Supporting Information N-Spirocyclic Quaternary Ammonium Ionenes for Anion- Exchange Membranes Thanh Huong Pham, Joel S. Olsson and Patric Jannasch* Polymer & Materials Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-221 00, Lund, Sweden E-mail: patric.jannasch@chem.lu.se 1. Materials Durene (98%, Aldrich), N-bromosuccinimide (NBS, 99%, Acros), azobisisobutyronitrile (AIBN, 98%, Acros), N-ethyldiisopropylamine (DIPEA, 99%, Sigma-Aldrich), 4,4 -bipiperidine dihydrochloride (99%, Alfa Aesar), 4,4 -trimethylenedipiperidine (97%, Aldrich), chloroform (reagent grade, Honeywell), N,N-dimethylformamide (DMF, reagent grade, Honeywell), dimethylsulfoxide (DMSO, reagent grade, Fluka), D 2 O (99.9 atom % D, Sigma-Aldrich), CDCl 3 ("100%", 99.96 atom % D, Sigma- Aldrich), KOD (40 wt. % in D 2 O, 98 atom % D, Sigma-Aldrich) were all used as received. The donation of poly[(2-(4,4 -diphenylether)-5-oxybenzimidazole)-2,5-benzimidazole] (PBI-OO) from FumaTech GmBH (Germany) via the Max-Planck-Institute for Solid State Research, Germany, is greatly acknowledged. S1
2. Structural characterization The chemical structures of all synthesized polymers were confirmed by 1 H and 13 C NMR spectroscopy. Spectra were recorded on a Bruker DRX400 spectrometer at 400 and 100 MHz, respectively. The solutions used were based on either CDCl 3 or D 2 O. 3. Synthesis of 1,2,4,5-tetrakis(bromomethyl)benzene Chloroform (160 ml) was added to a mixture of durene (10.32 g, 76.89 mmol, 1.00 eq.), NBS (54.49 g, 306.2 mmol, 4.0 eq.) and AIBN (1.283 g, 7.81 mmol, 0.10 eq.). The mixture was kept under reflux at 2 h during which the reaction mixture turned orange. When the boiling became too vigorous because of the exothermic reaction, the heating was temporarily stopped. More NBS (13.49 g, 75.79 mmol, 1 eq.) and AIBN (0.321 g, 1.95 mmol, 0.025 eq.) were added and the reaction mixture was refluxed overnight. The hot mixture was then filtered to remove insoluble succinimide. Chloroform was evaporated under reduced pressure until a dry residue was obtained. The residue was washed with cold methanol (3 50 ml) to give an off-white powder. The product was purified by two-fold recrystallization in chloroform, yielding colorless crystals (6.00 g, 17.3% isolated yield). 1 H NMR (400 MHz, CDCl 3 ) δ (ppm): 7.37 (s, 2H, Ar-H), 4.60 (s, 8H, Ar-CH 2 -Br) a b a CDCl 3 b ppm 7.50 7.40 7.30 7.20 7.10 4.90 4.80 4.70 4.60 4.50 4.40 4.30 Figure S1. 1 H NMR spectrum of 1,2,4,5-tetrakis(bromomethyl)benzene. S2
4. Synthesis of spiro-ionene 1 1,2,4,5-Tetrakis(bromomethyl) benzene (2.066 g, 4.593 mmol, 1.00 eq.) was dissolved in DMF (85 ml) in a 250 ml round flask. DIPEA (5.5 ml, 32.4 mmol, 7.00 eq.) and a solution of 4,4'-bipiperidine dihydrochloride (1.108g, 4.593 mmol, 1.00 eq.) in 15 ml water was added. Upon the addition, the clear solution immediately turned turbid. Additional water (55 ml) was added until the mixture became clear. The reaction mixture was then heated to 60 o C during 2 h. Subsequently, the product was precipitated in acetone, followed by washing in fresh acetone and drying under vacuum at 50 o C, to yield a yellowwhite powder (2 g, 95-109% isolated yield). 1 H NMR (400 MHz, D 2 O) δ (ppm): 7.39 (2H, Ar-H), 4.88 (8H, Ar-CH 2 -N), 3.74 (4H, N-CH 2 ), 3.51 (4H, N-CH 2 ), 2.04 (4H, N-CH 2 -CH 2 ), 1.71 (m, 6H, N-CH 2 -CH 2 and CH). 13 C NMR (100 MHz, D 2 O) δ (ppm): 133.8, 119.1,71.0, 62.4, 60.8, 36.4, 24.5. f a f a b c d e b c e d ppm 120 100 80 60 40 Figure S2. 13 C NMR spectrum of spiro-ionene 1. The sample had a mix of Br - and Cl - counter ions. 5. Synthesis of spiro-ionene 2 1,2,4,5-Tetrakis(bromomethyl) benzene (2.342g, 5.206 mmol, 1.00 eq.) was dissolved in DMF (70 ml) in a 250 ml round flask. Next, DIPEA (4 ml, 24 mmol, 4.50 eq.) and solution of 4,4 - trimethylenedipiperidine (1.107 g, 5.262 mmol, 1.01 eq.) in a mixture of DMF (10 ml) and deionized water (15 ml) was added. The reaction mixture remained optically clear during 1 h stirring at 60 o C. S3
