J. MATER. CHEM., 1994, 4(12), 1811-1814 Polyaniline Alloys with Poly(3-sulfonato-4-hydroxystyrene) Motomichi Inoue,*a Felipe Medrano,a Masanobu Nakamura,at Michiko 9. Inouea3band Quintus Fernando" a ClPM, Universidad de Sonora, Apartado Postal 730, Hermosillo, Sonora, Mexico Department of Chemistry, University of Arizona, Tucson, AZ 85727, USA Oxidation of aniline with ammonium peroxodisulfate in aqueous solutions containing poly(3-sutfonato-4-hydroxystyrene)gave poly- mer alloys (or polymer blends) with a general composition of {(-C,H,NH-)[-CH2-CH(C,H3.0H .SO,-)-~H,SO&*ZH~O}~. Their electrical conductivities depended on the composition and varied between and 0.5 S cm-' at 300 K. The polyaniline salts were soluble in water and exhibited an electronic absorption band characteristic of emeraldine salts at 800nm.The corresponding alkaline solutions showed a band due to emeraldine bases at 600nm. These bands showed a pH dependence that is a consequence of an interchain interaction between two kinds of polymer chains. A polymer with x =0.4, y =1.2 and z =3.6 was soluble enough to observe EPR spectra, whose pH dependence showed that, with increasing pH, deprotonation occurs at polarons prior to deprotonation at bipolarons. Preparation of polymer blends (or polymer alloys) of polyani- line is one of the more versatile approaches for the modifi- cation of the physical properties (including electrical, electrochemical and mechanical properties) of the electrically conducting polymer. It has been reported that the electro- chemical polymerization of aniline in polymer electrolytes such as poly(acry1ic acid), poly(vinylsu1fonic acid) and poly( 4- sulfonatostyrene) gives polymer alloys whose electrochemical properties are different from those of polyaniline Polyanilines in the form of water-insoluble particles of col- loidal dimensions also have been obtained by chemical oxi- dation of aniline in aqueous solutions containing polymers as stabilizers, and the morphology and electronic absorption spectra of these polyanilines have been When polyaniline is doped with organic or polymer acids such as alkylbenzenesulfonic acids and poly(alky1phosphonic acids), the resulting polyaniline salts are soluble in organic solvent^.^.^ Recently, it was reported that water-soluble poly- anilines were obtained by polymerizing aniline monomers on a polymer template, although the specific reaction conditions and the compositions of the polyanilines were not elucidated." Poly(4-~ulfonatostyrene)-dopedpolyaniline was also reported to be water-soluble when it was prepared by using a dopant which had been prepurified by dialysis;" earlier papers reported that this polymer alloy was water-in~oluble,~,~ and the origin of this discrepancy is not clear.The solubilities of these polyaniline salts are induced by the surfactant nature of the counter-anions; soluble polyaniline can be obtained when an appropriate dopant is selected. The introduction of an -OH group into poly(styrene) leads to significant changes in physical properties such as solubility and miscibility, owing to the formation of hydrogen bonding through the -OH group in the resulting poly(4- hydroxystyrene).12-14 This observation suggests that a sulfo- nated poly( 4-hydroxystyrene) may form a polyaniline alloy with higher solubility than the polyaniline-poly(su1fonatosty-rene) alloy.In our preliminary paper, we reported that water- insoluble polyaniline was soluble in an aqueous solution containing 50% sulfonated poly(4-hydroxystyrene), suggest- ing the formation of a polymer ~ornplex.'~ In the present study, we have used 100% sulfonated poly( 4-hydroxystyrene), i.e. poly (3-sulfonato-4-hydroxystyrene) (abbreviated as PSHS) as counter-anions, and obtained polymer alloys that are water-soluble and also electroconductive.This paper reports t On leave from Cosmo Oil Co. Ltd., Tokyo, Japan under a contract with the Japan International Cooperation Agency. poly (3-sulfonato-4-hydroxystyrene), PSHS the syntheses, the solution electronic absorption spectra and the EPR spectra of these new polyaniline alloys. Experimenta1 Materials Poly(3-sulfonato-4-hydroxystyrene sodium salt), NaPSHS, was supplied as a 32.7 wt.