Synthesis of Nanoparticle Copolymer Brushes via

Transcription

1 Synthesis of Nanoparticle Copolymer Brushes via Surface-Initiated seatrp Paweł Chmielarz,, Jiajun Yan, Pawel Krys, Yi Wang, Zongyu Wang, Michael R. Bockstaller, and Krzysztof Matyjaszewski, Department of Physical Chemistry, Faculty of Chemistry, Rzeszow University of Technology, Al. Powstańców Warszawy 6, Rzeszow, Poland. Department of Chemistry, Carnegie Mellon University, 4400 Fifth Ave., Pittsburgh, PA Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA Corresponding author. 1

2 EXPERIMENTAL SECTION Materials. Silica nanoparticles (NPs), 30 wt% solution in methyl isobutyl ketone (MIBK-ST) were kindly donated by Nissan Chemical and used as received. Tetherable initiator, 3- (chlorodimethylsilyl)propyl 2-bromo-2-methylpropionate (BiBSiCl), was synthesized as described in a previous report. 1 Methanol (MeOH, Aldrich, > 99.8%), tetrahydrofuran (THF, Aldrich, 99.5%), toluene (Aldrich, 99%), N,N-dimethylformamide (DMF, 99.9%, Acros), chlorodimethylsilane (Aldrich, 98%), 48 wt % aqueous hydrofluoric acid (HF, Aldrich, 99.99%), allyl alcohol (Aldrich, 99%), 2-bromoisobutyryl bromide (BriBBr, Aldrich, 98%), triethylamine (TEA, Aldrich, 99.5%), platinum cyclovinylmethylsiloxane complex (Gelest, 2% in cyclovinylmethylsiloxane), ammonium hydroxide aqueous solution (NH4OH, %, Fisher), anhydrous magnesium sulfate (MgSO4, Fisher), tetrabutylammonium perchlorate (TBAP, Aldrich, > 98%), and copper(ii) bromide (Cu II Br2, Aldrich, 99.9%) were used as received unless otherwise stated. Tris(2-pyridylmethyl)amine (TPMA) was synthesized according to a published procedure. 2 Stock solutions of Cu II Br2 and TPMA were prepared according to a published procedure. 3 tert-butyl acrylate (tba, Aldrich, > 99%), n-butyl acrylate (BA, Aldrich, > 99%) and styrene (S, 99%, Aldrich) were passed through a column filled with basic alumina prior to use to remove any inhibitor. Platinum (Pt) wire, Pt mesh and Pt disk (3 mm diameter, Gamry) were purchased from Alfa Aesar, USA. Cyclic voltammetry and preparative electrolysis were conducted in an electrochemical cell kit (Gamry, USA). Analysis. 1 H NMR spectra in CDCl3, used for calculation of monomer conversion, were measured using Bruker Avance 300 MHz spectrometer. The apparent number-average molecular weights (Mn,app) and dispersities (Đ, Mw/Mn) were measured by size exclusion chromatography (SEC). The SEC was conducted with a Waters 515 pump and Waters 2414 differential 2

3 refractometer using PSS columns (SDV 10 5, 10 3, 500 Å) with THF as eluent at 35 C and at a flow rate of 1 ml/min. Linear PS standards were used for calibration. All samples were etched with HF before SEC measurement. 4 Thermogravimetric analysis (TGA) was performed on a TA Instrument TGA 2950 and the data was processed with TA Universal Analysis software. The heating procedure involved four steps: (1) ramp up at 20 C/min to 120 C; (2) hold at 120 C for 20 min; (3) high-resolution ramp up at 20 C/min to 800 C; (4) hold at 800 C for 10 min. The organic contents of the samples were normalized to the weight loss between 120 C and 800 C. The grafting densities were calculated using a previously reported equation (S1) The value of in the equation is the silica fraction measured by TGA after exclusion of any residual solvent; NA is the Avogadro number; is the density of silica NPs (1.9 g/cm 3 ); d is the average diameter of silica NPs; and Mn is the number-average molecular weight of polymer brushes. The glass transition temperature (Tg) of polymer grafted SiO2 NPs with different compositions were measured by differential scanning calorimetry (DSC) using TA Instruments Q The same procedure was run three times, each involving the following steps: 1) hold at -80 ºC for 2 min; 2) heat to 130 ºC at a rate of 10 ºC/min; 3) hold for 2 min; 4) cool down to -80 ºC. The DSC data were analyzed with TA Universal Analysis and the Tg was directly acquired. Transmission electron microscopy (TEM) was performed using a JEOL 2000 EX electron microscope operated at 200 kv. All samples were dissolved in THF with concentration of 1 mg/ml, and solvent casting on Cu grids. To confirm results obtained from TEM, dynamic light scattering (DLS) using a Malvern Zetasizer Nano ZS at 25 C with THF as dispersant was employed to determine Z-average hydrodynamic diameter and intensity-weighted distribution. 3

