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.近数十年来，表面引发光聚合技术愈发受到学界关注，将光引发剂偶联至表面与颗粒已成为材料科学与表面科学领域的重要研究课题。在表面改性与功能化领域，共价偶联的光引发剂结合后续光聚合反应，可赋予表面丰富多样的性能，包括润湿性、刺激响应特性、防污性能、蛋白质结合能力、摩擦调控、药物递送等诸多功能。迄今为止，已有多种I型、II型光引发剂或其他光敏基团被连接至各类不同基底之上。本研究开发了一种简便直接的合成方案，以较高产率制备了一种新型锗基光引发剂：溴代三(2,4,6-三甲基苯甲酰基)锗烷（bromo-tris(2,4,6-trimethylbenzoyl)germane）。通过X射线光电子能谱（X-ray photoelectron spectroscopy, XPS）证实了该光引发剂在硅片与石英板表面的固定化。利用可见光触发的表面引发聚合反应，以丙烯酰胺、全氟癸基丙烯酸酯、荧光素-O-丙烯酸酯等不同功能单体为原料，成功制备了具备亲水/疏水特性及荧光性能等多样性能的表面，且该过程可实现空间分辨调控。通过接触角测量、紫外-可见/荧光光谱、光谱椭偏仪以及XPS对所得聚合物层进行了表征。表面接枝聚合物层的厚度介于10 nm至126 nm之间。