SUEMENTARY INRMATIN - media.nature.com · 4NBr (670 mg, 2.1 mmol), and DMF (23 mL) was prepared...

NATURE CHEMISTRY | www.nature.com/naturechemistry 1

SUPPLEMENTARY INFORMATIONDOI: 10.1038/NCHEM.2633

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Mechanicallycontrolledradicalpolymerizationinitiated

byultrasound

Hemakesh Mohapatra, Maya Kleiman, Aaron P. Esser-Kahn

Contents

1. Materials and methods 2

2. Procedure for obtaining UV-Vis-NIR spectra of the copper(II) precursor solution before

and after ultrasonic agitation 2

3. Experimental procedure for ultrasound initiated radical polymerization 3

4. Procedure for calculation of % monomer conversion for the ultrasound

initiated radical polymerization using 1H-NMR 6

5. Experiment demonstrating the absence of significant polymer chain growth

when the ultrasound initiated radical polymerization is carried out in the

absence of piezoelectric nanoparticle 6

6. Experiment demonstrating absence of thermally initiated polymerization of

butyl acrylate 12

7. Experiment demonstrating the effect of lowering nanoparticle loading on the

kinetics of ultrasound initiated radical polymerization 14

8. Experiment demonstrating the effect of changing the duration of on and off cycles

during the pulse mode operation of ultrasonic horn on the kinetics of ultrasound

initiated radical polymerization. 15

9. Experiment demonstrating evidence of Cu on the surface of BaTiO3 NPs 17

10. Experiment demonstrating ultrasound initiated radical polymerization can be restarted

after a staying dormant for few hours 19

11. References 20

© 2016 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.



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Materials and methods

Tetragonal Barium titanate (BaTiO3) nanopowder with a particle size of 200 nm was obtained

from US Research Nanomaterials, inc. and was used as received. The ligand N,N,N’,N’,N’’,N’’-

hexamethyl-[tris(aminoethyl)amine] (Me6TREN) was synthesized as described previously.1 Butyl

acrylate was obtained from Sigma-Aldrich and purified by passing it through a column of basic

alumina followed by distillation under reduced pressure. Dry DMF was obtained after

purification using in-house solvent purification system. All other reagents were purchased from

commercial sources and were used without further purification. UV-Vis-NIR spectra were

obtained using a Shimadzu UV-1700 absorption spectrometer. 1H-NMR spectra were obtained

using a 500 MHz Bruker Avance spectrometer and were referenced to the peak corresponding to

the residual protium of the nmr solvent (7.26 for CDCl3). Molecular weight of polymers were

determined using a Agilent 1100 Gel Permeation Chromatography (GPC) instrument equipped

with two Agilent PLGel Mixed-D (5 µm) and a refractive index detector. The GPC was calibrated

using polystyrene standards. The sonochemical reactions were carried out using a Qsonica Q500

ultrasonic processor equipped with a ½” diameter probe. The ultrasonic processor was operated at

20 kHz and at 75% of maximum amplitude.

Procedure for obtaining UV-Vis-NIR spectra of the copper(II) precursor solution

before and after ultrasonic agitation

An oven dried ultrasonic reaction vessel (250 mL) was charged with 200 nm tetragonal BaTiO3

nanopowder (1.6 g, 4.5 wt%) under a continuous stream of dry argon. A copper precursor

solution containing Cu(OTf)2 (504 mg, 1.4 mmol), Me6TREN (320 mg, 1.4 mmol), Bu4NBr (450

mg, 1.4 mmol), and DMF (35 mL) was prepared under inert atmosphere and transferred into the

reaction vessel. The resulting suspension was agitated using an ultrasonic horn. A pulse mode




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operation using a 4s on – 4s off cycle was used. The reaction vessel was held at 15 oC – 25 oC

using a water bath. At intervals, 3 mL aliquots of the suspension were filtered. 250 µL of the

resulting filtrate was diluted with 2.25 mL of DMF and the UV-Vis-NIR (300 nm – 1100 nm) of

the resulting solution was obtained. DMF was used as the blank.

