Cationic Polymerization of Vinyl Ethers Controlled by Visible Light

Transcription

1 Cationic Polymerization of Vinyl Ethers Controlled by Visible Light Veronika Kottisch, Quentin Michaudel, and Brett P. Fors* Cornell University, Ithaca, New York, 14853, United tates upporting Information Experimental Procedures General Reagent Information... 3 General Analytical Information... 3 General Reaction etup... 4 ynthesis of -1-isobutoxyethyl N,N-diethyl dithiocarbamate (2a)... 4 ynthesis of -1-isobutoxylethyl ʹ-ethyl trithiocarbonate (2b)... 5 General Procedure for Photocontrolled Cationic Polymerization of Isobutyl Vinyl Ether General Procedure for Photocontrolled Cationic Polymerization of Ethyl Vinyl Ether..11 General Procedure for Photocontrolled Cationic Polymerization of 2-Chloroethyl Vinyl Ether Procedure for Photocontrolled Cationic Polymerization of n-propyl Vinyl Ether Procedure for Photocontrolled Cationic Polymerization of n-butyl Vinyl Ether Procedure for Photocontrolled ynthesis of Diblock Copolymer Procedure for On/Off Photocontrolled Cationic Polymerization of Isobutyl Vinyl Ether (Figure 2a) Procedure for Kinetic Investigation of Photocontrolled Cationic Isobutyl Vinyl Ether Polymerization (Figure 2a and 2b) Procedure for Photocontrolled Cationic Isobutyl Vinyl Ether Polymerizations Using Neutral Density Filters to Modulate Light Intensity (Figure 2b) Procedure for Fluorescence Quenching tudies Attempts of 4-Methoxystyrene Polymerizations References

2 Figures Figure 1. 1 H NMR of -1-isobutoxyethyl N,N-diethyl dithiocarbamate (2a)... 5 Figure 2. 1 H NMR of -1-isobutoxylethyl ʹ-ethyl trithiocarbonate (2b)... 7 Figure 3a. 1 H NMR of poly(isobutyl vinyl ether)... 8 Figure 3b. 1 H NMR of poly(isobutyl vinyl ether) with chain-end analysis... 9 Figure 4. Polymerization setup Figure 5. Reaction before and after irradiation Figure 6. GPC traces of polymers in Table 1, entries Figure 7. 1 H NMR of poly(ethyl vinyl ether) Figure 8. 1 H NMR of poly(2-chloroethyl vinyl ether) Figure 9. 1 H NMR of poly(n-propyl vinyl ether) Figure 10a. 1 H NMR of poly(n-butyl vinyl ether) Figure 10b. 1 H NMR of poly(n-butyl vinyl ether) with chain-end analysis Figure H NMR of poly(ethyl vinyl ether-block-isobutyl vinyl ether) Figure 12a,b. GPC traces of aliquots and M n vs. time development of On/Off- Experiment (Figure 2a) Figure 13. Monomer conversion for reactions with modulated light intensity Figure 14. etup with neutral density filters Figure 15. Fluorescence quenching of 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate by CTA 2a Figure 16. tern-volmer plot for the fluorescence quenching of 2,4,6-tri-(pmethoxyphenyl)pyrylium tetrafluoroborate by CTA 2a Figure 17. Fluorescence quenching of 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate by IBVE Figure 18. tern-volmer plot for the fluorescence quenching of 2,4,6-tri-(pmethoxyphenyl)pyrylium tetrafluoroborate by IBVE and CTA 2a Figure 19. tern-volmer plot for the fluorescence quenching of 2,4,6-tri-(pmethoxyphenyl)pyrylium tetrafluoroborate by IBVE and CTA 2a at low concentrations Table 1. Results of initial photocatalyst screening

