Chem, Volume 2
Supplemental Information
Ultra-High Molecular Weights via Aqueous
Reversible-Deactivation Radical Polymerization
R. Nicholas Carmean, Troy E. Becker, Michael B. Sims, and Brent S. Sumerlin
Table of Contents
2) Materials and characterization
3-‐4) Experimental procedure
5) Figure S1. UHMW polymerization targeting 1.06 ´ 106 g/mol with trithiocarbonate iniferter.
6) Figure S2. UHMW polymerization targeting 2.04 ´ 106 g/mol with trithiocarbonate iniferter
7) Figure S3. UHMW polymerization targeting 5.11 ´ 106 g/mol with trithiocarbonate iniferter
8) Figure S4. On/off UHMW polymerization of DMA with a trithiocarbonate iniferter
9) Figure S5. Trithiocarbonate and xanthate iniferter Beer-‐Lambart plot
10) Figure S6. UHMW polymerization targeting 1.34 ´ 106 g/mol with xanthate iniferter
11) Figure S7. UHMW polymerization targeting 2.32 ´ 106 g/mol with xanthate iniferter
12) Figure S8. UHMW polymerization targeting 5.17 ´ 106 g/mol with xanthate iniferter
13) Figure S9. UHMW polymerization targeting 9.93 ´ 106 g/mol with xanthate iniferter
14) Figure S10. UHMW polymerization mediated by sunlight with trithiocarbonate iniferter
15) Figure S11. Temperature profile of UHMW polymerization of DMA with xanthate and trithiocarbonate iniferter
16) Figure S12. Background initiation of DMA under UV irradiation
17) Figure S13. Polymerization rates of UHMW xanthate mediated polymerizations
Materials
All chemicals were used as received, unless otherwise noted. 2-‐(2-‐Carboxyethylsulfanylthiocarbonylsulfanyl)-‐2-‐methylpropionic acid and ethyl 2-‐((ethoxycarbonothioyl)thio)propanoate were synthesized according to previous reports.[1,2] N,N-‐Dimethylacrylamide (DMA, Sigma-‐Aldrich, 99%) was passed through a column of basic alumina to remove inhibitors and acidic impurities prior to polymerization. N,N-‐Dimethylformamide (DMF, >99%) was purchased from Sigma-‐Aldrich. Dimethyl sulfoxide (DMSO) was purchased from Fischer. Water (deionized ASTM type II) was purchased from Aqua Solutions, Inc. Nuclear Magnetic Resonance (NMR) Spectroscopy. 1H NMR spectra were recorded in deuterated chloroform (CDCl3, Cambrdige Isotopes), deuterated dimethyl sulfoxide (DMSO-‐d6, Cambrdige Isotopes), or duterium oxide (D2O, Cambrdige Isotopes) using a Varian Mercury 300 or Varian Inova 500 MHz spectrometer. Size Exclusion Chromatography (SEC). Molecular weights and molecular weight distributions were determined via multi-‐angle laser light scattering size exclusion chromatography (MALS-‐SEC) in N,N-‐dimethylacetamide (DMAc) with 50 mM LiCl at 50 °C and a flow rate of 1.0 mL/min (Agilent isocratic pump, degasser, and autosampler; ViscoGel I-‐series 10 μm guard column and two ViscoGel I-‐series G3078 mixed bed columns, with molecular weight ranges 0−20×103 and 0−10×106 g/mol, respectively). Detection consisted of a Wyatt Optilab T-‐rEX refractive index detector operating at 658 nm and a Wyatt miniDAWN Treos light scattering detector operating at 659 nm. Absolute molecular weights and polydispersities were calculated using Wyatt ASTRA software. The absolute molecular weight for PDMA was determined using 100% mass recovery, a multiangle light scattering detector and the Wyatt ASTRA software. Each polymer was dehydrated by lyophilization and dissolved in SEC solvent (£1 mg/mL) at least 24 h prior to molecular weight characterization. UV-‐Vis Spectroscopy. All measurements were performed on a Molecular Devices SpectraMax M2 Multimode Microplate Reader at 25 °C. Absorbance measurements were conducted with 150 μL of sample on clear 96-‐well microplates (Greiner). Calibration curves and path length correction were constructed using the integrated SoftMax Pro software.