Experimental procedure for ultrasound initiated radical polymerization

Butyl acrylate 1 and dry DMF were degassed by bubbling dry argon for 30 minutes. An oven

dried ultrasonic reaction vessel (250 mL) was charged with 200 nm tetragonal BaTiO3

nanopowder (2.4 g, 4.5 wt%) under a continuous stream of dry argon. A copper precursor



reaction vessel. Butyl acrylate (30 mL, 210 mmol) and ethyl α-bromoisobutyrate 2 (310 µL, 2.1

mmol) were then added. The resulting suspension was agitated using a ultrasonic horn. A pulse

mode operation using a 4s on – 4s off cycle was used. The reaction vessel was held at 15 oC – 25

oC using a water bath. At intervals, aliquots (≈ 10 – 15 mg) of the reaction mixture were

analyzed using 1H-NMR and GPC.




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Figure 1. 1H-NMR spectra of ultrasound mediated polymerization mixture at (a) t = 0 h and (b) t = 1h. At intervals, aliquots (≈ 10 – 15 mg) of the reaction mixture were diluted with CDCl3 (0.6 mL), filtered through a syringe filtered, and the 1H-NMR was obtained.




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Figure 2. (a) Representative GPC traces depicting the evolution of molecular weight during the ultrasound mediated polymerization of butyl acrylate; and (b) Portion of the GPC traces showing peaks corresponding to poly(butyl acrylate). The polymerization mixture contained n-butyl acrylate 1 (4 M in DMF), ethyl α-bromoisobutyrate 2 (40 mM), Cu(OTf)2/Me6TREN/BuN4Br (40 mM), and BaTiO3 nanoparticles (4.5 wt%). The mixture was sonicated using an ultrasonic horn with a 4s on – 4s off cycle. The sonication was stopped at t = 2h. At intervals, aliquots (≈ 10 – 15 mg) of the reaction mixture were diluted with 1 mL toluene, filtered, and the filtrate was injected into the GPC instrument. The chromatographic peaks with retention time (r.t.) 21 minutes and 23 minutes correspond to butyl acrylate and DMF. The peaks at r.t. 16 – 18 minutes correspond to poly(butyl acrylate).




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Procedure for calculation of % monomer conversion for the ultrasound initiated

radical polymerization using 1H-NMR

The monomer % conversion for the polymerization was calculated as:

Conversion % = (Ib - 2Ia)/Ib × 100%,

Where, Ia = 1H-NMR integrals corresponding to the protons labeled as c,

Ib = combined 1H-NMR integrals corresponding protons labeled d and d’ in 1H-NMR.

The integrals c, d, and d’ are highlighted in 1H-NMR spectra in Figure 2.

Experiment demonstrating the absence of significant polymer chain growth when

the ultrasound initiated radical polymerization is carried out in the absence of

piezoelectric nanoparticle

Butyl acrylate and dry DMF were degassed by bubbling dry argon for 30 minutes. An oven dried

ultrasonic reaction vessel (250 mL) was charged with 200 nm carbon black powder (2.4 g or 0 g,

4.5 wt% or 0 wt%) under a continuous stream of dry argon. A copper precursor solution

containing Cu(OTf)2 (760 mg, 2.1 mmol), Me6TREN (480 mg, 2.1 mmol), Bu4NBr (670 mg, 2.1

mmol), and DMF (23 mL) was prepared under inert atmosphere and transferred into an oven

dried ultrasonic reaction vessel (250 mL). Butyl acrylate (30 mL, 210 mmol) and 2 (310 µL, 2.1

mmol) were then added. The resulting solution was agitated using a ultrasonic horn. A pulse

mode operation using a 4s on – 4s off cycle was used. The reaction vessel was held at 15 oC – 25

oC using a water bath. At intervals, aliquots (≈ 10 – 15 mg) of the reaction mixture were

analyzed using GPC.




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Figure 3. GPC chromatographs of polymerization reaction mixture sonicated in either the presence of nanoparticles (BaTiO3 or carbon black) or the absence of nanoparticles. The polymerization mixture contained n-butyl acrylate (4 M in DMF), 2 (40 mM), and Cu(OTf)2/Me6TREN/BuN4Br (40 mM). The mixture was sonicated using an ultrasonic horn with a 4s on – 4s off cycle. The sonication was stopped at t = 2h. Aliquots (≈ 10 – 15 mg) of the reaction mixture were diluted with 1 mL toluene, filtered, and the filtrate was injected into the GPC instrument.




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Figure 4. 1H-NMR spectra of polymerization reaction mixture sonicated in the absence of added BaTiO3 nanoparticles obtained at (a) t = 0 h and (b) t = 2h. The polymerization mixture contained n-butyl acrylate (4 M in DMF), 2 (40 mM), and Cu(OTf)2/Me6TREN/BuN4Br (40 mM). The mixture was sonicated using an ultrasonic horn with a 4s on – 4s off cycle. At intervals, aliquots (≈ 10 – 15 mg) of the reaction mixture were diluted with CDCl3 (0.6 mL), filtered through a syringe filtered, and the 1H-NMR was obtained.




