Metal-Free Removal of Polymer Chain Ends Using Light

Transcription

1 Supporting Information for: Metal-Free Removal of Polymer Chain Ends Using Light Kaila M. Mattson, 1,2 Christian W. Pester, 2,3 Will R. Gutekunst, 4 Andy T. Hsueh, 1,2 Emre H. Discekici, 1,2 Yingdong Luo, 1,2 Bernhard V. K. J. Schmidt, 1,2 Alaina J. McGrath, 2 Paul G. Clark, 5 and Craig J. Hawker* 1,2,3 1 Department of Chemistry & Biochemistry, University of California, Santa Barbara, CA 93106, USA 2 Materials Research Laboratory, University of California, Santa Barbara, CA 93106, USA 3 Materials Department, University of California, Santa Barbara, CA 93106, USA 4 Department of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA 5 The Dow Chemical Company, Midland, MI 48667, USA Table of Contents General Information... S2-3 Materials... S2 General Analytical Information... S2 Light Sources... S3 Methods... S4-7 Preparation of Polystyrene-Br... S4 Preparation of Poly(tert-butyl acrylate)-br... S4 Preparation of Polystyrene-Cl... S5 Preparation of Poly(tert-butyl acrylate)-raft... S5 Synthesis of 10-phenylphenothiazine (PTH)... S6 Representative Procedure for End Removal in Solution... S6 Preparation of Uniformly Functionalized Alkyl Bromide Silicon Surfaces... S6 Representative Procedure for Dehalogenation of Surfaced-Tethered Initiators and Brushes... S7 Characterization Data... S7-12 Debromination of Polystyrene-Br... S7 Dehalogenation of Polystyrene-Br: Necessity of Both Light and PTH... S8 Debromination of Poly(tert-butyl acrylate)-br... S10 Dehalogenation of Polystyrene-Cl... S11 Removal of RAFT Chain End... S12 References... S13 S1

2 GENERAL INFRMATIN Materials All reagents were purchased from Sigma-Aldrich and used as received, unless stated otherwise. Azobisisobutyronitrile (AIBN) was recrystallized twice in methanol before use. Methyl methacrylate (MMA), styrene, tert-butyl acrylate, and 2,2,2-trifluoroethyl methacrylate (TFEMA) were filtered through a plug of basic alumina immediately preceding use. All reactions were carried out at room temperature (ca. 23 C), unless otherwise noted. Silicon substrates with 100 nm of oxide were purchased from Silicon Quest International. General Analytical Information Nuclear magnetic resonance (NMR) spectra were recorded on a VNMRS 600 MHz spectrometer at room temperature using an acquisition time of 3.4 seconds, a 10 second relaxation delay, and at least 64 scans. Unless otherwise stated, all 1 H spectra are reported in parts per million (ppm), and were measured relative to the signal for residual chloroform in the deuterated solvent (7.26 ppm). A Micromass QTF2 Quadrupole/Time-of-Flight Tandem mass spectrometer was used for mass analysis using field desorption (FD). Size exclusion chromatography (SEC) was performed at ambient temperature using chloroform with 0.25% triethylamine as the mobile phase in a Water 2695 separation module with a Waters 2414 refractive index detector. Number average molecular weights (M n ) and weight average molecular weights (M w ) were calculated relative to linear polystyrene standards. Values for each sample s polydispersity (Đ) are reported as the quotient of M w /M n. Film thicknesses were measured with a Filmetrics F20 optical reflectometer (RI PMMA = 1.485) by setting silicon oxide (100 nm) as the first layer and polymer as a second layer. ptical micrographs were captured using a Nikon Elipse E600 optical microscope. X-ray photoelectron spectroscopy (XPS) measurements were performed using a Kratos Axis Ultra Spectrometer (Kratos Analytical, S2

3 Manchester, U.K.) with a monochromatic Aluminum K α X-ray source ( ev) operating at 225 W under a vacuum of 10-8 Torr. Tapping mode AFM data was acquired on a MFP-3D system (Asylum Research, Santa Barbara, CA) using commercial Si cantilevers. Dynamic Secondary Ion Mass Spectrometry (SIMS) imaging was performed using a Cameca IMS 7f system (Cameca SAS, Gennevilliers, France). A 10 kv Cs + ion beam and 5 kv negative sample potential were used, for a total impact energy of 15 kv. The 150 pa primary beam was focused to a spot size of approximately 2 µm, and rastered over a 100 µm area. Photomasks containing clear rectangles of 2.5 x 25 µm 2 and 20 x 200 µm 2 were purchased from Photronics, Inc. Light Sources Solution Experiments: LED strips (λ = 380 nm) were purchased from Elemental LED ( and used to line the inside of a Corning crystallization dish. The light intensity was measured to be 1.8 µw/cm 2. Surface Reactions: A collimated LED light (λ = 405 nm) was purchased from Thor Labs (part number M405L2-C1). Reactions were placed approximately 1.5 cm below the light source, where the light intensity was measured to be 1.1 mw/cm 2. Please see our recent publications for further details. 1,2 S3

