Supporting Information Controlled Radical Polymerization and Quantification of Solid State Electrical Conductivities of Macromolecules Bearing Pendant Stable Radical Groups Lizbeth Rostro, Aditya G. Baradwaj, and Bryan W. Boudouris* 480 Stadium Mall Drive, School of Chemical Engineering, Purdue University, West Lafayette, IN 47907 * To whom correspondence should be addressed: boudouris@purdue.edu General Methods The 1 H NMR spectra were measured on a Bruker DRX500 spectrometer using a ~1 wt % polymer solution in deuterated chloroform (Sigma-Aldrich). Size exclusion chromatography (SEC) data were collected on a Hewlett-Packard 1260 Infinity series equipped with a Hewlett- Packard G1362A refractive index (RI) detector and three PLgel 5 µm MIXED-C columns. The mobile phase was comprised of tetrahydrofuran (THF) at 40 C at a flow rate of 1 ml min -1. The SEC was calibrated using polystyrene standards (Agilent Easi Cal) with molecular weights ranging from 1 kg mol -1 to 200 kg mol -1. Differential scanning calorimetry (DSC) data were collected using a TA Instruments Q20 Series differential scanning calorimeter. The samples were initially heated to 250 C and cooled to 30 C at 10 C min -1 under a nitrogen gas purge. The data shown were from the final scans from 30 C to 250 C at 10 C min -1. Ultraviolet-visible (UV-Vis) light absorption spectra were taken on a Cary 60 spectrometer over a wavelength range of 300-800 nm using chloroform as the blank. Film thicknesses were determined using a KLA S1
Tencor profilometer by scratching the film and measuring the height change. Atomic force microscopy (AFM) images were taken with a VEECO Dimension 3100 Atomic Force Microscope operating in tapping mode in the repulsive regime. The probe tips were fabricated by Mikromasch USA (NSC15/Al BS tips, and they had a resonant frequency of 325 khz and a spring constant of 40 N m -1 ). Materials All chemicals were used as received from Sigma-Aldrich unless otherwise noted. Degassed toluene was purified by passage through an alumina column (Innovative Technology). meta-chloroperbenzoic acid (mcpba) was washed with water from ether and dried under reduced pressure. 2,2,6,6-tetramethyl-4-piperidyl methacrylate (TMPM) was purchased from TCI America, and it was used without purification. Synthesis of PTMPM-RAFT A reversible addition-fragmentation chain transfer (RAFT) polymerization mechanism was utilized for the synthesis of PTMPM-RAFT. The details for the example polymerization of PTMA(5) are as follows. The polymerization was performed in a 250 ml reaction flask containing a Teflon-coated magnetic stir bar. To the reaction flask, 20 ml of anhydrous toluene were added. 10 g (0.04 moles) of TMPM, 0.073 g (0.4 mmol) of 2,2 -azobis(2- methylpropionitrile) (AIBN), and 0.538 ml (2 mmol) 2-phenyl-2-propylbenzodithioate (chain transfer agent) were then added to the reaction flask. Once the solids were dissolved completely in the solution, three freeze-pump-thaw cycles were performed. Next, the reaction flask was refilled with argon, the reaction was heated to 75 C, and the reaction was stirred at this temperature overnight. The reaction was cooled to room temperature, exposed to air to terminate S2
the reaction, and precipitated in hexanes to generate PTMPM-RAFT. The polymer was filtered and dried under reduced pressure overnight. Synthesis of PTMPM The removal of the RAFT terminus was achieved by reacting PTMPM-RAFT with an excess of AIBN. The example reaction of PTMA(5) is as follows. The reaction was conducted in a 250 ml reaction flask with a Teflon-coated magnetic stir bar. To the reaction flask, 50 ml of toluene were added. Next, 1 g (0.25 mmol) of PTMPM-RAFT and 1 g (6 mmol) of AIBN were added to the reaction flask. Then three freeze-pump-thaw cycles were performed to the reaction solution prior to backfilling with argon. The reaction was heated to 75 C and reacted overnight. The solution was cooled to room temperature then exposed to air