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-S(2), with nearly exclusively disulfide bridges, and BTMA-S(n), with a mixture of oligosulfide bridges, to produce S(2) PE CAN and S(n) PE CAN, respectively. The two PE CANs exhibit identical crosslink densities, but the S(2) 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 S(2) 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 S(2) 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.