(336f) Understanding Differential Reactivity in Photopolymerizable Systems for Mechanically-Defined Networks

The degree of crosslinking in polymer networks dictates key mechanical properties including stiffness, toughness, and self-assembly. In this talk, I will present recent work in our lab on leveraging differential kinetics of various ternary thiol-ene systems as a function of light exposure for programmed material properties. Using both ¹H-NMR spectrometry and Fourier Transfer Infrared (FTIR) spectroscopy, we measure functional group conversion at various illumination times, probing the kinetics of thiol addition to both internal and terminal ene groups. In our investigation, we elucidate how steric hindrance, isomerization, and monothiol structure act in the radical addition. We find that thiols will add to terminal ene groups preferentially, and trans oriented internal acrylate groups homopolymerize on a similar time scale. We correlate these kinetics to crosslinking density of polymer networks formed using with dithiols in this ternary system and the emergent mechanical properties. Finally, I will discuss our recent work to understand these processes through photorheology using new protocols. This work is anticipated to have applications in additive manufacturing and designer polymer networks.