J . Am. Chem. SOC.1989, 111, 4091-4095 Acknowledgment. T h e research of H.J.S. a n d J.A.P. was supported in part by t h e National Science Foundation ( G r a n t C H E 84-17548), t h e National Institutes of Health ( G r a n t GM37994), a n d the David a n d Johanna Busch Foundation. T h e diffractometer-crystallographic computing facility a t Rutgers was purchased with NIH Grant 1510 R R O 1486 0 1 A 1 . The research of K.K.-J. was supported by t h e National Institutes of Health ( G r a n t GM-34111) and t h e donors of t h e Petroleum Research Fund, administered by the American Chemical Society. Generous grants of computer time from the I B M Corp., t h e John von N e u m a n n Supercomputer Center, and t h e N e w Jersey C o m -
409 1
mission on Science and Technology a r e gratefully acknowledged. W e thank Profs. S. S. Isied and H . B. Gray for helpful discussions and advice, Dr. J. T. Blair for installing t h e population analysis routines in our GAMESS program, a n d the Engelhard Corp. for a generous sample of RuCI3.6H2O. Supplementary Material Available: Tables of hydrogen atom parameters and anisotropic thermal parameters for 1-3 (7 pages); listings of observed and calculated structure factors for 1-3 (78 pages). Ordering information is given on any current masthead page.
Synthesis, Characterization, and Electrical Response of Phosphazene Polyelectrolytes S. Ganapathiappan, Kaimin Chen, and D. F. Shriver* Contribution from the Department of Chemistry and Materials Research Center, Northwestern University, Evanston, Illinois 60208. Received September 12, I988
Abstract: New phosphazene-based polymers have been synthesized, which function as single-ion conductors of either sodium or halide ions. As a prelude to the synthesis of these polymers, similar substitution reactions were carried out on hexchlorocyclotriphosphazeneand the products were well characterized. The polyelectrolytes were characterized by 'HN M R , 31PNMR, IR, DSC, and ac complex impedance studies. The temperature dependence of the conductivity of these polyelectrolytes follows the VTF equation, indicating that, as with polymer-salt complexes, ion transport is promoted by polymer-segment motion. The ionic conductivity of the polyelectrolytes containing bromide and iodide is 2 orders of magnitude higher than that of the sodium polyelectrolytes at 30-80 "C.
There has been considerable interest in the mechanism of charge transport in polymer a n d polyelectrolytes a n d in t h e potential applications of these materials in solid-state devices.'-4 Phosphazene- and siloxane-based comb polymers have been reported to exhibit high conductivity with alkali metal salts of trifluoromethanesulfonates, thiocyanates, and T h e drawback with these polymer-salt complexes as polymer electrolytes is that both cations and anions are mobile, and as a result, fundamental studies of single-ion transport a r e difficult. In addition, most applications of these materials are based on the transport of only one ion, such a s Li' in a lithium battery. In these applications the mobility of the anion leads to unwanted gradients in electrolyte concentration. A solution to this problem is to covalently attach the counterion to the polymer backbone. In the absence of solvent, conventional polyelectrolytes a r e rigid solids, which show poor conductivity. T h e introduction of plasticizers into polyelectrolytes greatly increases their conductivity, but plasticized systems a r e inherently less stable than pure polymers.8 Recently, polyelectrolytes of crosslinked phosphates9 a n d poly[(oligo(oxyethy1ene)methacrylate)-co-(alkali-metal methacrylates)] l o have ( 1 ) Tonge, J. S.; Shriver, D. F. Polymers f o r Electronic Applications; Lai, J . , Ed.; CRC: Boca Raton, FL, in press. (2) Ratner, M. A.; Shriver, D. F. Chem. Rev. 1988, 88, 109. ( 3 ) See for example: Polymer Elecrrolyre Reueiws; MacCallum, J. R., Vincent, C. A., Eds.; Elsevier Applied Science: New York, 1987; Chapters 1-3.
(4) Armand, M.B. Annu. Rev. Mater. Sci. 1986, 16, 245. (5) Blonsky, P. M.; Shriver, D. F.; Austin, P.; Allcock, H. R. J . A m . Chem. Sor. 1984, 106, 6854. (6) Blonsky, P.M.; Shriver, D. F.; Austin, P. E.; Allcock, H. R. Solid Stare tonics 1986, 18/19, 258. ( 7 ) Spindler, R.; Shriver, D. F. Macromolecules 1988, 21, 648. (8) Hardy, L. C.; Shriver, D. F. J . A m . Chem. Soc. 1985, 107, 3823. (9) LeNest, J. F.; Gandini, A.; Cheradame, H.; Cohen-Addad, J. P. Polym. Commun. 1987, 28, 302.
