Temperature-memory effect in 3D printed photopolymers with broad glass transition

The recent efforts towards the realization of shape memory polymer-based structures through additive manufacturing techniques (3D-printing) are often referred with the name 4D-printing (the 4th dimension representing the time-dependent shape evolution of the printed element) and aim at providing systems capable of complex shape changes and sequential motions. In this paper the shape memory capabilities of commercial photopolymer systems printed by stereolithography were investigated, allowing to describe the recovery process as a function of temperature. Particular attention was reserved towards the effect of the deformation temperature, which in presence of a broad glass transition region allows to achieve the so called "temperature memory effect", i.e. the possibility to modify the thermal trigger of the shape memory effect through the deformation temperature. The temperature memory features of the printed materials were quantified and a sequential thermally activated deployment was attempted.