The product was then precipitated in acetone (300 ml). Next, the white precipitate was washed with fresh acetone (2 300 ml), followed by drying under vacuum at 50 o C to yield an off-white powder (2.66 g, 102% isolated yield). 1 H NMR (400 MHz, D 2 O) δ (ppm): 7.43 (s, 2H, Ar-H), 4.92 (d, 8H, J = 6.7 Hz, Ar-CH 2 -N), 3.74 (d, 4H, J = 11.6 Hz, N-CH 2 ), 3.53 (t, 4H, J = 11.0 Hz, N-CH 2 ), 2.01 (d, 4H, J = 11.5 Hz, N-CH 2 -CH 2 ), 1.73-1.67 (m, 6H, N-CH 2 -CH 2 and CH), 1.41 (s, 6H, CH-CH 2 and CH-CH 2 -CH 2 ). 13 C NMR (100 MHz, D 2 O) δ (ppm): 133.8, 118.9,70.8, 62.6, 61.0, 34.3, 32.1, 27.1, 22.6. a d f c d h a h b c e g b e f g ppm 130 110 90 70 50 30 Figure S3. 13 C NMR spectrum of spiro-ionene 2. Table S1. Properties of the spiro-ionenes and their films Spiro-ionene [η] a M n b IEC theory IEC titrated T d,95 c q max d d [dl g -1 ] (kg mol -1 ) [meq g -1 ] [meq g -1 ] [ o C] [nm -1 ] [nm] 1 0.40 67 4.4-5.4 e 4.6 336 n.d. n.d. 2 0.56 80 4.0 4.0 318 4.8 1.3 a Measured at 25 o C using water solutions. b Calculated from 1 H NMR data. c Evaluated by TGA under N 2. d Evaluated by SAXS after equilibration at 75% RH, room temperature. e IEC range given because of mixed counter ions (Br - and Cl - ). n.d = ionomer peak not detected. S4
6. Preparation of spiro-ionene films Approximately 0.4 g of either spiro-ionene 1 in mixed Br - /Cl - form or 2 in Br - form was dissolved in 8 g deionized water. The solution was then poured into a Petri dish and casting was done overnight in an oven at 120 o C. Both spiro-ionenes formed transparent, free-standing and flexible film that could be easily peeled off the substrate. 7. Preparation of blend membranes Predetermined amounts of spiro-ionene 2 in Br - form and PBI-OO was weighed and co-dissolved in 8 g DMSO. The solution was then transferred to a Petri dish (φ 7 cm) and the membrane was cast in a ventilated casting oven. The weights of the blend components, casting temperature and casting time are presented in Table S2. The resulting membrane was easily detached from the Petri dish and was subsequently kept immersed in a 1 M aq. KBr solution. The AEMs in the Br - form were transferred to the OH - form by immersion in a 0.5 M aq. KOH solution under nitrogen atmosphere during at least 24 h. Under these conditions, at least a part of the -NH- groups of PBI-OO were deprotonated to form ammonium-imidazolate complexes with spiro-ionene 2 (Figure 4). Finally, the membranes were thoroughly washed with degassed deionized water and stored in degassed deionized water under N 2 atmosphere before measurements. Table S2. Preparation of blend membranes. AEM m spiro-ionene (g) m PBI-OO (g) T oven ( o C) casting time S80P20 0.3241 0.0804 80 48 h S75P25 0.2967 0.0980 80 48 h S70P30 0.2824 0.1218 65 96 h 8. Intrinsic viscosity The intrinsic viscosity of the spiro-ionenes was measured using an Ubbelohde viscometer at 25 o C. Samples were dried at 120 o C overnight, weighed, and dissolved in 15 ml 1 M aq. NaCl solution (blank solution). These stock solutions were later diluted by adding blank solution to reduce the concentrations (C). The resulting spiro-ionene solutions were used immediately after preparation. The flow times of blank solution (t blank ) and of polymer solutions (t sample ) through the capillary were taken as the average of S5
