Rapidly Self‐Healable and Melt‐Extrudable Polyethylene Reprocessable Network Enabled with Dialkylamino Disulfide Dynamic Chemistry

Abstract

Catalyst-free, radical-based reactive processing is used to transform low-density polyethylene (LDPE) into polyethylene covalent adaptable networks (PE CANs) using a dialkylamino disulfide crosslinker, BiTEMPS methacrylate (BTMA). Two versions of BTMA are used, BTMA-S₂, with nearly exclusively disulfide bridges, and BTMA-S_n, with a mixture of oligosulfide bridges, to produce S₂ PE CAN and S_n PE CAN, respectively. The two PE CANs exhibit identical crosslink densities, but the S₂ PE CAN manifests faster stress relaxation, with average relaxation times ∼4.5 times shorter than those of S_n PE CAN over a 130 to 160 °C temperature range. The more rapid dynamics of the S₂ PE CAN translate into a shorter compression-molding reprocessing time at 160 °C of only 5 min (vs 30 min for the S_n PE CAN) to achieve full recovery of crosslink density. Both PE CANs are melt-extrudable and exhibit full recovery within experimental uncertainty of crosslink density after extrusion. Both PE CANs are self-healable, with a crack fully repaired and the original tensile properties restored after 30 min for the S₂ PE CAN or 60 min for the S_n PE CAN at a temperature slightly above the LDPE melting point and without the assistance of external forces.