Light Intensity was measured with General UV513AB Digital UV AB Light Meter calibrated at 365 nm.
Experimental Typical ultrahigh molecular weight (UHMW) polymerization procedure (DMA polymerization initiated by a trithiocarbonate targeting Mn ³ 5.00 ´ 106 g/mol). DMA (394 mg, 3.97 mmol) and trithiocarbonate iniferter (20.0 µg, 7.45 ´ 10-‐5 mmol from 1.00 mg/mL DMSO stock solution) were dissolved in water (1.70 mL, 2 M [DMA]) in a 10 mL Schlenk flask, and DMF (0.100 mL) was added as an internal standard. The iniferter stock solution was stored between 2 and 6 °C for further use. Argon was bubbled through the polymerization solution for 20 min. The reaction vessel was positioned 2.50 cm from the UV light source for an intensity of 7.0 mW/cm2, and polymerization was initiated upon irradiation. Monomer conversion was determined by 1H NMR spectroscopy, monitoring the disappearance of the DMA vinyl peaks (d, 1H, 5.60 ppm) relative to DMF (s, 1H, 8.02 ppm). Each reaction aliquot was dried by lyophilization and dissolved in SEC solvent (£1 mg/mL) at least 24 h prior to molecular weight characterization. UHMW PDMA-‐b-‐PDMA. DMA (417 mg, 4.20 mmol) and trithiocarbonate iniferter (0.100 mg, 3.72 ´ 10-‐4 mmol from 1.00 mg/mL DMSO stock solution) were dissolved in water (3.70 mL 1 M [DMA]) in a 10 mL Schlenk flask and DMF (0.100 mL) was added as an internal standard. Argon was bubbled through the polymerization solution for 20 min. The reaction vessel was positioned 2.50 cm from the UV light source for an intensity of 7.0 mW/cm2 and polymerization was initiated upon irradiation. The reaction was irradiated for 24 h and a small amount was removed to determine monomer conversion via 1H NMR spectroscopy by monitoring the disappearance of the vinyl, DMA peaks (d, 1H, 5.60 ppm) relative to DMF (s, 1H, 8.02 ppm) and to characterize molecular weight via SEC. The polymerization of the PDMA first block reached >95% monomer conversion. DMA (420 mg, 4.24 mmol) was dissolved in water (3.10 mL), DMF (0.100 mL), and the preceding PDMA polymerization mixture. Argon was bubbled through the viscous solution for 20 min, and chain extension was initiated upon irradiation. End-‐group photolytic trapping with TEMPO (PDMA-‐Xanthate). Low molecular weight PDMA was prepared with a xanthate iniferter similar to the procedures described above. PDMA-‐XAN (85.0 mg, Mn,SEC 4500 g/mol, 1.89 ´ 10-‐2 mmol) and TEMPO (59.0 mg, 3.77 ´ 10-‐1 mmol) were dissolved in DMSO (0.800 mL) and DMF (0.100 mL). Argon was bubbled through the solution for 20 min. The reaction vessel was positioned 2.50 cm from the UV light source to give an intensity of 7.0 mW/cm2, and photolysis was induced upon irradiation. Photolytic decomposition was determined via 1H NMR spectroscopy by monitoring the disappearance of the terminal PDMA methyne proton (b, 1H, 5.58 ppm) adjacent to the xanthate iniferter relative to the methylene protons (b, 2H, 3.97 ppm) of the xanthate iniferter. End-‐group photolytic trapping with TEMPO (PDMA-‐Trithiocarbonate). Low molecular weight PDMA was prepared with a trithiocarbonate iniferter similar to UHMW procedure defined above. PDMA-‐TTC (168 mg, Mn,SEC 3500 g/mol, 4.80 ´ 10-‐2 mmol) and TEMPO (150 mg, 9.60 ´ 10-‐1 mmol) were dissolved in DMSO (0.800 mL) and DMF (0.100 mL). Argon was bubbled through the solution for 20 min. The reaction vessel was positioned 2.50 cm from the UV light source to give an intensity of 7.0 mW/cm2, and photolysis was induced upon irradiation.
