Dual‐Cure Coatings: Spiroorthoesters as Volume‐Controlling Additives in Thiol–Ene Reactions

摘要

Abstract Most thiol–ene systems exhibit shrinkage during cross‐linking, potentially resulting in micro‐cracks and delamination. Oligocyclic monomers like spiroorthoesters (SOEs), on the contrary, show expansion during the ring‐opening polymerization. In this communication, a photocurable thiol–ene system composed of a trifunctional thiol, a bisfunctional allyl‐bisphenol A compound, and an SOE compound bearing one olefin function shows expansion in the range from ?3.07 to +1.70 vol% if the SOE content is increased from 0–30?wt%. Network formation can be accomplished under visible light if a radical as well as a cationic photoinitiator (dual‐cure mechanism) and a sensitizer are used. The elasticity of the cured resin increases upon the addition of the SOE; correspondingly, the glass‐transition temperature shows a (minor) decrease from 16 to 3?°C. A tailor‐made combination of the allyl‐bisphenol A compound (90 wt%) and the SOE (10 wt%) yields networks that are volume‐neutral during curing.