15th October 2019
Marco Sangermano will be present at the VII International Baekeland Symposium held in Tarragona, Spain.
UV-activated frontal polymerization of epoxy composites
Cationic photopolymerization is an interesting UV-induced process since the mechanism is characterized by important advantages such as the absence of oxygen inhibition, low shrinkage upon curing, and good versatility of the crosslinked materials. While the main applications are in the field of coating and the electronic industry, we have recently investigated the use of cationic UV-induced polymerization for the fabrication of polymeric composites. The main limitation of UV-induced crosslinking reactions is related to the hindering of UV-light penetration towards thickness of the formulations, which limits this polymerization technique in the preparation of thick composite materials. This limitation has been overcome by the introduction of a Radical Induced Cationic Frontal Polymerization (RICFP) process. The suggested mechanism put together the so-called Radical Induced Cationic Polymerization (RICP) with Frontal Polymerization (FP). Frontal Polymerization (FP) can be activated by the dissociation of a radical thermal initiator promoted by the heat released by the surface UV-activated cationic ring-opening polymerization. Subsequently, the carbon-centered radical can be oxidized by the diaryliodonium salts forming a reactive carbocation which is able to start the cationic ring-opening polymerization. UV-cured bulk epoxy composites were successfully produced by Radical Induced Cationic Frontal Polymerization (RICFP). The propagation of the reaction is assured by the heat front propagation, in a frontal way. The crosslinked composite obtained by RICFP showed even slightly better properties by comparison with the same composite thermally cured. The important advantage of this crosslinking method is related to the very fast polymerization process compared with thermal curing, which allows getting high productivity maintaining the good thermo-mechanical properties of the epoxy composites.