TY  - JOUR
A1  - Wang, Li
A1  - Baudis, Stefan
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Characterization of bi-layered magnetic nanoparticles synthesized via two-step surface-initiated ring-opening polymerization
JF  - Pure and applied chemistry : official journal of the International Union of Pure and Applied Chemistry
N2  - 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.
KW  - degradable polyester
KW  - magnetic nanoparticles
KW  - nanoparticle characterization
KW  - NICE-2014
KW  - ring opening polymerization
KW  - surface functionalization
Y1  - 2015
U6  - https://doi.org/10.1515/pac-2015-0607
SN  - 0033-4545
SN  - 1365-3075
VL  - 87
IS  - 11-12
SP  - 1085
EP  - 1097
PB  - De Gruyter
CY  - Berlin
ER  -