pubs.acs.org/Langmuir © 2010 American Chemical Society
Bioinspired Blend Membranes Based on Adenine and Guanine Functional Poly(glycidyl methacrylate) Ays-e Aslan and Ayhan Bozkurt*
: Fatih University, Department of Chemistry, 34500 B€ uy€ ukc-ekmece-Istanbul, Turkey Received May 24, 2010. Revised Manuscript Received July 2, 2010 We have investigated adenine and guanine functional PGMAAdenine and PGMAGuanine as proton-conducting bioinspired membranes. Poly(glycidyl methacrylate) (PGMA) was prepared by free-radical polymerization and then modified with adenine and guanine molecules via ring opening of the epoxide ring. The complexed structure of the polymers was confirmed by FT-IR spectroscopy and 13C CP-MAS NMR and elemental analysis studies. The blends of adenine and guanine functional polymers with phosphoric acid (H3PO4) and poly(vinyl phosphonic acid) (PVPA) were prepared in several stoichiometric ratios. The thermal and proton-conducting properties of these membranes were investigated in the anhydrous state. Phosphoric acid-doped polymers had lower Tg values and higher proton conductivities than PVPA blends of adenine and guanine functional PGMA. (PGMAAdenine)-(H3PO4)2 had a maximum water-free proton conductivity of approximately 4 mS/cm at 150 °C.
1. Introduction In recent years, the development of proton-conducting bioinspired membranes dramatically increased because of their fundamental properties of chemical energy conversion in industrial devices such as proton-exchange membrane fuel cells (PEMFC).1-8 Many studies9,10 have focused on DNA and RNA as functional polymer materials, and nucleic acid bases adenine, guanine, and uracil have not been considered to be functional membranes. These heterocyclic compounds have high thermal stability up to 250 °C and can be expected to act as functional membranes for anhydrous proton exchange membrane fuel cells. Heterocyclic nucleic acid bases such as adenine and guanine can be utilized for anhydrous, protonconducting membranes and environmentally benign, nonhazardous PEMFCs could be constructed. Applications of proton-conducting biomembranes in electrical devices may encourage interdisciplinary research between the natural sciences and energy technology fields. There is growing interest in the development of new protonconducting membranes, which have higher proton-conducting properties than the present materials (such as Nafion as an ionexchanged membrane) under anhydrous conditions. These conducting membranes do not contain water but enable proton diffusion in polymeric membranes.11,12 Additionally Nafionbased systems have a higher cost, which makes it difficult to use PEMFC industrially. In particular, acid-base composite materials consisting of a low-cost artificial polymer have been reported *Corresponding author. Tel: þ90 212 8663300. E-mail:
[email protected].
(1) Kumar, M. N. V. R. React. Funct. Polym. 2000, 46, 1. (2) Yamada, M.; Honma, I. ChemPhysChem 2004, 5, 724. (3) Kreuer, K. D. J. Membr. Sci. 2001, 185, 29. (4) Rikukawa, M.; Sanui, K. Prog. Polym. Sci. 2000, 25, 1463. (5) Li, Q.; He, R.; Jensen, J. O.; Bjerrum, N. J. Chem. Mater. 2003, 15, 4896. (6) Yamada, M.; Honma, I. Bull. Chem. Soc. Jpn. 2007, 80, 11. (7) Hickner, M. A.; Ghassemi, H.; Kim, Y. S.; Einsla, B. R.; McGrath., J. E. Chem. Rev. 2004, 104, 4587. (8) Pome, R.; Roux, B. Biophys. J. 2002, 82, 2304. (9) Erdemi, H.; Bozkurt, A.; Meyer, W. H. Synth. Met. 2004, 143, 133. (10) Sevil, F.; Bozkurt, A. J. Phys. Chem. Solids 2004, 65, 1659. (11) Bozkurt, A.; Meyer, W. H.; Wegner, G. J. Power Sources 2003, 123, 126. (12) Takimoto, N. L.; Ohira, W.; Takeoka, A. Y.; Rikukawa, M. Polymer 2009, 50, 534. (13) Yamada, M.; Honma, I. Angew. Chem., Int. Ed. 2004, 43, 3688. (14) Li, Q.; He, R.; Jensen, J. O.; Bjerrum, N. J. Chem. Mater. 2003, 15, 4896.
