Effects of crosslink density and plasticizer on thermorheological properties of dissociative guanidine-based covalent adaptable networks

We report the effects of varying crosslink density and plasticizer loading on the thermorheological properties of guanidine-based covalent adaptable networks (CANs). CANs engage in dynamic bond-exchange reactions above T_g, resulting in shifts between thermoset-like materials and states capable of flow that can be greatly impacted by network characteristics beyond the exchange reaction itself. The synthesis of guanidine-based CANs by combination of carbodiimide-containing oligomers and various ratios of amine-containing crosslinker molecules and phthalate plasticizer was used to create a library of CANs with varying crosslink density and equal concentrations of guanidine functionalities. Additionally, T_g was tuned by modifying plasticizer loading. CANs at three degrees of crosslink density and three degrees of plasticizer loading were characterized by rheometry and dynamic mechanical analysis. The resulting data indicated that absolute relaxation times varied directly with crosslink density but were largely unaffected by plasticizer content or temperature relative to T_g; thus, plasticizer served to decouple T_g from relaxation dynamics. Moreover, little difference in activation energies was observed between each system, contrasting studies of associative CANs.