On the suitability of the α‐relaxation as novel trigger for a shape memory polymer

Abstract

Shape memory polymers typically utilize the glass transition or melting temperature to switch from one shape to another. The goal of this work is to check if the α-relaxation, which is attributed to the migration of chains through lamellar crystals, can be utilized as novel switch for any crosslinkable semi-crystalline thermoplastic. Using cross-linked low-density polyethylene (x-LDPE) as an example, it is shown that the α-relaxation is indeed suitable as switch, when the polymer is crystallized under strain to an intermediate shape. It is demonstrated that post-stretching at a temperature between the α-relaxation and the melting temperature, followed by subsequent cooling to room-temperature switches x-LDPE from the intermediate to a temporary shape and that reheating to this temperature initiates the retraction back to the intermediate shape. Switching between intermediate and temporary shapes is shown to be accompanied by a reversible change in morphology.