The Synthesis of Magnetic Core‐Shell Nanoparticles by Surface‐Initiated Ring‐Opening Polymerization of ε ‐Caprolactone

Summary: The synthesis of core‐shell particles with a poly( ε ‐caprolactone) (PCL) shell and magnetite (Fe 3 O 4 ) contents of between 10 wt.‐% and 41 wt.‐% proceeds by surface‐initiated ring‐opening polymerization of ε ‐caprolactone to give surface‐immobilized oligomers with $\overline M _{\rm n}$ between 1 400 g · mol −1 and 11 500 g · mol −1 . The particles are dispersable in good solvents for the PCL shell. Magnetization experiments on the resulting superparamagnetic ferrofluids give a core‐size distribution with an average diameter, d v , of about 9.7 nm.TEM image of Fe 3 O 4 /PCL core‐shell particles cast from CHCl 3 dispersion.