Nga Sze Ieong

Polymers with molecular weight dependent LCSTs are essential for cooperative behaviour

The potential to fine-tune the transition temperatures of polymers displaying lower-critical solution temperatures (LCST) by a simple mixing strategy is investigated. Using a panel of four distinct polymer classes (poly[oligo(ethyleneglycol)methacrylate], poly(N-vinylpiperidone), poly(N-vinylcaprolactam) poly(N-isopropylacrylamide)) it was shown that only those with strong molecular weight dependent LCSTs produced a single, cooperative, transition when blended together. Furthermore, the actual transition temperature was linked to the weight average not the number average molecular weight. The only polymer which did not show strong molecular-weight-LCST correlation was poly(oligo(ethyleneglycol)methacrylate), which showed two independent transitions, one for each polymer.

The critical importance of size on thermoresponsive nanoparticle transition temperatures: gold and micelle-based polymer nanoparticles

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.

pH-responsive chiral nanostructures

There is great current interest in the design of robust synthetic polymers for the preparation of novel functional, well-defined, biocompatible and tailorable materials for a range of possible applications. In this work we have used reversible addition fragmentation chain transfer (RAFT) polymerization to prepare chiral and responsive amphiphilic block copolymers (based on polyphenylalanine acrylamide), which can be assembled at different pHs to form well-defined nanostructures. The morphology and size of the derived block polymers were explored using TEM, DLS and SLS measurements, while stability was examined by fluorescence and NMR spectroscopy. The application of these chiral and responsive nanostructures in the resolution of hydrophilic racemic amino acids has also been explored.

Comparison of RAFT‐derived poly(vinylpyrrolidone) verses poly(oligoethyleneglycol methacrylate) for the stabilization of glycosylated gold nanoparticles

Carbohydrates dictate many biological processes including infection by pathogens. Glycosylated polymers and nanomaterials which have increased affinity due to the cluster glycoside effect, are therefore useful tools to probe function, but also as prophylactic therapies or diagnostic tools. Here, the effect of polymer structure on the coating of gold nanoparticles is studied in the context of grafting density, buffer stability and in a lectin binding assay. RAFT polymerization is used to generate poly(oligoethyleneglycol methacrylates) and poly(N-vinyl pyrolidones) with a thiol end-group for subsequent immobilization onto the gold. It is observed that poly(oligoethylene glycol methacrylates), despite being widely used particle coatings, lead to low grafting densities which in turn resulted in lower stability in biological buffers. A depression of the cloud point upon nanoparticle immobilization is also seen, which might compromise performance. In comparison poly(vinyl pyrolidones) resulted in stable particles with higher grafting densities due to the compact size of each monomer unit. The higher grafting density also enabled an increase in the number of carbohydrates which can be installed per nanoparticle at the chain ends, and gave increased binding in a lectin recognition assay. These results will guide the development of new nanoparticle biosensors with enhanced specificity, affinity and stability.

Unlocking the potential of poly(ortho ester)s: A general catalytic approach to the synthesis of surface erodible materials

Abstract Poly(ortho ester)s (POEs) are well‐known for their surface‐eroding properties and hence present unique opportunities for controlled‐release and tissue‐engineering applications. Their development and wide‐spread investigation has, however, been severely limited by challenging synthetic requirements that incorporate unstable intermediates and are therefore highly irreproducible. Herein, the first catalytic method for the synthesis of POEs using air‐ and moisture‐stable vinyl acetal precursors is presented. The synthesis of a range of POE structures is demonstrated, including those that are extremely difficult to achieve by other synthetic methods. Furthermore, application of this chemistry permits efficient installation of functional groups through ortho ester linkages on an aliphatic polycarbonate.