Straightforward and versatile surface modification, functionalization and coating have become a significant topic in material sciences. While physical modification suffers from severe drawbacks, such as insufficient stability, chemical induced grafting processes efficiently modify organic and inorganic materials and surfaces due to covalent linkage. These processes include the “grafting from” method, where polymer chains are directly grown from the surface in terms of a surface-initiated polymerization and the “grafting to” method where a preformed (macro)-molecule is introduced to a preliminary treated surface via a coupling reaction. Both methods require an initiating species that is immobilized at the surface and can be triggered either by heat or light, whereas light induced processes have recently received increasing interest. Therefore, a major challenge is the ongoing search for suitable anchor moieties that provide covalent linkage to the surface and include initiators for surface-initiated polymerization and coupling reactions, respectively. This review containing 205 references provides an overview on photoinitiators which are covalently coupled to different surfaces, and are utilized for subsequent photopolymerizations and photocoupling reactions. An emphasis is placed on the coupling strategies for different surfaces, including oxides, metals, and cellulosic materials, with a focus on surface coupled free radical photoinitiators (type I and type II). Furthermore, the concept of surface initiation mediated by photoiniferters (PIMP) is reviewed. Regarding controlled radical polymerization from surfaces, a large section of the paper reviews surface-tethered co-initiators, ATRP initiators, and RAFT agents. In combination with photoinitiators or photoredox catalysts, these compounds are employed for surface initiated photopolymerizations. Moreover, examples for coupled photoacids and photoacid generators are presented. Another large section of the article reviews photocoupling and photoclick techniques. Here, the focus is set on light sensitive groups, such as organic azides, tetrazoles and diazirines, which have proven useful in biochemistry, composite technology and many other fields.
Easy and residue‐free demolding is an everlasting topic in the plastics processing industry. Typically, facile ejection of the produced parts from the mold is provided by separation agents (silicon sprays, surface coatings). In this work, a perfluoroalkyl‐based organosilane coating is applied to exchangeable substrates of an injection mold. Besides the simple application, the coating can also be restored easily in a procedure based on flame treatment. Coating and recoating are proven by contact angle measurements with water, while the anti‐adhesive effect and the related relief during demolding are evaluated using a special measuring device in an instrumented two‐plate injection mold. The results reveal that the organosilane layer reduces the demolding forces and the resulting static friction coefficient by 50%. Furthermore, multiple recoating significantly improves the durability of the anti‐adhesive coating. Based on these findings, the easily applicable and renewable organosilane coating represents a suitable alternative to conventional release coatings.
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