3 General Reagent Information All polymerizations were set up in an Unilab MBraun glovebox with a nitrogen atmosphere and irradiated with blue LED light under nitrogen atmosphere outside the glovebox. Isobutyl vinyl ether (IBVE) (99%, TCI), ethyl vinyl ether (EVE) (99%, igma Aldrich), 2-chloroethyl vinyl ether (Cl-EVE) (97%, TCI), n-propyl vinyl ether (PVE) (99%, igma Aldrich), and n-butyl vinyl ether (BVE) (98%, igma Aldrich) were dried over calcium hydride (CaH 2 ) (ACRO organics, 93% extra pure, 0 2 mm grain size) for 12 h and distilled under nitrogen and degassed by vigorously sparging with nitrogen for 30 minutes. Ethanethiol (97%, Alfa Aesar) and carbon disulfide (99.9+%, Alfa Aesar) were distilled before use. 2.0 M HCl in Et 2 O (igma Aldrich) and sodium hydride (60%, dispersion in mineral oil, igma Aldrich) were used as received. odium N,Ndiethylcarbamate trihydrate (98%, Alfa Aesar) was azeotropically dried with toluene. Dichloromethane (DCM) and diethylether (Et 2 O) were purchased from J.T. Baker and were purified by vigorous purging with argon for 2 h, followed by passing through two packed columns of neutral alumina under argon pressure. 2,4,6-tri-(pmethoxyphenyl)pyrylium tetrafluoroborate was synthesized according to literature procedures. 1 General Analytical Information All polymer samples were analyzed using a Tosoh Ecoec HLC 8320GPC system with two uperhm-m columns in series at a flow rate of ml/min. THF was used as the eluent and all number-average molecular weights (M n ), weight-average molecular weights (M w ), and dispersities (Đ) for poly(isobutyl vinyl ether) were calculated from refractive index chromatograms against TKgel polystyrene standards. Numberaverage molecular weights (M n ), weight-average molecular weights (M w ), and dispersities (Đ) for all other polymers were determined by light scattering using a Wyatt minidawn Treos multi-angle light scattering detector. The dn/dc values were calculated from light scattering in THF for poly(ethyl vinyl ether), poly(2-chloroethyl vinyl ether), poly(n-propyl vinyl ether), poly(n-butyl vinyl ether) and block copolymers in THF. 3

4 Nuclear magnetic resonance (NMR) spectra were recorded on a Mercury 300 MHz, a Varian 400 MHz or a Varian 600 MHz instrument. General Reaction etup Irradiation of photochemical reactions was done using blue diode led BLAZE TM lights (450 nm, 2.88 W/ft) or a 9W Kobi Electric ( nm) bulb. Green LEDs (540 nm) can also be used and give similar polymerization results. For light intensity modulation, Rangers CLARITY series full neutral density filters ND2 and ND4 were used. Na NEt 2 HCl Me Cl Me NEt 2 O i Bu Et 2 O, 78 C O i Bu Et 2 O, 0 C O i Bu 2a ynthesis of -1-isobutoxyethyl N,N-diethyl dithiocarbamate (2a) In a flame dried flask, a solution of HCl in Et 2 O (5.15 ml, 2.0 M, 10.3 mmol, 1.2 equiv) was added dropwise to a solution of isobutyl vinyl ether (1.15 ml, 8.8 mmol, 1.0 equiv) in Et 2 O (10 ml) over 10 minutes at 78 C and stirred for 1.5 hours under nitrogen. This solution was then added dropwise to a solution of N,N-diethyl dithiocarbamate (11.7 mmol, 1.3 equiv) in Et 2 O (30 ml) over 30 min at 0 C. tirring was continued for one hour at 0 C, followed by 1.5 hours at room temperature. The reaction was diluted with Et 2 O (30 ml) and saturated aqueous sodium bicarbonate solution (30 ml) was added. The layers were separated, and the aqueous layer was extracted with Et 2 O (2 20 ml). The combined organic phases were washed with water (10 ml), brine (10 ml), then diluted with hexanes (40 ml), dried over Na 2 O 4 and evaporated to dryness in vacuo. The brown oil was further purified by column chromatography (io 2, gradient from 10:0 to 8.0:0.5 hexanes:ethyl acetate) to yield a pale yellow oil (1.34 g, 61% yield). The spectroscopic data for this compound were identical to those reported in the literature. 2 1 H NMR (CDCl 3, 600 MHz) δ: 5.88 (q, J = 6.2 Hz, 1 H), 4.02 (q, J = 7.2 Hz, 2 H), (m, 2 H), 3.46 (dd, J = 9.0, 6.6 Hz, 1 H), 3.34 (dd, J = 9.0, 6.6 Hz, 1 H), (m, 1 H), 1.73 (d, J = 6.3 Hz, 3 H), 1.28 (dt, J = 11,4, 7.2 Hz, 6 H), 0.90 (d, J = 6.7 Hz, 6 H) ppm. 4