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Figure 5. (a) Representative GPC traces depicting the evolution of molecular weight during the ultrasound mediated polymerization of butyl acrylate in absence of piezoelectric nanoparticles; and (b) Portion of the GPC with retention time 15 – 20 min shown for visual comparison with figure 2. The polymerization mixture contained n-butyl acrylate (4 M in DMF), 2 (40 mM), and Cu(OTf)2/Me6TREN/BuN4Br (40 mM). The mixture was sonicated using an ultrasonic horn with a 4s on – 4s off cycle. The sonication was stopped at t = 2h. At intervals, aliquots (≈ 10 – 15 mg) of the reaction mixture were diluted with 1 mL toluene, filtered, and the filtrate was injected into the GPC instrument.




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Figure 6. 1H-NMR spectra of polymerization reaction mixture sonicated in the presence of added carbon black nanoparticles obtained at (a) t = 0 h and (b) t = 2h. The polymerization mixture contained n-butyl acrylate (4 M in DMF), 2 (40 mM), and Cu(OTf)2/Me6TREN/BuN4Br (40 mM). The mixture was sonicated using an ultrasonic horn with a 4s on – 4s off cycle. At intervals, aliquots (≈ 10 – 15 mg) of the reaction mixture were diluted with CDCl3 (0.6 mL), filtered through a syringe filtered, and the 1H-NMR was obtained.




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Figure 7. (a) Representative GPC traces depicting the evolution of molecular weight during the ultrasound mediated polymerization of butyl acrylate in presence of carbon black particles; and (b) Portion of the GPC with retention time 15 – 20 min shown for visual comparison with figure 2. The polymerization mixture contained n-butyl acrylate (4 M in DMF), 2 (40 mM), Cu(OTf)2/Me6TREN/BuN4Br (40 mM), and 200 nm carbon black (4.5 wt%). The mixture was sonicated using an ultrasonic horn with a 4s on – 4s off cycle. The sonication was stopped at t = 2h. At intervals, aliquots (≈ 10 – 15 mg) of the reaction mixture were diluted with 1 mL toluene, filtered, and the filtrate was injected into the GPC instrument.




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Experiment demonstrating absence of thermally initiated polymerization of butyl

acrylate

Butyl acrylate and dry DMF were degassed by bubbling dry argon for 30 minutes. An oven-dried

flask (100 mL) was charged with 200 nm tetragonal BaTiO3 nanopowder (600 mg, 4.5 wt%)

under a dry argon. A copper precursor solution containing Cu(OTf)2 (190 mg, 0.52 mmol),

Me6TREN (120 mg, 0.52 mmol), Bu4NBr (170 mg, 0.52 mmol), and DMF (5.7 mL) was prepared

under inert atmosphere and transferred into the reaction vessel. Butyl acrylate (7.5 mL, 52 mmol)

and 2 (77 µL, 0.52 mmol) were then added. The resulting suspension was stirred at 80 oC. At

intervals, aliquots (≈ 10 – 15 mg) of the reaction mixture were analyzed using 1H-NMR.




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Figure 8. 1H-NMR spectra of polymerization reaction mixture stirred at 80 oC obtained at (a) t = 0 h and (b) t = 40h. At intervals, aliquots (≈ 10 – 15 mg) of the reaction mixture were diluted with CDCl3 (0.6 mL), filtered through a syringe filtered, and the 1H-NMR was obtained.




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Experiment demonstrating the effect of lowering nanoparticle loading on the

kinetics of ultrasound initiated radical polymerization


ultrasonic reaction vessel (250 mL) was charged with 200 nm tetragonal BaTiO3 nanopowder

(0.24 g, 0.47 wt%) under a continuous stream of dry argon. A copper precursor solution

containing Cu(OTf)2 (760 mg, 2.1 mmol), Me6TREN (480 mg, 2.1 mmol), Bu4NBr (670 mg, 2.1

mmol), and DMF (23 mL) was prepared under inert atmosphere and transferred into the reaction

vessel. Butyl acrylate (30 mL, 210 mmol) and 2 (310 µL, 2.1 mmol) were then added. The

resulting suspension was agitated using a ultrasonic horn. A pulse mode operation using a 4s on –

4s off cycle was used. The reaction vessel was held at 15 oC – 25 oC using a water bath. At

interval, aliquots (≈ 10 – 15 mg) of the reaction mixture were diluted with 0.6 mL CDCl3,

filtered, and the filtrate was analyzed by 1H-NMR.

