +/
S\ ~ n ~S+ I / C1- ~, ~/ I i S+_ Cl- Na0)H I Cl OMe HZO OMe (G) O~S03HPy S
wS+ ~ , C1-Cl-OMe (K) Scheme VI
..t 1..

1341 10~
Example 1 Synthesis of a Polyp-Phenylenevinylene) Synthesis of (A):
To 200 ml of absolute ethanol was added 10.5 g sodium pellets at room temperature (RT). After the sodium was completely consumed, a solution of 22.32 g 4-methoxy-phenol in 80 ml of absolute ethanol was added. The resulting solution was stirred for 10 min, then treated with 25.2 ml of 3-chloropropanol. The mixture was refluxed for 16 )hr, the solvent was removed in vacuum, and the residue was 'taken up in 200 ml of ether. After filtration over charcoal, the filtrate was concentrated to -~5 about 25 ml. A .Large amount of white solid crystallized out to give 21.5 g IR (KBr, cm 1) 3300, 3050, 2960, 2940, 2880, 2840, 1520, 1480, 1450, 1400, 1300, 1245, 1185, 1065, 1040, 950, 830, 730. 1H NMR (CD30D, d rel to TMS):
1.6-2.0 (Q,2H), 3.5-4.0 (M,7H), 6.7 (S,4H). MS(EI,~):
182(M,41), 124(100), 109(61).
Synthesis of (B):
To a solution of 5.10 g 3-(methoxyphenoxyl)pro panol(A) in 20 m.l of freshly distilled pyridine was added '~5 3.26 ml of methanesulfonyl chloride in 5 ml pyridine. The reaction mixture was stirred at RT overnight and then poured into a se~paratory funnel containing 80 ml of water and 80 ml of ether. The layers were separated and the aqueous layer wars extracted twice with 40 ml ether each ';0 time. The combined organic layers were extracted twice with 40 ml of 10~ hydrochloric acid followed by rinsing twice with 40 ml H20 and drying with sodium sulfate for two hr. After evaporation of the solvent, a light brown oil was obtained which upon passing through a 16 x 2.5 cm '35 silica gel column using CHC13 as eluent gave 6.04 g light yellow oil (65~). IR (KBr, cm 1): 3020, 2960, 2940, -16- 1 3 4 1 1 0 ~
2880, 2840, 1600, 1510, 1470, 1450, 1360, 1300, 1240, 1180, 1110, 1060, 980, 950, 830. 1H NMR (CDC13, d rel to TMS): 2.0-2.4 (~Q,2H), 3.1 (S,3H), 3.8 (S,3H), 3.9-4.2 (T,2H), 4.3-4.6 (T,2H), 6.8 (S,4H).
Synthesis of (C):
To a solution of 6.75 g of NaI in 100 ml of acetone was added 3.9 g (B). The mixture was allowed to :LO react at RT for 24 hr. The CH3S03Na, which had precipitated, was separated by filtration. The filtrate was poured into water extracted with chloroform and the organic layer was dried with MgS04. Evaporation of the solvent afforded 4.073 g of product (93~) which upon pass-:L5 ing through an 18 x 2.5 cm silica gel column using hexane as eluent gave 3.20 g of dark-red liquid (73~). IR (KBr, cm 1): 3020, 3000, 2950, 2870, 2820, 1600, 1510, 1470, 1450, 1390, 1300, 1230, 1180, 1110, 1040, 830, 740. 1H
NMR (CDC13, _d rel to TMS): 2.1-2.4 (M,2H), 3.2-3.5 (T,2H), 3.7-4.1 (M,SH), 6.8 (S,4H). MS(EI,~), 292 (M,25), 202(15), 200(39), 124(100), 123(71), 109(61), 95(25), 81(11), 77(11), 64(11), 63(13), 52(12).
Synthesis of (D):
''S To 80 ml of an aqueous solution of 15.36 g of Na2S03 was added 17.8 g of (C) and the reaction mixture was heated to 70°C for 85 hr. The resulting solution was extracted with CHC13 to remove unreacted iodide (1.98 g).
The aqueous layer was distilled in a rotary evaporator to '30 remove water. The residue was washed with anhydrous acetone to remove sodium iodide. The remaining solid was then dissolved in 600 ml of water and passed through Amberlite IR-120 (plus) ion-exchange resin. The solution was concentrated to 200 ml in vacuum at 80°C and was '35 neutralized by 0.5 N NaOH solution. After evaporation of the solvent, 12.8 g of grey-white solid was obtained (88$). IR (KBr, cm 1): 3020, 2960, 2920, 2880, 2840, 1520, 1480, 1450, 1300, 1250, 1230, 1200, 1120, 1070, 1040, 830, 740, 540. 1H NMR (D20, d rel to DSS): 2.1-2.4 (Q,2H), 2.9-3.3 (T,2H), 3.8 (S,3H), 4.0-4.2 (T,2H), 7.0 (S,4H).
Synthesis of (E):
To a stirred suspension of 20.5 g of (D) in 80 ml of DMF was added dropwise 20 ml of thionyl chloride, and the mixture Haas allowed to stir for 45 min. The mixture was then quenched with 400 ml of ice water and extracted with 300 ml of ether. The ether layer was washed twice witlh 200 ml of cold water, then the ether ~~5 layer was dried with MgS04. Evaporation of solvent af-forded 13.3 g of yellow solid product. IR (KBr, cm 1):