5 13 C NMR (CDCl 3, 150 MHz) δ: 195.1, 91.7, 76.2, 48.9, 47.0, 28.5, 23.6, 19.5, 12.7, 11.8 ppm. Me O i Bu 2a NEt 2 Figure 1. 1 H NMR of -1-isobutoxyethyl N,N-diethyl dithiocarbamate (2a). Me H 1) NaH 2) C 2 Et 2 O, 0 C Na Et Me Cl O i Bu Et 2 O, 0 C Me O i Bu 2b Et ynthesis of -1-isobutoxylethyl ʹ-ethyl trithiocarbonate (2b) 2b was synthesized according to a slightly modified literature procedure. 3 odium hydride (60%, 1.00 g, 25.0 mmol, 1.0 equiv) was placed in a flame-dried flask under nitrogen and then washed with anhydrous hexanes, also under nitrogen. Anhydrous Et 2 O (10 ml) was added and the reaction mixture was cooled to 0 C. Freshly distilled ethanethiol (1.85 ml, 25.0 mmol, 1.0 equiv) was added dropwise over 5

6 10 minutes at 0 C. The suspension was stirred at room temperature for 10 minutes, then cooled again to 0 C before freshly distilled carbon disulfide (1.65 ml, 27.5 mmol, 1.1 equiv) was added dropwise over 10 minutes at 0 C. The resulting thick yellow suspension was stirred at room temperature for 2 hours. A separate flame-dried flask containing a solution of HCl in Et 2 O (13.8 ml, 2.0 M, 27.5 mmol, 1.1 equiv) was cooled to 78 C and distilled isobutyl vinyl ether (3.26 ml, 25.0 mmol, 1.0 equiv) was added dropwise. The pale yellow solution was stirred at 78 C for 1 hour, then warmed to 0 C over 30 minutes. ubsequently, the cold solution was added dropwise to the suspension of sodium ethyl trithiocarbonate over 30 minutes. The resulting mixture was stirred at room temperature for 2 hours, then diluted with Et 2 O (10 ml) and quenched with sat. NaHCO 3 (10 ml). The layers were separated, and the aqueous layer was extracted with Et 2 O (2 20 ml). The combined organic phases were washed with water (10 ml), brine (10 ml), then diluted with hexanes (40 ml), dried over Na 2 O 4 and evaporated to dryness in vacuo. Column chromatography (io 2, hexanes) provided 2b as a yellow oil (3.59 g, 59%). The spectroscopic data for this compound were consistent with those reported in the literature. 3 1 H NMR (CDCl 3, 600 MHz,) δ: 5.97 (q, J = 6.3 Hz, 1 H), 3.43 (dd, J = 10.2, 6.6 Hz, 1 H), (m, 2 H), 3.27 (dd, J = 10.2, 6.6 Hz, 1 H), (m, 1 H), 1.71 (d, J = 6.3 Hz, 3 H), 1.35 (t, J = 7.4 Hz, 3 H), (m, 6 H). 13 C NMR (CDCl 3, 150 MHz) δ: 224.9, 89.1, 76.5, 31.0, 28.4, 22.9, 19.4, 13.1 ppm. 6

7 Me O i Bu 2b Et Figure 2. 1 H NMR of -1-isobutoxylethyl ʹ-ethyl trithiocarbonate (2b). General Procedure for Photocontrolled Cationic Polymerization of Isobutyl Vinyl Ether In a nitrogen filled glove box, an oven-dried one-dram vial was equipped with a stir bar and charged with isobutyl vinyl ether (0.26 ml, 2.00 mmol, 50 equiv), 0.2 ml of a stock solution of 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate (1) in DCM (2.0 mm, 0.40 µmol, 0.02 mol % relative to IBVE), and 0.04 ml of a stock solution of 2a or 2b in DCM (1 M, 0.04 mmol, 1 equiv). The vial was sealed with a septum cap under an atmosphere of nitrogen, placed next to blue LED strips (~450 nm) outside of the glove box, and stirred while cooling by blowing compressed air over the reaction vial. Following the desired amount of reaction time, benzene (89 µl, 1.0 mmol, 25 equiv) was added as an internal standard for NMR, and aliquots for NMR and GPC analysis were taken. Full conversion was generally reached after 3 5 hours. The solvent was 7