to terminate the reaction. The cooled solution was precipitated in hexanes to obtain PTMPM. Oxidation of PTMPM to PTMA A modified method similar to that of the Lee group was used for the synthesis of PTMA. 1 The details for the example PTMA(5) oxidation are as follows. A solution of mcpba (1 g, 5.8 mmol) in 10 ml of anhydrous dichloromethane was made. PTMPM (0.50 g, 0.13mmol) was dissolved in 10 ml of anhydrous dichloromethane. The mcpba solution was added drop-wise to the polymer solution and then allowed to stir at room temperature under nitrogen for 7 hours. The combined polymer-oxidizer solution was washed with an aqueous sodium carbonate solution (ph = 13). The organic fraction was then collected, precipitated in hexanes, filtered, and dried under reduced pressure overnight. Note that the polymer changed from a white powder to an orange powder after oxidation. S3
The deprotection of PTMPM was analyzed using UV-Vis spectroscopy by taking advantage of the color change that occurred after oxidation. First the molar absorptivity of the repeat radical unit was determined by analyzing TEMPO-OH at varying concentrations. This was achieved utilizing Beer s Law to relate the absorbance to molar absorptivity. To determine the conversion of radical sites, solutions of the polymers were made at a concentration of 30 mg of polymer in 1 ml of chloroform. The solution was characterized by UV-Vis and the absorbance was related through Beer s Law to obtain the concentration of radical sites. It is important to note that PTMPM is a white powder and colorless in the solution. As such, there is no absorbance in the UV-Vis spectra of the PTMPM precursor polymers. PTMA Thin Film Fabrication Solutions containing 100 mg of PTMA dissolved in 1 ml of chloroform were made. The solutions were stirred overnight at room temperature. The PTMA solutions were spun-coat onto glass substrates with patterned gold electrodes (fabricated using an in-house thermal evaporator and shadow mask) to produce films with thicknesses of ~1.2 µm, as measured through profilometry. Next the films were annealed at 65 C for 10 minutes to remove any residual solvent. All device testing was performed using a Lakeshore vacuum probe station. The currentvoltage sweeps were performed using a Keithley 2400 sourcemeter that was controlled using inhouse LabView codes. The devices were swept from 10 V to +10 V (Figure S4). The collected data provided current-voltage statistics of the PTMA thin films and the conductivities were calculated from these data. The same procedure was done for the TEMPO-OH doped PTMA thin films. In these cases, however, the total mass of solids was kept at 100 mg per 1 ml of solvent during the solution creation step. S4
Figure S1. 1 H NMR spectra for the TMPM monomer (lower) and the PTMPM-RAFT macromolecule (upper). The peak downfield of the solvent peak (d) highlights the chain transfer end group. S5
Figure S2. Expanded view of the 1 H NMR spectra of PTMPM before (lower) and after (upper) chain transfer end group removal. All peaks are normalized to the peak labeled c at δ 5.2 ppm for clarity. S6
Figure S3. DSC data for the (a) PTMPM series of polymers and (b) the PTMA series of polymers demonstrating thermal transition temperatures at T ~100 C and T ~175 C, respectively. S7
Figure S4. Representative current-voltage data for a PTMA(10) thin film conductivity testing measurement. The slope of this line was utilized to determine the resistance of the device, and thus, the average conductivity of the PTMA samples. S8
Figure S5. AFM images of representative weight percent TEMPO-OH doped PTMA thin films. The scale bar on each image represents 250 nm. Note that only minor blemishes are observed in all of the images (contrast bar 0 10 nm) even though the total film thicknesses were ~1.2 µm. This suggests that the TEMPO-OH is well-mixed with the PTMA thin films. References (1) Lin, C.-H.; Chau, C.-M.; Lee, J.-T. Polym. Chem. 2012, 3, 1467-1474. S9