3050, 2950, 2880, 2840, 1600, 1510, 1480, 1450, 1380, 1300, 1240, 1170, 1110, 1050, 930, 830, 750, 730, 700. 1H
NMR (CDC13, d ref to TMS): 2.2-2.6 (M,2H), 3.8-4.3 (M,7H), 6.9 (S,41H). MS(EI,~), 266 (M++2,16), 265 (M++1,5), 264 (M+,40), 143(20), 141(54), 137(20), 124(59), 123(100, 109(44), 95(23).
Synthesis of (F):
'~5 To 150 ml of 37~ formaldehyde aqueous solution was added 100 ml of concentrated hydrochloric acid at 0°C.
The mixture was saturated with hydrogen chloride gas for min before addition of 15 g of the above sulfonyl chloride (E) in ~BO ml of dioxane. The resulting mixture v0 was allowed to stir at room temperature for 3 hr. The white solid which formed was collected by filtration and was recrystallized from benzene to give 17.4 g white product (92~). ,Anal. calc'd for (C12H15C1304S): C 39.83;
H 4.15. Found: C 40.01; H 4.15. IR (KBr, cm 1): 3060, ~s5 3000, 2980, 2940, 2880, 2840, 1520, 1470, 1420, 1400, 1360, 1320, 1270, 1240, 1160, 1070, 1050, 1030, 940, 920, ~4~ ~ o ~
870, 800, 730, 6'.~0, 600. 1H NMR (CDC13, d rel to TMS):
2.4-2.8 (Q,2H), 3.8-4.3 (M,7H), 4.6 (S,4H), 7.3 (S,2H).
Synthesis of (G):
To 922 mg (F) in 10 ml of acetone and 10 ml of methanol was added 2 ml of dimethylsulfide. The mixture was stirred at room temperature for two days under nitrogen. After the solvent was removed, the residue was f0 precipitated witlh acetone and dried in vacuum to afford (G) in quantitative yield. IR (ICJ3r, cm 1): 3000, 2910, 2840, 1510, 1470, 1425, 1400, 1320, 1230, 1190, 1150, 1040, 940, 900, 870, 730, 700, 600. 1H NMR (CD30D, rel to TMS): 2.3-2.6 (JK,2H), 3.0 (S,12H), 3.9-4.4 (M,7H), 4.8 (S,4H, 7.3 (S,2H).
Polymerization of (G):
M.~~l.r.~-1 1 To a solution of monomer (G) (1.075, 2mmo1) in 5 '0 ml of MeOH was added 0.48 ml of 25~ NaOMe in MeOH at 0°C
under nitrogen. A viscous gum was formed immediately.
After a reaction time of 0.5 hr, the solvent was decanted and 8 ml of water and 2 ml of DMF were added. The result-ing mixture was :heated to reflux for half an hour to give '5 a clear yellow-greenish solution. The solution was dialyzed against deionized water with Spectropore membrane tubing for 24 hr to give the desired aqueous solution of precursor polymer (L) with pH value around 4.5. The pre-cursor polymer (:L) can be cast into films from aqueous solution. UV (film, max): 370. IR (film, v cm 1): 3450 (H20), 3080, 3010, 2950, 2880, 1650, 1510, 1470, 1330, 1210(broad), 104.5, 940, 880, 800, 730, 690, 610, 530.
~~ 5 ~ ~~~ 10 ~
M~+1,.~..d 7 Monomer (G) can also be polymerized by sodium hydroxide in water under similar conditions. But in the case of sodium hydroxide, one obtains a slightly viscous, milky solution instead of gum. This milky solution became clear after refluxing with a small amount of DMF. Upon water dialysis, the aqueous solution of the precursor polymer was obtained with the same UV and IR spectra as the above.
Conversion of (L) into PPV:
There are three ways to convert the precursor polymer (L) into fully conjugated PPV:
Method 1.
The precursor polymer (L) was cast into films from aqueous solution. The films then were heated to 200°C and maintained at this temperature for 4 hr in vacuo to yield an insoluble and infusible black film with bril-liant appearance. UV (~max, nm): 490. IR. (~/cm 1): 4000-2000 (broad dispersion), 1610, 1520s, 1410, 1350, 1210 (broad), 1040s, 960, 850, 800, 750, 600. Conductivity:
6(300K, air) - 2x10 6 S cm 1.
~r,~+ v"."-a 7 The aqueous solution of the precursor polymer (L) (10 ml) was mixed with 10 ml of ethylene glycol. The mixture was heated to the boiling point. After all the water was removed, the temperature of the solution was increased to 190oC and the solution turned red. The solu-tion was maintained at reflux for 6 hr under nitrogen, then cooled and dialyzed against deionized water for 24 hr to afford a red aqueous solution of substituted PPV from which a hygroscopic black film can be cast on a plastic weighing bowl at 45°C in vacuo.

