Stress Reduction and <i>T</i>_g Enhancement in Ternary Thiol–Yne–Methacrylate Systems via Addition–Fragmentation Chain Transfer

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 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 <i>T</i>_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

Origin of the Enhanced Electrocatalysis for Thermally Controlled Nanostructure of Bimetallic Nanoparticles

The thermal annealing process is a common treatment used after the preparation step to enhance the electrocatalytic properties of the oxygen reduction reaction (ORR). The structure of a Pt-based bimetallic nanoparticle, which is significantly affected by the catalytic properties, is reconstructed by thermal energy. We investigated the effect of structural reconstruction induced by thermal annealing on the improvement of the ORR using various physical and electrochemical methods. We found that the structural evolution of PtNi nanoparticles, i.e., the Pt–Ni ordering with the Pt shell and the surface reorientation into the (111) facet, is the source of the enhanced ORR activity as well as electrochemical stability through the thermal annealing. This result confirms the crucial factors for the ORR properties by the thermal annealing process and proposes a way to design advanced electrocatalysts