Norbornene-functionalized diblock copolymers via ring-opening metathesis polymerization for magnetic nanoparticle stabilization

There are a number of strategies in molecular nanoscience to prepare stabilized magnetic nanocomposites, including the use of polymeric surfactants. Ring-opening metathesis polymerization (ROMP) was used to prepare a series of novel, well-defined diblock copolymers of bicyclo[2.2.1]hept-5-ene 2-carboxylic acid 2-cyanoethyl ester and bicyclo[2.2.1]hept-2-ene, consisting of both anchoring and steric stabilizing blocks. Cyanoester groups were incorporated into the norbornene polymers to chelate and stabilize iron oxide magnetic nanoparticles. These polynorbornene-based copolymers were characterized by GPC, along with ¹H NMR, FTIR, DSC, and TGA. Nanostructured maghemite (γ-Fe₂O₃) magnetic ferrofluids were prepared using diblock copolymers as stabilizers in toluene or cyclohexanone, via thermal decomposition of Fe(CO)₅ and subsequent oxidation of the iron nanoparticles. Transmission electron microscopic images showed a highly crystalline structure of monodispersed γ-Fe₂O₃ nanoparticles, with average particle sizes varying from 5 to 7 nm.