at least four measurements. The inherent (η inh ) and reduced (η red ) viscosity at different concentrations were calculated as: ln 1 1 2 The intrinsic viscosity ([η]) was calculated as the average of the intersections of the linear regressions of η inh and η red with the y-axis. 9. Thermogravimetric analysis The thermal degradation of the AEMs in the Br - form was studied by thermogravimetric analysis (TGA) using a TGA Q500 (TA Instruments) during heating from 50 to 600 o C at 10 o C min -1 under N 2 atmosphere. In order to remove solvent residues, the samples were kept isothermally at 150 o C during 10 min prior to the analysis. The thermal decomposition temperature (T d,95 ) was determined at 5% weight loss. Figure S4. TGA profiles of the spiro-ionenes, PBI-OO and the blend membranes. S6
10. Ion exchange capacity The ion exchange capacity (IEC) of the spiro-ionenes was determined by Mohr s titration. First, the water contents of the films were determined by TGA as the weight loss recorded after 30 min at 150 o C. The films were then weighed and dissolved in 25 ml deionized water. The polymer solutions were titrated by Mohr s method using 0.01 M aq. AgNO 3 as titrant and 0.1 M aq. K 2 CrO 4 as indicator. The dry weights of the samples were obtained after subtracting the weight of water. 11. Water uptake The water uptake of the spiro-ionene films was determined after equilibration at 55, 75, 85 and 93% relative humidity (RH) at room temperature.. RH was controlled by saturated solutions of Mg(NO 3 ) 2, NaCl, KCl and KNO 3, respectively. The films were kept in closed desiccators together with the respective salt solutions during at least 48 h, and then quickly weighed to obtain the weight in the hydrated state (m humid ). The weights in the dry state were obtained after drying the spiro-ionene film at 120 o C for 24 h (m dry ). The water uptake (WU) and λ was calculated as: 100% 3 1000 100 18 4 The water uptake of the blend AEMs were measured at 20, 40, 60, 80 and 90 o C respectively. Samples in Br - form were dried in a vacuum oven at 50 o C during 48 h to obtain the dry weight (m dry,br ). They were then ion-exchanged to the OH - form and immersed in water at each temperature during 24 h to reach equilibrium. Next, the samples were wiped dry with tissue paper and quickly weighed to obtain the wet weight (m wet,oh ). By assuming that all Br - was exchanged to OH -, the dry weight of the membranes in the OH - form (m dry,oh ) was calculated based on the dry weight in the Br - form (m dry,br ). Finally, the water uptake was calculated. S7
70 9 60 Spiro-ionene 1 8 Spiro-ionene 1 Water uptake (wt %) 50 40 30 20 Spiro-ionene 2 λ 7 6 5 4 3 Spiro-ionene 2 10 50 60 70 80 90 100 RH (%) 2 50 60 70 80 90 100 RH (%) Figure S5. Water uptake and λ values of the spiro-ionene films after equilibration during 48h at different RHs at room temperature. Water uptake (wt %) 900 800 700 600 500 400 300 200 S80P20 S75P25 S70P30 100 10 30 50 70 90 Temperature ( C) Figure S6. Water uptake of the blend membranes in the OH - form as a function of temperature. 12. Small angle X-ray scattering measurements The ionic clustering in the spiro-ionene films and the AEMs was studied by SAXS measurements of the humidified AEMs in the halogen ion form. Data was collected in the q-range 0.14-7.5 nm -1 using a S8
SAXSLAB SAXS instrument (JJ X-ray Systems Aps, Denmark) equipped with a Pilatus detector. The radiation was Cu K α with wavelength (l) of 1.542 Å and the wave vector (q) was calculated as: 4 2 5 where 2θ is the scattering angle. The characteristic separation length (d) was calculated using the Bragg s law: 2 6 To ensure the humidity throughout the measurements, all the films in halogen ion form were enclosed in SAXS cells after equilibration at 75% RH for at least 48 h. log[scattering intensity (a.u.)] Blend membrane S70P30 Spiro-ionene 2 Spiro-ionene 1 Reference 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 q (Å -1 ) Figure S7. SAXS profiles of spiro-ionene 1 and 2 and the blend membrane S70P30, all in the halogen ion form after equilibration at 75% RH. The reference data was measured with an empty cell. 13. Hydroxide ion conductivity The OH - conductivity of fully immersed blend AEMs was measured by electrochemical impedance spectroscopy using a sealed cell with a two-probe set up and a Novocontrol high-resolution dielectric analyzer V 1.01S. The voltage was kept constant at 50 mv while varying the frequency from 10 7 to 10-1 Hz in temperature range -20 to 90 o C. S9
