Electronic Supplementary Material (ESI) for Polymer Chemistry.
This journal is © The Royal Society of Chemistry 2015
Supporting Information
Modular amphiphilic copolymer-grafted nanoparticles: “nanoparticle
micelle” behavior enhances utility as dispersants
Muhammad Ejaz,a Alina M. Alb,b Karolina A. Kosakowska,a and Scott M. Graysona,*
aTulane
University, Chemistry Department, New Orleans, LA, USA
bTulane
University, Physics and Engineering Physics Department, New Orleans, LA, USA
*Address correspondence to: [email protected]
TABLE OF CONTENTS:
Experimental
S4
Materials & Synthesis
S4
Instrumentation details
S7
Characterization of the silica nanoparticles
Figure S1. MSD data from DLS experiments for SiO2NPs in isopropanol
General procedure for cleavage of (co)polymers from silica nanoparticles
S9
S9
S10
Characterization of the free PCL, grafted PCL cleaved from SiO2NP-PCL, and PCL-PEG
cleaved from SiO2NP-PCL-PEG
S10
Figure S2. SEC: RI data of cleaved and free PCL from SiO2NP-PCL
S11
Figure S3. MALDI TOF-MS spectrum of free PCL
S11
Figure S4. 1H NMR spectrum of HF treated native silica nanoparticle
S12
Figure S5. 1H NMR spectrum of SiO2NP-PCL-PEG treated with HF
S13
Figure S6. 1H NMR Integration of -hydrogen of cleaved PCL-PEG
S13
S1
Figure S7. 1H NMR Integration of -hydrogen of cleaved PCL-PEG
S14
Figure S8. 1H NMR Integration of -hydrogens of cleaved PCL-PEG
S14
Table S1. TGA-based PCL and PEG Mn estimation
S15
Table S2. 1H NMR-based mass PCL and PEG Mn estimation
S15
General procedure for basic hydrolysis of SiO2NP-PCL-PEG
Figure S9. Comparison of 1H NMR spectra of HF treated SiO2NP-PCL and PCL
S18
S16
Figure S10. Comparison of 1H NMR spectra of SiO2NP-PCL-PEG treated with HF, neat
PCL, neat PEG and native nanoparticle HF etch
Figure S11.
1H
S17
NMR spectrum of SiO2NP-PCL-PEG treated with NaOH, PCL
degradation followed by PEG extraction in CH2Cl2 (no acid quench)
S18
Figure S12. MALDI TOF mass spectrum of SiO2NP-PCL-PEG treated with NaOH, PCL
degradation followed by acid quench
Figure S13.
1H
S19
NMR spectrum of SiO2NP-PCL-PEG treated with NaOH, PCL
degradation (with acid quench)
S20
Particle size and stability of the nanoparticles in aqueous solutions
S20
Figure S14. MSD data from DLS experiments for the bare SiO2NP; the surfacefunctionalized SiO2NP-GPS; the hydrophobic, grafted SiO2NP-PCL; and finally, the amphiphilic
copolymer-grafted SiO2NP-PCL-PEG
S21
Table S3. Intensity-averaged Dh values from DLS measurements made on SiO2NP-PCLPEG dispersed in fresh water, salt water, and water samples from the Gulf of Mexico
S22
Figure S15. PDI (top) and Dh and LS90 LS vs. temperature for SiO2NP-PCL-PEG in sea
water
S22
Small hydrophobic molecule sequestration by SiO2NP-PCL-PEG
S22
S2
Figure S16. MSD data from DLS experiments for SiO2NP-PCL-PEG/Hph aqueous
mixtures compared to Hph
S23
Figure S17. UV spectra from pyrene encapsulation for SiO2NP-PCL-PEG, SiO2NP2xPCL-PEG, and Corexit (0.1mg mL-1) in water
S24
Characterization of HO-PEG-OCH3 starting material
S24
Figure S18. MALDI TOF-MS Spectrum of -hydroxymethoxy PEG 5000
S25
Figure S19. 1H NMR spectrum of -hydroxy--methoxy PEG 5000
S26
Figure S20. 1H NMR integration of -hydroxy--methoxy PEG 5000
S26
Figure S21. 13C NMR spectrum of -hydroxy-methoxy PEG 5000
S27
Characterization of HOOC-PEG-OCH3 product for DCC coupling
S27
Figure S22. MALDI TOF-MS Spectrum of -carboxy--methoxy PEG 3360
S27
Figure S23. 1H NMR spectrum of -carboxy--methoxy PEG 3360
S28
Figure S24. 1H NMR integration of -carboxy--methoxy PEG 3360
S28
Figure S25. 13C NMR spectrum of -carboxy--methoxy PEG 3360
S29
S3
Experimental part and additional experiments made for the characterization of the polymers and
the nanoparticles at different stages of the synthesis are presented.
