(721f) Mechanically Ductile and Stiff, Triazole-Based Glassy Photopolymer Network

Photopolymerization is an indispensable technique broadly utilized in numerous applications including coatings, adhesives, additive manufacturing, and dental composites. Dominantly, conventional thermosetting photopolymers in the industrial applications are based on acrylate free radical polymerization using multi-functional monomeric systems. While these polymer networks provide rapid in situ photo-curing kinetics with desirable mechanical performance, the nature of chain-growth polymerization often limits the maximum conversion achieved in these polymers and generates heterogeneous network structures that are highly brittle; thereby, frequently causing mechanical failure.

Step-growth polymerizations utilizing “click” chemistries, which are classified as efficient and orthogonal reactions, possess numerous potential advantages. While the nature of “click” chemistries supports orthogonal and selective reactions without forming byproducts, step-growth polymers yield more homogeneous networks with narrow glass transition temperatures in comparison with chain-growth polymers. Moreover, variable backbone functionalities in step-growth polymers as well as high reactive functional group densities are readily achievable. This behavior consequently enables systematic modification of vitrification-induced polymerization kinetics, gel-point conversion, and overall mechanical performance and enables structure-property relationship determination.

Herein, we present a densely crosslinked glassy polymer network formed via photo-initiated CuAAC (copper-catalyzed azide-alkyne cycloaddition) polymerization in bulk that exhibits considerably improved mechanical stability, through both high tensile toughness and strength. For various monomer structures, a universal testing machine (MTS) was utilized to evaluate mechanical properties of CuAAC-based polymer films. The scope of the research is extended to not only the mechanical performance of the CuAAC polymers but also the physical aging behavior and shape memory-recovery properties of the polymer networks. Furthermore, the application in resin-based composites as high-performance materials is studied.