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as anhydrous electrolytes at intermediate temperatures.13-15 However, for the applications of a proton-conducting membrane, the cost of the polymer electrolyte has to be further reduced. The proton-conducting mechanism in biomembranes (i.e., bioenergetic proteins) is essential for efficient energy transduction in living systems.16-18 An interesting approach is the proton solvent comprising functional polymers that are thermally stable and have a proton-transport pathway. From this point of view, polymer membranes including adenine and guanine units would be interesting where these biopolymers can be used as proton charge carriers in a membrane under anhydrous conditions. The utilization of biopolymers as a membrane material was reported in an earlier study.19 In this context, Park et al. reported the DNA/ PEI and DNA/PEO proton-conducting systems.20,21 In this study, anhydrous proton-conducting properties and thermal properties of the PVPA functional and phosphoric acid-doped PGMAAdenine and PGMAGuanine were investigated. The complexed structure of the materials was elucidated by FT-IR spectroscopy and 13C CP-MAS NMR and elemental analysis studies. The polymer was characterized via FT-IR, TG, DSC, and SEM. Proton-conducting properties of the copolymers were investigated with an impedance analyzer, and the results are discussed and compared with previously reported systems.
2. Experimental Section 2.1. Chemicals. Glycidyl methacrylate (>97%), adenine (>99%), and guanine (>99%) were supplied from SigmaAldrich Chemical Company. o-Phosphoric acid (>99%), toluene (>99%), diethyl ether (>99.5%), and DMSO (>99.5%) were purchased from Merck. Azobisisobutyronitrile (AIBN; Merck) was recrystallized from THF prior to use. Vinyl phosphonic acid (>95%, reagent grade) and R,R0 -azodiisobutyramidin dihydrochloride (15) Sone, Y.; Ekdunge, P.; Simonsson, D. J. Electrochem. Soc. 1996, 143, 1254. (16) Arslan, A.; Kıralp, S.; Toppare, L.; Bozkurt, A. Langmuir 2006, 22, 2913. (17) Wakizoe, M.; Velev, O. A.; Srinivasan, S. Electrochim. Acta 1995, 40, 335. (18) Yamada, M.; Honma, I. Biosens. Bioelectron. 2006, 21, 2064. (19) Won, J.; Chae, S. K.; Kim, J. H.; Park, H. H.; Kang, Y. S.; Kim, H. S. J. Membr. Sci. 2005, 249, 113. (20) Park, J. K.; Won, J.; Kim, C. K. Macromol. Res. 2007, 15, 581. (21) Park, J. K.; Kang, Y. S.; Won, J. Membr. Sci. 2008, 313, 217.
Published on Web 07/23/2010
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Figure 1. Synthesis of adenine functional PGMA.
Figure 2. Synthesis of guanine functional PGMA.