4 The particles were suspended in filtered THF (220 nm PTFE filter) at low concentrations. Cyclic voltammetry and preparative electrolysis were recorded on a Gamry Ref 600 potentiostat. Each electrolysis was carried out under N2 atmosphere using a Pt disk for CV, (A = cm 2 ) and Pt mesh for electrolysis, (A 6 cm 2 ) working electrodes (WE). The counter electrode (CE, sacrificial anode) was Al wire (l = 15 cm, d = 1 mm). Values of potentials applied for preparative electrolysis were established from CV measurements at a 100 mv/s scan rate using Ag/AgI/I - reference electrode (RE) according to the previously published report. 6 Surface modification of silica nanoparticles. Silica nanoparticles were modified as described in a previous report. 4, 5 The molar concentration of tetherable initiator was determined to be 1.5 initiator molecules per nm 2 of silica nanoparticles (assuming a sphere with a diameter of 15.8 nm). 7 Synthesis of PtBA brushes from silica nanoparticles by SARA ATRP. Silica nanoparticles (0.098 g, 91 µmol, assuming ~1 accessible Br/nm 2 ), DMF (5 ml), tba (5 ml, 34 mmol) and 0.07 ml of Cu II Br2/TPMA stock solution (0.05 M in DMF) were mixed in a Schlenk flask and stirred for 24 h. The flask was heated to 55 C and subsequently a Cu 0 wire (l = 1 cm, d = 1 mm) was added to the solution. Polymerization conditions were as follows: [tba]/[sio2- Br]/[Cu II Br2]/[TPMA] = 1050/1/0.105/0.21, [tba]0 = 3.4 M in DMF, T = 55 C, Cu 0 wire (l = 1 cm, d = 1 mm), Vtot = 10 ml. Samples were withdrawn periodically to follow the monomer conversion using 1 H NMR. The Mn and Mw/Mn were determined by THF SEC measurements (with PS standards). The final product was recovered by precipitation in methanol/water mixtures. 4

5 Reaction cell configuration for cyclic voltammetry. Electrochemical experiments were carried out under N2 atmosphere using a Pt disk WE, a Ag/AgI/I - RE, and an Al wire CE. TBAP (1.93 g, 5.6 mmol) was placed in an electrolysis cell maintained at 55 C under N2 purge. Then, 14 ml of N2 purged tba (96 mmol), 14 ml of N2 purged DMF, and 0.19 ml of N2 purged Cu II Br2/TPMA stock solution (0.05 M in DMF) were added to the reaction cell. The CV of the catalyst complex was recorded (Figure 1a) and used for determining the appropriate applied potential (Eapp = Epc 120 mv, Eapp = Epc 80 mv, Eapp = Epc 40 mv, and Eapp = Epc vs. Ag/AgI/I - ). Synthesis of PtBA brushes from silica nanoparticles by seatrp. Silica nanoparticles (0.27 g, 91 µmol, assuming ~1 accessible Br/nm 2 ), TBAP (1.93 g, 5.6 mmol), DMF (14 ml), tba (14 ml, 96 mmol), 0.19 ml of Cu II Br2/TPMA stock solution (0.05 M in DMF) were placed in an electrolysis cell and stirred for 24 h. The mixture was purged with N2 for 45 min, after which a CV was recorded (Figure 1a) using a Pt disk WE, a Ag/AgI/I - RE, and an Al wire CE. Then a Pt mesh WE, Al wire CE, and Ag/AgI/I - RE were immersed in the reaction solution and the selected potential (Eapp = Epc 120 mv, Eapp = Epc 80 mv, Eapp = Epc 40 mv, and Eapp = Epc vs. Ag/AgI/I - ) was applied using the controlled potential preparative electrolysis method. Polymerization conditions were as follows: [tba]/[sio2-br]/[cu II Br2]/[TPMA] = 1050/1/0.105/0.21, [tba]0 = 3.4 M in DMF, T = 55 C, [TBAP] = 0.2 M, Vtot = 28.2 ml. Samples were withdrawn periodically to follow the monomer conversion using 1 H NMR. The Mn and Mw/Mn were determined by THF SEC measurements (with PS standards). The final product was recovered by precipitation in methanol/water mixtures and dried under vacuum for 1 day. 5