8 removed under vacuo to yield the pure polymer. A typical 1 H NMR for poly(isobutyl vinyl ether) is shown in Figure 3a,b. For a picture of the experimental setup, see Figure 4. Me n O i Bu O i Bu NEt 2 Figure 3a. 1 H NMR of poly(isobutyl vinyl ether); M n = 35.0 kg/mol, Đ = 1.30 (Table 1, entry 5). 8

9 H 3 C A,B H 2 C H C n O i Bu O O i Bu CH 2 H 3 C C H CH 3 H 2 C CH 3 C N CH 3 CH2 A,B C Figure 3b. 1 H NMR of poly(isobutyl vinyl ether); ratios of chain-end and backbone integrations can be used to calculate M n and show good chain-end fidelity; M n (NMR) = 4.4 kg/mol (M n (GPC) = 5.6 kg/mol, M n theo = 5.0 kg/mol). 9

10 Figure 4. Polymerization setup. Figure 5. Reaction before (left) and after (right) irradiation. 10

11 kg/mol 10.0 kg/mol 17.5 kg/mol 35.0 kg/mol Retention Time (min) Figure 6. GPC traces of polymers in Table 1, entries 2 5. General Procedure for Photocontrolled Cationic Polymerization of Ethyl Vinyl Ether (M theo n = 10.0 kg/mol) (Table 2, entry 2). In a nitrogen filled glove box, an oven-dried one-dram vial was equipped with a stir bar and charged with ethyl vinyl ether (0.27 ml, 2.78 mmol, 140 equiv) 0.2 ml of a stock solution of 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate (1) in DCM (2.0 mm, 0.40 µmol, 0.02 mol % relative to EVE), and 0.02 ml of a stock solution of 2b in DCM (1 M, 0.02 mmol, 1 equiv). The vial was sealed with a septum cap under an atmosphere of nitrogen, placed next to blue LED strips (~450 nm) outside of the glove box, and stirred while cooling by blowing compressed air over the reaction vial. Following the desired amount of reaction time, benzene (89 µl, 1.0 mmol, 50 equiv) was added as an internal standard for NMR, and aliquots for NMR and GPC analysis were taken. Full conversion was generally reached after 2 3 hours. The solvent was removed under vacuo to yield the pure polymer. A typical 1 H NMR for poly(ethyl vinyl ether) is shown in Figure 7. 11

12 Me n O i Bu OEt Et Figure 7. 1 H NMR of poly(ethyl vinyl ether); M n = 9.6 kg/mol, Đ = 1.20 (Table 2, entry 2). General Procedure for Photocontrolled Cationic Polymerization of 2-chloroethyl Vinyl Ether (M theo n = 10.0 kg/mol) (Table 2, entry 4). In a nitrogen filled glove box, an oven-dried one-dram vial was equipped with a stir bar and charged with 2-chloroethyl vinyl ether (0.18 ml, 1.8 mmol, 90 equiv relative to 2b), 0.2 ml of a stock solution of 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate (1) in DCM (2.0 mm, 0.40 µmol, 0.02 mol % relative to Cl-EVE), and 0.02 ml of a stock solution of 2b in DCM (1 M, 0.02 mmol, 1.0 equiv). The vial was sealed with a septum cap under an atmosphere of nitrogen, placed next to blue LED strips (~450 nm) outside of the glove box, and stirred while cooling by blowing compressed air over the reaction vial. Following the desired amount of reaction time, benzene (89 µl, 1.0 mmol, 50 equiv) was added as an internal standard for NMR, and aliquots for NMR and GPC analysis were taken. Full conversion was generally reached after 18 hours. The solvent 12