(AIBHC, >98%, reagent grade) were obtained from Fluka and used as received. 2.2. Preparation. Poly(glycidyl methacrylate) was produced by the free radical polymerization of glycidyl methacrylate.22,23 Adenine (Mw = 135 g/mol) and PGMA were dissolved in DMSO to get PGMAAdenine. The molar stoichiometric ratio of adenine to the PGMA repeat unit was fixed to 1:1.2, and the temperature was set to 105 °C (Figure 1). PGMAAdenine was obtained after precipitation with THF and then washed with hot water to remove excess adenine. After purification, it was filtered and dried at 70 °C under vacuum and yellow, rigid polymers were obtained. Polymers were swelling and were in an aqueous medium and polar organic solvents. The same method was used for the synthesis of PGMAGuanine in DMSO. After the reaction, the solution was filtered to remove excess guanine and dialized against water to remove the DMSO solvent. The polymer was dried at 70 °C under vacuum. Polymers in powder form were obtained. The materials are insoluble in common organic solvents but swell in aqueous media. In the second step, poly(vinyl phosphonic acid) was produced by the free radical polymerization of vinyl phosphonic acid as discussed in an earlier study.24 PGMAAdenine, PGMAGuanine, and PVPA were dissolved in hot DMSO. Stoichiometric amounts of PGMAAdenine, PGMAGuanine, and PVPA solutions PGMAAdenine-(PVPA)x and PGMAGuanine-(PVPA)x (x = 0.5, 1, 1.5, 2 (i.e., x is the number of moles of PVPA per moles of adenine and guanine units in the polymer)) were mixed. Rigid polymer blend membranes were obtained. To prepare (PGMAAdenine)-(H3PO4)x, adenine functional polymer was dissolved in hot DMSO and phosphoric acid was added in different ratios (x = 0.5, 1, 1.5, 2 (i.e., x is the number of moles of acid per moles of adenine unit in the polymer)). After the solvent was evaporated, polymers were dried completely in a vacuum oven. Hard, rigid polymer films were obtained. The same method was used to prepare (PGMAGuanine)-(H3PO4)x. 2.3. Characterization. Prior to FT-IR spectral measurements, samples were dried under vacuum and stored in a glovebox. The IR spectra (4000-400 cm-1, resolution 4 cm-1) were recorded with a Bruker Alpha-P in the ATR system. Solid-state 13C CP-MAS NMR studies of the samples were performed using a Bruker Avance spectrometer equipped with a 2.5 mm fast MAS probe. The spectra were recorded at room temperature at a 125.76 MHz 13C Larmor frequency with a MAS frequency of 20 kHz and a CP contact time of 2 ms. 1 H MAS NMR experiments on the samples were performed with a Bruker Avance spectrometer and by using a 2.5 mm fast MAS probe. All 1H experiments were performed at a 25 kHz MAS frequency to suppress the homonuclear dipolar couplings of
Figure 3. (a) Solid-state 13C CP-MAS NMR spectra of PGMAA-
(22) C-elik, S. U.; Akbey, U.; Graf, R.; Bozkurt, A.; Spiess, H. W. Phys. Chem. Chem. Phys. 2008, 10, 6058. (23) Lubczak, R.; Duliban, J. React. Funct. Polym. 2002, 52, 127. (24) Bing€ol, B.; Meyer, W. H.; Wagner, M.; Wegner, G. Macromol. Rapid Commun. 2006, 27, 1719.
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denine. (b) Solid-state 13C CP-MAS NMR spectra of PGMAGuanine.
the dense proton network sufficiently. The 90° pulse lengths were 2.5 μs. Two-dimensional DQ MAS experiments were performed using a one-rotor period of the back-to-back (BABA) recoupling pulse sequence for the excitation and reconversion of dipolar 1 H-1H DQ coherences.25 The oxidative stability of the membranes was tested by immersing the films in Fenton’s reagent (a 3% H2O2 aqueous solution containing 2 ppm FeSO4). The dissolution time of the membranes in the reagent was used to evaluate their oxidative stability. The surface morphology of blend membranes was investigated by scanning electron microscopy (SEM, Philips XL30S-FEG). All of the samples were sputtered with gold for 150 s before SEM measurements. Thermal stabilities of the complex polymer electrolytes were examined by thermogravimetry (TG) analysis with a Perkin-Elmer STA 6000. The samples (∼10 mg) were heated from room temperature to 700 °C under a N2 atmosphere at a heating rate of 10 °C/min. Differential scanning calorimetry (DSC) data were obtained using a Perkin-Elmer JADE DSC instrument. The measurements were carried out at a rate of 10 °C min-1 under nitrogen flow. The proton conductivity studies of the samples were performed using a Novocontrol dielectric impedance analyzer. The samples were sandwiched between platinum blocking electrodes, and the conductivities were measured in the frequency range of 0.1 Hz to (25) Feike, M.; Demco, D. E.; Graf, R.; Gottwald, J.; Hafner, S.; Spiess, H. W. J. Magn. Reson. A 1996, 122, 214.
