Preparation of ellipsoidal hematite/polymer hybrid materials and the corresponding hollow polymer ellipsoids

Ellipsoidal hematite/poly(ethyleneglycol dimethacrylate) core–shell hybrid materials were prepared by distillation precipitation polymerization of ethyleneglycol dimethacrylate (EGDMA) in the presence of 3-(methacryloxy)propyl trimethoxysilane (MPS)-modified hematite (α-Fe2O3) particles as the seeds. The polymerization of EGDMA was performed in neat acetonitrile with 2,2′-azobisisobutyronitrile (AIBN) as initiator to coat MPS-modified hematite seeds through the capture of EGDMA oligomer radicals with the aid of vinyl groups on the surface of the MPS-modified hematite particles in absence of any stabilizer or surfactant. The shell-thickness of the core–shell hybrid particles was controlled by the feed of EGDMA monomer during the polymerization. Other hematite/polymer core–shell hybrid particles, such as hematite/polydivinylbenzene (α-Fe2O3/PDVB) and hematite/poly(divinylbenzene-co- methacrylic acid) (α-Fe2O3/P(DVB-co-MAA)) were also prepared by this procedure. Hematite/poly(N,N′-methylenebisacrylamide-co-methacrylic acid) (α-Fe2O3/P(MBAAm-co-MAA)) were synthesized with unmodified hematite particles as the seeds. Hollow polymer ellipsoids were subsequently developed after the selective removal of the hematite core with hydrochloric acid (HCl) from hematite/polymer core–shell hybrids. The resultant core–shell hybrid particles and hollow polymer ellipsoids were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR) and vibrating sample magnetometer (VSM).