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ABSTRACT: The aim of this review is to highlight some of the challenges in designing thermally responsive nanoparticles, where the responsivity is endowed by a responsive polymeric corona. A review of the literature reveals many contradictory observations upon heating these particles through their transition temperature. Indeed, both an increase in size due to aggregation and particle shrinkage have been reported for apparently similar materials. Furthermore, careful review of the literature shows that responsive nanoparticles do not have the same transition temperature or properties as their constituent polymers. These observations raise serious questions as to how to achieve the rational design of a responsive particle with a predictable and reproducible response. Here we highlight specific cases where conflicting results have been observed for spherical particles and put these results into the context of flat-surface grafted polymer brushes to explain the behaviour in terms of grafting density, curvature, chain end effects and the role of the underlying substrate. A better understanding of these observations should lead to the improved design of nanoparticles with real function and applications.
Chemical Society Reviews 04/2013; · 28.76 Impact Factor
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ABSTRACT: The spontaneous one-step synthesis of hollow nanocages and nanotubes from spherical and cylindrical micelles based on poly(acrylic acid)-b-polylactide (P(AA)-b-P(LA)) block copolymers (BCPs) has been achieved. This structural reorganization, which occurs simply upon drying of the samples, was elucidated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). We show that it was necessary to use stain-free imaging to examine these nanoscale assemblies, as the hollow nature of the particles was obscured by application of a heavy metal stain. Additionally, the internal topology of the P(AA)-b-P(LA) particles could be tuned by manipulating the drying conditions to give solid or compartmentalized structures. Upon resuspension, these reorganized nanoparticles retain their hollow structure and display significantly enhanced loading of a hydrophobic dye compared to the original solid cylinders.
ACS Nano 02/2013; · 10.77 Impact Factor
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ABSTRACT: A new amphiphilic homopolymer bearing an SCS pincer palladium complex has been synthesized by reversible addition fragmentation chain transfer polymerization. The amphiphile has been shown to form spherical and worm-like micelles in water by cryogenic transmission electron microscopy and small angle neutron scattering. Segregation of reactive components within the palladium containing core results in increased catalytic activity of the pincer compound compared to small molecule analogues. This allows carbon-carbon bond forming reactions to be performed in water with reduced catalyst loadings and enhanced activity.
Polymer Chemistry 01/2013; 4(6):2033-2039. · 5.32 Impact Factor
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ABSTRACT: Site isolation, compartmentalization and substrate specificity are a few of the characteristics responsible for the catalytic efficiency demonstrated by enzymes in natural systems. In efforts to mimic these highly efficient systems, research has been directed towards macromolecular chemistry. Robust polymer assemblies can create a favorable and isolated environment around the catalytic site allowing specific and sometimes incompatible reactions to take place within this protected reaction pocket. Further exploring the use of 'smart' polymers, control over both the catalytic activity and substrate specificity is achieved. In addition, polymeric systems provide the opportunity for recycling of the active catalysts, further enhancing the advantages of polymer supported catalytic systems.
Current opinion in biotechnology 12/2012; · 7.82 Impact Factor
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ABSTRACT: The concept of using polymeric micelles to catalyze organic reactions in water is presented and compared to surfactant based micelles in the context of molecular recognition. We report for the first time enzyme-like specific catalysis by tethering the catalyst in the well-defined hydrophobic core of a polymeric micelle.
Chemical Communications 08/2012; 48(83):10280-2. · 6.17 Impact Factor
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ABSTRACT: The use of functional core-shell micelles as asymmetric catalytic nanoreactors for organic reactions in water is presented. An unprecedented increase in rate of reaction was achieved, which is proposed to be associated with the ability of the nanostructures to effectively concentrate the reagents in the catalytically active micelle core.
Chemical Communications 08/2012; 48(78):9699-701. · 6.17 Impact Factor
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ABSTRACT: Using a strand exchange mechanism we have prepared, by DNA templated chemistry, two 10-mers with defined and tunable monomer sequences. An optimized reaction protocol achieves 85% coupling yield per step, demonstrating that DNA-templated chemistry is a powerful tool for the synthesis of macromolecules with full sequence control.
