Controlling the Relaxation Dynamics of Polymer Networks by Combining Associative and Dissociative Dynamic Covalent Bonds.

Dynamic polymer networks offer a promising solution to key challenges in polymers such as recyclability, processability, and damage repair. However, the trade-off between combining facile processability, fast self-healing, and high creep resistance remains a major obstacle to implementation. To overcome this, two very distinct dynamic covalent chemistries, Diels-Alder and transesterification, is combined in a single network. The resulting dual dynamic networks offer an unprecedented set of properties and control over the relaxation times. The system decouples the relaxation dynamics of the network from the spatial motifs, and the tuning of the ratio between chemistries enables to control of the relaxation dynamics over six orders of magnitude. Taking advantage of this control, the composition and rheological behavior is optimized to drastically improve the resolution for extrusion-based additive manufacturing of dynamic covalent networks. Additionally, two well-defined and separated stress relaxation peaks are observed at compositions close to 50% of each dynamic chemistry, accentuating the double character of the system's relaxation dynamics. This atypical situation, enables to preparation of self-healing materials with negligible creep, and with shape-memory properties solely leveraging the two distinct relaxation dynamics, instead of the glass transition temperature or the melting point.