A new breed of initiators that aid the formation of biodegradable polymers without the need for solvents has been developed.  UK researchers claim the advantages of these are faster production rates and more control of the polymer properties.  

Matthew Davidson at the University of Bath and colleagues, have produced zirconium and hafnium alkoxide based initiators, which are very active and well controlled, with the potential to transform polylactide production.  Significantly unlike most initiators produced over the last few years they don't only perform well in dilute conditions, and promote stereoselective polymers in solvent-free melt conditions.  Tuning the stereochemistry is useful as it allows the properties of the polymer to be controlled.

Polylactide has applications ranging from packaging, to sutures and implants, and is biodegradable and derived from renewable resources such as corn starch - making it an attractive alternative to petrochemical based polymers.  The need to replace petrochemical products with biorenewable alternatives, and moving away from tin-based initiators to more benign Group 4 metals has been the motivation behind the work carried out by Davidson and co-workers.  

A leading specialist in polymerisation catalysis, Malcolm Chisholm from Ohio State University, Columbus, US, said 'melt polymerisation is of industrial interest and stereoselective polymerisation is even more interesting. Currently no other catalysts do this in the melt'.  

Davidson plans to develop more benign metal based initiators for other biodegradable polymers.  To do this 'a greater mechanistic understanding of the origin of stereocontrol in these systems is needed in order to design catalysts with the desired selectivity', he said.  He suggested collaborations with computational chemists and detailed kinetic studies were needed next.

Michael Brown