Table 1. Effect of lowering the amount of added BaTiO3 on Mn and degree of polymerization

4.5 wt% BaTiO3 0.47 wt% BaTiO3 Time (h) % Conversion Mn DP* Time (h) % Conversion Mn DP*

0.50 17 739 6 0.33 15 764 6 1.00 31 1383 11 0.67 17 1078 8 1.33 39 1642 13 1.00 20 1285 10 1.67 57 2208 17 1.33 24 1449 11 2.00 68 2486 19 1.67 25 1635 13

2.00 27 1804 14

2.33 30 1877 15

2.67 33 1980 15 * DP = degree of polymerization = Mn /(molecular weight of monomer = 128 g/mol)




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Figure 9. Effect of BaTiO3 nanoparticles loading on the kinetics of ultrasound mediated polymerization of butyl acrylate. The polymerization mixture contained n-butyl acrylate (4 M in DMF), 2 (40 mM), Cu(OTf)2/Me6TREN/BuN4Br (40 mM), and BaTiO3 nanoparticles: (a) 4.5 wt% and (b) 0.47 wt%. The mixture was agitated using an ultrasonic horn with a 4s on – 4s off cycle. The time in x-axis refers to clock time. At interval, aliquots (≈ 10 – 15 mg) of the reaction mixture were diluted with 0.6 mL CDCl3, filtered, and the filtrate was analyzed by 1H-NMR.

Experiment demonstrating the effect of changing the duration of on and off cycles

during the pulse mode operation of ultrasonic horn on the kinetics of ultrasound

initiated radical polymerization


ultrasonic reaction vessel (250 mL) was charged with 200 nm tetragonal BaTiO3 nanopowder (2.

0 g, 4.5 wt%) under a continuous stream of dry argon. A copper precursor solution containing

Cu(OTf)2 (630 mg, 1.7 mmol), Me6TREN (400 mg, 1.7 mmol), Bu4NBr (560 mg, 1.7 mmol), and

DMF (19 mL) was prepared under inert atmosphere and transferred into the reaction vessel. Butyl




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acrylate (25 mL, 170 mmol) and 2 (250 µL, 1.7 mmol) were then added. The resulting suspension

was agitated using an ultrasonic horn. A pulse mode operation using 2s on – 8s off cycle was

used. The reaction vessel was held at 15 oC – 25 oC using a water bath. At interval, aliquots (≈ 10

– 15 mg) of the reaction mixture were diluted with 0.6 mL CDCl3, filtered, and the filtrate was

analyzed by 1H-NMR. The conversion was calculated as: conversion % = (Ib - 2Ia)/Ib × 100%,

where Ia is the 1H-NMR integrals corresponding to the protons labeled as c, and Ib is the

combined 1H-NMR integrals corresponding protons labeled d and d’ in 1H-NMR spectra similar

to one shown in Figure 2.

Figure 10. Effect of changing the duration of on and off cycles on the kinetics of ultrasound mediated polymerization of butyl acrylate. The polymerization mixture contained n-butyl acrylate (4 M in DMF), 2 (40 mM), Cu(OTf)2/Me6TREN/BuN4Br (40 mM), and BaTiO3 nanoparticles (4.5 wt%). The mixture was sonicated at 20 kHz using an ultrasonic horn with (a) 4s on – 4s off cycle or (b) 2s on – 8s off cycle. The time in x-axis refers to clock time. At interval, aliquots (≈ 10 – 15 mg) of the reaction mixture were diluted with 0.6 mL CDCl3, filtered, and the filtrate was analyzed by 1H-NMR.




