Preparation and characterization of two-way shape memory olefin block copolymer/silicone elastomeric blends

Very few olefin block copolymer (OBC)-based shape memory polymers (SMPs) studies were reported in the literature so far. This study investigated the preparation of OBC and silicone elastomeric blends (70/30 and 50/50) using a melt-blending technique to form the first two-way OBC-based SMPs, to our best knowledge. Two phr of ((2,5-bis(tert-butylperoxy)-2,5-dimethylhexane (DHBP) was used to prepare flexible OBC/silicone D2 (D2 representing 2 phr of DHBP) networks. DHBP not only assisted the curing of OBC and silicone but also increased their compatibility in the blends. Despite the very low crystallinity of the OBC elastomer component, 10.4%, corresponding to only similar to 7% based on total resins in the OBC/silicone D2 70/30 blend, the rare two-way shape memory behavior at such a low crystallinity was still envisaged. Regarding two-way shape memory results at various loads, both entropy-driven and crystallization-driven contributions to the overall actuation magnitude (R-act) were at the highest level under 450 kPa, attributing to the highest orientation of molecular networks in the blends. With increasing the applied stress, the R-act of OBC/silicone (70/30) sample increased from 4.1% to 23.7% due to the increased strain-induced crystallization effect confirmed by the XRD (X-ray diffraction) evaluation, while the recovery magnitude (R-act) was maintained at the high level, close to 90%, without the hindrance of high load on the recovery due to high elasticity of silicone rubber. Besides, the crystallization-driven contribution to the overall actuation magnitude was higher for the blends containing the higher amount of crystalline OBC elastomer in the blends. On behalf of silicone with outstanding thermal stability, high elastic behavior, and high hydrophobicity, OBC/silicone SMP blends with versatile properties could meet different applications.