Design of Experiments Analysis of Crosslink Density and Plasticizer Effects on Rheological Properties of Guanidine-based…

We report the use of a design of experiments (DOE) analysis to study 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 the glass transition, 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, glass transition was tuned by modifying plasticizer loading. CANs at three degrees of crosslink density and two degrees of plasticizer loading were characterized by rheometry and dynamic mechanical analysis. The resulting data were analyzed using linear regression and two-factor analysis of variance (ANOVA), which provided statistically significant evidence that relaxation times and activation energies varied directly with crosslink density but exhibited little change due to plasticizer content.