Photolytic decomposition was determined via 1H NMR spectroscopy by monitoring the disappearance of the terminal PDMA methyne proton (b, 1H, 5.58 ppm) adjacent to the trithiocarbonate iniferter relative to DMF (s, 1H, 8.02 ppm). Sunlight mediated polymerization of DMA with trithiocarbonate iniferter. DMA (779 mg, 7.86 mmol) and trithiocarbonate iniferter (100 µg, 3.73 ´ 10-‐4 mmol from 1.00 mg/mL DMSO stock solution) were dissolved in water (3.00 mL, 2 M [DMA]) in a 10 mL Schlenk flask, and DMF (0.100 mL) was added as an internal standard. Argon was bubbled through the polymerization solution for 20 min. Three syringes were purged with argon in the side arm of the Schlenk flask, and the reaction vessel was covered in foil then transferred to the roof of Sisler Hall on the campus of the University of Florida in Gainesville, FL. The polymerization was initiated upon removal of the foil mask. To keep the polymerization under constant sunlight irradiation, a balloon was filled with argon and transferred to the roof to purge the side arm of the Schelnk flask during removal of reaction aliquots. The polymerization was quenched by removing the vessel from sunlight. Monomer conversion was determined by 1H NMR spectroscopy, monitoring the disappearance of the DMA vinyl peaks (d, 1H, 5.60 ppm) relative to DMF (s, 1H, 8.02 ppm). Each reaction aliquot was dried by lyophilization and dissolved in SEC solvent (£1 mg/mL) at least 24 h prior to molecular weight characterization. Measurement of polymerization exotherm. DMA (500 mg) was dissolved in water (2.00 mL, 2 M [DMA]) and transferred to a 10 mL Schlenk flask with an electronic thermocouple fitted through a rubber septa in place of a glass stopper. Argon was bubbled through the aqueous solution for 15 min. With a slow flow of argon through the top rubber septa, the experiment was initiated by turning on the light source. The solution temperature was recorded every 5 min. This aqueous solution served as a control to compare against and active DMA polymerization targeting UHMW. DMA (500 mg, 5.04 mmol) and xanthate iniferter (70.0 µg, 3.15 ´ 10-‐4 mmol from 1.00 mg/mL DMSO stock solution) were dissolved in water (2.00 mL, 2 M [DMA]) and transferred to a 10 mL Schlenk flask with an electronic thermocouple fitted through a rubber septa in place of a glass stopper. Argon was bubbled through the aqueous solution for 15 min. With a slow flow of argon through the top rubber septa, the polymerization was initiated by turning on the light source. The solution temperature was recorded every 5 min. DMA (500 mg, 5.04 mmol) and trithiocarbonate iniferter (85.0 µg, 3.16 ´ 10-‐4 mmol from 1.00 mg/mL DMSO stock solution) were dissolved in water (2.00 mL, 2 M [DMA]) and transferred to a 10 mL Schlenk flask with an electronic thermocouple fitted through a rubber septa in place of a glass stopper. Argon was bubbled through the aqueous solution for 15 min. With a slow flow of argon through the top rubber septa, the polymerization was initiated by turning on the light source. The solution temperature was recorded every 5 min.
Figure S1. N,N-‐Dimethylacrylamide (DMA) was irradiated with long-‐wave UV light in the presence of a trithiocarbonate iniferter to produce ultrahigh molecular weight (UHMW) poly(DMA). The polymerization of DMA to UHMW (Mn,SEC 1.03 ´ 106 g/mol) displays near-‐linear pseudo-‐first order kinetics, indicating a constant radical concentration up to >95% monomer conversion. Size-‐exclusion chromatography (SEC) traces shift to shorter elution times and higher molecular weights throughout the polymerization was the SEC traces remain monomodal. The predicted molecular weights (Mn, theory) closely matches measured values (Mn,
SEC) as monomer conversion increases, while molecular weight distributions (Ð) remained low.
