Class Of Cross-linked Polymers Research Articles

Stress Relaxation Behavior and Electrically Activated Dynamic Exchange in Carbon Nanotube-Modified Epoxy Vitrimers

Vitrimers are a class of cross-linked polymers with the potential of reprocessing/reshaping, repairing, and recycling. In this paper, carbon nanotubes were either dispersed in the epoxy matrix or used as functional coatings for the development of vitrimer-based polymer systems with short stress relaxation times, relatively high electrical conductivities, and possibility of reshaping using electro-triggering. By selecting the location where the electrical voltage was applied, it was possible to control through electrical resistance heating the activation of the dynamic bonds of the vitrimer matrix, enabling the reconfiguration of the material. It is worth noting that this strategy will pave way for the manufacture of thermosetting polymers with both reconfigurability and functional properties.

Thermal Guanidine Metathesis for Covalent Adaptable Networks.

We demonstrate that a dynamic chemical reaction that we term thermal guanidine metathesis (TGM) can serve as the basis for covalent adaptable network (CAN) materials. CANs are a class of cross-linked polymers that transition from thermoset to thermoplastic-like rheological behavior upon significant activation of reversible exchange reactions within the network and thus can be reprocessed. Small molecule studies indicate the TGM reaction proceeds by a dissociative mechanism, and guanidine-cross-linked network polymers can be reprocessed at elevated temperature. These TGM-based CANs exhibit dynamic behavior, such as dissolution in the presence of monofunctional exchange partners and stress relaxation above Tg. Additionally, differences in the activation energies obtained by small molecule kinetic studies and stress relaxation analysis are consistent with key predictions of the Semenov-Rubinstein model of thermoreversible gelation of highly cross-linked networks.