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2010 DIPC Highlight
A versatile “click” chemistry
precursor of functional polystyrene
nanoparticles
L. Oria, R. Aguado, J.A. Pomposo, and J. Colmenero
Advanced Materials 22, 3038 (2010)
Highly efficient routes to well-defined single-chain nanoparticles with size below 10 nm are really
scarce. Recently, we have reported the facile synthesis of a versatile “click” chemistry precursor
of ultra-small polystyrene single-chain nanoparticles (size ≈4 nm).
Functional nanoparticles (NPs) are becoming important building blocks in the emerging fields of
nanomedicine, nanolithography and nanoelectronics, among others. In recent years several unexpected
nano-scale effects have been discovered for these new materials. However, useful synthetic routes to
single-molecule polymeric NPs in the 2–15 nm size range are certainly scarce in spite of the enormous
potential predicted for these materials. In this sense, the main requirements for a versatile synthetic route
to single-chain cross-linked polymeric NPs are: i) easy incorporation of coupling precursors into the individual
polymer chains, ii) highly efficient and selective cross-linking (coupling) reaction, and iii) appropriate
room temperature reaction conditions favoring intramolecular coupling versus intermolecular cross-linking.
Figure 1. Illustration of the “click” chemisty concept: in the present of a copper-catalyst, azide group (blue color)
reacts very fast with alkyne group (grey color) to give a triazole ring.
A versatile “click” chemistry precursor of ultra-small functional polystyrene
nanoparticles (size ≈4 nm) has been synthesized.
In recent years, exquisite control over the composition, molecular weight and molecular weight distribution
of synthetic macromolecules (including block and random copolymers) has been achieved using
(user-friendly) controlled/living radical polymerization techniques, such as reversible addition-fragmentation
chain transfer (RAFT) polymerization. Additionally, “click” chemistry methodologies and specifically
the copper-catalyzed cycloaddition of alkynes and azides (Figure 1) are currently being used in polymer
and materials science for easy and almost quantitative functionalization of synthetic polymers, biomolecules
and inorganic nanoparticles. In fact, the combination of RAFT polymerization and “click” chemistry
meets all the above requirements for the synthesis of well-defined single-chain cross-linked polymeric NPs.
(A)
(B)
Recently, we have “mise-a-point” the synthesis of a new and versatile “click” chemistry precursor of functional
polystyrene nanoparticles (PS-NPs) by the combination of RAFT copolymerization and a subsequent
very efficient functionalization step. This procedure allows the preparation of the “clickable” nanoparticleprecursor
starting from a simple styrene copolymer, opening the way to PS-NPs that could be potentially
used as processing additives or fluorescent contrast agents, among other applications. As illustrated in
Figure 2 (A), a significant viscosity drop was found in nanocomposites of neat natural rubber (cis-1,4-polyisoprene)
and ultra-small functional PS-NPs at very low NP content. In fact, this is the first report of rubber
nanocomposites with reduced melt viscosity arising from the presence of well-dispersed individual polymeric
NPs. In addition, Figure 2 (B) demonstrates the useful fluorescence emission properties of ultrasmall
PS-NPs.
Figure 2. Illustration of the properties of ultra-small functional polystyrene nanoparticles (size ≈4 nm): (A) as processing
additives, inducing a significant viscosity drop in neat natural rubber (cis-1,4-polyisoprene); (B) as fluorescent
contrast agents, showing a strong fluorescence emission band with two clear peaks at 391 and 407 nm.
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