Programming of shape memory natural rubber for near-discrete shape transitions.

Typical shape memory polymers are hot-programmed and show a shape transition over a broad temperature range of 10 K and more. Cold-programmed shape memory natural rubber (SMNR) recovers more than 80% of its original shape within 1 K. The trigger point can be increased upon aging the stretched SMNR over several weeks without losing the narrow trigger range. This process can be accelerated by treatment of the stretched SMNR with nonaffine solvent vapors. Affine solvent vapors of low concentrations afford higher trigger points than that achieved by aging. This way, even higher cross-linked natural rubber can be cold-programmed.