Experimental
Materials.
Stannous
octanoate
(Sn(Oct)2,
95%,
Sigma-Aldrich),
(3-
glycidoxypropyl)triethoxysilane (GPS, Gelest), NaOH (97%, Fisher Scientific), polyethylene
glycol) methyl ether (-hydroxy--methoxy PEG, Sigma-Aldrich), average Mn = 5000 g/mole,
Chromium(VI) oxide (CrO3, 99.9%, Sigma-Aldrich), H2SO4 (95-98 w/w %, Fisher Scientific), 4(dimethylamino)pyridine (DMAP, 99%, Sigma-Aldrich), N,N′-dicyclohexylcarbodiimide (DCC,
99%, Sigma-Aldrich), 4-heptyphenol (Hph, Sigma-Aldrich), tetrahydrofuran (THF, SigmaAldrich), pyrene (Sigma-Aldrich, 99.0%) and all other reagents were used as obtained from
commercial sources. -Caprolactone (CL, 99%, Acros Organics) was dried over CaH2 and
vacuum distilled before polymerization. Silica suspension (IPA-ST-ZL) was provided by Nissan
Chemical Industries, LTD and consisted of ~30 wt% of colloidal silica particles with an average
diameter of ~ 100 nm, in isopropanol. The pristine silica particles were obtained in powdered
form from IPA-ST-ZL by centrifugation to collect the particles followed by washing with
methanol and finally drying under vacuum overnight at room temperature.
Synthesis
“One-pot” immobilization of the epoxysilane coupling agent onto the silica
nanoparticles surface and concurrent hydrolysis of the epoxy groups. The SiO2NPs were
treated with GPS by modification of a previously reported method.1 The isopropanol solvent
from the commercial SiO2NPs suspension was replaced with water by a solvent-exchange
method. The suspension was diluted with water and centrifuged. The collected SiO2NPs were
S4
then dispersed in water and centrifuged again. This cycle was repeated a total of five times
yielding a suspension of SiO2NPs in water.
For the surface functionalization, the SiO2NPs suspension in water (4.8 g of particles present in
16.0 g of 30 wt% SiO2NPs) was added to a round bottom flask with a magnetic stir bar and fitted
with a reflux condenser. GPS (5.6 g, 0.02 mol) was added and the resultant reaction mixture was
diluted with deionized water to reach a concentration of SiO2NPs of approximately 0.2 g mL−1.
This suspension was sonicated for 15 min, at which point the pH was adjusted to 11 by the
addition of a 1 M aqueous NaOH solution. The reaction mixture was then refluxed for 36 h to
assure both silanol condensation and subsequent epoxy hydrolysis to yield diol functionalized
nanoparticles. After cooling the reaction mixture down to room temperature, the SiO2NPs were
repeatedly sonicated in neutral water to disperse them in solution and centrifuged for a period of
30 min at 10,000 rpm to isolate from the solvent, until achieving a neutral pH. The removal of
any unattached GPS from the diol functionalized nanoparticles was then achieved by successive
centrifuging-redispersion cycles in methanol. Finally, the SiO2NPs were dried overnight under
vacuum at room temperature before pursuing SIROP. After drying, 4.1 g of functionalized
nanoparticles were isolated (84% yield based on TGA measurement of 1.2 weight % GPS on
SiO2NP-GPS).
SIROP of CL from the diol functionalized silica nanoparticles (SiO2NP-OH) to produce
SiO2NP-PCL. 2.1 g of SiO2NP-OH were dispersed in 60 g of CL (0.526 mol) by sonication in a
100 mL two-neck round bottom flask fitted with a stir bar. After 40 min of Ar purge, 48.00 mg
(0.12 mmol) of Sn(Oct)2 was added to the suspension under Ar flow. The flask was placed in a
thermostatic oil bath at 130 C and the suspension was stirred for 7 h under Ar. The polymergrafted SiO2NPs were isolated from free polymer by repeatedly dispersing in THF (by
S5
sonication), centrifuging, and decanting the THF solution to remove any unbound PCL. The
same procedure was followed in the case of the PCL grafting reactions monitored online. After
drying under vacuum, 1.8 g of the SiO2NP-PCL product was isolated (76 % yield based on TGA
measurement of 12.1 weight % PCL on SiO2NP-PCL).
