Controlling Dynamics of Associative Networks through Primary Chain Length

Dynamic networks couple the robust nature of thermosets with the shapeability and recyclability of thermoplastics. Though a wealth of exchange chemistries can be leveraged to fabricate dynamic networks, reversibly cross-linked systems that are comprised primarily of chains with nonexchangeable backbones increase the network complexity and render flow behavior difficult to predict. Here, we report the flow behavior of polymethacrylate-based vitrimers prepared by cross-linking beta-ketoester-containing polymers with multifunctional amines and demonstrate that the molecular weight and dispersity of the primary chains can be tuned to actively tailor the dynamics of the resulting networks. Vitrimers of similar composition and cross-link density made from polymers below and well above the entanglement molecular weight exhibited distinct viscoelastic flow properties with energies of activation ranging from 93 to 264 kJ/mol. Resistance to creep increased dramatically with increasing primary chain length. Finally, blending of prepolymers to skew Mn above/below Me was demonstrated, showing a distinguishable effect of prepolymer breadth and skewness on vitrimer flow. Our results suggest that tailoring the molecular weight and chain-length distribution of the primary chain polymers is a viable strategy to design materials with predictable viscoelastic properties and customizable vitrimer flow behavior.

Automated summary

Dynamic networks combine the durability of thermosets with the adaptability and recyclability of thermoplastics. By tuning the molecular weight and chain-length distribution of the polymers, it is possible to actively tailor the flow behavior and viscoelastic properties of the resulting networks.