Thermal/Blue light Induced Crosslinking of Acrylic Coatings with Diazo Compounds

de Zwart, F.J. Wolzak, L.A.; Laan, P.C.M.; Mathew, S.; Flapper, J.; van den Berg, K.J.; Reek, J.N.H.; de Bruin, B.

Macromolecular Rapid Communications, 2023, 2300380

https://www.doi.org/10.1002/marc.202300380 

The thermal curing of industrial coatings (e.g., car painting and metal coil coatings) is accompanied by a substantial energy consumption due to the intrinsically high temperatures required during the curing process. Therefore, the development of new photochemical curing processes—preferably using visible light—is in high demand. This work describes new diazo-based cross-linkers that can be used to photocure acrylic coatings using blue light. This work demonstrates that the structure of the tethered diazo compounds influences the cross-linking efficiency, finding that side reactions are suppressed upon engineering greater molecular flexibility. Activation of these cross-linkers create free carbenes which are used to insert into O–H bonds, creating strong covalent linkages in the films. The composite films can be cured with blue light and provide excellent material properties, comparable to other acryl coatings. Importantly, this work shows that these diazo compounds can be employed as either thermal or photochemical cross-linkers, exhibiting identical crosslinking performances. The performance of diazo-cross-linked coatings is evaluated to reveal excellent water resistance and demonstrably similar material properties to UV-cured acrylates. These studies pave the way for further usage of diazo-functionalized cross-linkers in the curing of paints and coatings.