14. Alkaline stability The alkaline stability of the two spiro-ionenes was evaluated after dissolution in 1 M KOD in D 2 O at 80 and 120 o C, respectively. The structural degradation of the materials over time was monitored by 1 H NMR spectroscopy. Samples were first dissolved in 1 M KOD/D 2 O at room temperature. These solutions were then transferred into four glass pressure tubes with teflon inserts (Figure S8) and kept at 80 o C for 1896 h or at 120 o C during 336 h. During this period the samples were taken out and immediately analyzed by 1 H-NMR spectroscopy (Figure S9, S10, S11, S12). The exchange from H to D at aromatic and benzylic positions of the spiro-ionenes during the treatment of the samples in 1 M KOD/D 2 O was verified and studied by 1 H NMR spectroscopy. A sample of spiroionene 1 previously kept in 1 M KOD/D 2 O during 336 h at 120 o C was dissolved in 1 M KOH in water. The solution was stored at 120 o C during 72 h before neutralization with concentrated aq. HCl. The water was removed by evaporation at 80 o C and the residue was then analyzed by 1 H NMR spectroscopy (Figure S13). Figure S8. Sample container used in the alkaline stability evaluations (from left to right: glass pressure test tube, teflon insert to prevent corrosion by KOD/D 2 O solution and teflon back seal). S10
672 h 336 h 168 h Initial ppm 7.0 6.0 5.0 4.0 3.0 2.0 1.0 Figure S9. 1 H NMR spectra of spiro-ionene 1 before and after storage in 1 M KOD/D 2 O at 80 o C during different time periods. The spectra indicate no detectable degradation after 672 h. The signals at 7.3 ppm and 4.9 ppm decreased in intensity due to H-D exchange of aromatic and benzylic protons, respectively. S11
1896 h 672 h 336 h 168 h Initial ppm 7.0 6.0 5.0 4.0 3.0 2.0 1.0 Figure S10. 1 H NMR spectra of spiro-ionene 2 before and after storage in 1 M KOD/D 2 O at 80 o C during different time periods. The spectra indicate no detectable degradation after 1896 h. The signals at 7.3 ppm and 4.9 ppm decreased in intensity due to H-D exchange of aromatic and benzylic protons, respectively. S12
336 h 168 h 72 h Initial ppm 7.0 6.0 5.0 4.0 3.0 2.0 1.0 Figure S11. 1 H NMR spectra of spiro-ionene 1 before and after storage in 1 M KOD/D 2 O at 120 o C for different time periods. The arrows indicate changes due to polymer structure degradation. The signals at 7.3 ppm and 4.9 ppm decreased in intensity due to H-D exchange of aromatic and benzylic protons, respectively.. S13
336 h 168 h 72 h Initial ppm 7.0 6.0 5.0 4.0 3.0 2.0 1.0 Figure S12. 1 H NMR spectra of spiro-ionene 2 before and after storage in 1 M KOD/D 2 O at 120 o C for different time periods. The arrows indicate changes due to polymer structure degradation. The signals at 7.3 ppm and 4.9 ppm decreased in intensity due to H-D exchange of aromatic and benzylic protons, respectively. S14
After Before ppm 7.0 6.0 5.0 4.0 3.0 2.0 1.0 Figure S13. 1 H NMR spectra of spiro-ionene 1 kept in 1 M KOD/D 2 O during 336 h at 120 o C, before and after a second storage period in 1 M KOH/H 2 O during 336 h at 120 o C. The arrows indicate the reappearance of benzylic and aromatic protons after D-H exchange. Scheme S1. Proposed reaction pathway for the cyclo-polycondensation (a) and plausible side reactions (b) and (c) leading to branching and defects during the preparation of spiro-ionene 1. S15
Scheme S2. Possible degradation pathways of the spiro-ionenes through (a) ring-opening substitution in the 5-membered ring, (b) ring-opening substitution in the 6-membered ring, and (c) ring-opening elimination. S16