@article{WangBaudisKratzetal.2015,
  author    = {Wang, Li and Baudis, Stefan and Kratz, Karl and Lendlein, Andreas},
  title     = {Characterization of bi-layered magnetic nanoparticles synthesized via two-step surface-initiated ring-opening polymerization},
  series = {Pure and applied chemistry : official journal of the International Union of Pure and Applied Chemistry},
  volume    = {87},
  journal   = {Pure and applied chemistry : official journal of the International Union of Pure and Applied Chemistry},
  number    = {11-12},
  publisher = {De Gruyter},
  address   = {Berlin},
  issn      = {0033-4545},
  doi       = {10.1515/pac-2015-0607},
  pages     = {1085 -- 1097},
  year      = {2015},
  abstract  = {A versatile strategy to integrate multiple functions in a polymer based material is the formation of polymer networks with defined nanostructures. Here, we present synthesis and comprehensive characterization of covalently surface functionalized magnetic nanoparticles (MNPs) comprising a bi-layer oligomeric shell, using Sn(Oct)(2) as catalyst for a two-step functionalization. These hydroxy-terminated precursors for degradable magneto-and thermo-sensitive polymer networks were prepared via two subsequent surfaceinitiated ring-opening polymerizations (ROPs) with omega-pentadecalactone and e-caprolactone. A two-step mass loss obtained in thermogravimetric analysis and two distinct melting transitions around 50 and 85 degrees C observed in differential scanning calorimetry experiments, which are attributed to the melting of OPDL and OCL crystallites, confirmed a successful preparation of the modified MNPs. The oligomeric coating of the nanoparticles could be visualized by transmission electron microscopy. The investigation of degrafted oligomeric coatings by gel permeation chromatography and H-1-NMR spectroscopy showed an increase in number average molecular weight as well as the presence of signals related to both of oligo(omega-pentadecalactone) (OPDL) and oligo(e-caprolactone) (OCL) after the second ROP. A more detailed analysis of the NMR results revealed that only a few.-pentadecalactone repeating units are present in the degrafted oligomeric bi-layers, whereby a considerable degree of transesterification could be observed when OPDL was polymerized in the 2nd ROP step. These findings are supported by a low degree of crystallinity for OPDL in the degrafted oligomeric bi-layers obtained in wide angle X-ray scattering experiments. Based on these findings it can be concluded that Sn(Oct)(2) was suitable as catalyst for the preparation of nanosized bi-layered coated MNP precursors by a two-step ROP.},
  language  = {en}
}