Thermomechanical Formation-Structure-Property Relationships in Photopolymerized Copper-Catalyzed Azide-Alkyne (CuAAC) Networks

Bulk photopolymerization of a library of synthesized multifunctional azides and alkynes was carried out toward developing structure property relationships for CuAAC-based polymer networks. Multifunctional azides and alkynes were formulated with a copper catalyst and a photoinitiator, cured, and analyzed for their mechanical properties. Material properties such as the glass transition temperatures (T-g) show a strong dependence on monomer structure with T-g values ranging from 41 to 90 degrees C for the series of CuAAC monomers synthesized in this study. Compared to the triazoles, analogous thioether-based polymer networks exhibit a 45-49 degrees C lower T-g whereas analogous monomers composed of ethers in place of carbamates exhibit a 40 degrees C lower T-g. Here, the formation of the triazole moiety during the polymerization represents a critical component in dictating the material properties of the ultimate polymer network where material properties such as the rubbery modulus, cross-link density, and T-g all exhibit strong dependence on polymerization conversion, monomer composition, and structure postgelation.