4 METHDS Preparation of Polystyrene-Br Styrene (20 ml, 174 mmol, 50 equiv) was passed through basic alumina to remove inhibitor and transferred to a 50 ml schlenk flask containing ethyl bromoisobutyrate (512 µl, 3.5 mmol, 1 equiv) and N,N,N,N,N -pentamethyldiethylenetriamine (PMDETA) (146 µl, 0.7 mmol, 0.2 equiv). The reaction mixture was degassed using freeze-pump-thaw three times, frozen once more, uncapped, and CuBr (100 mg, 0.7 mmol, 0.2 equiv) was added on top of the frozen mixture. While still frozen, the flask was evacuated and backfilled with argon three times, then warmed to room temperature. The flask was placed into an oil bath set to 100 C for 3 hours. Then, the flask was rapidly cooled in liquid nitrogen and opened to air to oxidize the catalyst. The crude polymer was diluted with dichloromethane and passed though neutral alumina to remove the copper catalyst. The filtered solution was concentrated in vacuo and precipitated twice into methanol to isolate polystyrene-br as a white solid. M n (SEC): 1.6 kg mol -1, Đ: 1.11 Preparation of Poly(tert-butyl acrylate)-br tert-butyl acrylate (17 ml, 117 mmol, 150 equiv) was passed through basic alumina to remove inhibitor and transferred to a 40 ml vial with septum containing ethylene carbonate (3.5 g), ethyl bromoisobutyrate (114 µl, 0.78 mmol, 1 equiv) and PMDETA (163 µl, 0.78 mmol, 1 equiv). The reaction mixture was degassed using freeze-pump-thaw three times, frozen once more, uncapped, and CuBr (112 mg, 0.78 mmol, 1 equiv) was added on top of the frozen mixture. While still frozen, the flask was evacuated and backfilled with argon three times, then warmed to room temperature. The flask was placed into an oil bath set to 70 C for 30 minutes. Then, the flask was rapidly cooled in liquid nitrogen and opened to air to oxidize the catalyst. The crude polymer was diluted with diethyl ether and passed though neutral alumina to remove the copper catalyst. The filtered solution was concentrated in vacuo and precipitated twice into a cold S4

5 methanol/water (3:1) mixture to isolate poly(tert-butyl acrylate)-br. M n (SEC): 6.5 kgmol -1, Đ: 1.18 Preparation of Polystyrene-Cl Styrene (20 ml, 174 mmol, 50 equiv) was passed through basic alumina to remove inhibitor and transferred to a 50 ml schlenk flask containing ethyl 2-chloropropionate (445 µl, 3.5 mmol, 1 equiv) and PMDETA (146 µl, 0.7 mmol, 0.2 equiv). The reaction mixture was degassed using freeze-pump-thaw three times, frozen once more, uncapped, and CuCl (69 mg, 0.7 mmol, 0.2 equiv) was added on top of the frozen mixture. While still frozen, the flask was evacuated and backfilled with argon three times, then warmed to room temperature. The flask was placed into an oil bath set to 100 C for 20 hours. Then, the flask was rapidly cooled in liquid nitrogen and opened to air to oxidize the catalyst. The crude polymer was diluted with dichloromethane and passed though neutral alumina to remove the copper catalyst. The filtered solution was concentrated in vacuo and precipitated twice into methanol to isolate polystyrene-cl as a white solid. M n (SEC): 4.1 kgmol -1, Đ: 1.48 Preparation of Poly(tert-butyl acrylate)-raft 2-(Dodecylthiocarbonothioylthio)-2-methylpropionic acid (DMP) was obtained according to a literature procedure. 3,4 tert-butyl acrylate (3.00 g, mmol, 41.8 equiv), DMP (203.0 mg, 0.56 mmol, 1.0 equiv), AIBN (18.3 mg, 0.11 mmol, 0.2 equiv), and ethyl acetate (5.5 ml) were charged into a reaction tube. The tube was sealed with a septum and the mixture bubbled with argon for 30 minutes. The reaction tube was placed into an oil bath set to 60 C for 1 hour. Then, the mixture was cooled, opened to air, and the crude polymer was precipitated into a mixture of deionized water/methanol (3:1) to yield poly(tert-butyl acrylate)-raft as a yellow solid. M n (SEC): 3.4 kgmol -1, Đ: 1.12 S5