Figure S2. N,N-‐Dimethylacrylamide (DMA) was irradiated with long-‐wave UV light in the presence of a trithiocarbonate iniferter to produce ultrahigh molecular weight (UHMW) poly(DMA). The polymerization of DMA to UHMW (Mn,SEC 2.52 ´ 106 g/mol) displays near-‐linear pseudo-‐first order kinetics, indicating a constant radical concentration up to >95% monomer conversion. Size-‐exclusion chromatography (SEC) traces shift to shorter elution times and higher molecular weights throughout the polymerization was the SEC traces remain monomodal. The predicted molecular weights (Mn, theory) closely matches measured values (Mn,
SEC) as monomer conversion increases, while molecular weight distributions (Ð) remained low.
Figure S3. N,N-‐Dimethylacrylamide (DMA) was irradiated with long-‐wave UV light in the presence of a trithiocarbonate iniferter to produce ultrahigh molecular weight (UHMW) poly(DMA). The polymerization of DMA to UHMW (Mn,SEC 4.79 ´ 106 g/mol) displays near-‐linear pseudo-‐first order kinetics, indicating a constant radical concentration up to 94% monomer conversion. Size-‐exclusion chromatography (SEC) traces shift to shorter elution times and higher molecular weights throughout the polymerization was the SEC traces remain monomodal. The predicted molecular weights (Mn, theory) closely match measured values (Mn,
SEC) as monomer conversion increases, while molecular weight distributions (Ð) remained low.
Figure S4. N,N-‐Dimethylacrylamide (DMA) was irradiated with long-‐wave UV light in the presence of a trithiocarbonate iniferter to produce ultrahigh molecular weight (UHMW) poly(DMA). Turning off the UV light stopped the polymerization, which could be reinitiated by turning on the light source, demonstrating the rapid reversible termination between the propagating chain-‐end and sulfur-‐centered iniferter radical. The polymerization of DMA to UHMW (Mn,SEC 1.26 ´ 106 g/mol) maintains a similar polymerization rate through activation cycles. Size-‐exclusion chromatography (SEC) traces shift to shorter elution times and higher molecular weights throughout the polymerization was the SEC traces remain monomodal. The predicted molecular weights (Mn, theory) closely matches measured values (Mn, SEC) as monomer conversion increases, while molecular weight distributions (Ð) remained low.
Figure S5. a) The trithiocarbonate iniferter shows an increased extinction coefficient (lmax 310 nm) compared to b) the xanthate iniferter (lmax 281 nm) in water. Absorbance measurements were conducted with 150 μL of sample on clear 96-‐well microplates (Greiner). Calibration curves and path length correction were constructed using the integrated SoftMax Pro software.
Figure S6. N,N-‐Dimethylacrylamide (DMA) was irradiated with long-‐wave UV light in the presence of a xanthate iniferter to produce ultrahigh molecular weight (UHMW) poly(DMA). The polymerization of DMA to UHMW (Mn,SEC 1.30 ´ 106 g/mol) displays near-‐linear pseudo-‐first order kinetics, indicating a constant radical concentration up to 93% monomer conversion. Size-‐exclusion chromatography (SEC) traces shift to shorter elution times and higher molecular weights throughout the polymerization was the SEC traces remain monomodal. The predicted molecular weights (Mn, theory) closely match measured values (Mn, SEC) as monomer conversion increases, while molecular weight distributions (Ð) remained low.
Figure S7. N,N-‐Dimethylacrylamide (DMA) was irradiated with long-‐wave UV light in the presence of a xanthate iniferter to produce ultrahigh molecular weight (UHMW) poly(DMA). The polymerization of DMA to UHMW (Mn,SEC 2.96 ´ 106 g/mol) displays near-‐linear pseudo-‐first order kinetics, indicating a constant radical concentration up to 93% monomer conversion. Size-‐exclusion chromatography (SEC) traces shift to shorter elution times and higher molecular weights throughout the polymerization was the SEC traces remain monomodal. The predicted molecular weights (Mn, theory) closely match measured values (Mn, SEC) as monomer conversion increases, while molecular weight distributions (Ð) remained low.