Synthesis of -carboxy--methoxy-PEG (HOOC-PEG-OCH3). The polyethylene glycol
(5000 g mol−1), bearing one terminal methyl ether and one carboxylic acid functional group, was
prepared as follows.2 In a round-bottom flask, 47.50 g (9.50 × 10−3 mol, 1 eq.) of -hydroxy-methoxy PEG were dissolved in 310 mL of acetone. Jones reagent (10.60 g of CrO3 dissolved in
9.20 mL of H2SO4 and 40 mL of water) was added dropwise until the solution maintained a
reddish color for ca. 10 min. The mixture was then diluted with 200 mL of water and washed
three times with 300 mL of CH2Cl2. Organic phases were combined, washed three times with
water and dried with anhydrous MgSO4. The solvent was evaporated and 45.36 g of HOOCPEG-OCH3 were obtained (yield 95%). The observed average weight (Mn = 3360 g/ mole)
appeared to be slightly reduced, presumably from oxidative scission of the backbone. The
reactant (Fig. S18-S21) and final product (Fig. S22-S25) were characterized by 1H NMR,
13C
NMR and MALDI mass spectra.
Attachment of HOOC-PEG-OCH3 on SiO2NP-PCL-OH by ester coupling to produce
SiO2NP-PCL-PEG. HOOC-PEG-OCH3 (6.35 g, 1.27 mmol) was dissolved in 45 mL of
anhydrous DCM in two-neck round bottom flask under N2 flow. 1.30 g of SiO2NP-PCL-OH
suspended by sonication in 45 mL of anhydrous DCM was charged with the above solution of
HOOC-PEG-OCH3 under N2 flow and the mixture was cooled to 0 C while stirring. A solution
of 790 mg of DCC (3.83 mmol) and 48.50 mg (0.39 mmol) of DMAP was prepared in 12 mL of
S6
DCM and added dropwise to the above reaction mixture over a period of 15 min. After 1 h, the
reaction mixture was allowed to warm to room temperature, at which time the stirring was
continued for an additional 36 h. The DCC-urea by-product could be removed by selectively
centrifugation of the nanoparticles, and decanting off the urea suspended in solution. The
resulting particles were cleaned with a series of different solvents (DCM, THF, acetone, water,
and methanol) by redispersion/centrifugation and finally vacuum dried overnight. After drying,
1.1 g of functionalized nanoparticles were isolated (83 % yield based on TGA measurement of
1.8 weight % PEG on SiO2NP-PCL-PEG).
Synthesis of SiO2NP-2xPCL-PEG. In the first step 0.7 g of SiO2NP-PCL were dispersed in
21 g of CL (0.184 mol) by sonication in a 50 mL two-neck round bottom flask fitted with a stir
bar. After 40 min of Ar purge, 24.00 mg (0.06 mmol) of Sn(Oct)2 was added to the suspension
under Ar flow. The flask was placed in a thermostatic oil bath at 130 C and the suspension was
stirred for 5 h under Ar. The SiO2NP-PCL with OH terminal ends act as immobilized
macroinitiators for SIROP of additional CL. The polymer-grafted SiO2NP-2xPCL were isolated
from free polymer as mentioned above in SIROP of CL from SiO2NPs-OH. In the second step
SiO2NP-2xPCL were attached with HOOC-PEG-OCH3 by ester coupling using same protocol as
mentioned above for attachment of HOOC-PEG-OCH3 on SiO2NP-PCL-OH by ester coupling.
Characterization
The PCL grafting reactions on the functionalized silica nanoparticles via surface-initiated ring
opening polymerization (SIROP) were monitored using Automatic Continuous Online
Monitoring of Polymerization reactions (ACOMP),3 a non-chromatographic method that relies
S7
on continuous extraction and dilution of a small stream of reactor contents on which
measurements are simultaneously made by multiple detectors, as the reaction proceeds. A twostage dilution with tetrahydrofuran (THF) of a small reactor stream was made throughout the
reaction using an ensemble of HPLC pumps. Characterization of the amphiphilic SiO2NP-PCLPEG copolymer grafted particles in terms of stability in aqueous media, size, and loading
capabilities was made by Automatic Continuous Mixing (ACM).
