Synthesis of branched and telechelic functional polymers

Much of our work on novel biomaterials and nano-materials is underpinned by a long standing research effort aimed at developing improved methods for the synthesis of functional polymers. The work in this area has concentrated on the synthesis of well-defined short chain polymers with chemical functionality at the chain ends (telechelic oligomers) and the synthesis of branched polymers (brushes, graft copolymers ad highly branched polymers. Highlights of the work in this area include several unique synthetic methodologies involving cationic and radical polymerizations.

We are pioneering the use of a technique that we have termed ab initio cationic polymerization. This method involves adding species to non-living cationic polymerizations that can react with the propagating chain end to terminate the chain and provide chain and functionality. Typically we use silyl enol ethers as the chain capping agents. However, recently we have shown that silyl ketal enol ethers can also be used and that these agents produce ester groups at the chain ends. By attaching the initiating group of these polymerizations to a surface we have been able to produce functional surfaces with thicknesses of around 1nm as shown in figure 3 and currently we are beginning to explore the use of this method to produce nano-patterned surfaces. In other aspects of this work we have developed the use of the controlled cleavage of high molecular weight polymers, in particular by using ozonolysis of in-chain alkenes, to give telechelic oligomers with carbonyl chain end functionality.

ab-initio_cationic_polymerisation

Above: Schematic showing the ab initio cationic polymerization of vinyl ethers from functional surfaces.

The use of controlled radical polymerization is perhaps the most important development in polymer chemistry in recent times and these developments are enabling the creation of many new nano-scale devices. Our contribution to this area has been to use radical addition fragmentation termination (RAFT) polymerization to produce functional branch polymers. Using this technique we were the first to produce stimulus responsive highly branched polymers and we were the first to prepare highly branched block copolymers by RAFT polymerization.