13 was removed under vacuo to yield the pure polymer. A typical 1 H NMR for poly(2- chloroethyl vinyl ether) is shown in Figure 8. Me O i Bu n Et Cl Figure 8. 1 H NMR of poly(2-chloroethyl vinyl ether); M n = 8.8 kg/mol, Đ = 1.30 (Table 2, entry 4). Procedure for Photocontrolled Cationic Polymerization of n-propyl Vinyl Ether (M theo n = 5.0 kg/mol) (Table 2, entry 5). In a nitrogen filled glove box, an oven-dried one-dram vial was equipped with a stir bar and charged with n-propyl vinyl ether (0.26 ml, 2.32 mmol, 60 equiv relative to 2b), 0.12 ml of a stock solution of 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate (1) in DCM (2.0 mm, 0.25 µmol, 0.01 mol % relative to PVE), and 0.02 ml of a stock solution of 2b in DCM (1 M, 0.02 mmol, 1.0 equiv). The vial was sealed with a septum cap under an atmosphere of nitrogen, placed next to blue LED strips (~450 nm) outside of the glove box, and stirred while cooling by blowing compressed air over the reaction 13

14 vial. Following the desired amount of reaction time, benzene (89 µl, 1.0 mmol, 50 equiv) was added as an internal standard for NMR, and aliquots for NMR and GPC analysis were taken. Full conversion was generally reached after 2 3 hours. The solvent was removed under vacuo to yield the pure polymer. A typical 1 H NMR for poly(n-propyl vinyl ether) is shown in Figure 9. Me n O i Bu O n Pr Et Figure 9. 1 H NMR of poly(n-propyl vinyl ether); M n = 4.8 kg/mol, Đ = 1.27 (Table 2, entry 5). Procedure for Photocontrolled Cationic Polymerization of n-butyl Vinyl Ether (M theo n = 5.0 kg/mol) (Table 2, entry 6). In a nitrogen filled glove box, an oven-dried one-dram vial was equipped with a stir bar and charged with n-butyl vinyl ether (0.26 ml, 2.00 mmol, 50 equiv relative to 2b), 0.2 ml of a stock solution of 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate (1) in DCM (2.0 mm, 0.40 µmol, 0.02 mol % relative to BVE), and 0.02 ml of a stock solution 14

15 of 2b in DCM (1 M, 0.02 mmol, 1.0 equiv). The vial was sealed with a septum cap under an atmosphere of nitrogen, placed next to blue LED strips (~450 nm) outside of the glove box, and stirred while cooling by blowing compressed air over the reaction vial. Following the desired amount of reaction time, benzene (89 µl, 1.0 mmol, 50 equiv) was added as an internal standard for NMR, and aliquots for NMR and GPC analysis were taken. Full conversion was generally reached after 2 3 hours. The solvent was removed under vacuo to yield the pure polymer. A typical 1 H NMR for poly(n-butyl vinyl ether) is shown in Figure 10a,b. Me n O i Bu O n Bu Et Figure 10a. 1 H NMR of poly(n-butyl vinyl ether); M n = 5.8 kg/mol, Đ = 1.23 (Table 2, entry 6). 15

16 A,B C H 3 C H 2 C H C O i Bu O n H C O n Bu CH 3 CH 2 H 2 C CH 2 CH 3 C A,B Figure 10b. 1 H NMR of poly(n-butyl vinyl ether); ratios of chain-end and backbone integrations can be used to calculate M n and show good chain-end fidelity; M n (NMR) = 6.1 kg/mol (M n (GPC) = 5.8 kg/mol, M n theo = 5.0 kg/mol). Procedure for Photocontrolled ynthesis of Diblock Copolymer (Figure 3) In a nitrogen filled glove box, an oven-dried one-dram vial was equipped with a stir bar and charged with ethyl vinyl ether (0.27 ml, 2.78 mmol, 70 equiv relative to 2), 0.2 ml of a stock solution of 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate (1) in DCM (2.0 mm, 0.40 µmol, 0.02 mol % relative to EVE) and 0.02 ml of a stock solution of 2b in DCM (1 M, 0.02 mmol, 1.0 equiv). The vial was sealed with a septum cap under an atmosphere of nitrogen, placed next to blue LED strips (~450 nm) outside of the glove box, and stirred while cooling by blowing compressed air over the reaction vial. The reaction was run to full conversion (1 hour). The vial was brought back in the glove box and an aliquot for 1 H NMR and GPC analysis was taken prior to the addition of isobutyl vinyl ether (0.52 ml, 4 mmol, 100 equiv relative to 2b). The vial was sealed with a 16