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Figure 4. 1H MAS NMR spectra of adenine and guanine functional PGMA polymers recorded at 320 K and 25 kHz MAS. 3 MHz at 10 °C intervals. The temperature was controlled with a Novocontrol cryosystem, which is applicable between -100 and 250 °C.
3. Results and Discussion 3.1. Characterization. Adenine and guanine immobilizations are very important to this study, and elemental analysis is used to verify this reaction. The backbone of PGMA does not contain nitrogen, so the nitrogen contribution to the functional polymers comes from the adenine and guanine units. The nitrogen contents of the samples were used to calculate the adenine and guanine ratio in the functional polymers. As illustrated from elemental analysis, more than 80% of the epoxide rings were opened by adenine units and more than 50% of the epoxide rings were opened by guanine units. 3.1.1. Solid-State 13C CP-MAS NMR. The solid-state 13C CP-MAS NMR spectra of PGMAAdenine and PGMAGuanine are shown in Figure 3. The characteristic C peaks of adenine are between 140 and 160 ppm, and the peak located at around 180 ppm belongs to C of the carbonyl group. The characteristic C peak of guanine is between 150 and 170 ppm, and the peak located at around 180 ppm belongs to the C of the carbonyl group. Signals corresponding to the methyl and methylene groups appear between 15 and 75 ppm. Resonances are similar for both samples, except those in the 120-170 ppm region. This difference in the adenine functional polymer may originate from the polymerization procedure, where the additional NH sites in adenine may result in some side reactions leading to interchain and/or intrachain cross linking. 3.1.2. 1H MAS NMR. From Figure 4, different proton sites in the studied materials can be identified. The aliphatic, aromatic, and hydrogen-bonded acidic protons are observed at different spectral positions. No indication of strong hydrogen bonding is observed for the adenine functional polymer because there is no high chemical shift proton resonance in the spectrum. Guanine functional polymer, however, has a broad resonance at ∼12 ppm, which indicates the presence of hydrogen bonding. The resonance is not well resolved and relatively broad. This observation indicates the lack of molecular mobility in the system, which is observed in all of the 1H spectra at low temperature and even at high temperature. This also manifests itself in the observed proton (26) Kim, J.; Mori, T.; Hayashi, S.; Honma, I. J. Electrochem. Soc. 2007, 154, A290.
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conductivity values, which are relatively small compared to those of other studied materials having phosphoric acid or azole derivatives.22,26 The spectra recorded at 420 K have slightly narrower lines. However, the molecular mobility is not high enough to result in the removal of any resonance from the 1H spectra after the application of double-quantum filtration. 3.1.3. Two-Dimensional 1H DQ MAS NMR. Figure 5a,b represents the 2D 1H DQ MAS NMR spectra recorded at 320 K and 25 kHz MAS. The spectra explicitly show proton proximities of less than 4.5 A˚ in the polymer materials. Aliphatic-aliphatic and aliphatic-aromatic proton cross peaks are present. Additionally, several autopeaks that are on the diagonal line are observed, showing the proximities of the same type of protons to each other. An interesting observation is the absence of the hydrogenbonded proton autopeak in any of the spectra. This indicates that the hydrogen-bonded protons are not close to each other in space. Moreover, the lack of cross peaks with respect to other types of protons indicates that the hydrogen-bonded proton is either isolated or relatively mobile and does not represent the dipolar coupling to other proton species. The latter is not likely because double-quantum filtration did not result in any signal loss for those sites. As a result, it can be said that the hydrogen-bonded protons are relatively distant from each other and from other protons because of the organization of the aromatic sites. 3.1.4. Oxidative Stability. The oxidative stability of the phosphoric acid-doped and PVPA blend membranes was evaluated in Fenton’s reagent (a 3% H2O2 aqueous solution containing 2 ppm FeSO4).27 (PGMAAdenine)-(PVPA) and (PGMAGuanine)-(PVPA) membranes were not dissolved in Fenton’s reagent over 24 h, whereas the phosphoric acid-doped PGMAAdenine and PGMAGuanine membranes partially dissolved in Fenton’s reagent within 24 h. (PGMAAdenine)(PVPA) and (PGMAGuanine)-(PVPA) membranes have better oxidative stability against Fenton’s reagent than do phosphoric acid-doped membranes. 3.1.5. SEM Micrographs. Surface morphologies of (PGMAAdenine)-(PVPA) and (PGMAGuanine)-(PVPA) membranes at different magnifications were investigated by scanning electron microscopy (Figure 6a,b). Because of the strong interaction between phosphonic acid groups of PVPA with the adenine units (27) Nakabayashi, K.; Higashihara, T.; Ueda, M. J. Polym. Sci., Part A: Polym. Chem. 2010, 48, 2757.