4
The technique used a Shimadzu HPLC pump, connected to a mixing unit and a detector train
containing multi-angle light scattering (Brookhaven), refractive index and UV detectors
(Shimadzu). Particle hydrodynamic diameter, Dh (the intensity-weighted average diameter) was
determined by dynamic light scattering (DLS) measurements made using a Brookhaven 90-plus
detector ( = 670 nm) operating at a scattering angle of 90o.5 Further polymer characterization of
the grafted PCL-PEG in terms of molecular weight distribution and polydispersity was made by
Size Exclusion Chromatography (SEC), with THF as eluent, at 0.8 mL/min. A SDV linear
chromatographic column (100 Å single porosity, 3 m particle size) from Polymer Standards
Service and same detectors as in ACM were employed. Molecular weight determination was
based on direct measurements from light scattering (LS) data and/or calibration with PCL
standards. The Fourier transform infrared (FTIR) spectroscopy was performed using a NEXUS
670 FT-IR SEP. Analyte was mixed with KBr and ground into a fine powder by mortar and
pestle and compacted into a pellet by applying pressure. Thermogravimetric analysis (TGA) data
was acquired using TA Instruments TGA 2950 Thermogravimetric Analyzer with heating rate of
20 °C per minute under N2 atmosphere. Data was processed using TA Instruments Universal
Analysis software. Transmission electron (TEM) microscopy data was collected with a FEI G2
F30 Tecnai TEM operated at 200 kV. All the samples were suspend in ethanol and casted on the
S8
TEM grid. Chemical shifts are reported in parts per million (ppm) relative to CDCl3 (7.26 ppm
for 1H and 77.36 for
13C),
as internal reference. MALDI spectra were collected using a Bruker
UltraFlex MALDI-TOF MS with a SCOUT-MTP Ion Source (Bruker Daltonics, Bremen), N2laser (337nm), and reflector design was used. The intensity of the laser was set to the lowest
possible level to acquire high resolution spectra of the product and all spectra were acquired
using reflector-positive mode. The instrument was calibrated using SpheriCalTM calibrants
purchased from Polymer Factory Sweden AB. The received spectra were analyzed using the
software FlexAnalysis from Bruker Daltonics, Bremen, version 2.2. A Bruker Avance 400 MHz
NMR instrument was used for 1H NMR and 13C NMR experiments. Proton NMR spectra were
acquired with a spectral window of 20 ppm, an acquisition time of 4 seconds and a relaxation
delay of 2 seconds.
13C
NMR spectra were acquired with a spectral window of 250 ppm, an
acquisition time of 0.7 seconds and a relaxation delay of 5 seconds.
Characterization of the silica nanoparticles. Initial characterization of the commercially
available starting material provided by Nissan Chemical Industries, LTD as ~30 wt% of colloidal
silica particles in isopropanol was carried out to confirm their well-defined structure.
S9
Figure S1. MSD data from DLS experiments for SiO2NPs in
isopropanol.
Results of the DLS measurements made on diluted nanoparticles (SiO2NPs) in isopropanol
give an average Dh value of 135 nm and narrow polydispersity (PDI) ~ 0.1, confirming their
excellent dispersibility. Figure S1 shows a graphical representation in terms of multimodal size
distribution (MSD), based on the non-negatively constrained least squares (NNLS) algorithm
used to fit data.1
General procedure for cleavage of (co)polymers from silica nanoparticles.6,7 SiO2polymer nanoparticles (100.0 mg) were suspended in 4 mL of toluene or dichloromethane
(DCM) in a Teflon flask. Aliquat 336 (phase transfer catalyst, 50.0 mg) and 48% HF (aq)
solution (5 mL) were added to the particle suspension and the reaction mixture was allowed to
stir at room temperature overnight. The reaction mixture was washed with aqueous NaHCO3 and
S10
water and organic layer containing polymer was separated. Polymer was recovered by
evaporation of solvent.