6 Temporal Control in Synthesis of PtBA brushes from silica nanoparticles by seatrp. Silica nanoparticles (0.27 g, 91 µmol, assuming ~1 accessible Br/nm 2 ), TBAP (1.93 g, 5.6 mmol), DMF (14 ml), tba (14 ml, 96 mmol), 0.38 ml of Cu II Br2/TPMA stock solution (0.05 M in DMF) were placed in an electrolysis cell and stirred for 24 h. The mixture was purged with N2 for 45 min, after which a CV was recorded using a Pt disk WE, a Ag/AgI/I - RE, and an Al wire CE. Then a Pt mesh WE, Al wire CE, and Ag/AgI/I - RE were immersed in the reaction solution and a potential program (Eapp = Epc 80 mv for the on stage and Eapp = Epc mv for the off stage vs. Ag/AgI/I - ) was applied using the controlled potential preparative electrolysis method. Polymerization conditions were as follows: [tba]/[sio2-br]/[cu II Br2]/[TPMA] = 1050/1/0.021/0.042, [tba]0 = 3.4 M in DMF, T = 55 C, [TBAP] = 0.2 M, Vtot = 28.2 ml. Samples were withdrawn periodically to follow the monomer conversion using 1 H NMR. The Mn and Mw/Mn were determined by THF SEC measurements (with PS standards). The final product was recovered by precipitation in methanol/water mixtures and dried under vacuum for 1 day. Synthesis of PtBA-b-PS brushes from silica nanoparticles by seatrp. The seatrp method was used for the chain extension of SiO2-g-PtBA-Br macroinitiator with S (Table 1, entry 3). Polymerization conditions were as follows: [S]/[SiO2-g-PtBA-Br]/[Cu II Br2]/[TPMA] = 4000/1/0.4/0.8, [S]0 = 4.3 M in DMF, Eapp = Epc 80 mv vs. Ag/AgI/I - (Figure S3a), T = 55 C, [TBAP] = 0.2 M, Vtot = 28.2 ml. Samples were withdrawn periodically to follow the monomer conversion using 1 H NMR. The Mn and Mw/Mn were determined by THF SEC measurements (with PS standards). The final product was recovered by precipitation in methanol/water mixtures and dried under vacuum for 1 day. 6

7 Synthesis of PtBA-b-PBA brushes from silica nanoparticles by seatrp. The seatrp method was used for the chain extension of SiO2-g-PtBA-Br macroinitiator with BA (Table 1, entry 3). Polymerization conditions were as follows: [BA]/[SiO2-g-PtBA-Br]/[Cu II Br2]/[TPMA] = 4000/1/0.4/0.8, [BA]0 = 3.5 M in DMF, Eapp = Epc 80 mv vs. Ag/AgI/I - (Figure S5a), T = 55 C, [TBAP] = 0.2 M, Vtot = 28.2 ml. Samples were withdrawn periodically to follow the monomer conversion using 1 H NMR. The Mn and Mw/Mn were determined by THF SEC measurements (with PS standards). The final product was recovered by precipitation in methanol/water mixtures and dried under vacuum for 1 day. 7

