Tailored Composite Polymer-Metal Nanoparticles by
Miniemulsion Polymerization and Thiol-ene
Functionalization
Kim Y. van Berkel and Craig J. Hawker*
Materials Research Laboratory and Department of Chemistry and Biochemistry, University of
California, Santa Barbara, California 93106
Composite Nanoparticle Synthesis Using Styrene Monomer. Initially composite miniemulsion
polymerizations were attempted using styrene as monomer. The experimental procedure was identical to
that described in the main text, but with variations in the monomer content as detailed below.
First, miniemulsion polymerization was carried out with a monomer content of ~20 wt% (relative to
the total mass of the reaction mixture), consistent with typical literature formulations.1 2,2'-azobis-(2amidinopropane)dihydrochloride (V-50, 7.5 mg) and cetyltrimethylammonium bromide (CTAB, 125
mg) were dissolved in 2 mL of water in a 10 mL round-bottom flask charged with a stirring bar.
Polymer-grafted gold nanoparticles (9 mg) were dispersed in 0.5 g of styrene and this mixture was
emulsified with the aqueous solution by sonication for 15 minutes over an ice-water bath, using a Fisher
Scientific Model 500 Ultrasonic Dismembrator at 25% output power. The reaction vessel was sealed
with a rubber septum, purged with argon for 10 minutes, and heated at 50C, with stirring, for four
hours.
The latex product was inspected by transmission electron microscopy (TEM), which revealed a large
majority of pure polystyrene latex particles and a small population of composite particles containing
gold nanoparticles (see Figure S1).
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Figure S1. Representative transmission electron micrograph of composite latex particles obtained using
styrene monomer content of ~20 wt%.
Next, in order to decrease the relative amount of polymer to gold and hence increase the proportion of
composite latex particles obtained, the monomer content was significantly scaled down, while keeping
the mass of gold nanoparticles constant. The synthetic procedure was the same as above, but using only
60 mg of styrene and 1.3 mg of CTAB to give a monomer content of ~3 wt% (relative to the total mass
of the reaction mixture).
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Figure S2. Representative transmission electron micrograph of composite latex particles obtained using
styrene monomer content of ~3 wt%.
As shown in Figure S2, TEM confirmed a substantial increase in the proportion of composite latex
particles compared with pure polystyrene particles. However, the morphology of these composite
particles was poorly defined, and in many cases gold nanoparticles were not completely encapsulated by
polystyrene. Here, the low monomer content gives rise to a very dilute emulsion system; it is likely that
dissolution of styrene monomer into the aqueous phase significantly destabilizes the emulsion droplets
during the course of the polymerization.
Finally, a small amount of divinylbenzene was added to styrene as a cross-linking comonomer. Once
again, the synthetic procedure was the same as described above, but using 1.3 mg of CTAB and 60 mg
of a monomer mixture consisting of 10 wt% divinylbenzene in styrene (giving total monomer content of
~3 wt%).
Figure S3. Representative transmission electron micrograph of composite latex particles obtained using
styrene with added divinylbenzene cross-linker (comonomer mixture of 90/10 styrene/divinylbenzene by
weight).
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As shown in Figure S3, inspection by TEM revealed that the addition of the cross-linking comonomer
resulted in polymer-gold composite particles having a more clearly defined core-shell structure, with
gold nanoparticles completely encapsulated by polymer. Based on this observation, and the expectation
that divinylbenzene should form more stable emulsions than styrene (due to its significantly lower water
solubility2), subsequent composite miniemulsion polymerizations were carried out with divinylbenzene
as the sole monomer, as described in the main text.
UV-vis Spectra of Gold Nanoparticles and Composite Polymer-Gold Nanoparticles.
Figure S4. UV-vis spectra of citrate-stabilized gold nanoparticles (———–), gold nanoparticles grafted
with polystyrene thiol (– – – –), and composite poly(divinylbenzene)-gold nanoparticles (   ).
Variation of Gold Nanoparticle Size
To determine the effect of varying the size of inorganic nanoparticles used, a series of gold
nanoparticles were prepared with average diameters of 13, 18, 24, and 46 nm, using the seeded growth
procedure described previously.3 For each size of gold nanoparticle, composite nanoparticles were
prepared using the same amount of added gold (corresponding to ~19 wt%) in each case.
TEM imaging, as in Figure S5, showed that in all four cases the average diameter of composite
polymer-gold particles was approximately 100 nm, however, the average number of encapsulated gold
nanoparticles per composite particle decreased as gold nanoparticle size increased. In the case of 13 nm
gold particles the average number of encapsulated gold particles was 4.5, with only 10% “empty”
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(containing no gold) polymer particles, whereas, when gold nanoparticles of 46 nm diameter were
employed, the fraction of empty polymer particles (approx. 60%) exceeded that of gold-containing
particles—making the average number of encapsulated particles less than one per composite particle in
this case.
Figure S5. Transmission electron micrographs illustrating the effect on composite nanoparticle
synthesis of increasing the diameter of gold nanoparticles used from: (a) 13 nm, to (b) 18 nm, (c) 24 nm,
or (d) 46 nm.
This trend is to be expected: if the same mass of gold is used in each case, then an increase in the
average size of gold nanoparticles means a decrease in the number of gold nanoparticles in the system.
On average, each composite particle must therefore contain fewer gold nanoparticles, and the number of
empty particles must also increase.
1H-NMR
Spectrum of PEG-Grafted Composite Nanoparticles.
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Figure S6. 1H-NMR spectrum of PEG-grafted composite poly(divinylbenzene)-gold latex particles,
showing broad resonance due to PEG methylene groups at 3.5–4 ppm (resonance due to HOD present in
solvent appears at 4.5–5 ppm).
REFERENCES.
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Landfester, K.; Bechthold, N.; Tiarks, F.; Antonietti, M., Macromolecules 1999, 32, 2679-2683.
Bechthold, N.; Tiarks, F.; Willert, M.; Landfester, K.; Antonietti, M., Macromol. Symp. 2000,
151, 549-555.
Chai, X. S.; Schork, F. J.; DeCinque, A.; Wilson, K., Ind. Eng. Chem. Res. 2005, 44, 5256-5258.
van Berkel, K. Y.; Piekarski, A. M.; Kierstead, P. H.; Pressly, E. D.; Ray, P. C.; Hawker, C. J.,
Macromolecules 2009, 42, 1425-1427.
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