Stereocontrolled Polymerisation: New Frontiers in Synthesis and Supramolecular Self Assembly

Nature has evolved the ability to create large and complex molecules in which the precise control over both the sequence and spatial arrangement of the atoms is critical to their performance. The 3-dimensional control over the arrangement of bonds is as important to the function and behaviour of molecules as any other factor and is critical to the structure-function relationships that occur within biological systems. While the effects of stereochemistry on functionality are probably best known for small molecule drugs such as thalidomide (one enantiomer is effective against morning sickness, the other is teratogenic) or naproxen (one enantiomer is used to treat arthritis pain, the other causes liver poisoning and has no analgesic effect), it is also clearly represented in biopolymers where stereochemistry has pronounced effects on structure and hence function. For example, DNA, which is at the heart of all biological systems, requires the chirality of the deoxyribose sugar in its backbone to ensure that the double helical structure can form by supramolecular interaction between the complementary nucleobase residues that are attached to them. Furthermore, the simple stereochemical difference between natural rubber and gutta-percha (the cis- and trans-isomers of high molecular weight polyisoprene respectively) results in remarkable differences in their mechanical properties, with gutta-percha being a harder, more brittle and less elastic material than its isomer.

The distinct influence of the stereochemistry in biopolymers on their structure and hence performance makes it reasonable to expect such aspects of synthetic materials to be equally important. Yet this area has received little study, partially a consequence of the challenges of creating large macromolecules with well-defined sequence and stereochemistry at each repeat unit. Clearly, creating materials with controlled stereochemistry in particular has the potential to result in novel materials with complex behaviour and function. Being able to achieve and understand these phenomena will unlock a new paramter in materials design that will enable us to make better materials for a range of applications that will address complex societal issues in the area of sustainability through materials resourcing and more energy/resource efficient materials synthesis - as well as in the biomedical field by developing new therapies and medical devices.

In STEREOPOL, we are inspired by nature to design polymers with exquisite structural control in which the behaviour and properties of the resultant materials will be dependent on their stereochemistry. The objectives are to better control stereochemistry in polymers and to understand it's influence on materials behaviour and properties so that we can use stereochemistry to control polymeric materials properties.

The program has progressed well and several significant steps have been taken towards achieving the goals of the grant. Good progress has been made towards the development and application of new catalytic methods for the generation of functional stereocontrolled polymer materials. This work has focussed on the development of new organic catalysts for stereosepcific polymerisation as well as new monomers that have,to date, not been subjected to stereocontrolled polymerisation. In these ways, new and better materials can be accessed. Beyond these discoveries, much fundamental understanding of crystallisation-driven self-assembly of stereoregular polymers has been achieved. We no can insert functional groups into materials without disturbing crystalinity and also can control the assembly of stereoregular polymers to control particle dimensions and shape. These studies have delivered new higher-order assemblies that will be able to deliver materials in which stereochemistry controls their function. Finally, we have begun to show the effects of stereochemistry on materials properties in elastomers using renewably-sourced materials.

Significant progress beyond the state of the art has been made in both the new polymerisation systems that are being studied (catalysts and monomers) as well as in the understanding of crystallisation-driven self assembly to underpin the stereocontrolled morphology switching. The role of stereochemistry in materials assembly and ordering has been extensively advanced beyond the state of the art and is now delivering new materials with several potential applications.

Periodic Reporting for period 4 - STEREOPOL (Stereocontrolled Polymerisation: New Frontiers in Synthesis and Supramolecular Self Assembly)

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