8 Additional Experimental Data Table S1. Inorganic fraction in the final samples and corresponding graft densities. Entry (according to Table 1) Monomer conversion (%) a Mn,app ( 10 3 ) b Inorganic fraction (%) c (nm 2 ) d a Monomer conversion was determined by 1 H NMR; b Apparent Mn was determined by THF SEC with PS standards; c Inorganic fraction was determined by TGA; d The grafting density ( ) was calculated from TGA inorganic fraction and eq. S1. 5 8

9 (a) ln([m] 0 /[M]) SARA ATRP time (h) (b) M n ( 10-3 ) 60 SARA ATRP monomer conversion (%) Mw /M n (c) 1.25h 1.5h 1.73h molecular weight Fig. S1. SARA ATRP of tba from silica nanoparticles. (a) First-order kinetic plot of monomer conversion vs time, (b) Mn and Mw/Mn vs monomer conversion, and (c) SEC traces. Reaction conditions: [tba]/[sio2-br]/[cu II Br2]/[TPMA] = 1050/1/0.105/0.21, [tba]0 = 3.4 M, Cu 0 wire (d = 1 mm, l = 1 cm), T = 55 C, Vtot = 10 ml. Table 1, entry 1. 9

10 (a) 0.5h 1h 1.73h (b) 0.5h 1.5h 1.73h (c) molecular weight 1h 1.5h 1.73h (d) molecular weight 0.5h 1.5h 1.73h molecular weight molecular weight (e) 0h 2h 3h 5h (f) 0h 2h 3h 5h molecular weight molecular weight 10

11 (g) 3h molecular weight Fig. S2. SEC traces of PtBA prepared via seatrp under different reaction conditions: constant potential electrolysis as a function of Eapp ((a) Epc 120 mv, (b) Epc 80 mv, (c) Epc 40 mv, and (d) Epc). (e) PtBA-b-PS, (f) PtBA-b-PBA prepared via seatrp under constant potential electrolysis, and (g) PtBA prepared via seatrp under multiple-step potential electrolysis. 11

12 (a) I (ma) mv -80 mv -40 mv time (h) (b) ln([m] 0 /[M]) mv -80 mv -40 mv time (h) (c) k app p (h-1 ) (d) k app p (h-1 ) mv -80 mv -40 mv (E app -E 1/2 / V) M (x n 10-3 ) (e) mv -80 mv d Z-ave (nm) mv DP Fig. S3. Synthesis of PtBA brushes from silica nanoparticles as a function of applied potential. (a) Current profile vs time, (b) first-order kinetic plots for different Eapp values, (c) apparent polymerization rate coefficients (kp app ) vs the overpotential (ƞ), (d) kp app vs Mn, and (e) evolution of Z-average hydrodynamic diameters (dz-ave) vs DP. Reaction conditions: [tba]/[sio2- Br]/[Cu II Br2]/[TPMA] = 1050/1/0.105/0.21, [tba]0 = 3.4 M, T = 55 C, [TBAP] = 0.2 M, Vtot = 28.2 ml. Table 1, entries

13 (a) 6 Cu II Br 2 /TPMA w/ SiO 2 -g-ptba-br 3 (b) Q = (-)4.51 C [e - ] = mmol I ( A) mv = 100 mv/s E (V vs. Ag/AgI/I - ) I (ma) time (h) Fig. S4. Chain extension of the PtBA-functionalized silica nanoparticles with S. (a) Cyclic voltammetry (CV) of Cu II Br2/TPMA with and without macroinitiator (the arrow indicates the applied potential during electrolysis), and (b) current profile vs time. Reaction conditions: [S]/[SiO2-g-PtBA-Br]/[Cu II Br2]/[TPMA] = 4000/1/0.4/0.8, [S]0 = 4.3 M, T = 55 C, [TBAP] = 0.2 M, Vtot = 28.2 ml. Table 1, entry 6. 13

14 (a) 4 Cu II Br 2 /TPMA w/ SiO 2 -g-ptba-br mv E (V vs. Ag/AgI/I - ) I ( A) = 100 mv/s (b) I (ma) Q = (-)3.31 C [e - ] = mmol time (h) Fig. S5. Chain extension of the PtBA-functionalized silica nanoparticles with BA. (a) Cyclic voltammetry (CV) of Cu II Br2/TPMA with and without macroinitiator (the arrow indicates the applied potential during electrolysis), and (b) current profile vs time. Reaction conditions: [BA]/[SiO2-g-PtBA-Br]/[Cu II Br2]/[TPMA] = 4000/1/0.4/0.8, [BA]0 = 3.5 M, T = 55 C, [TBAP] = 0.2 M, Vtot = 28.2 ml. Table 1, entry 7. 14

