Preparation of click thiol-ene/thiol-epoxy thermosets by controlled photo/thermal dual curing sequence

Abstract

A new sequential two steps photo and thermal process for the preparation of click thiol-ene/thiol-epoxy thermosets is described. Commercially available diglycidyl ether of bisphenol A (DGEBA), triallylisocyanurate (TAIC) and pentaerythritol tetrakis (3-mercaptopropionate) (PETMP) were combined to produce tailored materials with a 75, 50 and 25% of thiol-ene/thiol-epoxy networks. A photoinitiator was used to trigger the radical thiol-ene polymerization and a latent amine precursor was used to start the base-catalyzed thiol-epoxy click reaction. Neat thiol-ene and thiol-epoxy materials were prepared and taken as the references. The use of a latent amine precursor in adequate proportion and under suitable reaction conditions allowed us to reach a dual system with two well-defined steps, stable intermediate materials and well-controlled structure after the first curing stage and at the end of the curing process. This process overcomes some limitations observed in analogous curing systems reported previously such as the absence of latency for the second curing stage leading to unstable materials in the intermediate stage. Both chemical reactions were studied by FTIR and calorimetry. The latency of the different formulations was studied by DSC and rheometry. The materials prepared were characterized by thermal mechanical analysis and thermogravimetry.