In an article published in Nature Chemistry this week, the Kilbinger group at the University of Fribourg reports a new polymerization method to prepare well-defined ring opening metathesis polymers. This technique previously required relatively large amounts of a costly and potentially toxic ruthenium complex, especially if short polymer chains were targeted. The new polymerization method allows the reduction of the amount of this ruthenium complex by a factor of 50 while maintaining good control over the polymerization process.
The Figure illustrates this process. At the top, one can see the previous polymerization process, where one catalyst molecule (in blue) could produce exactly one polymer chain (chain of grey balls). Using the newly reported polymerization method (shown below), one catalyst molecule (in blue), with the help of so-called chain transfer agents (shown in red, these can be up to 50 times as many as there are blue balls) can produce as many polymer chains (chains of grey balls) as there are chain transfer agents (red balls). In other words, instead of carrying an expensive blue ball at the chain end, the new polymers carry cheaper and less toxic red balls at their chain ends.
This makes the entire process more environmentally friendly.