Characterization of the free PCL, grafted PCL cleaved from SiO2NP-PCL, and grafted
PCL-PEG cleaved from SiO2NP-PCL-PEG. Characterization of the free and grafted polymers
obtained during SIROP reactions (and subsequently cleaved from the nanoparticles) in terms of
molecular weight was conducted by size exclusion chromatography (SEC) in THF, relative to
PCL standards (previously synthesized by ROP with each Mn determined by MALDI). Weight
average molecular weight (Mw) values of 7400 g/mole and 12,000 g/mole and rather low
polydispersity values (~1.1) for the free and cleaved PCL, respectively, were determined.
S11
Figure S2. SEC: RI data from PCL cleaved from SiO2NP-PCL,
compared to the free PCL during SIROP led to Mn values of 11243
(Đ=1.1806) and 6894 g/mole (Đ=1.1822) for the cleaved and free
PCL, respectively, based on calibration curve with linear PCL
9079.061
8050.529
7821.482
7478.771
9765.969
9536.963
3823.585
3024.201
2224.626
1.0
3366.307
2567.965
1.5
Mass range:
0 kDa—10.9 kDa
Mn: 6983.03
Mw: 7963.42
Ð: 1.140
Representative Peak
Assignment:
Calc. Mn 61-mer+K+:
7020.760
Observed Mn : 7021.413
∆ Mass: 0.653
9307.736
OH
n
O
8393.599
H
1312.170
2.0
* 7.9.14 Free PCL Ref Cal K 2 m ercapto 961\0_J4\1\1Ref
O
8736.342
Intens. [a.u.]
x104
1198.076
To provide a measure of the accuracy of the molecular weight determination by SEC,
MALDI data for the free PCL was also acquired in Figure S3.
0.5
0.0
2000
4000
6000
8000
10000
12000
m/z
S12
Figure S3. MALDI TOF mass spectrum of free PCL. MS conditions: matrix: 2-mercapto-benzothiazole 10
mg mL-1, analyte: 20 mg mL-1, and added cation: potassium trifluoroacetate 1 mg mL-1 [7:7:1], calibrated,
reflector mode.
In order to quantify the ratio of PEG to PCL, the SiO2NP-PCL-PEG were treated with HF to
isolate free block copolymer, and the block ratio determined by 1H NMR (Figures S4-S10).
Figure S4. 1H NMR spectrum of product of native silica nanoparticles (without polymer grafting) after treatment
with HF/Aliquot 336 catalyst, in CDCl3
S13
Figure S5. 1H NMR spectrum in CDCl3 of SiO2NP-PCL-PEG treated with HF/Aliquot 336.
ppm Integration
Species
4.036
2
PCL: –COO-CH2—
3.624
1.1
PEG: —CH2-CH2—
Species
PCL: –COO-CH2— PEG :—CH2-CH2—
Integration
2
1.1
Normalized
2
0.55
Ratio
3.63
1
Estimated PCL:PEG RU
277
76
Estimated PCL: PEG Mass
31600
3360
Figure S6. Integration of significant peaks from 1H NMR spectrum in CDCl3 of SiO2NP-PCL-PEG treated
with HF/Aliquot 336; values calculated against PCL ester -position hydrogens, and molecular weight
estimations based on PEG = 3360.
S14
ppm Integration
Species
2.285
2
PCL: –CH2-COO—
3.624
1.03
PEG: —CH2-CH2—
Species
PCL: –CH2-COO— PEG: —CH2-CH2—
Integration
2
1.03
Normalized
2
0.515
Ratio
3.88
1
Estimated PCL:PEG RU
296
76
Estimated PCL: PEG Mass
33700
3360
Figure S7. Integration of significant peaks from 1H NMR spectrum in CDCl3 of SiO2NP-PCL-PEG treated
with HF/Aliquot 336; values calculated against ester -position hydrogens, and molecular weight
estimation based on PEG = 3360.
Species
PCL: –CH2-CH2-CH2— PEG: —CH2-CH2—
Integration
4
0.87
Normalized
4
0.435
Ratio
4.60
1
Estimated PCL:PEG RU
351
76
Estimated PCL: PEG Mass
40000
3360
ppm Integration
Species
1.543
4
PCL: –CH2-CH2-CH2—
3.624
0.87
PEG: —CH2-CH2—
Figure S8. Integration of significant peaks from 1H NMR spectrum in CDCl3 of SiO2NP-PCL-PEG treated
with HF/Aliquot 336; values calculated against ester ,-position hydrogens, and molecular weight
estimation based on PEG =3360.
