Chemistry of Materials 1989,1 , 483-484 The silver colloid did not flocculate over 2-3 days at room temperature; it was stable up to 1week if kept at 5 OC in the dark. The palladium colloids in these organic monomers were smaller in particle size and more uniform compared with gold and silver. Particle sizes obtained for the various metals are shown in Table 11.
483
Table I. Conductivities and Glass Transition Temperatures of [NP(O(CIH,O),~CHIJ,.~-
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Acknowledgment. The support of 3M Corporation and the National Science Foundation through the Materials Chemistry Initiative and the Latin American collaborative research program is acknowledged with gratitude. Registry NO.PMMA, 9011-14-7; CU,7440-50-8;Ag, 7440-22-4; Au, 7440-57-5;Pd, 7440-05-3;styrene, 100-42-5;polystyrene, 9003-53-6; methyl methacrylate, 80-62-6.
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Cryptate Effects on Sodium-Conducting Phosphazene Polyelectrolytes
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Kaimin Chen, S. Ganapathiappan, and D. F. Shriver*
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Department of Chemistry and Materials Research Center Northwestern University, Evanston, Illinois 60208 Received May 8,1989 Solvent-free polymer-salt complexes have attracted wide interest because of their potential applications as electrolytes in electrochemical devices.'p2 The mechanism of charge transport in this class of ion conductors has been partially elucidated,3r4but the mobility of both cations and anions complicates the interpretation and reduces the performance of the electrolyte in electrochemical devices. To solve this problem, single-ion-conducting polymeric electrolytes have been synthesized very r e ~ e n t l y . ~For example, we have reported the synthesis of both cation (Na+) and anion (I-, Br-, and C1-) conducting phosphazene polyele~trolytes.~JOnly one type of mobile ion is present in these new polyelectrolytes, so fundamental studies of the factors that influence ion transport are greatly simplified. In the present research, we have studied the influence of cation size on mobility by a comparison of Na+ with the much larger Na+ cryptand complexes. The [2.2.2] cryptand ligand N(CH2CH20CH2CH20CH2CH2)3N used in this study forms highly stable complexes with alkalimetal ions, in which the cation is contained within the ligand cavity.8 In a previous study? it was observed that (1)Armand, M.B. Annu. Reu. Mater. Sci. 1986,16,245-61. (2) Abstracts, First Intemational Symposium on Polymer Electrolytes, St. Andrews, Scotland, 1987. (3)Ratner, M.A.; Shriver, D. F. Chem. Rev. 1988,88,109-124. (4)See,for example: Polymer Electrolyte Reviews; MacCallum, J. R., Vincent, C. A,, Eds.; Elsevier: New York, 1987. (5) (a) Hardy, L. C.; Shriver, D. F. J. Am. Chem. SOC.1986, 107, 3823-3828. (b) Tsuchida, E.;Kobayashi, N.; Ohno, H. Macromolecules 1988,21,96-100.(c) LeNest, J. F.; Gandini, A.; Cheradame, H.; CohenAddad, J. A. Polym. Commun. 1987,28,302.(d) Zhou, G.; Khan, I. M.; Smid, J. Polymer Commun. 1989,30(2).(e) Doan, K.E.; Ganapathiappan, S.; Chen, K.; Ratner, M. A.; Shriver, D. F. Mater. Res. SOC.Symp. Proc., 1989,135,343-349.(0Liu, H.; Okamoto, Y.; Skotheim, T.; Pak, Y. S.; Greenbaum, S. G.; Adamic, K. J. Ibid. 337-341. (6) Ganapathiappan, S.; Chen, K.; Shriver, D. F. Macromolecules 1988, 21, 2299. (7)Ganapathiappan, S.;Chen, K.; Shriver, D. F. J. Am. Chem. SOC. 1989,111, 4091. (8)Lehn, J. M.Acc. Chem. Res. 1978,lI(2). (9)Kaplan, M.L.;Rietman, E. R.; Cava, R. J.; Hott, L. K.; Chandroas, E. A. Solid State Ionics 1987,25,37-40.
