Cyclic olefin copolymers (COC) are characterised by high transparency, thermal stability and low moisture absorption. A new study now shows how COC can be converted into block copolymers through targeted functionalisation, which can then self-organise into nanostructured materials. The researchers synthesised a COC-block polycaprolactone (COC-b-PCL) via a metallocene-catalysed chain transfer mechanism that enables the introduction of a hydroxyl group at the end of the COC chain. This functionalised COC chain then served as a macroinitiator for the living polymerisation of ε-caprolactone. This resulted in a block copolymer with a well-controlled block length distribution.