S15
Table S1. TGA relative mass estimation, based on the assumption that PEG Mn = 3360 for
SiO2NP-PCL-PEG.
Polymer
PCL
PEG
Weight Loss
(%)
12.1
1.8
Mass Ratio
6.72
1
Estimated
Mass
22600
3360
Estimated
Repeat Unit
198
76
Repeat Unit
Ratio
2.59
1
Table S2. 1H NMR relative mass estimation based on the assumption that PEG Mn = 3360 for
SiO2NP-PCL-PEG.
Position
α
ω
β, δ
Average
Ratio
PEG:PCL
1:3.64
1:3.88
1:4.60
1:4.04
Calculated PCL
Repeat Units
277
296
351
308
Calculated
PCL Mass
31600
33700
40000
35100
General procedure for basic hydrolysis of SiO2NP-PCL-PEG
S16
Figure S9. 1H NMR spectrum in CDCl3 of SiO2NP-PCL treated with HF/Aliquot 336; overlay with neat
PCL 1H NMR spectrum to confirm the presence of PCL in the HF treated product.
S17
Figure S10. 1H NMR spectrum of SiO2NP-PCL-PEG treated with HF/Aliquo 336, in CDCl3; overlay with
neat PCL, neat PEG and native SiO2NP after HF/Aliquot 336 etch 1H NMR spectra to confirm the
assignment of PEG (purple), PCL (orange), and SiO2NP/aliquot byproducts (pink).
As an additional confirmation of the attachment of PEG, the PEG-PCL functionalized
nanoparticles were reacted with NaOH to complete degrade the PCL, enabling the PEG (and
degraded PCL) to be characterized by NMR and MALDI-ToF MS (Figures S11-S13):
S18
General procedure for treatment of silica nanoparticles grafted with PCL and PEG with
NaOH. SiO2-polymer nanoparticles (50.0 mg) were suspended in 15 mL of THF. 3 mL of 0.01
NaOH (aq) solution was added to the above suspension and reaction mixture was allowed to stir
at room temperature for 12 h. At this stage, the reaction mixture could be extracted with CH2Cl2
to isolate the PEG. Alternatively, the reaction could be acidified to neutrality with 1 M HCl and
extracted with CHCl3 in order to isolate PEG along with the degradation product
(hydroxyhexanoic acid) of the PDL.
Figure S11. 1H NMR spectrum in CDCl3 of SiO2NP-PCL-PEG treated with NaOH, PCL degradation
followed by PEG extraction in CH2Cl2 (no acid quench).
S19
Mass range: 2.0 kDa—6.1 kDa
Mn: 3616.74
Mw: 4046.16
Ð: 1.119
Representative Peak Assignment:
Calc. Mn 115-mer+Na+: 5176.012
Observed Mn : 5176.884
∆ Mass: 0.872
6058.462
5882.828
2
5969.448
5793.385
5617.936
3
5705.648
5529.731
5441.427
5353.314
5176.844
5265.294
5089.072
4956.976
4868.675
4780.598
4604.614
4692.280
4383.935
O
n
4516.017
4250.862
O
4163.805
3943.099
4030.629
HO
3855.920
4
O
3722.084
Intens. [a.u.]
x104
1
4000
4500
5000
5500
6000
6500
7000
m/z
Figure S12. MALDI TOF mass spectrum of PEG carboxylic acid, removed from SiO2NP-PCL-PEG by
treatment with NaOH, (to achieve PCL degradation) followed by acid quench. MS conditions: matrix: trans-2[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) 20 mg/mL, analyte: 20 mg/mL, and
added cation: sodium trifluoroacetate 2 mg mL-1 [3:2:1], calibrated, reflector mode.
S20
a
HO
O
O
O
O
a
HO
n
c
c
b
d
OH
e
c
a
e
b
d
Figure S13. 1H NMR spectrum in CDCl3 of the degraded polymer grafts (hydrolyzed PCL as well as PEG)
obtained by treatment of SiO2NP-PCL-PEG with NaOH, PCL degradation, followed with acid quench and
extraction into CHCl3.