% aqueous solution from Cosmo Oil Co. Ltd., Tokyo, Japan. The mean molecular weights were: M, =4500 and M, =27 500. Aniline suppliad from Merck was distilled before use. Ammonium peroxodisulfate supplied from Aldrich was used without further purification. Polymerization Polymer I was synthesized in the molar ratio AN :SHS-unit = 1 :1.1, as follows.4.2 ml (6.2 mmol for the monomer unit) of the NaPSHS solution were diluted up to 20m1, and passed twice through a column of strongly acidic ion-exchauge resin (DOWEX 50x8-100). The eluent was concentrated to 20 ml. In the resulting solution was dissolved 0.52 ml (5.7 nzmol) of aniline (AN), and solid ammonium peroxodisulfate (1.3 g, 5.7 mmol) was added slowly with stirring. After the reaction mixture had been stirred for 2 h, the dark solid 1hat was formed was separated by filtration, washed with 50ml of 0.05 mol 1-' sulfuric acid and with a small amount of water, and dried in vacuum. Analytical data are shown in Table 1. Polymer I1 was obtained for the molar ratio AN :SHS =1:3; other reaction conditions were identical with those for polymer I.The product that was formed as a suspension was separated by centrifugation. Polymer I11 was synthesized by using NaPSHS in dilute sulfuric acid in the molar ratio AN:SHS= 1: 1.1. 4.2 ml (6.2 mmol) of the NaPSHS solution were mixed wiith 20 ml of 1 mol 1-' sulfuric acid containing 0.52 ml (5.7 mmol) of aniline. To the resulting mixture was added 1.3 g (5,7 mmol) of solid ammonium peroxodisulfate with stirring. 4fter the reaction had continued for 2 h, the dark solid that was formed J. MATER. CHEM., 1994, VOL. 4 Table 1 Powder electrical conductivity, CT,at 298 K and analytical data of {(-C,H4NH-)[-CH, -CH(C,H,.OHSO;)-],( H,SO,);zH,O}, ' composition found(%)(required) polymer X Y 2 a/S cm-' C H I 0.3 0.8 1.4 0.5' 40.40 4.58 (39.63) (4.55) I1 0.4 1.2 3.6 10-5 31.78 5.02 (3 1.27) (4.96) I11 0.6 0.2 1.5 0.2b 50.24 4.93 (50.42) (4.93) 'Sulfate ions are shown as sulfuric acid, but some of them may be involved as anilinium sulfate.temperature limit was 0.070 eV for polymer I and 0.08 eV for polymer 111. N S 5.41 13.50 (5.50) (13.85) 3.91 15.01 (3.96) (14.51) 5.52 10.24 (5.44) (9.97) The activation energy at the high-was collected by filtration, washed with 50 ml of 0.05 mol 1-' sulfuric acid followed by a small amount of water, and dried in vacuum. Physical Measurements The electrical conductivity of a compressed pellet was deter- mined by van der Pauw's four-probe method or the standard two-probe method.The IR spectra of the compounds in KBr pellets were obtained with a Perkin-Elmer 1600 FTIR spec- trometer. The electronic absorption spectra were recorded with a Perkin-Elmer Lambda 2 UV-VIS spectrophotometer. For the measurements of pH dependence, sample solutions were prepared as follows. 200 mg of polymer 11, for example, were dissolved in 50 ml of 0.1 rnol I-' sodium sulfate. The pH of a 5 ml aliquot of the solution was adjusted by adding 1 mol 1-' NaOH or 1 mol 1-l H2S04; each of the resulting solutions was diluted to 16 ml with 0.1 rnol 1-' sodium sulfate so that the ionic strengths of the sample solutions were almost identical with one another. For polymers I and 111, a small amount of insoluble components was eliminated by filtration prior to the sample preparation.The EPR spectra were obtained with the aid of a Bruker ESP-300E spectrometer operating at a microwave frequency of 9.65 GHz. Each sample solution was sealed in a quartz tube under vacuum. Results and Discussion Table 1 shows the compositions determined by elemental analyses, together with the electrical conductivity data. The elemental analyses showed that SO,2-ions are intrinsically involved in addition to PSHS- anions; the former anions were not removed by washing with water. In Table 1, sulfate ions are shown as sulfuric acid, but some of them may be involved as anilinium sulfate; the real charge density located on a polyaniline unit may differ from that calculated from the composition shown in Table 1.The temperature dependence of the electrical conductivities of polymers I and 111 fits the equation, 0=go exp(-E/kT) at