17 septum cap under an atmosphere of nitrogen, placed next to blue LED strips (~450 nm) outside of the glove box, and stirred while cooling by blowing compressed air over the reaction vial until the reaction reached full conversion (14 hours). The solvent was removed under vacuo to yield the pure polymer. The 1 H NMR for poly(ethyl vinyl ether-block-isobutyl vinyl ether) is shown in Figure 11. Me b n O i Bu OEt m O i Bu Et Figure H NMR of poly(ethyl vinyl ether-block-isobutyl vinyl ether); M n = 10.7 kg/mol, Đ = 1.20 (Figure 3). Procedure for On/Off Photocontrolled Cationic Polymerization of Isobutyl Vinyl Ether (Figure 2a) In a nitrogen filled glove box, an oven-dried 20 ml scintillation vial was equipped with a stir bar and charged with isobutyl vinyl ether (1.3 ml, 10 mmol, 50 equiv), 0.5 ml of a stock solution of 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate (1) in DCM (2.0 mm, 1.0 µmol, 0.01 mol % relative to IBVE), 0.2 ml of a stock solution of 2a in DCM (1 M, 0.2 mmol, 1.0 equiv), and benzene (89 µl, 1.0 mmol, 50 equiv) as an internal 17

18 standard for NMR. The vial was sealed with a septum cap under an atmosphere of nitrogen, placed next to blue LED strips (~450 nm) outside of the glove box, and stirred while cooling by blowing compressed air over the reaction vial. Aliquots were taken after 30 min intervals under positive nitrogen pressure and subjected to 1 H NMR and GPC analysis. The vial was covered in aluminum foil during off periods. The GPC traces of all aliquots and the development of M n vs. time are depicted in Figure 12. (a) min, after 30 min on 60 min, after 30 min off min, after 30 min on 120 min, after 30 min off min, after 30 min on 180 min, after 30 min off min, after 60 min on (b) Retention Time (min) Mn (g/mol) Time (min) Figure 12. (a) GPC traces of aliquots and (b) M n vs. time development of On/Off- Experiment (Figure 2a). 18

19 Procedure for Kinetic Investigation of Photocontrolled Cationic Isobutyl Vinyl Ether Polymerization (Figure 2a and 2b) In a nitrogen filled glove box, an oven-dried 20 ml scintillation vial was equipped with a stir bar and charged with isobutyl vinyl ether (1.3 ml, 10 mmol, 100 equiv), 0.5 ml of a stock solution of 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate (1) in DCM (2.0 mm, 1.0 µmol, 0.01 mol % relative to IBVE), 0.1 ml of a stock solution of 2a in DCM (1 M, 0.1 mmol, 1.0 equiv), and benzene (89 µl, 1.0 mmol, 100 equiv) as an internal standard for NMR. The vial was sealed with a septum cap under an atmosphere of nitrogen, placed next to blue LED strips (~450 nm) outside of the glove box, and stirred while cooling by blowing compressed air over the reaction vial. Aliquots were taken after 10 min, 20 min, 30 min, 45 min, 75 min and 120 min under positive nitrogen pressure and subjected to 1 H NMR and GPC analysis. Procedure for Photocontrolled Cationic Isobutyl Vinyl Ether Polymerizations Using Neutral Density Filters to Modulate Light Intensity (Figure 2b) In a nitrogen filled glove box, an oven-dried one-dram vial was equipped with a stir bar and charged with isobutyl vinyl ether (0.52 ml, 4 mmol, 100 equiv), 0.2 ml of a stock solution of 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate (1) in DCM (2.0 mm, 0.40 µmol, 0.01 mol % relative to IBVE), 0.04 ml of a stock solution of 2a in DCM (1 M, 0.04 mmol, 1.0 equiv), and benzene (30 µl, 0.34 mmol, 8.5 equiv) as an internal standard for NMR. The vial was sealed with a septum cap under an atmosphere of nitrogen, taken outside of the glove box, and placed about 2 cm away from a 9W Kobi Electric ( nm) bulb. The reaction was stirred while cooling by blowing compressed air over the reaction vial and aliquots for 1 H NMR and GPC were taken at specified time points (Figure 13). The reaction was repeated three times with different light intensities: 1) 100% transmission, 2) 50% transmission, and 3) 25% transmission. In order to achieve 50% and 25% light transmission, a Rangers CLARITY series full neutral density filter was intercalated between the light bulb and the reaction vial, touching the latter. A ND2 filter (50%) and a ND4 filter (25%) were used. For a picture of the experimental setup, see Figure

