Covalent Adaptable Networks from Ethylene/1-Octene Multi-block Copolymers: Effects of Melt Flow Index and Crystallinity on Thermomechanical Properties and Reprocessability

Olefin block copolymers (OBCs) such as ethylene/1-octene multi-block copolymers are widely produced for numerous industrial applications. The properties of OBCs stem from parameters such as average block length, number of blocks per chain, etc., which lead to complexity associated with establishing structure-property relationships between precursor OBCs and properties of both permanently and dynamically cross-linked OBCs. Here, we synthesized dynamically cross-linked OBCs, or OBC covalent adaptable networks (CANs), by melt-state reactive processing of neat OBCs of varying crystallinity and melt flow index (MFI) with a cross-linker capable of dialkylamino disulfide dynamic chemistry. Increasing crystallinity and decreasing MFI in precursor OBCs lead to higher cross-link densities in OBC CANs. Dynamically cross-linking OBCs into CANs also significantly improves their elevated-temperature creep resistance. Distinct from other CANs capable of dialkylamino disulfide chemistry for which the stress relaxation behaviors are largely governed by the dissociation of dialkylamino disulfide bonds, the stress relaxation behaviors of OBC CANs of higher cross-link density show evident dependence on their network viscoelasticity. Finally, the OBC CANs exhibit full cross-link density and thermomechanical property recovery after reprocessing, whereas permanently cross-linked OBCs cannot be reprocessed.