high temperatures, but gradu- ally deviates from the semiconductive relation with decreasing temperature. The IR spectra of polymers I and I1 are shown in Fig. 1. The strong IR bands of the phenol group in PSHS are superimposed on the IR bands of polyaniline. The apparent difference between the spectra of the two polymers is due to the difference in the PA:PSHS ratios. In the spectrum of polymer 1, a strong band at ca. 1160 cm-', which is character- istic of conducting p~lyaniline,'~,'~ can be identified. This band is shifted in the spectrum of polymer 11.This suggests that the chain conformation of polyaniline is altered by interchain interactions with PSHS. Polyaniline I1 (ca. 8 mg) was completely dissolved in 1 ml of water to give a clear solution; this polymer was partly 4000 3000 2000 1000 450 wavenurnberkm-' Fig. 1 IR spectra of ((-C6H,NH-)[ -CH, -CH(C6H3 * OH-SO,-)-I,( H2S04)y-zH,O},: (a) polymer 1, x=0.3 and y=0.8; (b)polymer 11, x=0.4 and y= 1.2. The spectrum of poly(3-sulfonato-4-hydroxystyrene) (PSHS) is shown for comparison (c).The position corresponding to ca. 1160 cm-', where there is a band characteristic of polyaniline, is marked x. soluble in dimethyl sulfoxide (DMSO) and N-methylpyrrolidi- none (NMP). Polyanilines I and 111contained a small amount of water-insoluble component, and had a higher solubility in DMSO and NMP than in water, although a small amount of insoluble component also remained in the organic solvents.The solubilities of the polyaniline salts in water are the result of the interaction of polyaniline with PSHS, which is highly water-soluble owing to the hydrophilic groups. Self-doped polyaniline, which has an -SO3-substituent in the ring system, is soluble in a dilute NaOH solution.18 In contrast to this polymer, our polymer is soluble in acidic solution in the protonated state as well as in basic solution in the depro- tonated state. Fig. 2 shows the solution electronic spectra observed for polymer I1 at different pH values. The spectra did not show the increasing baseline with decreasing wavelength due to light scattering that might be observed if fine particles were dispersed in the solution.An aqueous solution of polymer I1 had a pH of 4.3 and its spectrum was identical to spectrum B observed for the Na2S04 solution of the polymer. PSHS showed a sharp peak at 285 nm, and no absorption band at wavelengths above 350 nm. The polymer alloy showed broad bands characteristic of emeraldine salts in the 400 and 800 nm regions. This is evidence for the formation of emeraldine with a significant number of benzenoid-quinoid linkages in the polymer alloy, although the molecular weight of the polyani- line cation is not expected to be large. The molar absorptivities of the 800nm bands observed for acid solutions were of the order of 500 1 mol-' cm-'; these molar absorptivities are given in the legend for Fig.2. Essentially the same spectra were observed in acid solutions, but the 800 nm band showed a small red shift with increasing pH. In alkaline solutions, a J. MATER. CHEM., 1994, VOL. 4 Ahm Fig. 2 Solution electronic absorption spectra of polymer I1 ((-C6H,NH -)[ -CH2 -cH(C6H3 .OH *so3-)-H2S04),,2* 3.6H20}, at different pH values (the polymer concentrations were identical for all the sample solutions): pH (a) 1.6 (~=5201 mol-'cm-'); (b)4.3 (530); (c) 6.3 (450); (d) 8.3 (300); (e) 9.1 (420); (f)11.1 (390). band characteristic of an emeraldine base was observed at 600 nm. and also a band attributable to deprotonated phenol groups was observed at 310nm; the 400nm and 800nm bands disappeared at high pH values.In the pH range of 7-9, the nature of the spectrum changed significantly with pH, and at pH z 8 a very broad band was observed with an absorption maximum at 700nm. Essentially the same pH dependence was observed for polymer I, but the 700nm band appeared at a lower pH of 7 (Fig. 3). Polymer I11 showed a large spectrum change in the region pH 7-8 (Fig. 4). Jiang and Dong" reported the pH dependence of solution spectra of a soluble polyaniline involving inorganic counter- anions; in the spectrum of polyaniline with inorganic counter- anions, the intense band that was observed