Enhanced Tunable Stress-Free Reversible Shape-Memory Effect in a Cross-Linked Cocrystallizable Polymer Blend

Semicrystalline polymers are promising candidates for preparing reversible or two-way shape-memory polymer (SMP) networks. However, there is a lack of facile and effective strategies for improving and tuning the stress-free reversible shape-memory effect (rSME) in semicrystalline networks. This paper reported such a strategy based on melt-blending and cross-linking of cocrystallizable polymers. Specifically, we constructed several blended networks by melt-blending and cross-linking of the cocrystallizable poly(ethylene-propylene-diene monomer) (EPDM) and linear low-density polyethylene (LLDPE). The blended networks show an ultrabroad melting transition ranging from -25 to 120 degrees C and demonstrate significantly enhanced tunable stress-free rSME compared to the EPDM and LLDPE networks. It is revealed that the EPDM can be physically cross-linked by a small amount of LLDPE due to the cocrystallization. The cocrystals can work as dynamic cross-linkages to help fix the orientation and enhance the crystallization-induced elongation of the EPDM chains, which is the main reason for the enhanced tunable stress-free rSME. The melt-blending of cocrystallizable polymers provides a facile way for tailoring both the chain orientation and the mobility of semicrystalline networks, opening up new opportunities for designing and developing high-performance and tunable reversible SMPs.