Controlled Degradation of Cast and 3-D Printed Photocurable Thioester Networks via Thiol-Thioester Exchange

This work examined and quantitatively predicted the degradation of thioester-containing networks facilitated by base-catalyzed thiol-thioester exchange. A statistical model was developed that incorporated polymer structure, thiol-thioester exchange reaction kinetics, and mass gain resulting from dynamic bond exchange, and this model was compared to mass loss studies. Experimental results matched model predictions, showing that degradation times could be controlled from 2.5 to 12 h with optimal conditions by varying the free thiol butyl 3-mercaptopropionate concentration from 0.0 to 4.9 M and the base-catalyst triethylamine molar ratio from 0 to 40 mol %. Furthermore, thioester-based composite materials were formed by stereolithography (SLA) three dimensional (3-D) printing and subsequently degraded, achieving 91% recovery of the composite filler. This work provides insight into thioester-facilitated degradation and its future use in selective material release or encapsulated filler recovery applications.