6 Synthesis of 10-phenylphenothiazine (PTH) PTH was synthesized according to a previously published procedure. 1 Representative Procedure for End Removal in Solution mmol polymer (1.0 equiv with respect to the polymer chain end) was weighed into a 1 dram glass vial ("VWR Vial Borosilicate Glass, with Phenolic Screw Cap, 1 dram ). A 0.50 ml aliquot of a stock solution of 1.1 mg PTH in 1.62 ml solvent (0.34 mg PTH/ 0.5 ml solvent) was added to the vial (thus, mmol, 0.05 equiv PTH was added to the vial), along with a micro stir bar. Formic acid (4.7 µl, mmol, 5.0 equiv) was added to the vial, followed by tributylamine (29.7 µl, mmol, 5.0 equiv). Please note that, depending on the substrate s solubility, either acetonitrile (MeCN) or N,N-dimethylacetamide (DMA) was used as the solvent. The vial was capped with a "Thermo Scientific National PTFE/Silicone Septa for Sample Screw Thread Cap and gently shaken until the run mixture was homogenous. The vial s cap was removed to take an NMR sample for T=0. (NMR samples prepared using 50 µl aliquot of crude reaction mixture and 0.50 ml CDCl 3 ). The cap was replaced and the vial was placed in a Corning dish lined with 380 nm LED lights. A small piece of tape from the outside of the light dish to the top of the vial ensured the vial did not move away from the lights during the reaction. Throughout the reaction, the solution was rapidly stirred, and cooled to room temperature by a constant stream of air being blown into the middle of the light setup. Preparation of Uniformly Functionalized Alkyl Bromide Silicon Surfaces 11-(trichlorosilyl)undecyl 2-bromo-2-methylproanoate was synthesized and immobilized on silicon substrates as described by Poelma and coworkers. 5 S6

7 Representative Procedure for Dehalogenation of Surfaced-Tethered Initiators and Brushes As shown in a recent publication from our group, 2 a simple benchtop apparatus comprised of a modified Petri dish with a covering glass slide can be used instead of a glovebox for PTH surface reactions. Accordingly, this benchtop apparatus was used interchangeably with the glovebox. For a more detailed description, please see Discekici and coworkers recent publication. A stock solution was prepared by thoroughly mixing 1.4 mg PTH, 19 µl HCH, 0.12 ml NBu 3, and 1.0 ml MeCN (due to the brushes solubility, DMA was used as the solvent for reactions with polymer brushes) in a 1 dram vial. The solution was added dropwise to cover the entire surface of the functionalized silicon wafer substrate. The substrate was covered with either a coverslip or a photomask and irradiated with 405 nm collimated light for a predetermined time. CHARACTERIZATIN DATA Debromination of Polystyrene-Br Before After Normalized RI Response Time / Minutes Figure S1. SEC traces showing PS-Br (solid black line, reaction time = 0 h, M n = 1.6 kgmol -1, M w/m n = 1.11) and the dehalogenated product PS-H (dashed red line, reaction time = 6 h, M n = 1.9 kgmol -1, M w/m n = 1.10). The slight increase in M n following dehalogenation is due to loss of lower molecular weight species during purification by precipitation. S7

8 Dehalogenation of Polystyrene-Br: Necessity of Both Light and PTH As controls, portions of the same PS-Br were subjected to our optimized reaction conditions, excluding either PTH or light. Though we have shown the dehalogenation to be complete within six hours in the presence of light and all necessary reagents, after 24 hours, both reactions yielded polymers with fully intact chain ends. This demonstrates that both the PTH catalyst and light are necessary for the dehalogenation reaction to proceed, and that no deleterious side reactions occur with or without light. Figure S2. (a) General reaction scheme for control reactions. 1 H NMR spectra showing (b) unmodified PS-Br, (c) PS- Br after being subjected to our optimized dehalogenation reaction conditions excluding PTH for 24 hours, and (d) PS- Br after being subjected to our optimized dehalogenation conditions excluding light (24 hour reaction time). Insets present to emphasize the signature chain end signal. In the absence of either PTH or light, there is no change in the polymer chain end. S8

