A Brief Overview of Shape Memory Effect in Thermoplastic Polymers

Abstract

Like shape memory alloys (SMAs) and shape memory ceramics, some polymers also exhibit shape memory effect. The polymeric materials demonstrating shape memory effect are commonly referred to as shape memory polymers (SMPs), intelligent or adaptive polymers. These SMPs have the ability to respond to an external stimulus such as heat, magnetism, electricity, light, moisture, pH and some specific chemicals. SMPs possess many advantages over SMAs and shape memory ceramics, i.e., better shape memory effect, lower density, biodegradability, easier processing, better control on recovery behavior, programmability and lower cost. Many different kinds of polymers can exhibit shape memory behavior, and more than twenty types of SMPs have already been reported in the literature. Interestingly, the shape memory behavior in SMPs mainly depends on the glass transition temperature of the polymer. SMPs are attractive materials for research, both for academia and industry, mainly because of their potential usage in, i.e., smart textiles, active aircraft equipment, biomedical instruments, smart electronic apparatuses, space deployable structures, actuators and smart self-healing systems. SMPs can be categorized into thermoset SMPs (chemically crosslinked) and thermoplastic SMPs (physically crosslinked). SMPs can be further subcategorized into linear polymers, branched polymers or a polymer complex. Thermoplastic SMPs are important class of polymeric-based shape memory materials. In this class of SMPs, two phase morphology is the main cause of the thermally induced shape memory effect. One phase causes the physical crosslinking, and the other phase behaves as a molecular switch. Linear thermoplastic SMPs are the most important members of the group of thermoplastic SMPs. The linear thermoplastic SMPs can be further subdivided into the categories of block copolymers and high molecular weight polymers. However, the block copolymers have emerged as relatively more important class of linear thermoplastic SMPs. Polyurethanes and polyether esters are important examples of block copolymers. The current chapter focuses on the development, characterization and applications of thermoplastic SMPs and presents a comprehensive review of the recent advancements made in the area of thermoplastic SMPs.