Stress-Induced Melting of Crystals in Natural Rubber: a New Way to Tailor the Transition Temperature of Shape Memory Polymers

Lightly cross-linked natural rubber (NR, cis-1,4-polyisoprene) was found to be an exceptional cold programmable shape memory polymer (SMP) with strain storage of up to 1000%. These networks are stabilized by strain-induced crystals. Here, we explore the influence of mechanical stress applied perpendicular to the elongation direction of the network on the stability of these crystals. We found that the material recovers its original shape at a critical transverse stress. It could be shown that this is due to a disruption of the strain-stabilizing crystals, which represents a completely new trigger for SMPs. The variation of transverse stress allows tuning of the trigger temperature Ttrig(s) in a range of 45 to 0 degrees C, which is the first example of manipulating the transition of a crystal-stabilized SMP after programming.