Functional off-stoichiometry thiol-ene-epoxy thermosets featuring temporally controlled curing stages via an UV/UV dual cure process

Abstract

We present a facile two-stage UV/UV activation method for the polymerization of off-stoichiometry thiol-ene-epoxy, OSTE+, networks. We show that the handling and processing of these epoxy-based resins is made easier by introducing a material with a controlled curing technique based on two steps, where the first step offers excellent processing capabilities, and the second step yields a polymer with suitable end-properties. We investigate the sequential thiol-ene and thiol-epoxy reactions during these steps by studying the mechanical properties, functional group conversion, water absorption, hydrolytic stability, and thermal stability in several different thiol-ene-epoxy formulations. Finally, we conclude that the curing stages can be separated for up to 24 h, which is promising for the usefulness of this technique in industrial applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2604-2615 Thiol-ene-epoxy thermosets are polymerized in a two-stage UV/UV curing process. The curing stages are temporally separated up to 24 h using two different photoinitiators activated at different wavelengths. The polymers feature distinctly different mechanical and chemical properties after each curing stage. After the first cure, a soft thiol-ene network is formed with unreacted thiol and epoxy groups being present in the network. After the second cure, a stiff highly crosslinked thiol-ene-epoxy network is formed. Copyright © 2014 Wiley Periodicals, Inc.