9 Before No Catalyst No Light Normalized RI Signal Time (min) Figure S3. Size exclusion chromatographs showing no change in PS-Br before (solid black line, reaction time = 0 h, M n = 1.6 kgmol -1, M w/m n = 1.11), after being exposed to optimized reaction conditions excluding PTH (red dashed line, reaction time = 24 h, M n = 1.7 kgmol -1, M w/m n = 1.22), or after being subjected to optimized reaction conditions for 24 h in the dark (blue dotted line, reaction time = 24 h, M n = 1.7 kgmol -1, M w/m n = 1.20). S9

10 Debromination of Poly(tert-butyl acrylate)-br a) 54 Br 5 mol% PTH HCH (5 equiv.) NBu 3 (5 equiv.) 54 H MeCN, λ = 380 nm, rt 4 h b) + c) Chemical Shift (ppm) Figure S4. (a) Reaction scheme for the dehalogenation of poly(tert-butyl acrylate)-br. 1 H NMR spectra annotated to show the diagnostic peaks (b) before and (c) after dehalogenation. Figure S5. Size exclusion chromatographs of the initial poly(tert-butyl acrylate)-br before reaction (solid black line, reaction time = 0 h, M n = 6.5 kgmol -1, M w/m n = 1.18), and the dehalogenated sample (dashed red line, reaction time = 4 h, M n = 6.6 kgmol -1, M w/m n = 1.21). S10

11 Dehalogenation of Polystyrene-Cl Figure S6. (a) Reaction scheme for the dechlorination of PS-Cl. (b) 1 H NMR spectrum of PS-Cl before dehalogenation, (c) 1 H NMR spectrum of the dehalogenated polymer. (d) SEC traces showing PS-Cl before (solid black line, M n = 4.1 kgmol -1, M w/m n = 1.48) and after (dashed red line, M n = 5.1 kgmol -1, M w/m n = 1.48) dehalogenation. The slight increase in M n following dehalogenation is due to loss of lower molecular weight species during purification by precipitation. S11

12 Removal of RAFT Chain End a) H S n-1 n S 10 S 5 mol% PTH HCH (5 equiv.) NBu 3 (5 equiv.) MeCN, λ = 380 nm, rt 48 h H H n-1 n b) c) Chemical Shift (ppm) Figure S7. (a) Reaction scheme (top) and 1 H NMR spectra highlighting (b) the presence of signals from RAFT chain end protons before reaction and (c) the corresponding disappearance of those peaks, indicative of chain end removal. Figure S8. SEC traces showing the poly(tert-butyl acrylate)-raft polymer before and after chain end removal. (a) UV detector signal at 310 nm showing the presence of the strongly absorbing RAFT chain end (black, reaction time = 0 h), and its disappearance after the reaction (blue, reaction time = 48 h). (b) SEC chromatograms showing the starting polymer (black solid line, M n = 3.4 kgmol -1, M w/m n = 1.12) and the chain end removed sample after 48 h (dashed blue line, M n = 3.3 kgmol -1, M w/m n = 1.17). S12

13 REFERENCES (1) Discekici, E. H.; Treat, N. J.; Poelma, S..; Mattson, K. M.; Hudson, Z. M.; Luo, Y.; Hawker, C. J.; de Alaniz, J. R. A Highly Reducing Metal-Free Photoredox Catalyst: Design and Application in Radical Dehalogenations. Chem. Commun. 2015, 51 (58), (2) Discekici, E. H.; Pester, C. W.; Treat, N. J.; Lawrence, J.; Mattson, K. M.; Narupai, B.; Toumayan, E. P.; Luo, Y.; McGrath, A. J.; Clark, P. G.; Read de Alaniz, J.; Hawker, C. J. Simple Benchtop Approach to Polymer Brush Nanostructures Using Visible-Light- Mediated Metal-Free Atom Transfer Radical Polymerization. ACS Macro Lett. 2016, 5 (2), (3) Schmidt, B. V. K. J.; Hetzer, M.; Ritter, H.; Barner-Kowollik, C. Cyclodextrin-Complexed RAFT Agents for the Ambient Temperature Aqueous Living/Controlled Radical Polymerization of Acrylamido Monomers. Macromolecules 2011, 44 (18), (4) Skey, J.; 'Reilly, R. K. Facile ne Pot Synthesis of a Range of Reversible Addition Fragmentation Chain Transfer (RAFT) Agents. Chem. Commun. 2008, No. 35, (5) Poelma, J. E.; Fors, B. P.; Meyers, G. F.; Kramer, J. W.; Hawker, C. J. Fabrication of Complex Three-Dimensional Polymer Brush Nanostructures Through Light-Mediated Living Radical Polymerization. Angew. Chem. Int. Ed. 2013, 52 (27), S13