Responsive polymeric nanoreactors

The overall goal of the project is to create and control the properties and local environment of catalysts and reagents by tethering or encapsulating them to new 'smart' nanoscale polymeric scaffolds. These small discrete molecules or nanoparticles (10-150 nanometers in diameter) when constructed, will be functionalised in a 'bottom-up' strategy by the introduction of reactive groups in their shell, core or surface domain, to allow for the specific examination of the effect of surrounding environment on their reactivity. Such a 'bottom up' strategy for the synthesis of these materials will allow for the introduction of the functional groups and specific responsive properties early in the synthesis helping to ensure that the functionality is maintained throughout the process, to afford well-defined functionalised nanomaterials. Investigation of these nanoparticles as nanosized carrier/recovery vehicles that respond to external triggers/stimuli to release or sequester a specific moiety is proposed to enable packaging of reactive functionality, that is incompatible with the surrounding media or other reagents, within the nanoparticle and enable selective and controlled release when required. The nanoparticles are made up from many polymer 'arms', which in turn possess hydrophilic (water liking) and hydrophobic (water repelling) parts; such polymers are called amphiphilic copolymers. Due to the different solvent affinity of the hydrophobic and hydrophilic parts, these polymers arrange themselves into sphere-like structures, called micelles, with a core and shell structure. For example, the structure of a micelle in water (or any incompatible solvent for the core domain) consists of the micelle's outer shell which is made up of hydrophilic polymer segments in direct contact with water and the hydrophobic polymer segments are hidden inside the micelle core, minimising unfavourable interactions with the solvent (and vice versa in organic media). These micelles are inherently unstable to concentration changes but they can be stabilised using covalent bonding or crosslinking chemistries selectively in the shell layer, to afford robust nanoparticles. The degree of crosslinking must be carefully considered to ensure a robust nanoparticle is formed, but this chemistry should not significantly affect the permeability of the shell layer and still allow for the diffusion of small molecules through this layer to the functionality which is located within the core domain. The unique core-shell morphology of these nanoparticles imparts novel properties including the ability to behave as hosts or vessels to carry or sequester cargo and also the ability to embed reactive functionality within the nanoparticle whilst protecting it from the surrounding media. As a result these nanoparticles can be envisaged as 3-dimensional modifiable supports to provide unique environments in which the selective reaction, encapsulation or transformation of small molecules can occur. The chemistry proposed in this Fellowship application will explore these two aspects of these polymeric materials. The first will develop new water soluble and responsive polymeric scaffolds that contain distinct domains in which selective catalysis can occur to allow for the development of greener industrial methodologies, by reducing the amount of costly and environmentally damaging organic solvents required. The mediation of reactions within the specific environments within or on the surface of the nanoparticles is also proposed to lead to control over the composition and nature of products. The second approach will utilise responsive polymers to allow for the triggered release of reagents or catalysts into the surrounding media for applications in controlled sequential reactions. These methodologies are proposed to enable the development of novel 'smart' nanoreactors for catalysis and multi-step organic reactions.