@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}
}
@article{WangRazzaqRudolphetal.2018,
  author    = {Wang, Li and Razzaq, Muhammad Yasar and Rudolph, Tobias and Heuchel, Matthias and N{\"o}chel, Ulrich and Mansfeld, Ulrich and Jiang, Yi and Gould, Oliver E. C. and Behl, Marc and Kratz, Karl and Lendlein, Andreas},
  title     = {Reprogrammable, magnetically controlled polymeric nanocomposite actuators},
  series = {Material horizons},
  volume    = {5},
  journal   = {Material horizons},
  number    = {5},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {2051-6347},
  doi       = {10.1039/c8mh00266e},
  pages     = {861 -- 867},
  year      = {2018},
  abstract  = {Soft robots and devices with the advanced capability to perform adaptive motions similar to that of human beings often have stimuli-sensitive polymeric materials as the key actuating component. The external signals triggering the smart polymers' actuations can be transmitted either via a direct physical connection between actuator and controlling unit (tethered) or remotely without a connecting wire. However, the vast majority of such polymeric actuator materials are limited to one specific type of motion as their geometrical information is chemically fixed. Here, we present magnetically driven nanocomposite actuators, which can be reversibly reprogrammed to different actuation geometries by a solely physical procedure. Our approach is based on nanocomposite materials comprising spatially segregated crystallizable actuation and geometry determining units. Upon exposure to a specific magnetic field strength the actuators' geometric memory is erased by the melting of the geometry determining units allowing the implementation of a new actuator shape. The actuation performance of the nanocomposites can be tuned and the technical significance was demonstrated in a multi-cyclic experiment with several hundreds of repetitive free-standing shape shifts without losing performance.},
  language  = {en}
}
@article{WangHeuchelFangetal.2012,
  author    = {Wang, Li and Heuchel, Matthias and Fang, Liang and Kratz, Karl and Lendlein, Andreas},
  title     = {Influence of a polyester coating of magnetic nanoparticles on magnetic heating behavior of shape-memory polymer-based composites},
  series = {Journal of applied biomaterials \& functional materials},
  volume    = {10},
  journal   = {Journal of applied biomaterials \& functional materials},
  number    = {3},
  publisher = {Wichtig},
  address   = {Milano},
  issn      = {2280-8000},
  doi       = {10.5301/JABFM.2012.10293},
  pages     = {203 -- 209},
  year      = {2012},
  abstract  = {Background: Magnetic composites of thermosensitive shape-memory polymers (SMPs) and magnetite nanoparticles (MNPs) allow noncontact actuation of the shape-memory effect in an alternating magnetic field. In this study, we investigated whether the magnetic heating capability of cross-linked poly(epsilon-caprolactone)/MNP composites (cPCLC) could be improved by covalent coating of MNPs with oligo(epsilon-caprolactone) (OCL). Methods: Two different types of cPCLC containing uncoated and OCL-coated MNP with identical magnetite weight content were prepared by thermally induced polymerization of poly(epsilon-caprolactone) diisocyanatoethyl methacrylate. Both cPCLCs exhibited a melting transition at T-m = 48 degrees C, which could be used as switching transition. Results: The dispersion of the embedded nanoparticles within the polymer matrix could be substantially improved, when the OCL-coated MNPs were used, as visualized by scanning electron microscopy. We could further demonstrate that in this way the maximal achievable bulk temperature (T-bulk) obtained within the cPCLC test specimen in magnetic heating experiments at a magnetic field strength of H = 30 kA.m(-1) could be increased from T bulk = 48 degrees C to T bulk = 74 degrees C.},
  language  = {en}
}