Reversible addition fragmentation transfer (RAFT) agent functionalized polydimethylsiloxane (PDMS-RAFT) was used as a macro-RAFT agent to polymerize a mixed sandwich cobaltocene containing monomer featuring eta(5)-cyclopentadienyl-cobalt-eta(4)-cyclobutadiene. High molecular weight block copolymers (BCP) consisting of a metallic block and a PDMS block with excellent control over molecular weight and polydispersity were prepared. Solid-state self-assembly of this BCP resulted in hexagonal domains of metallopolymer phase-separated from PDMS. In solution, spherical micelles with a metallic core, stabilized by a PDMS corona were prepared. Pyrolysis of the BCP resulted in magnetic nanoparticles with 30% char yield. The BCP was used as an ink material for microcontact printing (CP) to transfer long-ranged patterns. (c) 2015 Wiley Periodicals, Inc.