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Bode plot of [ N P ( O ( C ~ H ~ O ) ~ . ~ ~ C H ~ ) ~ . ~ O (OC2H4S03Na)o~lo[2.2.2]cryptand)]o,lo],, at 25 O C : 0 , phase angle; A, impedance. Cell geometric factor: l / a = 0.113 cm-'.
Figure 2.
the addition of a crown ether to a polymer-salt complex increases the ionic conductivity, but it is unclear whether this arises from increased mobility of cations, anions, or both. Details of the synthesis of [NP(O(C2H40)7.22CH3)l.,,,(OC2H4S03Na)o,lo], (1)were described previously.6J The complexes [NPIO(C2H40)7.22CH3)1.9~(0C2H4S03Na)~.10([2.2.2]cryptand),],, r = 0.05,0.10, and 0.20, were prepared by the combination of 1 and [2.2.2] cryptand in acetonitrile followed by solvent removal under vacuum. The resulting polymers were further dried under high vacuum and then stored in dry nitrogen-filled glovebox. The glass transition temperatures of the polyelectrolytes were evaluated from differential scanning calorimetry measurements. T values are listed in Table I. The addition of cryptand %as negligible influence on Tr This may in part be due to the low ionic concentration in these polyelectrolytes. One set of conductivity measurements was carried out with ac impedance spectroscopy in the frequency range 10
0897-4756/89/2801-0483$01.50/00 1989 American Chemical Society
Chemistry of Materials 1989, 1, 484-486
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Figure 3.
mer-bound ether groups. Balanced against the greater effective mobility of the cation in the presence of [2.2.2] cryptand is a decreased efficiency of interfacial charge transport, apparently due to slow release of the sodium ion from the cryptand ligand. Even with this apparent charge-transfer resistance, the materials containing the [ 2.2.21 cryptand are significantly better electrolytes than the cryptand-free polyelectrolyte.
Acknowledgment. This research was supported by the NSF through the Northwestern University Materials Research Center. Registry No. Cryptand 222, 23978-09-8.
Hz to 5 MHz, using stainless steel electrodes, and some Crystal Growth and Phase Selectivity of results are listed in Table I. A significant increase in ionic Organic Superconductors [j3-(ET),13(T, = conductivity was observed when [2.2.2] cryptand was 1.5 K) and K-(ET),CU(NCS), (T, = 10.4 K)] on added into polymer 1. The conductivity increases as [2.2.2] Graphite Electrodes cryptand is added and reaches the maximum when the molar ratio of sodium ion to [2.2.2] cryptand is 1:l. AdHau H. Wang,* Lawrence K. Montgomery, dition of more [2.2.2] cryptand has negligible influence on Chad A. Husting, Bradley A. Vogt, conductivity. Arrhenius plots of the conductivities of the Jack M. Williams,* Sandra M. Budz, polyelectrolytes (Figure 1)show a gentle curvature, which Michael J. Lowry, K. Douglas Carlson, is a typical behavior of ion transport in amorphous polyWai-Kwong Kwok, and Vladimir Mikheyev mers. A second set of ac impedance data was collected in the Chemistry and Materials Science Divisions Argonne National Laboratory frequency range 10 mHz to 5 MHz,l0 using saturated soArgonne, Illinois 60439 dium amalgam coated on copper plate as electrodes. The Na(Hg) electrodes are nonblocking with respect to the Received June 9, 1989 polyelectrolytes studied, [NP(O(C2H40)7.22CH3)~.~~(OC2H,S03Na)0.10([2.2.2]cryptand),]~, x = 0,0.05,0.10, and In the relatively short period of time since supercon0.20. In addition to the single arc obtained in the absence ductivity was first observed in organic salts in 1980 [bisof cryptand, a smaller low-frequency arc is observed in the (tetramethyltetraselenafulvalenium)hexafluorophosphate, presence of cryptand. The Bode plot, Figure 2, of a T,= 0.9 K/25 kbar],' almost three dozen organic supercryptand-contained polyelectrolyte ( x = 0.10) at 25 "C conductors have been reported,2 and the maximum sushows one minimum phase angle at which the impedance perconducting transition temperature (T,) has risen by a corresponds to the bulk resistance (Rb),around 0.5 kHz. factor of 10 [(ET-d8)2Cu(NCS)2,T, = 11.4 K/ambient A second minimum phase angle occurs around 60 mHz. pres~ure].