Catalytic living ring-opening metathesis polymerization with Grubbs’ second- and third-generation catalysts

In a conventional living ring-opening metathesis polymerization (ROMP), an equal number of ruthenium complexes to the number of polymer chains synthesized are required. This can lead to high loadings of ruthenium complexes when aiming for shorter polymers. Here, a reversible chain-transfer agent was used to produce living ROMP polymers from norbornene derivatives using catalytic amounts of Grubbs’ ruthenium complexes. The polymers obtained by this method showed all of the characteristics of a living polymerization (that is, good molecular weight control, narrow molecular weight dispersities and the ability to form block copolymers). Monomers carrying functional moieties such as ferrocene, coumarin or a triisopropylsilyl-protected primary alcohol could also be catalytically polymerized in a living fashion. The method presented follows a degenerative chain-transfer process and is more economical and environmentally friendly compared with previous living ROMP procedures as it utilizes only catalytic amounts of costly and toxic ruthenium complexes. In a ruthenium-catalysed living ring-opening metathesis polymerization, one metal centre is required for each polymer chain, and this requires high catalyst loadings when aiming for short polymer chains. Now, it has been shown that a degenerative reversible chain-transfer process enables the synthesis of ring-opened metathesis polymers with controlled molecular weight, using only catalytic amounts of a ruthenium complex.