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Experiment demonstrating evidence of Cu on the surface of BaTiO3 NPs


ultrasonic reaction vessel (250 mL) was charged with 200 nm tetragonal BaTiO3 nanopowder (2.4

g, 4.5 wt%) under a continuous stream of dry argon. A copper precursor solution containing

Cu(OTf)2 (760 mg, 2.1 mmol), Me6TREN (480 mg, 2.1 mmol), Bu4NBr (670 mg, 2.1 mmol), and

DMF (23 mL) was prepared under inert atmosphere and transferred into the reaction vessel. Butyl

acrylate (30 mL, 210 mmol) and 2 (310 µL, 2.1 mmol) were then added and mixed. A small

aliquot (≈ 0.2 mL) of the resulting suspension was saved for SEM analysis. The polymerization

suspension was agitated using a ultrasonic horn for 2h. A pulse mode operation using a 4s on – 4s

off cycle was used. The reaction vessel was held at 15 oC – 25 oC using a water bath. 1µl of the

test samples (i.e, reaction mixtures with and without sonication) was dropped on a carbon tape

glued to a SEM pin stub. The solvent was dried in a fumehood over night. The samples were then

imaged using FEI Magellan 400 XHR SEM at 2kV and 25pA using a TLD detector at immersion

mode. The samples were further subjected to an Energy Dispersive Spectroscopy (EDS) using an

80mm2 detector with Aztec software from Oxford Instruments. These measurements were

performed at 20kV and 1.6nA.




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Figure 12. Structural and elemental analysis of BaTiO3 nanoparticles using SEM-EDS. The polymerization mixture contained n-butyl acrylate (4 M in DMF), 2 (40 mM), Cu(OTf)2/Me6TREN/BuN4Br (40 mM), and BaTiO3 nanoparticles (4.5 wt%). The mixture was either sonicated for 2h (Sample 2) or held without sonication at room temperature for 2h (Sample 1). The samples were imaged at lower (A) and higher (B) magnifications. EDS of the samples (C) reveal presence of copper as demonstrated by semi-quantitative EDS composition data (table in panel C) as well as the Cu Kα peak (inset in panel C)




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Experiment demonstrating ultrasound initiated radical polymerization can be

restarted after a staying dormant for few hours

All of the butyl acrylate and dry DMF were degassed by bubbling dry argon for 30 minutes prior

to use. An oven dried ultrasonic reaction vessel (250 mL) was charged with 200 nm tetragonal

BaTiO3 nanopowder (2.4 g, 4.5 wt%) under a continuous stream of dry argon. A copper precursor



reaction vessel. Butyl acrylate (30 mL, 210 mmol) and 2 (310 µL, 2.1 mmol) were then added.

The resulting suspension was agitated using an ultrasonic horn. A pulse mode operation using a

4s on – 4s off cycle was used. The reaction vessel was held at 15 oC – 25 oC using a water bath.

The sonication was stopped at reaction time of t = 1h. The reaction vessel was cooled over liquid

nitrogen (-196 oC) under inert atmosphere. The reaction vessel was sealed using rubber septa and

all sealed joints were reinforced using several layers of black electrical tape. The reaction vessel

was held at -196 oC for about 3 h. The reaction mixture was degassed further using 3 cycles of

freeze-pump-thaw. Previously degassed butyl acrylate (15 mL) and dry DMF (12 mL) were

added to the mixture and the sonication resumed at t = 4.6 h. At intervals throughout the

experiment, aliquots (≈ 10 – 15 mg) of the reaction mixture were diluted with toluene (1 mL), the

resulting solution was filtered and analyzed using GPC.




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Figure 11. Restarting ultrasound mediated polymerization after a dormant state. The evolution of the number average molecular weight (Mn) as a function of clock time (t). The polymerization mixture contained n-butyl acrylate (30 mL, 4 M final concentration), DMF (23 mL), 2 (40 mM), Cu(OTf)2/Me6TREN/BuN4Br (40 mM), and BaTiO3 nanoparticles (4.5 wt%). The mixture was sonicated at 20 kHz using an ultrasonic horn with a 4s on – 4s off cycle. The time in x-axis refers to clock time . Sonication was stopped at t = 1h and entire reaction mixture was held at -196 oC for 3h. The reaction was thawed, additional n-butyl acrylate (15 mL) and DMF (12 mL) were added, and the sonication resumed at t = 4.6h. Aliquots from the reaction were analyzed by gel permeation chromatography (GPC). Mn were determined by GPC calibrated to polystyrene standards.

Reference

1. Ciampolini, M. & Nardi, N. Five-Coordinated High-Spin Complexes of Bivalent Cobalt, Nickel, and Copper with Tris(2-dimethylaminoethyl)amine. Inorg. Chem. 166, 41–44 (1966).


SUEMENTARY INRMATIN - media.nature.com · 4NBr (670 mg, 2.1 mmol), and DMF (23 mL) was prepared...

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