~No experimental technique has played a more By contrast, the Bode plot of the cryptand-free polyelecimportant role in the rapid development of this area than trolyte (Figure 3) does not have a second minimum phase electrocrystallization. The preponderance of organic suangle down to 10 mHz. The resistance associated with this perconductors has been prepared by anodic oxidation of low-frequency feature is independent of potential (10, 20, suitable organic substrates in the presence of supporting and 30 mV were applied) and sample thickness. The latter electrolytes that supply the desired counter ion^.^ Alobservation strongly implicates an interfacial origin for the though solvent, temperature, and current density are imlow-frequency arc. The Arrhenius plot of the low-freportant experimental variables in electrocrystallization,the quency arc is linear over the temperature range studied electrode material is the very heart of the oxidation re(25-50 "C). We attribute the low-frequency arc to interaction. To date, platinum has been the most commonly facial charge-transfer resistance primarily associated with employed electrode material, and to prepare high-quality the rate of sodium ion release from the [2.2.2] cryptand crystals, its treatment before electrocrystallization is complex to the amalgam electrode. The activation energy ~ r i t i c a l . ~It is surprising that the composition of the (E,) for this process is 17 kcal mol-'. For comparison, the working electrode has received so little systematic attenactivation energy for the release of (Na+C2.2.2) in tion, since it is one of the most obvious components to vary ethylenediamine solvent is 12.9 kcal mol-'." in seeking new conducting materials, and electrodes can When a [2.2.2] cryptand is added to a sodium phosbe constructed from a variety of different substances (e.g., phazene polyelectrolyte, a large increase in conductivity is obtained. Because the counterion is immobile, all of this (1) JCrome, D.; Mazaud, A.; Ribault, M.; Bechgaard, K. J . Phys. Lett. conductivity increase can be attributed to the cation. 1980,41, L95. Judging from Tgdata, the presence of [2.2.2] cryptand does (2) For recent summaries see: (a) Ishiguro, T. Physica C 1988, 153, 1055. (b) Inokuchi, H. Angew. Chem., Int. E d . Engl. 1988, 27, 1747. not alter the gross polymer dynamics, so the likely origins (3) (a) Urayama, H.; Yamochi, H.; Saito, G.; Nozawa, K.; Sugano, T.; of increased conductivity are reduced cation-anion pairing Kinoshita, M.; Sato, S.; Oshima, K.; Kawamoto, A.; Tanaka, J. Chem. and/or decreased interaction of the cation with the polyLett. 1988, 55. (b) Schweitzer, D.; Polychroniadis, K.; Klutz, T.; Keller, ~~
~
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(10) Archer, W. I.; Armstrong, R. D. In Electrochemistry; Chemical Society Specialist Periodical Reports 7; Royal Society of Chemistry: London, 1980; Chapter 3. (11)Ceraso, J. M.; Smith, P. b.; Landers, J. S.; Dye, J. L. J . Phys. Chem. 1977,81.
0897-4756/89/2801-0484$01.50/0
H. J.; Henning, I.; Heinen, I.; Haeberlen, U.; Gogu, E.; Giirtner, S.Synth. Met. 1988, 27, A465. (4) Williams, J. M.; Wang, H. H.; Emge, T. J.; Geiger, U.; Beno,M. A.; Leung, P. C . W.; Carlson, K. D.; Thorn, R. J.; Schultz, A. J.; Whangbo, M.-H. Prog. Inorg. Chem. 1987, 35, 51. (5) Emge, T. J.; Wang, H. H.; Beno, M. A.; Williams, J. M.; Whangbo, M.-H.; Evain, M. J . Am. Chem. SOC.1986, 108, 8215.
0 1989 American Chemical Society