0002-7863/89/1511-4091$01 S O / O
been shown to be sodium ion conductors b u t show poor conductivity a t room temperature. We report the synthesis of elastomeric phosphazene polyelectrolytes in which the side groups are short chain oligo ether alkoxy and alkoxy sulfonate, quaternary or trialkylammonium salts. These new polyelectrolytes exhibit good ionic conductivity without added plasticizers or inorganic salts. A preliminary communication has appeared." Experimental Section Materials. All the experimental manipulations were carried out under an inert atmosphere of dry nitrogen. Tetrahydrofuran (THF) was distilled under nitrogen from sodium benzophenone ketyl. Acetonitrile (MeCN) was distilled from calcium hydride. The sodium salt of 2hydroxyethanesulfonic acid, 15-crown-5, and sodium spheres (Aldrich) were used as received; 2-(2-methoxyethoxy)ethanol(MeeOH) (Aldrich) was dried over molecular sieves (4A) and distilled before used. Poly(ethylene glycol methyl ether) (PEGOH) of average molecular weight 350, N,N-dimethylethanolamineand N,N-diethylethanolamine (Aldrich) were dried over molecular sieves (4A) before used. All haloalkanes were distilled prior to use, and other chemicals were reagent-grade purity. Dialysis tubes (American Scientific Products) used in the purification of the polymer normally had a cutoff molecular weight of 1000, but a molecular weight cutoff of 3500 was used for polymers synthesized with the sodium salt of PEGOH. Sodium ethane sulfonate was prepared by the neutralization of ethanesulfonic acid with sodium hydroxide in an aqueous solution and was recrystallized from methanol. Reactions involving iodoalkanes were carried out in the dark. Poly(dichlorophosphazene), (NPC12), (1) was prepared by the thermal polymerization of hexachlorocyclo(10) (a) Tsuchida, E.; Kobayashi, N.; Ohno, H. Macromolecules 1988, 21, 96. (b) Kobayashi, N.;Hamada, T.; Ohno, H.; Tsuchida, E. Polym. J . 1986, 18, 661. ( 1 1) Ganapathiappan, S.; Chen, K.; Shriver, D. F. Macromolecules 1988, 21, 2299.
0 1989 American Chemical Society
4092 J. Am. Chem. SOC.,Vol. 111, No. 11, 1989
Ganapathiappan et ai.
Table I. Experimental Details” for the Synthesis of Polv(DhosDhazene sulfonates) 6-15 NaOC2H4S03Na B mmol 6.88 2.92 2.04 1.63 1.17 0.59
40.5 17.2 12.0 9.6 6.9 3.5
alcoholb g mmol g mmol ROH 24.0 I109.1 7.3 60.8 11.4 51.8 11.2 93.3 8.4 38.2 12.0 100.0 6.3 28.6 12.2 101.7 4.5 20.5 12.7 105.8 2.3 10.5 13.2 110.0
X
15-crown-5
~
sodiumc (polymer g mmol obtained)d
~~
1.3 4.0 4.0 4.0 2.5 2.6
56.5 173.9 173.9 173.9 108.7 113.0
1.54 (6) 1.75 (7) 1.80 (8) 1.86 (9)f 1.90 (10) 1.96 (11)
R‘OH 2.04 12.0 8.4 38.2 35.0 100.0 4.0 173.9 1.80 (12) 1.63 9.6 13.6‘ 31.8 35.9 102.6 4.0 173.9 1.86 (13) 1.17 6.9 4.5 28.6 36.9 105.4 4.0 173.9 1.90 (14) 10.5 37.0 105.7 4.0 173.9 1.96 (15) 0.59 3.5 2.3 ‘In all the reactions linear (NPCI,), (1) (4g, 34.5 mmol) in THF (350 mL) was used. * R = C2H40C2H,0CH3and R’ = (C2H40)722CH3.In the alkoxide preparation, THF(2OO mL) was used. Unreacted sodium was removed wherever excess was used. Where the polymers are of the formula [NP(OR),(OC2H,S03Na)z-x]. Yield of the polymers was 60-70%. cDibenzo-18-crown-6 was used. /Anal.I4 Calcd: C, 40.07; H, 7.38; N, 4.88; P, 10.78. Found: C, 41.75; H, 8.19; N, 5.12; P, 8.01. triphosphazene, N3P3CI6(2), at 250 ‘ C in vacuum12 and stored under a dry nitrogen atmosphere. Poly[bis[(methoxyethoxy)ethoxy]phosphazene] (MEEP) was prepared by the method described previ0us1y.l~ Polymer-salt complexes of MEEP with sodium ethane sulfonate were prepared from weighed amounts of dried NaC2H5S03and MEEP in deionized water. After 24 h, the water was removed