Frontal Polymerization of a Thiol‐Ene Free‐Radical and Vinyl Ether Cationic Hybrid System

ABSTRACT

This is the first reported study of a frontally‐polymerizable thiol‐ene free‐radical and vinyl ether cationic hybrid system. Front kinetics, temperature, and mechanical properties of the hybrid polymerization containing trimethylolpropane tris(3‐mercaptopropionate) and tri(ethylene glycol) divinyl ether with the radical initiator 1,1‐bis(tert‐butylperoxy)‐3,3,5‐trimethylcyclohexane (Luperox 231) and cationic superacid generator (octyloxyphenyl)phenyliodonium hexafluoroantimonate (IOC‐8) are studied. The front velocity decreases dramatically when the thiol is added to the vinyl ether and decreases steadily as the thiol concentration increased. It was found that IOC‐8 is necessary to support frontal polymerization, and the concentration of Luperox 231 significantly impacts the front velocity. The addition of a trithiol increases the flexibility of the materials. The pot life of the formulations ranged from hours to minutes, unless a free‐radical inhibitor (MeHQ) was added, which increased the stability to up to 20 days. The polymers degraded over several months when exposed to ambient humidity, which is consistent with hydrolysis of thiol‐acetal linkages formed by the free‐radical addition of the thiol to the vinyl ether.