20 Conversion (%) % Transmission 50% Transmission 25% Transmission Time (min) Figure 13. Monomer conversion (%) at specified time point during the reaction at 100% transmission (blue), 50% transmission (red), and 25% transmission (black) of light. The slope represents the initial reaction rates used for Figure 2b. Air flow Light ource Reaction Vial Neutral Density Filter Figure 14. etup with neutral density filters. 20

21 Procedure for Fluorescence Quenching tudies A Varian Cary Eclipse Fluorescence pectrophotometer was used for the quenching studies. The solutions of 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate (1) were excited at 475 nm and the fluorescence spectra were recorded between 480 and 700 nm. The emission of a 0.21 mm solution of 1 in DCM was measured at varying concentrations of -1-isobutoxyethyl N,N-diethyl dithiocarbamate (2a) (0 26 mm). As shown in Figures 15, 16, 18 and 19 a concentration dependent fluorescence quenching was observed. The emission of a 0.21 mm solution of 1 in DCM was also measured at varying low concentrations of IBVE (0 260 mm) then at higher concentrations ( M). As shown in Figures no quenching of the emission of 1 was observed at low concentrations of IBVE, but a concentration dependent fluorescence quenching was observed at molar concentrations. Emission pyrylium pyrylium mmol CTA 2a pyrylium mmol CTA 2a pyrylium mmol CTA 2a pyrylium mmol CTA 2a Wavelength (nm) Figure 15. Fluorescence quenching of 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate by CTA 2a (λ ex = 475 nm). 21

22 I 0 /I x10-3 [CTA] (M) Figure 16. tern-volmer plot for the fluorescence quenching of 2,4,6-tri-(pmethoxyphenyl)pyrylium tetrafluoroborate by CTA 2a. Emission pyrylium pyrylium mmol IBVE pyrylium mmol IBVE pyrylium mmol IBVE pyrylium + 2 mmol IBVE pyrylium + 3 mmol IBVE pyrylium + 4 mmol IBVE Wavelength (nm) Figure 17. Fluorescence quenching of 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate by IBVE (λ ex = 475 nm). 22

23 I 0 /I IBVE quenching CTA quenching Concentration (M) Figure 18. tern-volmer plot for the fluorescence quenching of 2,4,6-tri-(pmethoxyphenyl)pyrylium tetrafluoroborate by IBVE and CTA 2a CTA quenching IBVE quenching 2.0 I 0 /I x10-3 Concentration (M) Figure 19. tern-volmer plot for the fluorescence quenching of 2,4,6-tri-(pmethoxyphenyl)pyrylium tetrafluoroborate by IBVE and CTA 2a (low concentration section of Figure 18). 23

24 Table 1. Results of initial photocatalyst screening Catalyst mol %* reaction conversion time Ru(bpy) 3 (PF 6 ) h Ru(bpz) 3 (PF 6 ) h (Ir[dF(CF 3 )ppy] 2 (dtbpy))pf h 9-(2,6-diisopropylphenyl)-10-methylacridinium h perchlorate 9-(mesityl)-10-methylacridinium tetrafluoroborate h 9-(mesityl)-10-methylacridinium perchlorate h 2,4,6-tri-(p-methoxyphenyl)pyrylium tetrafluoroborate h 100% *Catalyst loading is reported with respect to monomer concentration Attempts of 4-Methoxystyrene Polymerizations 4-methoxystyrene can be polymerized with this catalytic system, however, the reaction proceeds only very slowly and does not reach full conversion even after several days. Polymerization typically produced only short polymers (M n = 1.7 kg/mol) with moderate control (Đ = 1.7). Higher catalyst loading improved the conversion but was detrimental to the control of the chain-length. References 1. Martiny, M.; teckhan, E.; Esch, T. Chem. Ber. 1993, 126, Uchiyama, M.; atoh, K.; Kamigaito, M. Angew. Chem. Int. Ed. 2015, 54, Kumagai,.; Nagai, K.; atoh, K.; Kamigaito, M. Macromolecules 2010, 43,