Nanocomposites consisting of a polymer matrix and metallic nanoparticles can merge the functional, structural, and mechanical properties of the two components and are useful for applications that range from catalysis to soft electronics. Gaining spatial control over the nanoparticle incorporation is useful, for example to confine catalytic sites or create electrically conducting pathways. Here, we show that this is possible by the controlled disassembly of a metal-losupramolecular polymer containing zerovalent platinum complexes to form nanoparticles in situ. To achieve this, a telechelic poly(ethylene-co-butylene). was end-functionalized with diphenylacetylene ligands and chain -extended through the formation of bis(eta 2-alkyne)Pt-0 complexes. These complexes are stable at ambient conditions, but they can be dissociated upon heating or exposure to ultraviolet light, which allows producing Pt nanoparticles when and where needed and without auxiliary reagents or formation of byproducts. This approach was exploited to create objects with well-defined catalytically active areas.