15 (a) weight percentage [%] temperature ( o C) Figure S6. TGA plots of 7 final samples from Table 1 and Table S1. All weights normalized to 100% after isotherm at 120 ºC. 15

16 Fig. S7. TEM image of 15.8 nm silica nanoparticles modified with BiBSiCl initiator used to form grafted PtBA. 16

17 (a) (b) normalized distribution (%) hydrodynamic diameter (nm) Fig. S8. (a) TEM image and (b) DLS hydrodynamic size distribution by intensity (in THF) of PtBA-functionalized silica NPs prepared via SARA ATRP. Table 1, entry 1. 17

18 (a) (b) normalized distribution (%) hydrodynamic diameter (nm) (c) (d) normalized distribution (%) hydrodynamic diameter (nm) 18

19 (e) (f) normalized distribution (%) hydrodynamic diameter (nm) (g) (h) normalized distribution (%) hydrodynamic diameter (nm) Fig. S9. TEM images and DLS hydrodynamic size distribution by intensity (in THF) of PtBAfunctionalized silica NPs via seatrp as a function of Eapp. (a,b) Epc 120 mv (Table 1, entry 2), (c,d) Epc 80 mv (Table 1, entry 3), (e,f) Epc 40 mv (Table 1, entry 4), and (g,h) Epc (Table 1, entry 5). 19

20 (a) (b) (c) (d) Fig. S10. TEM images of PtBA-functionalized silica NPs via seatrp with periodically applied different values of potential as a function of molecular weight. (a,b) M n,th = 11,100 (2h) and (c,d) M n,th = 14,200 (3h). 20

21 (a) (b) (c) (d) PBA b PtBA g SiO2 NPs Figure S11. DSC plots of brushes grafted on silica NPs via seatrp: PtBA (a; Table 1, entry 3), PtBA-b-PS (b; Table 1, entry 6), and PtBA-b-PBA (c and d; Table 1, entry 7). 21

22 References 1. Yan, J.; Pan, X.; Wang, Z.; Zhang, J.; Matyjaszewski, K. Influence of Spacers in Tetherable Initiators on Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP). Macromolecules 2016, DOI: /acs.macromol.6b Xia, J.; Zhang, X.; Matyjaszewski, K. Synthesis of Star-Shaped Polystyrene by Atom Transfer Radical Polymerization Using an Arm First Approach. Macromolecules 1999, 32 (13), DOI: /ma Chmielarz, P.; Krys, P.; Park, S.; Matyjaszewski, K. PEO-b-PNIPAM Copolymers via SARA ATRP and eatrp in Aqueous Media. Polymer 2015, 71, DOI: /j.polymer Yan, J.; Kristufek, T.; Schmitt, M.; Wang, Z.; Xie, G.; Dang, A.; Hui, C. M.; Pietrasik, J.; Bockstaller, M. R.; Matyjaszewski, K. Matrix-free Particle Brush System with Bimodal Molecular Weight Distribution Prepared by SI-ATRP. Macromolecules 2015, 48 (22), DOI: /acs.macromol.5b Yan, J.; Pan, X.; Schmitt, M.; Wang, Z.; Bockstaller, M. R.; Matyjaszewski, K. Enhancing Initiation Efficiency in Metal-Free Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP). ACS Macro Letters 2016, 5, Park, S.; Chmielarz, P.; Gennaro, A.; Matyjaszewski, K. Simplified Electrochemically Mediated Atom Transfer Radical Polymerization using a Sacrificial Anode. Angewandte Chemie International Edition 2015, 54 (8), DOI: /anie Choi, J.; Hui, C. M.; Pietrasik, J.; Dong, H.; Matyjaszewski, K.; Bockstaller, M. R. Toughening fragile matter: mechanical properties of particle solids assembled from polymergrafted hybrid particles synthesized by ATRP. Soft Matter 2012, 8 (15),