Propagation rate coefficients from
pulsed-laser polymerization

The principle of PLP is relatively simple. The intermittent laser illumination starts and stops polymer chains. We then measure the length of polymer chains that grow between two successive laser pulses and from this we can determine the propagation rate coefficient.

We have successfully applied PLP to a range of homopolymerizations, copolymerizations and ring-opening polymerizations. We are also developing techniques for minimising the errors in PLP by using advanced GPC or MALDI analyses of the molecular weight distributions generated by PLP.

We are taking two approaches to star polymer synthesis. We have adopted the strategy first suggested by Professor Haddleton at Warwick University of using sugar based cores. From these cores we grow acrylic or styrenic polymer chains. The two approaches we have taken are atom transfer radical polymerization (ATRP) using the iron-mediated version developed by Sawamoto:

And reversible-addition -fragmentation-transfer polymerization (RAFT) using a novel synthetic approach:

This method - invented by our collaborators at CSIRO see links can be used to induce living free radical polymerization. We are currently working on the kinetics and mechanism of RAFT. In addition we are utilising RAFT to make tapered glassy copolymers and macromonomers.

Solutions of polymer stars have been shown to produce highly-regular honeycomb structures. In the original work by Francois, stars manufactured by anionic polymerization were used. In our work we are using stars made by living free radical polymerization and we are studying the influence of molecular structure on the controlled formation of the honeycomb morphology.

We are interested in developing polymer systems that bind to specific entities in gastro-intestinal tract. We are currently working on N-acryloxysuccinimide. Using living free radical techniques to control the architecture of the chains. The succinimide group can then be reacted to form a variety of substituted acrylamides that can be used to bind to certain species. For example, an ammonium group on the acrylamide side chain gives an active site that binds to microbial toxins.

Cobalt chain transfer can be used to manufacture a range of oligomers and macromers. In the course of our recent work we discovered a new class of reaction: catalytic chain transfer isomerism. This new reaction enables the production of oligomers with aldehyde end-groups.

We have been developed this work in two areas

i) Self-reinforcing hydrogels. In this work we synthesise hydrophobic macromers and copolymerize them with hydrophilic monomers. The resultant gels swell in water and exhibit high elastic moduli.

ii) High oxygen permeability hydrogels. These are based on copolymers of dimethyl acrylamide and some acrylates with long perfluorinated side-chains. The resultant hydrogels exhibit high equilibrium water contents and high oxygen permeabilities. We assume that the pathway for oxygen transmission is through a phase-separated structure

This project is run in collaboration with Sola Optical within the Commonwealth Cooperative Research Centre (CRC) for Polymers see links. The aim is to produce polymers for spectacle lens applications that have a very fast photochromic response.

This project is run in collaboration with Mimotopes Ltd see links. The aim of the work is to optimise the loading of available functional groups on the solid-phase lanterns developed by Mimotopes. We also aim to produce robust solid phases suitable for a wide range of organic reactions.

This project is a collaboration with Dr Ezio Rizzardo and Dr Richard Evans at the CSIRO see links. The aim is to investigate the kinetics of novel S-containing ring-opening monomers.

This project is in collaboration with BHP Steel Coatings and we aim to produce tough, hard, flexible coatings containing a liquid crystalline phase.

Experimental studies can provide macroscopic rate coefficients for chemical reactions, and in many cases empirical relationships between these rate coefficients and molecular structures can be established. However, it is often not possible to access the microscopic physics which determines these relationships. In those cases theoretical chemistry, in particular chemical dynamics and quantum chemistry, can provide the desired information. Previous studies in collaboration with Professor Radom at the Australian National University have successfully dealt with some outstanding issues in propagation and chain transfer reactions. Current projects are dealing with hydrogen-transfer reactions, which are important for many chain transfer reactions in free-radical polymerization.

Transition state of hydrogen-abstraction reaction between ethyl radical and propene

1. Macromolecular drugs

The growing problem of bacterial resistance to conventional antibiotics and the paucity of effective antiviral agents both point to the need for new approaches to the treatment of microbial infections. For instance, studies have demonstrated that polyvalent compounds, such as polymers bearing pendant N-acetylneuraminic acid groups, bind influenza virus with association constants that are several orders of magnitude higher than those of monomeric N-acetylneuraminic acid derivatives. This phenomenon is referred to as "polyvalent effect".

 

Figure 1. Structure of the influenza A vibrion [Cartoon from J. S. Oxford and R. Lambkin Drug Discovery Today 1998, 3, 448-456] and the N-Acetylneuramic acid molecule (b).

The aim of the project is to synthesise new saccharide containing polymers able to bind key receptors on viruses and other pathogenic microbes' surfaces. The resulting inhibition is expected to be several orders of magnitude higher than those of monomeric anti microbial agents.

2. Hydrogels for tissue engineering and      replacement

We are applying our expertise in living radical polymerisation techniques with the chemoenzymatic synthesis of functionalised monomers to design polymers with controlled architecture and bearing complex functionalities of biological relevance. The aim is to produce highly immune-compatible hydrogels for cartilage replacement, wound dress and cell delivery.

Figure 2. Scheme of two typical tissue engineering approaches. From K. Y. Lee and D. J. Mooney Chemical Reviews 2001, 101, 1869-1879.