Helen Willcock

End group removal and modification of RAFT polymers

This paper describes both well-established routes and recent advances in the end group modification of polymers synthesised by reversible addition–fragmentation chain transfer (RAFT) polymerisation. The lability of the thiocarbonylthio group, which facilitates the RAFT mechanism, allows for ready post-polymerisation functionalisation of RAFT polymers by a number of techniques. In particular, end group thermolysis, radical induced reduction, hetero-Diels–Alder reactions and reaction with nucleophiles are discussed as are the applications and limitations of each method. The versatility of RAFT as a polymerisation tool for the synthesis of polymers with functional end groups for a range of applications is demonstrated.

Exploiting nucleobase-containing materials – from monomers to complex morphologies using RAFT dispersion polymerization

The synthesis of nucleobase-containing polymers was successfully performed by RAFT dispersion polymerization in both chloroform and 1,4-dioxane and self-assembly was induced by the polymerizations. A combination of scattering and microscopy techniques were used to characterize the morphologies. It is found that the morphologies of self-assembled nucleobase-containing polymers are solvent dependent. By varying the DP of the core-forming block, only spherical micelles with internal structures were obtained in chloroform when using only adenine-containing methacrylate or a mixture of adenine-containing methacrylate and thymine-containing methacrylate as monomers. However, higher order structures and morphology transitions were observed in 1,4-dioxane. A sphere-rod-lamella-twisted bilayer transition was observed in this study. Moreover, the kinetics of the dispersion polymerizations were studied in both solvents, suggesting a different formation mechanism in these systems.

One-pot synthesis of responsive sulfobetaine nanoparticles by RAFT polymerisation: the effect of branching on the UCST cloud point

We describe the one-pot synthesis of temperature-responsive branched polymer nanoparticles. Reversible addition–fragmentation chain transfer (RAFT) polymerisation has been utilised to synthesise ultra-high molecular weight sulfobetaine polymers (up to ca. 500 kDa) with good control over molecular weight (Mn) and dispersity (Mw/Mn). The UCST cloud points of these linear polymers were found to increase with both Mn and concentration, and represent one of the few recent descriptions of polymers exhibiting UCST behaviour in aqueous solution. The incorporation of difunctional monomers results in branched polymers which display vastly reduced transition temperatures compared to their linear counterparts. Furthermore, the incorporation of a permanently hydrophilic monomer results in the formation of stable core–shell particles which no longer exhibit a cloud point in water, even at very high concentrations (ca. 50 mg mL−1). The branched polymers are shown to form discrete well-defined nanoparticles in aqueous solution, and these have been characterised by DLS, SLS, TEM and DOSY. Their reversible swelling behaviour in response to temperature is also demonstrated.

Aminomaleimide fluorophores: a simple functional group with bright, solvent dependent emission

Amino-substituted maleimides form a new class of highly emissive compounds, with large Stokes shifts (>100 nm) and high quantum yields (up to ∼60%).

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.

A multifunctional azobenzene-based polymeric adsorbent for effective water remediation

The efficient removal of trace carcinogenic organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs) and ionic dyes, from water is an important technical challenge. We report a highly effective recyclable multifunctional azobenzene (AZ)-based silica-supported polymeric adsorbent which can simultaneously remove both PAHs and anionic dyes from water to below parts per billion (ppb) level based on multiple interactions such as the hydrophobic effect, π–π stacking and electrostatic interactions, thus providing a new strategy for designer water remediation materials.

CO2/pH-responsive particles with built-in fluorescence read-out

A novel fluorescent monomer was synthesized to probe the state of CO2-responsive cross-linked polymeric particles. The fluorescent emission of this aminobromomaleimide-bearing monomer, being sensitive to protic environments, can provide information on the core hydrophilicity of the particles and therefore indicates the swollen state and size of the particles. The particles’ core, synthesized from DEAEMA (N,N-diethylaminoethyl methacrylate), is responsive to CO2 through protonation of the tertiary amines of DEAEMA. The response is reversible and the fluorescence emission can be recovered by simply bubbling nitrogen into the particle solution. Alternate purges of CO2 and N2 into the particles’ solution allow several ON/OFF fluorescence emission cycles and simultaneous particle swelling/shrinking cycles.

Hybrid inorganic–organic composite nanoparticles from crosslinkable polyfluorenes

Polyfluorenes with pendant alkoxysilyl groups have been used to prepare inorganic–organic composite nanoparticles (diameter = 80–220 nm) in which the conjugated polymer is dispersed within a silica matrix. Preparation of these nanoparticles is achieved by simultaneous nanoprecipitation of the conjugated polymer and hydrolysis/crosslinking of the alkoxysilyl groups under basic conditions. The composition of the nanocomposites is controlled by addition of an alkoxysilane monomer, tetramethylorthosilicate. The hybrid nanoparticles form highly stable dispersions in water and buffer (pH 9.2). The size of the nanoparticles can be tuned by varying the amount of the alkoxysilane monomer added during the nanoprecipitation process. Increasing the relative amount of alkoxysilane monomer also increases the proportion of polyfluorene chains that adopt the higher energy β-phase conformation within the resultant nanoparticles. Nanoparticles with the highest silica content were found to have increased photoluminescence quantum yields. This work provides a controllable method for optimisation of the photophysical properties of light-emitting conjugated polymer nanoparticles via a simple aqueous processing technique.