Novel Shape-Memory Polymer with Two Transition Temperatures

Investigation of Multiple Shape Memory Behaviors, Thermal and Physical Properties of Benzoxazine Blended with Diamino Polysiloxane

In this research, benzoxazine (BA-a) and diamino polysiloxane (PSX750) blends were prepared at 0-50 wt% of BA-a. The interactions between two polymeric components were investigated via a Fourier Transform Infrared Spectrometer (FT-IR). The thermal properties of the blends were also determined with Dynamic Mechanical Analyzer (DMA) and Thermogravimetric Analyzer (TGA). The mechanical properties and shape memory behaviors of the blends were also investigated. The FTIR spectra exhibited the shift of the peak from 1672 to the range of 1634-1637 cm-1, which could be identified as hydrogen bonds between two polymeric domains at the contents from 30 to 50 wt%. The DMA thermograms revealed two glass transition temperatures, which could indicate a partially miscible system. The char yield values were increased, while the decomposition temperatures were decreased with an increasing benzoxazine content. Interestingly, the blends at the contents of 10 and 20 wt% presented dual-shape memory behaviors, whereas triple- or multiple-shape memory behaviors were observed with benzoxazine contents of 30 to 50 wt%. For the high-temperature recovery state, a shape memory ratio of 97.5% with a recovery time of 65 s and a shape fixity ratio of 66.7% was recorded at the content of 50 wt%. For the low-temperature recovery state, a shape recovery ratio of 98.9% was observed at the same content. Moreover, the values of the recovery ratio for four shape-recovery cycles revealed multiple shape memory behaviors with high recovery ratios in the range of 95-98%.

Shape Memory Polymer-Based Endovascular Devices: Design Criteria and Future Perspective

Devices for the endovascular embolization of intracranial aneurysms (ICAs) face limitations related to suboptimal rates of lasting complete occlusion. Incomplete occlusion frequently leads to residual flow within the aneurysm sac, which subsequently causes aneurysm recurrence needing surgical re-operation. An emerging method for improving the rates of complete occlusion both immediately after implant and in the longer run can be the fabrication of patient-specific materials for ICA embolization. Shape memory polymers (SMPs) are materials with great potential for this application, owing to their versatile and tunable shape memory properties that can be tailored to a patient’s aneurysm geometry and flow condition. In this review, we first present the state-of-the-art endovascular devices and their limitations in providing long-term complete occlusion. Then, we present methods for the fabrication of SMPs, the most prominent actuation methods for their shape recovery, and the potential of SMPs as endovascular devices for ICA embolization. Although SMPs are a promising alternative for the patient-specific treatment of ICAs, there are still limitations that need to be addressed for their application as an effective coil-free endovascular therapy.

High-strength, high-toughness, self-healing thermosetting shape memory polyurethane enabled by dual dynamic covalent bonds

Smart materials that integrate multiple functions into one system will broaden the application range of materials, but there are still challenges to obtain a material with excellent shape memory, toughness,...

Shape memory hierarchical AB copolymer networks

Herein, the novel shape memory hierarchical AB copolymer networks (HAB-CPNs) with heterophase structures were presented, which showed perfect shape fixity and recovery, rapid response, outstanding cycle performance, and high recovery force.

A rapidly recoverable shape memory polymer with a topologically well-controlled poly(ethyl methacrylate) structure

Many of the unique properties of a conventionally crosslinked shape memory network are not found at the same time, and this is a large challenge for the development of advanced shape memory functional materials. In this work, a topologically well-controlled network shape memory poly(ethyl methacrylate) (CN-SMPEMA) is designed and fabricated by introducing two tetra-armed functional structures simultaneously as well-defined structure units to promote switch segment and net-point uniform distribution via the combined technology of the unique controllable atom transfer radical polymerization (ATRP) and copper(i)-catalyzed azide-alkyne cycloaddition (CuAAC). Compared with conventionally crosslinked networks, the as-prepared CN-SMPEMA not only exhibits a combination of excellent mechanical properties, shape fixity, shape recovery ratios and outstanding cycling stability, but also displays rapid recoverability. Additionally, a feasible molecular mechanism for the shape memory effect of the CN-SMPEMA system is analyzed and proposed. We anticipate that such a topologically well-defined network shape memory material with multiple excellent properties will broaden the practical application range of acrylate-based shape memory polymer materials.

