Thermo/chemo-responsive shape memory effect in polymers: a sketch of working mechanisms, fundamentals and optimization

Facile Fabrication of a Shape Memory Polymer by Swelling Cross-Linked Natural Rubber with Stearic Acid

A facile method was developed for fabrication of a robust shape memory polymer by swelling cross-linked natural rubber with stearic acid. Commercial rubber bands were swollen in molten stearic acid at 75 °C (35 wt % stearic acid loading). When cooled the crystallization of the stearic acid formed a percolated network of crystalline platelets. The microscopic crystals and the cross-linked rubber produce a temporary network and a permanent network, respectively. These two networks allow thermal shape memory cycling with deformation and recovery above the melting point of stearic acid and fixation below that point. Under manual, strain-controlled, tensile deformation the shape memory rubber bands exhibited fixity and recovery of 100% ± 10%.

Shape memory polymer nanocomposites for application of multiple-field active disassembly: experiment and simulation

Active disassembly (AD) uses innovative materials that can perform a designed disassembly action by the application of an external field. AD provides improvements over current disassembly processes by limiting machine or manual labor and enabling batch processing for end-of-life products. With improved disassembly operations, more reuse of components and purer recycling streams may be seen. One problem with AD, however, has been with the single-field actuation because of the probability of accidental disassembly. This presentation will discuss the application of shape memory polymer (SMP) nanocomposites in a new AD process. This novel AD process requires multiple-field actuation of the SMP nanocomposite fastener. In the analysis of this AD process, thermal and magnetic field tests were performed on the SMP nanocomposite. From these tests, finite-element analysis was performed to model and simulate the multiple-field AD process. The results of the simulations provide performance variables for the AD process and show a better performance time for the SMP nanocomposite fastener than for a comparable SMP fastener.

Reversible bidirectional shape-memory polymers

Free-standing copolymer network samples with two types of crystallizable domains are capable of a fully reversible bidirectional shape-memory effect. One set of crystallizable domains determines the shape-shifting geometry while the other provides the thermally controlled actuation capability.

Inherently Photohealable and Thermal Shape-Memory Polydisulfide Networks

Structurally dynamic polydisulfide networks that inherently exhibit both shape-memory and healable properties have been synthesized. These materials are semicrystalline, covalently cross-linked network polymers and as such exhibit thermal shape-memory properties. Upon heating above its melting temperature (T_m) films of the material can be deformed by a force. Subsequent cooling and removal of the force result in the material being "fixed" in this strained temporary shape through a combination of crystallinity and covalent cross-links until it is exposed to temperatures above the T_m at which point it recovers to its remembered processed shape. The incorporation of disulfide bonds, which become dynamic/reversible upon exposure to light or elevated temperatures, into these networks results in them being structurally dynamic upon exposure to the appropriate stimulus. Thus, by activating this disulfide exchange, the network reorganizes, and the material can flow and exhibit healable properties. Furthermore, exposure to light also allows the film's permanent "remembered" shape to be reprogrammed. Shape-memory experiments on these films show high degrees of both fixing and recovery (>95%), and photohealing experiments showed that the films were able to recover from a scratch whose depth is approximately half the thickness of the film. Using a combination of the thermal shape-memory behavior followed by photohealing allows wide scratches to also be efficiently healed.

"Grafting to" as a novel and simple approach for triple-shape memory polymers

Maleated-polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (m-SEBS) is a block copolymer with two melting temperatures belonging to soft poly(ethylene-co-butylene) (EB) and hard polystyrene (PS) segments. As EB segments contain anhydride reactive groups, this allows grafting polybutylene succinate (PBS) as another soft segment to m-SEBS backbone to obtain triple-shape memory polymers based on two transition temperatures, i.e., Tm values of EB (at 55-65 °C) and PBS (at 105-115 °C). The present work shows a novel and simple approach of "grafting to" to develop triple-shape memory polymers.