Advancing the performance of dual-thiol holographic photopolymers via kinetic selectivity

Dual-thiol holographic photopolymers have been approached from various material schemes; however, optimal performance has yet to be developed, understood and explored. Exploiting the orthogonal nature of the base catalyzed thiol-Michael reaction and the radical mediated thiol-ene photopolymerization, two-stage dual-thiol materials were applied to form holographic photopolymers. Through thiol monomer selection, kinetic selectivity was applied to the thiol-Michael reaction pathway—opening the possibility of wider monomer selection. This approach enables one thiol to be chosen for the low refractive index matrix crosslinking agent, and a different thiol to be chosen for the high refractive index photopolymer. The flexibility of this technique facilitates one-pot synthesis of multiple different thiols while maintaining control and separation of the two thiol-click reactions. Herein, we expanded upon a previous approach using kinetic selectivity by pushing the performance of dual-thiol holographic photopolymers through driving up the refractive index contrast of the thiol monomers while exploring the fidelity of thiol-Michael selectivity. High refractive index thiol monomers previously developed are natural candidates to improve holographic photopolymer performance; however, the molecular composition that affects refractive index also impacts the reaction kinetics. By exploring the performance as indicated by the refractive index contrast while understanding the impact on the kinetic selectivity of such monomers, we present a more comprehensive approach to this dual-thiol holographic photopolymer approach.