and the salt complex was dired under vacuum a t 60 OC for 40 h. The concentration of salt in the complex is expressed as a molar ratio. Instrumental Methods. Proton and 31PN M R spectra were recorded on a JEOL FX 90 spectrometer operating at 90 MHz. Proton N M R spectra for all the samples were recorded in either CDC13 or D,O containing T M S or DSS as an internal standard. Chemical shifts (6/ppm) are referenced to internal TMS or DSS for ‘H N M R and to external 85% H3P0, for I’P NMR; upfield shifts are negative. Conductivity values were obtained by complex impedance spectra’ with a Hewlett-Packard 4192A in the frequency range 10 Hz to 3 MHz. Infrared spectra were recorded on a Perkin-Elmer Model 283 spectrophotometer; IR spectra for all polymers show a strong band in the range 1220-1260 cm-’ attributable to v(P=N). DSC measurements were performed on a Perkin-Elmer DSC-2 with 1 i q ~ i d - Ncooling. ~ Glass-transition temperatures were measured at four heating rates (5, 10, 20, 40 K/min), and the Tg for the sample was determined by extrapolating to a zero heating rate. Preparation of NaOC2H,S03Na (3). The sodium salt of 2-hydroxyethanesulfonic acid (50 g, 0.34 mol) was mixed with sodium hydride (8.2 g, 0.34 mol) in T H F (300 mL). This mixture was heated under reflux for 120 h and cooled. Methanol (100 mL) was slowly added to the above mixture and then warmed. The mixture was filtered and the precipitate was extracted with hot methanol (4 X 200 mL). The precipitate, Na2OC2HpS03(3), was obtained in 58.3% yield: ‘H N M R 3.16 (t, 2 H), 3.95 (t. 2 H) and 3J(HH) = 6.6 Hz. Reaction of N3P3CI6 (2) with NaOC2H4S0,Na (3). Compound 3 (0.34 g, 2 mmol) and 15-crown-5 (2.64 g, 12 mmol) were stirred in T H F (50 mL). Compound 2 (0.7 g, 2 mmol) in T H F (50 mL) was added over a period of 30 min and then heated to a reflux for 36 h. The reaction mixture was filtered and the filtrate was evaporated in vacuum to obtain (4) and N3P3C1S(OS0,C2an oil consisting of N3P3CI5(OC2H4SO3Na) H,ONa) (5) in a 3:2 molar ratio. Reaction of N3P3CI6 (2) with NaC2H5S03. Compound 2 (0.7 g, 2 mmol) in T H F (50 mL) was added to a slurry of NaC,HSS03 (0.26 g, 2 mmol) in T H F containing 1 S-crown-5.( 1.32 g, 6 mmol). The contents were heated under reflux for 24 h. The reaction mixture was filtered and the solvent from the filtrate was evaporated to obtain a hygroscopic oil, N3P3CIS(OSO2C2HJ) in 15-crown-5. The chloro precursors were further characterized by converting them into their 2-(2-methoxyethoxy)ethoxy derivatives. This alkoxylation was carried out in refluxing T H F with an excess of the sodium salt of MeeOH. (1 2) Allcock, H. R. Phosphorus-Nitrogen Compounds; Academic: New
York, 1972.
Table 11. NMR,” Conductivity, and Thermal Data for Sodium Polv(ohosDhazene sulfonates) 6-15 ratio of ether 31PNMR conductivity, R-’ cm-l oxygen to oolvmer (PI) (P2) at 30 OC at 80 ‘C sodium ion Te. K d d 6.7 6 4 to -6‘ 7 4 to -6‘ d d 14.0 208 8 -6.0 -2 to -4 2.6 X 5.4 X 18.0 204 9 -6.7 -1.4 4.2 X 7.4 X 26.6 194 10 -6.9 -1.5 4.6 X IO-’ 1.3 X lod 38.0 197 2.3 X 4.8 X 98.0 195 11 -6.6 -1.3 12 0 to -6c 8.2 X 1.7 X 10” 65.0 206 4.9 X 1.9 X 10” 96.0 205 13 -7.0 -5.1 14 -7.1 -5.0 7.2 X 2.9 X IO” 137.0 206 15 -7.4 -5.7 2.4 X 1.5 X 10” 354.0 206 ‘Solvent was D20. Proton NMR spectra show the following peaks for polymers 6-11: 3.4 (s, OCH,), 3.7 (b, OCH,), 4.2 (b, POCH2); in addition, a peak at 6 1.9 (b, CH2S) are observed for polymers 6-9. The IH NMR spectra for polymers 12-15 show peaks at 6 3.4 (G, OCH3), 3.7 (b, OCH2), and 4.1 (b, POCH2). b P 1= (=P(OR), and P2 ; =P(OR)(OC2H4S03Na). cBroad signals. dConductivity too low to measure.