Figure S8. N,N-‐Dimethylacrylamide (DMA) was irradiated with long-‐wave UV light in the presence of a xanthate iniferter to produce ultrahigh molecular weight (UHMW) poly(DMA). The polymerization of DMA to UHMW (Mn,SEC 5.20 ´ 106 g/mol) displays near-‐linear pseudo-‐first order kinetics, indicating a constant radical concentration up to 95% monomer conversion. Size-‐exclusion chromatography (SEC) traces shift to shorter elution times and higher molecular weights throughout the polymerization was the SEC traces remain monomodal. The predicted molecular weights (Mn, theory) closely match measured values (Mn, SEC) as monomer conversion increases, while molecular weight distributions (Ð) remained low.
Figure S9. N,N-‐Dimethylacrylamide (DMA) was irradiated with long-‐wave UV light in the presence of a xanthate iniferter to produce ultrahigh molecular weight (UHMW) poly(DMA). The polymerization of DMA to UHMW (Mn,SEC 8.57 ´ 106 g/mol) displays near-‐linear pseudo-‐first order kinetics, indicating a constant radical concentration up to 89% monomer conversion. Size-‐exclusion chromatography (SEC) traces shift to shorter elution times and higher molecular weights throughout the polymerization was the SEC traces remain monomodal. The predicted molecular weights (Mn, theory) closely match measured values (Mn, SEC) as monomer conversion increases, while molecular weight distributions (Ð) remained low.
Figure S10. N,N-‐Dimethylacrylamide (DMA) was irradiated by sunlight in the presence of a trithiocarbonate iniferter to produce ultrahigh molecular weight (UHMW) poly(DMA). The polymerization of DMA to UHMW (Mn,SEC 1.60 ´ 106 g/mol) displays near-‐linear pseudo-‐first order kinetics, indicating a constant radical concentration up to 62% monomer conversion. Size-‐exclusion chromatography (SEC) traces shift to shorter elution times and higher molecular weights throughout the polymerization was the SEC traces remain monomodal. The predicted molecular weights (Mn, theory) closely match measured values (Mn, SEC) as monomer conversion increases, while molecular weight distributions (Ð) remained low.
Figure S11. The exothermicity of the UHMW DMA polymerization via a xanthate or trithiocarbonate iniferter was recorded with an external thermocouple. Within 5 min, the xanthate initiated polymerization solution temperature rapidly increased by +11.7 °C, eventually reaching a peak temperature of 38.0 °C before plateauing to ~36 °C. However, the trithiocarbonate showed a delayed and much less pronounced exotherm, reaching a constant temperature near 37 °C. These polymerizations are compared to an aqueous monomer solution without iniferter.
Figure S12. Kinetic plots for polymerizations of DMA in the presence and absence of iniferter. UV irradiation of DMA in the absence of iniferter results in slow, adventitious background initiation; however, this result has little impact on photoiniferter-‐mediated polymerizations. The slow iniferter-‐free polymerization resulted in an Mn of 2.04 ´ 106 g/mol and Ð of 1.16 at 30% conversion in 8 h. Importantly, during the uncontrolled iniferter-‐free polymerization the molecular weight was constant regardless of monomer conversion. Xanthate and trithiocarbonate mediated polymerizations targeted similar degrees of polymerizations with [DMA]:[Iniferter] = 50,000:1. The xanthate and trithiocarbonate mediated polymerizations reached near quantitative conversion in 1 and 8 h, respectively (Table 1 entry 7 and 3).
Figure S13. Kinetic plots for polymerizations of DMA with various concentrations of Xanthate. Increasing [DMA]:[Xanthate] ratios and degrees of polymerization lead to slower polymerization rates. [1] Wang R.; McCormick, C. L; Lowe, A. B. Synthesis and Evaluation of New Dicarboxylic Acid
Functional Trithiocarbonates: RAFT Synthesis of Telechelic Poly(n-‐butyl acrylate)s. Macromolecules 2005, 38 (23), 9518–9525.
[2] Smulders W.; Monteiro, M. J. Seeded Emulsion Polymerization of Block Copolymer Core−Shell Nanoparticles with Controlled Particle Size and Molecular Weight Distribution Using Xanthate-‐Based RAFT Polymerization. Macromolecules 2004, 37 (12), 4474-‐4483.