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

Abstract

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 meltblending 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~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 rec ) 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.

Novel covalent adaptable networks (CANs) of ethylene/1-octene copolymers (EOCs) made by free-radical processing: comparison of structure–property relationships of EOC CANs with EOC thermosets

“…14,15 These strong, physical cross-links provide EOCs with elasticity and strength, and EOCs are desirable as low-cost impact modifiers and tougheners in thermoplastic elastomers, foams, and shape memory polymers for applications like footwear, cushioning, and catheters. [16][17][18][19][20][21][22][23] EOCs are common components in blends with other polymers such as polypropylene (PP), [24][25][26][27][28] ethylene propylene diene monomer (EPDM) rubber, [29][30][31][32] ethylene-vinyl acetate copolymer (EVA), [33][34][35] and polydimethylsiloxane (PDMS). 36,37 Like PE, EOCs and their blends may be vulcanized or covalently crosslinked using radical initiators such as peroxides to enhance properties like elasticity and temperature resistance.…”

Shape memory elastomers: A review of synthesis, design, advanced manufacturing, and emerging applications

“…This partially crosslinked structure typically allows elastomers to behave as amorphous polymers or thermosets 4 . However, elastomers can also be copolymerized or physically mixed to perform in similar fashion to thermoplastics, which suit some applications as they are easy to use in manufacturing, for example, injection or compression molding 5,6 . Currently, these materials are exploited in a wide range of applications such as seals and hoses in the oil and gas industry, 7,8 automotive, agricultural, and medical applications, 9–11 soft robotics, 12,13 and wearable devices 14 .…”

“…4 However, elastomers can also be copolymerized or physically mixed to perform in similar fashion to thermoplastics, which suit some applications as they are easy to use in manufacturing, for example, injection or compression molding. 5,6 Currently, these materials are exploited in a wide range of applications such as seals and hoses in the oil and gas industry, 7,8 automotive, agricultural, and medical applications, [9][10][11] soft robotics, 12,13 and wearable devices. 14 Moreover, elastomers have become essential smart-functional materials, exhibiting shape memory or self-healing effects due to their intrinsically flexible molecular structure.…”

Stress-Free Two-Way Shape Memory Effect of Poly(ethylene glycol)/Poly(ε-caprolactone) Semicrystalline Networks

“…10−14 Furthermore, the influence of material architecture on this effect was studied, for example, using various macromolecular architectures (e.g., linear, threearm, and four-arm branched macromonomers) 15 or by varying the cross-link density while keeping the degree of crystallinity almost constant 16 and by cross-linking melt-blended systems. 17,18 Recently, the possibility of achieving reversible shape changes upon cooling−heating cycles without the need of an external load, also referred to as "reversible" or "stress-free twoway" SME, was demonstrated for specific classes of SMPs. In such SMPs, the effect is achieved by means of two domains in the material architecture: (i) an actuation domain and (ii) a structural domain.…”

“…Starting from the first evidence of the two-way SME reported for a cross-linked poly­(cyclo octene) by Chung et al in 2008, for a poly­(ε-caprolactone) (PCL)-based shape memory polyurethane by Hong et al in 2010, and in the same year, for a multiphase polymeric network containing polypentadecalactone and PCL by Zotzmann et al, several interesting works were carried out to elucidate the physics behind, derive structure–property correlations, and optimize the effect. In fact, various thermodynamic and/or thermomechanical descriptions and modeling of the effect were developed ,, together with the synthesis of novel materials for tuning such an effect. − Furthermore, the influence of material architecture on this effect was studied, for example, using various macromolecular architectures (e.g., linear, three-arm, and four-arm branched macromonomers) or by varying the cross-link density while keeping the degree of crystallinity almost constant and by cross-linking melt-blended systems. , …”