20 149 'f(~ 7 M.-..42.~.-.~.1 Z
The aqueous solution of the precursor polymer (L) was mixed wii~h the same volume of DMF and excess of sodium methoxide. The mixture was heated to reflux for 4 hr to yield a red solution. After water dialysis, a red aqueous solution of substituted PPV was obtained.
The polymers obtained from Methods 2 and 3 have the same UV and :fR spectra as that from Method 3, but have higher conductivity, ranging from 10 ~ to 10 2 S cm 1.
Reversible Doping:
The curves of Figure 1 are superimposed infrared spectra of the polymer prepared via Method 1 at different ~~5 pH values. CurvE~ (a) is the infrared spectrum of the pristine polymer film; curve (c) is the same polymer film after exposure to acid (HC1) at pH 1; curve (b) is the same material after compensation with NH40H base (pH

10.5). The growl~h of the infrared band at the expense of the initial ~-x band is a clear signature of doping and is a fingerprint of the transformation of a conducting polymer to the conducting form. These data, therefore, demonstrate that the polymer can be reversibly doped upon exposure to an a<:id medium.
The curves of Figure 2 represent infrared spectra of the s<~me polymer at additional pH values, as follows: curve (a), pH 13; curve (b), pH 12.7; curve (c) pH 7.7; curve (d), pH 1.0; curve (e), pH 0.5; curve (f), pH 0.5. Again, ithe growth of the infrared band at the :30 expense of the initial3iC-~ band indicates the transforma-tion to the conducting form.

Claims (12)

1. A conducting self-doped polymer having along its backbone a p-electron conjugated system which comprises a plurality of monomer units, between about 0.01 and 100 mole % of said units having the structure wherein Y2 is selected from the group consisting of hydrogen and -R-X-M, wherein R is a linear or branched alkylene, ether, ester or amide moiety having between 1 and about 10 carbon atoms, X is a Bronsted acid anion and M is an atom which when oxidized yields a positive monovalent counterion.

2. The polymer of claim 1, wherein Y2 is hydrogen, R is a straight chain alkyl or ether group having between about 1 and 10 carbon atoms, X is CO2 or SO3, and M is selected from the group consisting of H, Li, Na and K.

3. The polymer of claim 2, wherein R is a linear alkyl having from 2 to about 4 carbon atoms, and M
is selected from the group consisting of H, Li and Na.

4. A homopolymer according to claim 1.

5. A copolymer according to claim 1.

6. A zwitterionic polymer according to claim 1.

7. The polymer of claim 1, wherein said monomer units are given by the following structure in which R' is selected from the group consisting of -(CH2)n SO3-M+, alkyl (1-10C), and monocyclic aryl, unsubstituted or substituted with at least one alkyl (1-10C) moiety, and n is an integer in the range of 1 to 10 inclusive.

8. An electrode for use an electrochemical cell, comprising a conductive substrate coated with a polymer according to claim 1.

9. The compound represented by the structure

10. The compound represented by the structure

11. The compound represented by the structure

12. The compound represented by the structure