at 830nm for strongly acidic solutions weakened with increasing pH without showing appreciable chromatic shift and disappeared at pH 35.0; at pH ~4.2, a 620 nm band appeared and strength- ened with increasing pH without a chromatic shift.The significant differences between the present polymer alloys and the inorganic anion salts are: (1)the 800 nm band disappeared at a higher pH in our polymer alloy; (2) the polymer alloy showed a 700 nm band at intermediate pH values; and (3) the 800 nm band showed a red shift with increasing pH. These differences in the pH dependence indicate the presence of an interaction between polyaniline and the PSHS chains. The sulfonic acid protons of PSHS are completely dissociated in I I I I I I I 1 1 200 400 600 800 1000 A/nm Fig. 3 Solution electronic absorption spectra of polymer 1 { (-c6H4NH-)[-CH, CH(C6H3 -OH * SO3-H2S04),,, * ~ 1.4H2O).at different pH values (a small quantity of insoluble components was removed by filtration; the polymer concentrations were identical for all the sample solutions): pH (a) 1.0; (b)3.0; (c) 5.0 (d) 7.0; (e) 8.5; (f)11.0. 800 E 700 t \ 4 600 Fig. 4 pH dependence of the electronic absorption band in the region 600-800 nm: 0,polymer I; 0,polymer 11; V , polymer I11 solution throughout the pH range studied. In contrast, the dissociation of the hydroxy protons is dependent on pH, and consequently the conformation of PSHS varies with pH. The conformational change of a PSHS chain influences the confor- mation of a neighbouring polyaniline chain. The 600 nm band characteristic of an emeraldine base has been attributed to a charge transfer between the quinoid and benzenoid units;I8 the 800 nm band arises from the protonated-nitrogen yuinoid and/or the benzenoid Both the 600nm ;md the 800 nm bands are sensitive to the conjugation, which is related to the conformation or the ring distortion of the polyaniline chains.18 Thus, the different conformations of PSHS at differ-ent pH values result in the chromatic shift of the (100 and 800 nm bands.When a polyaniline molecule is surrounded by PSHS chains, the local pH around the polyaniline may be different from that of the entire solution, owing to interactions between aniline cations and sulfonate anions. This effect results in the disappearance of the 800nm band at a higher pH in the polymer alloy than in the polyaniline containing inorganic counter-anions.The observation of the 700 nrn band at pHx7 suggests the presence of a partially protonated polyaniline chain, whose conformation is different from that in acidic or in alkaline solution. The solubility of polymer I1 in water was high enough for observation of EPR spectra, which were successfully obtained for the saturated aqueous solutions (8 mg in 1 ml H,O) at different pH values. An acidic solution with pH 1.5 exhibited a sharp signal at g=2.005 with a maximum-slope width, W, of 0.8 G, which was almost identical with W=0.7 G orserved for the solid sample. The EPR spectra were broadened with increasing pH: W=1.8 G at pH 5.8, 2.5 G at 8.4.The signal broadening is caused by the decreasing spin-diffusion ~~~elocity and/or spin concentration. An important observation is that the line broadening occurs even at pH 5.8, where the KO0 nm band is observed without appreciable change in in tensity. This behaviour can be explained by assuming that: (3 ) pola-rons and bipolarons coexist in the polymer;21 (2) the KO0 nm band is due mainly to bipolarons (protonated-nitrogen quin- oids) rather than polarons (anilinium radical cations:\ which are responsible for the EPR signal; (3) with increasing pH, deprotonation occurs at polarons prior to deprotona tion at bipolarons. In conclusion, the new polyaniline alloys containinq PSHS as counter-anions are water-soluble and exhibit novel sbectro- scopic properties.These properties have not been olxerved for polyaniline salts with inorganic or organic counter-anions, and can be explained as the result of an interchain interaction between the two component polymers. 1814 J. MATER. CHEM., 1994, VOL. 4 References 13 S. Arichi, N. Sakamoto, S. Himuro, M. Miki and M. 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