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Figure 6. (a) SEM micrographs of P(VPA) blend PGMAAdenine (100 μm). (b) SEM micrographs of P(VPA) blend PGMAGuanine (20 μm).
Figure 5. (a) Two-dimensional 1H DQ MAS NMR spectra of the adenine functional PGMA polymer recorded at 320 K and at 25 kHz MAS. (b) Two-dimensional 1H DQ MAS NMR spectra of the guanine functional PGMA polymer recorded at 320 K and 25 kHz MAS.
of PGMAAdenine and the guanine units of PGMAGuanine, no phase separation occurred during solvent evaporation, hence homogeneous transparent films formed. This result is also consistent with the DSC curves of the impregnated membranes that have no separate Tg transition. 3.2. Thermal Analysis. The weight loss in PGMA occurs in two steps within 200-400 °C. Figure 7a,b shows the thermograms of PVPA blends and H3PO4-doped PGMAAdenine samples. The slight weight change until 100-150 °C can be attributed to absorbed humidity. Clearly, PGMAAdenine is thermally stable up to at least 250 °C. After 250 °C, a remarkable weight loss is derived from the thermal decomposition of the polymer main chain. In (PGMAAdenine)-(PVPA)x, the stepwise decomposition after 200 °C can be attributed to water liberation due to the self-condensation of the phosphonic acid, and also the decomposition the polymer main chain contributes to further weight loss. 13658 DOI: 10.1021/la102096y
TG profiles of H3PO4-doped PGMAAdenine illustrate no weight change up to approximately 180 °C. The area after 200 °C can be attributed to water liberation due to the selfcondensation of the phosphoric acid, and also the decomposition of the polymer main chain contributes to further weight loss. Clearly, in (PGMAAdenine)-(H3PO4)x the materials are thermally stable up to 200 °C and then they decompose. Figure 8a,b shows the thermograms of the PVPA blends of functional polymer (PGMAGuanine)-(PVPA)x and the (PGMAGuanine)-(H3PO4)x doped sample. Clearly, PGMAGuanine is thermally stable up to at least 230 °C. For (PGMAGuanine)-(PVPA)x, an elusive weight change until 180 °C may be attributed to the loss of absorbed humidity, and then degradation of the polymer main chain and the functional units starts. The doped samples exhibit an insignificant weight change until 180 °C. The stepwise decomposition above this temperature can be attributed to water liberation due to the self-condensation of the phosphoric acid as well as the decomposition of the polymer. The glass-transition temperature, Tg, of homopolymer PGMA was reported to be near 74 °C28 whereas the Tg of PGMAAdenine is 161 °C, that of (PGMAAdenine)-(PVPA) is 173 °C, and that of (PGMAAdenine)-(PVPA)1.5 is 192 °C. The DSC results demonstrated that as the quantity of PVPA increased, the glasstransition temperature of the samples shifted to higher values. The Tg of PGMAAdenine shifts to 106, 175, and 113 °C for (PGMAAdenine)-(H3PO4), (PGMAAdenine)-(H3PO4)1.5, and (PGMAAdenine)-(H3PO4)2, respectively (Table 1). The presence of a single Tg confirms the homogeneity of the doped samples. According to the DSC results the PGMAGuanine has a Tg of 192 °C. The Tg of (PGMAGuanine)-(PVPA) which was found to be 161 °C, shifted to 31 °C for (PGMAGuanine)-(PVPA). In the Tg of phosphoric acid doped PGMAGuanine shifts to lower (28) Nanjundan, S.; Unnithan, C. S.; Selvamalar, C. S. J.; Penlidis, A. React. Funct. Polym. 2005, 62, 11.