Chemical Communications 05/2012; 48(45):5614-6. · 6.17 Impact Factor
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ABSTRACT: A system for multistep DNA-templated synthesis is controlled by the sequential formation of DNA junctions. Reactants are attached to DNA adapters which are brought together by hybridization to DNA template strands. This process can be repeated to allow sequence-controlled oligomer synthesis while maintaining a constant reaction environment, independent of oligomer length, at each reaction step. Synthesis can take place in a single pot containing all required reactive monomers. Different oligomers can be synthesized in parallel in the same vessel, and the products of parallel synthesis can be ligated, reducing the number of reaction steps required to produce an oligomer of a given length.
Journal of the American Chemical Society 01/2012; 134(3):1446-9. · 9.91 Impact Factor
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ABSTRACT: Segregation and templating approaches have been honed by billions of years of evolution to direct many complex biological processes. Nature uses segregation to improve biochemical control by organizing reactants into defined, well-regulated environments, and the transfer of genetic information is a primary function of templating. The ribosome, wherein messenger RNA is translated into polypeptides, combines both techniques to allow for ideal biopolymer syntheses. Herein is presented a biomimetic segregation/templating approach to synthetic radical polymerization. Polymerization of a nucleobase-containing vinyl monomer in the presence of a complementary block copolymer template of low molecular weight yields high molecular weight (M(w) up to ~400,000 g mol(-1)), extremely low polydispersity (≤1.08) daughter polymers. Control is attained by segregation of propagating radicals in discrete micelle cores (via cooperative assembly of dynamic template polymers). Significantly reduced bimolecular termination, combined with controlled propagation along a defined number of templates, ensures unprecedented control to afford well-defined high molecular weight polymers.
Nature Chemistry 01/2012; 4(6):491-7. · 20.52 Impact Factor
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ABSTRACT: Block copolymers are well-known to self-assemble into a range of 3-dimensional morphologies. However, due to their nanoscale dimensions, resolving their exact structure can be a challenge. Transmission electron microscopy (TEM) is a powerful technique for achieving this, but for polymeric assemblies chemical fixing/staining techniques are usually required to increase image contrast and protect specimens from electron beam damage. Graphene oxide (GO) is a robust, water-dispersable, and nearly electron transparent membrane: an ideal support for TEM. We show that when using GO supports no stains are required to acquire high contrast TEM images and that the specimens remain stable under the electron beam for long periods, allowing sample analysis by a range of electron microscopy techniques. GO supports are also used for further characterization of assemblies by atomic force microscopy. The simplicity of sample preparation and analysis, as well as the potential for significantly increased contrast background, make GO supports an attractive alternative for the analysis of block copolymer assemblies.
Soft Matter 01/2012; · 4.39 Impact Factor
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ABSTRACT: The synthesis and application of thermally-responsive macromolecules and nanoparticles relies on the underpinning control of their transition temperatures. The present study shows that two structurally diverse classes of nanoparticle have very strong diameter-dependent responses to temperature-stimuli, demonstrating that the exact size of the nanostructure can significantly impact its performance.
Chemical Communications 09/2011; 47(42):11627-9. · 6.17 Impact Factor
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ABSTRACT: We have prepared a range of well-defined copolymers of styrene and L-proline functionalized styrene (5-11 kDa) using reversible addition-fragmentation chain transfer (RAFT) polymerization techniques and explored their use in supported catalysis. Upon deprotection of the L-proline functionalities, the solution self-assembly of these copolymers was investigated in mixed solvent systems. The resulting assemblies were characterized by dynamic light scattering, transmission electron microscopy (on graphene oxide substrates, along with cryo-TEM and tomography), and scanning electron microscopy. The application of these functional assemblies as supported catalysts for the aldol condensation reaction was explored using cyclohexanone and 4-nitrobenzaldehyde. The rate and selectivity of solution catalysis in our self-assembled system were comparable to those of L-proline, and a significant advantage of our system was that the polymer support could be utilized at lower catalyst loadings with comparable activity and also could be recycled a number of times while maintaining activity and selectivity.
Macromolecules 09/2011; 44(18):7233-7241. · 5.17 Impact Factor
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ABSTRACT: Herein we report the use of a tetrazine-norbornene inverse electron demand Diels-Alder conjugation applied to polymer end-functionalization and polymer-polymer coupling. The reaction was found to be applicable to polymer-polymer coupling, as judged by SEC, DOSY NMR, and LCxSEC analyses, giving diblock copolymers by merely mixing the constituent homopolymers together under ambient conditions, using no catalyst, additive, or external stimulus.
