Surface-Immobilized Photoinitiators for Light Induced Polymerization and Coupling Reactions

Abstract

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.

A Fusion of Molecular Imprinting Technology and Siloxane Chemistry: A Way to Advanced Hybrid Nanomaterials

“…This approach was previously extended by Sulitzky and co-workers [ 132 ] for the application of 3-(glycidoxypropyl)trimethoxysilane to a functional silica-based surface followed by the cleavage of the epoxy ring. Recently, new siloxane-derived initiators for surface tethering were synthesized, opening the way for applications in the fabrication of imprinted materials [ 133 ].…”

A practical perspective for chromatic orthogonality for implementing in photolithography

“…Current soft-matter materials research and polymer chemistry may chemically support numerous photoactive materials. Photoresists, medicinal supplies, and surface coatings are some materials (reaction mixtures that solidify under the influence of light) 9 . In the past, these photoresists were usually cured with a specific hue of light (or a limited spectrum of colors given by an LED or, in certain situations, with extremely broad emitting light sources), producing a particular material feature 10 .…”

Surface-Initiated Polymerizations Mediated by Novel Germanium-Based Photoinitiators

“…Successful surface modification can be done in various ways, reaching from etching with highly reactive species, e.g., ozone or oxygen plasma, over silanization and vapor deposition methods over (spatially resolved) polymer coatings for high end applications. Overviews of different surface modification techniques applicable for various materials and even enzymes are given in refs − . Among all these surface modification methods, coatings based on polymers are used in different applications and industries, as they provide a huge number of diverse functionalities for the underlying substrates …”

“…This is based on the formation of highly reactive species such as radicals or ions derived from surface tethered initiators upon heat exposure or irradiation. , Therefore, much progress has been made to covalently couple (photo)­initiating species to different surfaces. An overview of these reactions, including numerous initiating species and coupling strategies, is given in one of our previous contributions …”

“…The high reaction rate, low process cost, and energy efficiency make light-triggered polymerization processes also desirable for industrial applications. However, first and foremost, the possibility to spatially and temporally control the polymerization simply by switching on and off the light is the most outstanding feature of this method. ,, …”