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Figure 7. (a) Thermogravimetry analysis of a P(VPA) blend of PGMAAdenine. (b) Thermogravimetry analysis of H3PO4-doped PGMAAdenine.
temperature (Table 1). The presence of single Tg confirms the homogeneity of the doped samples. 3.3. Conductivity Measurement. The alternating current (ac) conductivities, σac(ω), of the polymers were measured at several temperatures using impedance spectroscopy. The ac conductivity of H3PO4-doped PGMAAdenine and H3PO4doped PGMAGuanine are shown in Figure 9. Frequencydependent ac conductivities (σac(ω)) were measured using eq 2 σ0 ðωÞ ¼ σ ac ðωÞ ¼ ε00 ðωÞωεo
ð2Þ
where σ0 (ω) is the real part of the conductivity, ω = 2πf is the angular frequency, εo is the vacuum permittivity (εo = 8.852 10-14 F/cm), and ε00 is the imaginary part of the complex dielectric permittivity (ε*). The proton conductivities of anhydrous samples were measured from 20 to 150 °C. The proton conductivity of all anhydrous phosphoric acid-doped samples was compared in Figures 10 and 11. Among phosphoric acid-doped PGMAAdenine, (PGMAAdenine)-(H3PO4)2 showed the highest proton conductivity of 4 mS/cm at 150 °C in the anhydrous state. Normally, there are two different transport mechanisms that contribute to the proton conductivity in phosphoric acid-doped Langmuir 2010, 26(16), 13655–13661
Figure 8. (a) Thermogravimetry analysis of the P(VPA) blend of PGMAGuanine. (b) Thermogravimetry analysis of H3PO4-doped PGMAGuanine. Table 1. Tg Temperature and Maxiumum Proton Conductivity of the Samples sample
Tg (°C)
max proton conductivity (mS/cm)
PGMAAdenine (PGMAAdenine)-(PVPA)0.5 (PGMAAdenine)-(PVPA) (PGMAAdenine)-(PVPA)1.5 (PGMAAdenine)-(H3PO4) (PGMAAdenine)-(H3PO4)1.5 (PGMAAdenine)-(H3PO4)2 PGMAGuanine (PGMAGuanine)-(PVPA)0.5 (PGMAGuanine)-(PVPA) (PGMAGuanine)-(PVPA)1.5 (PGMAGuanine)-(H3PO4) (PGMAGuanine)-(H3PO4)1.5 (PGMAGuanine)-(H3PO4)2
161 168 173 192 106 175 113 192 155 161 176 156 111 108
4.4 10-10 1.8 10-8 1.6 10-7 8.6 10-7 0.03 0.05 4 2.3 10-5 1.0 10-9 3 10-7 6.3 10-7 2.0 10-6 0.07 3.0 10-3
polymer systems. The first is the structural diffusion (Grotthuss mechanism) in which the conductivity is mainly controlled by proton transport through phosphate ions (i.e. H4PO4þ and H2PO4-) (Grotthuss proton transport). The second is the vehicle mechanism where the protons travel through the material on a neutral or charged “vehicle”. Several studies reported the DOI: 10.1021/la102096y
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Figure 11. dc conductivity measurements of H3PO 4-doped PGMAGuanine membranes vs reciprocal temperature.
Figure 9. (a) ac conductivity of (PGMAAdenine)-(H 3PO4)1.5. (b) ac conductivity of (PGMAGuanine)-(H 3PO4)1.5.
