Surface-Initiated Polymerizations Mediated by Novel Germanium-Based Photoinitiators

Since surface-initiated
photopolymerization techniques have gained
increasing interest within the last decades, the coupling of photoinitiators
to surfaces and particles has become an important research topic in
material and surface sciences. In terms of surface modification and
functionalization, covalently coupled photoinitiators and subsequent
photopolymerizations are employed to provide a huge variety of surface
properties, such as wettability, stimulus responsive features, antifouling
behavior, protein binding, friction control, drug delivery, and many
more. For this purpose, numerous type I and type II photoinitiators
or other photosensitive moieties have been attached to different substrates
so far. In our studies, a convenient and straightforward synthetic
protocol to prepare a novel germanium-based photoinitiator (bromo-tris(2,4,6-trimethylbenzoyl)germane)
in good yields was developed. The immobilization of this photoinitiator
at the surface of silicon wafers and quartz plates was evidenced by
X-ray photoelectron spectroscopy (XPS). Employing visible-light-triggered
surface-initiated polymerization of different functional monomers,
including acrylamide, perfluorodecyl acrylate, and fluorescein-o-acrylate, surfaces with various features such as hydrophilic/hydrophobic
and fluorescent properties were prepared. This was also achieved in
a spatially resolved manner. The polymer layers were characterized
by contact angle measurements, UV–vis/fluorescence spectroscopy,
spectroscopic ellipsometry, and XPS. The thicknesses of the surface
grafted polymer layers ranged between 10 and 126 nm.