Tunable phenyl diazo ester containing polymers for C-H insertion crosslinking (CHic)

The interaction between a material and its environment depends on the materials surface chemistry. To tune the surface properties and therefore the interaction, polymeric coatings can be applied. Polymer coatings can either change the surface properties to a desired outcome or shield the material from damage. In order to achieve such resilient properties, the coatings have to be mechanical and chemical stable and the interaction between the coating and the surface must be highly adhesive. The approach taken here was to study the crosslinking behavior of functionalized Rx-phenyl diazo ester based crosslinkers to improve the photochemical and thermal crosslinking reaction and expand the toolbox of crosslinker systems that can be used. The activation leads to a loss of nitrogen, forming a carbene that serves as the reactive intermediate to carry out the C-H insertion based crosslinking (CHic) reaction. This crosslink technique is universally applicable in polymers since the reaction partner is a C-H group, which is abundant in a polymer chain and can simultaneously react to the surface as well, if any C-H bonds are available, forming chemically surface-attached polymer networks. Utilizing this approach, a variety of different donor and acceptor substituted phenyl diazo ester (Rx-PEDAz) crosslinker molecules were synthesized, copolymerized and on their thermal and photochemical crosslinking behavior studied. The higher thermal and photochemical reactivity of the new crosslinkers open the path to gentler activation parameters and therefore more delicate polymers and substrates can be used in applications. Crosslinking below 100 °C, using 365 nm UV- or even sunlight can all be achieved in seconds and the reactivity can be adjusted depending on the needs using the acceptor/donor strength of substituents.