Figure 10. dc conductivity measurements of H 3 PO 4-doped PGMAAdenine membranes vs reciprocal temperature.
contribution of these mechanisms to the proton conductivity of pure phosphoric acid, and it was indicated that the former is much more predominant and the conduction mechanism is mainly controlled by structural diffusion rather than the vehicle mechanism. In the current system, the presence of HPO42- and H2PO4anions implies that proton diffusion can also occur throughout these ionized species.29 (29) Dippel, T.; Kreuer, K. D.; LassMgues, J. C.; Rodriguez, D. Solid State Ionics 1993, 61, 41.
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It seems that the proton hopping from one N-H site to a free nitrogen may contribute to the conductivity of (PGMAAdenine)-(H3PO4)x systems, as in the case of imidazole where long-range proton transfer occurs throughout the protonic defects (i.e., proton transport between protonated and unprotonated heterocyclic units).30-33 In addition, proton hopping from one N-H site to phosphate ions may also contribute to the conductivity. In the phosphoric acid-doped PGMAGuanine and PVPA functional PGMAGuanine systems, the doping ratio is very effective with respect to the proton conductivity of the sample, which indicates that the major part of proton transport is provided over H3PO4 and PVPA as well as over guanine units. Previously, the proton conductivity of an acid-doped PBI system was reported to follow the Arrhenius law, suggesting a hoppinglike conduction mechanism.34 From the conductivity and FTIR results, it can be concluded that the host matrix, PGMAGuanine, includes excess phosphoric acid without a significant change in the mechanical properties and that conductivity occurs throughout the material predominantly by the Grotthuss mechanism. Among phosphoric acid-doped PGMAGuanine, (PGMAGuanine)-(H3PO4)1.5 showed the highest proton conductivity of 0.07 mS/cm at 150 °C in the anhydrous state.
4. Conclusions In the present work, adenine and guanine functional poly(glycidyl methacrylate) polymers have been synthesized. Poly(glycidyl methacrylate) was produced by the free radical polymerization of GMA, and then adenine and guanine biomolecules were immobilized by ring opening of the epoxide ring. Elemental analysis verified about 80% adenine immobilization and about 50% guanine immobilization. The structures of the adenine and guanine functional polymers were proved by FT-IR, solid state 13C CP-MAS NMR, 1H MAS SQ, and 2D 1H DQ MAS NMR. DSC and SEM results illustrated the homogeneity of the materials. Anhydrous proton-conducting properties and thermal properties of the PVPA functional and phosphoric acid-doped (30) Kreuer, K. D.; Fuchs, A.; Ise, M.; Spaeth, M.; Maier, J. Electrochim. Acta 1998, 43, 1281. (31) Kreuer, K. D. Chem. Mater. 1996, 8, 610. (32) Yan, F.; Yu, S.; Zhang, X.; Qiu, L.; Chu, F.; You, J.; Lu, J. Chem. Mater,. 2009, 21, 1480. (33) Lin, B.; Cheng, Si.; Qiu, L.; Yan, F.; Shang, S.; Lu, J. Chem. Mater. 2010, 22, 1807. (34) He, R.; Li, Q.; Xiao, G.; Bjerrum, N. J. J. Membr. Sci. 2003, B226, 169.
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PGMAAdenine and PGMAGuanine were investigated. The proton conductivity of the materials increased with dopant concentration and temperature. However, low conductivity was obtained for PVPA blend polymers. This was attributed to the aggregation of the phosphonic acid units in the host matrix, which inhibited defect-type conduction. Phosphoric acid-doped polymers showed lower Tg values and higher proton conductivities than PVPA blend systems. (PGMAAdenine)-(H3PO4)2 and (PGMAGuanine)-(H3PO4)1.5 showed a maximum water-free proton conductivity of approximately 4 mS/cm at 150 °C and
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0.07 mS/cm at 150 °C. The (PGMAAdenine)-(H3PO4)2 membrane can be suggested for applications in high-temperature polymer electrolyte membrane fuel cells (PEMFC). :: Acknowledgment. Dr. Umit Akbey is gratefully acknowledged for his help with NMR measurements and interpretation. Supporting Information Available: FT-IR studies. This material is available free of charge via the Internet at http:// pubs.acs.org.
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