No abstract

Living radical polymerization is often considered as an unsuitable method of surface modification for reactive metals such as iron. Necessary noble metal catalyst systems may react with the surface to be modified, causing deactivation of the catalyst. Here, surface-initiated atom transfer radical polymerization (SI-ATRP) using the typical Cu I-based catalyst was used to synthesize welldefined poly(methyl methacrylate) thin films grafted on iron. Alkoxy-and chloro-silane initiators were anchored to the metal surface via Si-O-Fe bonds in a metal pretreatment step, yielding a thin cross-linked multilayer sol/gel coating. Except for the precursor's leaving group, the resulting 10s of nm thick polymer layers were almost identical. Assessment of the delamination kinetics of the model coatings by scanning Kelvin probe (SKP) showed the average delamination to be ≈40 % lower in the systems with alkoxyprecursor compared to those with chloro-precursor. In addition, the spread of the measured delamination rates decreased to 1/3 in the alkoxy system, despite identical polymers. The higher delamination rate in the case of chloro-precursors was attributed to residual chloride at the interface. Initiator surface coverage differences may also contribute to stability differences. The ATRP-Cu I-catalyst is consequently also suitable for surface modification of non-noble metals after appropriate pretreatment.

Optical whispering gallery mode microresonators (WGM-µRs) are powerful sensitive components with many analytical applications. Here, spherical WGM-µRs have been synthesised in a single-step microwave (MW)-assisted heterophase polymerisation. The microresonators are based on poly(styrene) beads into which the organic lasing dye nile red was incorporated as gain medium in situ during the polymerisation. The particle diameter and diameter distribution of the synthesised particles were tuned in the range of around 200 nm up to 50 µm by adjusting the concentration between stabiliser poly-(N-vinyl pyrrolidone) (PVP) and monomer styrene, and the solvent composition in the dispersion process. Lower water content enabled the synthesis of spherical particles with large size polydispersity, from which WGM-µRs with a variety of diameters were selected. Microspheres with diameters ≳3.5 µm supported WGMs. The WGMs were excited through free space via the fluorescence of the laser dye. Pumping power levels <1 µW were sufficient to excite WGMs. WGM shifts of beads with diameter between ≈5 and 30 µm measured in air and water show a sensitivity up to 54 nm/RIU for the smallest particles. Dye doped WGM-µR in the low µm size range obtained by the