Stress Reduction and Tg Enhancement in Ternary Thiol–Yne–Methacrylate Systems via Addition–Fragmentation Chain Transfer

Abstract

Since polymerization-induced shrinkage stress is detrimental in many applications, addition-fragmentation chain transfer (AFCT) was employed to induce network relaxation and adaptation that mitigate the shrinkage stress. Here, to form high glass transition temperature, high modulus polymers while still minimizing stress, multifunctional methacrylate monomers were incorporated into allyl sulfide-containing thiol-yne resins to provide simultaneously high glass transition temperatures and a facile mechanism for AFCT throughout the network. As a negative control, in an attempt to isolate just the effects of AFCT in the polymerization, a propyl sulfide-based diyne, which has a nearly identical chemical structure though absent any AFCT-capable functional group, was synthesized and implemented in place of the allyl sulfide-based diyne. The glass transition temperature of the ternary systems increased from 39°C to 79°C as the methacrylate content increased while the shrinkage stress of the optimal ternary resin was lower than either the binary thiol-yne resin or the pure methacrylate resin. The stress relaxation benefit associated with AFCT increased with increasing allyl sulfide concentration as shown by a decrease in the relative stress from 0.98 to 0.53. The allyl sulfide-based thiol-yne-methacrylate system exhibits stress relaxation up to 55% and increased T(g) up to 40°C compared with the control, AFCT-incapable thiol-yne. This ternary system has less than 1/3 of the stress of conventional dimethacrylate monomer resins while possessing similarly outstanding mechanical behavior.