Particle size and stability of the nanoparticles in aqueous solutions. DLS experiments
made on aqueous solutions containing nanoparticles at different stages of the synthesis:
the bare SiO2NP, the surface-functionalized SiO2NP-GPS, the hydrophobic, grafted
SiO2NP-PCL, and the amphiphilic copolymer-grafted SiO2NP-PCL-PEG confirmed that
the nanoparticles were rather stable when dispersed in aqueous media and exhibited
homogeneous particle distributions, with the notable exception of the hydrophobic PCL
grafted nanoparticles which exhibited limited stability and a tendency to aggregate. An
illustration of their behavior is shown in Fig. S19 containing multimodal size distribution
(MSD) data for all the above types of nanoparticles in aqueous solutions. The numberweighted distributions are shown in the figure. Data for SiO2NP-PCL are included only to
show the presence of aggregated particles, otherwise not quantitatively meaningful.
S21
Figure S14. MSD data from DLS experiments for SiO2NP, SiO2NP-GPS, SiO2NP-PCL,
and SiO2NP-PCL-PEG
Results from additional studies shown in Table S3 confirmed that the behavior of the
SiO2NP-PCL-PEG nanoparticles was not significantly affected by variations of the aqueous
media, including fresh water, salt water or water samples extracted from the Gulf of Mexico.
S22
Table S3. Intensity-averaged Dh values from multiple DLS measurements made on aqueous
SiO2NPs-PCL-PEG dispersed in fresh water, salt water, and in water samples from the Gulf of
Mexico
In water
In 0.6 M NaCl
In sea water
Dh(nm)
PDI
LS90
Dh(nm)
PDI
LS90
Dh(nm)
PDI
LS90
211
0.129
270.5
203
0.047
235.4
232
0.210
366.1
Shown in Figure S15 are PDI (top) and Dh and LS90o vs. temperature for SiO2NP-PCL-PEG
in sea water, indicating no significant effect of the temperature on the physical characteristics
studied.
Figure S15. PDI (top) and Dh and LS90 LS vs. temperature for SiO2NP-PCLPEG in sea water
Small hydrophobic molecule sequestration by SiO2NPs-PCL-PEG copolymer grafted
particles. Additional DLS data – MSD (intensity-weighted distributions) for SiO2NP-PCLPEG/Hph aqueous mixtures compared to data for Hph alone - are shown in Figure S16. Narrow
S23
MSDs for the copolymer nanoparticles & Hph mixture contrasts to the bimodal MSD of the
aggregated hydrophobic Hph and confirm, by the disappearance of the clustered particles, the
Hph sequestration.
Figure S16. MSD data from DLS experiments for SiO2NP-PCL-PEG/Hph
aqueous mixtures compared to Hph
Discrete UV and fluorescence experiments with pyrene shown in Figure S17 allowed
comparing SiO2NP-PCL-PEG and Corexit loading capabilities. Excess pyrene was added to the
aqueous nanoparticle with different PCL layer and Corexit solutions (0.1 mg mL-1) and, after
filtering off the undissolved dye, UV spectra were acquired. Based on the UV data at 335 nm,
Corexit could load about twice the amount of guest than the single layer SiO2NP-PCL-PEG and
1.6 times as much as the double layer SiO2NP-2xPCL-PEG.
The intensity ratio of the two characteristic absorbance peaks at 383 nm and 373 nm (I3/I1)
from uncalibrated fluorescence experiments, also shown in the figure (top), indicate higher
loading capabilities of the SiO2NP-2xPCL-PEG and Corexit, compared to SiO2NP-1xPCL-PEG.
S24
Figure S17. Fluorescence emission spectra (top) and UV spectra
(bottom) from pyrene encapsulation for SiO2NP-PCL-PEG, SiO2NP2xPCL-PEG, and Corexit (0.1mg mL-1) in water
Data from the reactant and final product characterization by 1H NMR, 13C NMR and MALDI
mass spectra are shown in Figures S18-S21 and Figures S22-S25, respectively.