Journal of the American Chemical Society 08/2011; 133(35):13828-31. · 9.91 Impact Factor
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ABSTRACT: Unusual self-assembly behavior is observed for a range of hydrophilic homopolymers. This self-assembly behavior is contrary to the expected behavior of such hydrophilic polymers and instead mimics more commonly reported amphiphilic block copolymers. It is proposed that the unique combination of hydrophobic end groups at both the α and ω chain end accounts for this unusual self-assembly behavior. Complex internal polymer micelles are spontaneously formed when hydrophilic homopolymer polyelectrolytes and neutral polymers (with a weight fraction of the hydrophobic end groups <10 wt%) are directly dissolved in water. The homopolymers, poly[2-(diethylamino)ethyl methacrylate], poly(N-isopropylacrylamide), and poly(ethoxyethylacrylate) are synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization using S'-1-dodecyl-(S')-(α,α'-dimethyl-α″-acetic acid) trithiocarbonate (DDMAT) and its derivatives as chain transfer agents (CTAs). A range of polyelectrolyte homopolymers with different terminal groups are designed and synthesized, which under acidic aqueous solution direct the self-assembly to form well-defined nanostructures. This assembly behavior was also observed for neutral polymers, and it was determined that the structure of the hydrophobic end groups (and thus choice of RAFT CTA) are very important in facilitating this unusual self-assembly behavior of hydrophilic homopolymers. It is proposed that the functionality of commonly used CTAs such as DDMAT, can affect the solution association of the resultant homopolymers and can in fact afford ABA' type polymers, which can undergo self-assembly to form higher-order nanostructures.
Small 06/2011; 7(14):2070-80. · 8.35 Impact Factor
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ABSTRACT: Anisotropic particles, such as patchy, multicompartment and Janus particles, have attracted significant attention in recent years due to their novel morphologies and diverse potential applications. The non-centrosymmetric features of these particles make them a unique class of nano- or micro-colloidal materials. Patchy particles usually have different compositional patches in the corona, whereas multicompartment particles have a multi-phasic anisotropic architecture in the core domain. In contrast, Janus particles, named after the double-faced Roman god, have a strictly biphasic geometry of distinct compositions and properties in the core and/or corona. The term Janus particles, multicompartment particles and patchy particles frequently appears in the literature, however, they are sometimes misused due to their structural similarity. Therefore, in this critical review we classify the key features of these different anisotropic colloidal particles and compare structural properties as well as discuss their preparation and application. This review brings together and highlights the significant advances in the last 2 to 3 years in the fabrication and application of these novel patchy, multicompartment and Janus particles (98 references).
Chemical Society Reviews 03/2011; 40(5):2402-16. · 28.76 Impact Factor
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ABSTRACT: The efficiencies of DNA-templated acyl transfer reactions between a thioester modified oligonucleotide and a series of amine and thiol based nucleophiles are directly compared. The reactivity of the nucleophile, reaction conditions (solvent, buffer, pH) and linker length all play important roles in determining the efficiency of the transfer reaction. Careful optimisation of the system enables the use of DNA-templated synthesis to form stable peptide-like bonds under mild aqueous conditions close to neutral pH.
Organic & Biomolecular Chemistry 03/2011; 9(5):1661-6. · 3.70 Impact Factor
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ABSTRACT: The design and synthesis of a tuneable and reversible morphology switching copolymer system is reported. The kinetics of the transition under a range of conditions has been explored, as has the stabilization of the resultant structures.
Chemical Communications 01/2011; 47(1):355-7. · 6.17 Impact Factor
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Angewandte Chemie International Edition 10/2010; 49(43):7948-51. · 13.45 Impact Factor
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Macromolecular Chemistry and Physics 05/2010; 211(14):1530 - 1537. · 2.36 Impact Factor
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ABSTRACT: A quaternary amine end functionalised diblock copolymer (PtBuA-b-PNIPAM) has been synthesised using RAFT polymerisation and shown to undergo a thermally induced morphology transition from micelles to vesicles, as evidenced by TEM, AFM, SLS and DLS analyses.
Chemical Communications 02/2010; 46(7):1091-3. · 6.17 Impact Factor
