Evaluation and control of thiol–ene/thiol–epoxy hybrid networks

The development of thiol–ene/thiol–epoxy hybrid networks offers the advantage of tailorable polymerization kinetics while producing a highly crosslinked, high Tg polymer that has significantly reduced shrinkage and stress. Stoichiometric mixtures of pentaerythritol tetra(3-mercaptopropionate) (PETMP)/triallyl-1,3,5-triazine-2,4,6-trione (TATATO) (thiol–ene, mixture 1) and PETMP/bisphenol a diglycidyl ether (BADGE) (thiol–epoxy, mixture 2) were prepared and hybrid mixtures of 75/25, 50/50, 25/75, and 10/90 w/w of mixtures 1 and 2 were polymerized using a combination of both radical and anionic initiation. The light exposure timing and the relative initiation conditions of the two types were used to control the order and relative rates of the radical and anionic polymerizations. The 50/50 w/w thiol–ene/thiol–epoxy hybrid material exhibited a final stress of only 0.2 MPa, which is 90% lower than the stress developed in a control dimethacrylate resin. Kinetic analysis indicates that composition affects network development in thiol–ene/thiol–epoxy hybrid networks and produces materials with robust mechanical properties.