Characterization of HOOC-PEG-OCH3 starting material
S25
5381.048
4250
4750
5000
5250
5500
5750
6000
6086.393
5998.669
5822.070
5734.233
4543.980
4500
5909.503
4367.951
5645.621
4631.934
4000
4280.042
0.2
4192.915
4104.001
0.4
4455.996
0.6
0.0
Mass range: 4.1 kDa—6.1 kDa
Mn: 5149.63
Mw: 5184.92
Ð: 1.0069
Representative Peak Assignment:
Calc. Mn 118-mer+Na+: 5294.110
Observed Mn : 5292.999
∆ Mass: 1.111
5557.439
4720.012
0.8
5469.113
4807.953
1.0
5292.999
4984.053
O
n
5204.356
O
HO
1.2
5071.987
* 11.26.14 MeO-PEG-OH starting material ref cal na\0_D2\1\1Ref
4895.973
Intens. [a.u.]
x104
6250
m/z
Figure S18. MALDI TOF mass spectrum of -hydroxy--methoxy PEG 5000 (MeO-PEG-OH). MS conditions:
matrix: trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) 20 mg mL-1, analyte: 20
mg mL-1, and added cation: sodium trifluoroacetate 2 mg/ mL [3:2:1], calibrated, reflector mode
S26
HO
O
a
b
a O
n
a
b
Figure S19. 1H NMR spectrum in CDCl3 of  -hydroxy--methoxy PEG 5000 (MeO-PEG-OH) in CDCl3
ppm Integration
Species
3.354
3
—CH3
3.617
462.920
—CH2-CH2—
Species
—CH3 —CH2-CH2—
Integration
3
462.920
Normalized
3
231.460
Ratio
1
115.730
Estimated Mass
5171.182
Figure S20. Integration of significant peaks from 1H NMR spectrum of -hydroxy---methoxy PEG 5000
(MeO-PEG-OH) in CDCl3; mass calculation
S27
O
HO
b
a
a O
n
a
Figure S21. 13C NMR spectrum of  -hydroxy--methoxy PEG 5000 (MeO-PEG-OH) in CDCl3
Characterization of HOOC-PEG-OCH3 product for DCC coupling
O
883.610
HO
O
Mass range: 0 kDa—6.0 kDa
Mn: 3356.78
Mw: 3841.90
Ð: 1.145
Representative Peak Assignment:
Calc. Mn 66-mer+Na+: 3018.784
Observed Mn : 3017.480
∆ Mass: 1.304
O
n
1103.744
0.00
1000
1500
2000
2500
3000
3500
4000
4500
5000
5855.690
5987.346
5591.886
5500
5723.455
5327.555
5438.591
5019.374
5129.971
4887.204
4755.179
4579.209
4403.207
4271.166
3985.104
3765.296
3875.233
3523.412
3633.351
3281.429
3413.434
3017.480
0.25
3149.438
2753.492
2885.542
2489.634
2621.684
2225.702
2357.657
1961.769
2093.764
1675.798
1829.751
1323.818
1433.781
0.50
1543.820
0.75
1191.782
1.00
1015.698
971.677
1.25
4095.343
1.50
927.651
Intens. [a.u.]
x105
m/z
Figure S22. MALDI TOF mass spectrum of -carboxy--methoxy PEG 3360 (MeO-PEGCOOH).
MS
conditions:
matrix:
trans-2-[3-(4-tert-butylphenyl)-2-methyl-2propenylidene]malononitrile (DCTB) 20 mg mL-1, analyte: 20 mg/mL, and added cation: sodium
trifluoroacetate 2 mg mL-1 [3:2:1], calibrated, reflector mode.
S28
a
O
HO
c
O
a
a
O
n
b
c
b
Figure S23. 1H NMR spectrum of -carboxy--methoxyPEG 3360 (MeO-PEG-COOH) in CDCl3
Species
—CH3
—CH2-CH2—
Integration
3
480.097
Normalized
3
240.049
Ratio
1
120
Estimated Mass
5290
Species
—CH2-COO— —CH2-CH2—
Integration
6.452
480.097
Normalized
6.452
240.049
Ratio
1
37
Estimated Mass
1630
Mass Average
3460
ppm Integration
Species
3.359
3
—CH3
3.623
480.097
—CH2-CH2—
4.139
6.452
—CH2-COO—
Figure S24. Integration of significant peaks from 1H NMR spectrum of -carboxy--methoxy PEG 3360
(MeO-PEG-COOH) in CDCl3; values calculated against methyl and carboxy-position hydrogens.
S29
Figure S25. 13C NMR spectrum of -carboxy--methoxy PEG 3360 (MeO-PEG-COOH) in CDCl3
Additional raw data are available through: https://data.gulfresearchinitiative.org/data-discovery
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G. L. Chakkalakal, M. Alexandre, C. Abetz, A. Boschetti-de-Fierro and V. Abetz, Macromol.
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