Triple-Shape Memory Polymers Based on Self-Complementary Hydrogen Bonding

Triple shape memory polymers (TSMPs) are a growing subset of a class of smart materials known as shape memory polymers, which are capable of changing shape and stiffness in response to a stimulus. A TSMP can change shapes twice and can fix two metastable shapes in addition to its permanent shape. In this work, a novel TSMP system comprised of both permanent covalent cross-links and supramolecular hydrogen bonding cross-links has been synthesized via a one-pot method. Triple shape properties arise from the combination of the glass transition of (meth)acrylate copolymers and the dissociation of self-complementary hydrogen bonding moieties, enabling broad and independent control of both glass transition temperature (T(g)) and cross-link density. Specifically, ureidopyrimidone methacrylate and a novel monomer, ureidopyrimidone acrylate, were copolymerized with various alkyl acrylates and bisphenol A ethoxylate diacrylate. Control of T(g) from 0 to 60 °C is demonstrated: concentration of hydrogen bonding moieties is varied from 0 to 40 wt %; concentration of the diacrylate is varied from 0 to 30 wt %. Toughness ranges from 0.06 to 0.14 MPa and is found to peak near 20 wt % of the supramolecular cross-linker. A widely tunable class of amorphous triple-shape memory polymers has been developed and characterized through dynamic and quasi-static thermomechanical testing to gain insights into the dynamics of supramolecular networks.

Multifunctional shape-memory polymers

The thermally-induced shape-memory effect (SME) is the capability of a material to change its shape in a predefined way in response to heat. In shape-memory polymers (SMP) this shape change is the entropy-driven recovery of a mechanical deformation, which was obtained before by application of external stress and was temporarily fixed by formation of physical crosslinks. The high technological significance of SMP becomes apparent in many established products (e.g., packaging materials, assembling devices, textiles, and membranes) and the broad SMP development activities in the field of biomedical as well as aerospace applications (e.g., medical devices or morphing structures for aerospace vehicles). Inspired by the complex and diverse requirements of these applications fundamental research is aiming at multifunctional SMP, in which SME is combined with additional functions and is proceeding rapidly. In this review different concepts for the creation of multifunctionality are derived from the various polymer network architectures of thermally-induced SMP. Multimaterial systems, such as nanocomposites, are described as well as one-component polymer systems, in which independent functions are integrated. Future challenges will be to transfer the concept of multifunctionality to other emerging shape-memory technologies like light-sensitive SMP, reversible shape changing effects or triple-shape polymers.

Fabrication and Analysis of Porous Shape Memory Polymer and Nanocomposites

The porous structure and shape memory effect (SME) were studied for a porous shape memory polymer (SMP) with varying densities, two different thicknesses and the addition of varying weight percentages of organoclay. In order to alter the density of the SMP, a batch processing technique was utilized in which the saturation pressure and foaming time were varied and saturation time and foaming temperature were kept constant. The change in density as the effect of reducing the thickness of the SMP on the time response of the SME was investigated. In addition, the effects of the change in density, change in thickness or the addition of organoclay on the recovery force of the SMP were elucidated. With the objective of designing an SMP to be used as an actuator, response time, recovery force and weight savings are critical parameters.

Polymeric triple-shape materials

Shape-memory polymers represent a promising class of materials that can move from one shape to another in response to a stimulus such as heat. Thus far, these systems are dual-shape materials. Here, we report a triple-shape polymer able to change from a first shape (A) to a second shape (B) and from there to a third shape (C). Shapes B and C are recalled by subsequent temperature increases. Whereas shapes A and B are fixed by physical cross-links, shape C is defined by covalent cross-links established during network formation. The triple-shape effect is a general concept that requires the application of a two-step programming process to suitable polymers and can be realized for various polymer networks whose molecular structure allows formation of at least two separated domains providing pronounced physical cross-links. These domains can act as the switches, which are used in the two-step programming process for temporarily fixing shapes A and B. It is demonstrated that different combinations of shapes A and B for a polymer network in a given shape C can be obtained by adjusting specific parameters of the programming process. Dual-shape materials have already found various applications. However, as later discussed and illustrated by two examples, the ability to induce two shape changes that are not limited to be unidirectional rather than one could potentially offer unique opportunities, such as in medical devices or fasteners.