50th Anniversary Perspective: Solid-State Multistimuli, Multiresponsive Polymeric Materials

Abstract

The field of stimuli-responsive polymers has grown in the past three decades from a few obscure examples to one of the most vibrant domains of modern macromolecular science. Indeed, the research, development, and implementation of tailored materials that can respond in predefined ways to specific stimuli now cut across most areas in which “traditional” polymers play a role, and an ever-growing range of commercial products benefits from this class of materials. This Perspective is devoted to multistimuli, multiresponsive (MSMR) polymers, which are those materials that are able to respond to multiple, different stimuli with multiple, distinct responses. Somewhat akin to living systems, which have evolved to adapt and respond in complex ways to (combinations of) different environmental cues, MSMR polymers can offer a broad range of complex properties and functions. While much of the work on MSMR polymers has been devoted to the investigation of solutions or gels, this Perspective concentrates on solid materials, as this is the state of matter in which the vast majority of polymers are currently employed. In a tutorial fashion, an outline of some of the most common mechanisms used to implement stimuli-responsive behavior in polymer solids is provided. To convey a glimpse of the potential and the challenges of these general design principles, select examples of materials that display multistimuli, single-response as well as single-stimulus multiresponse behavior are presented, before polymeric materials that are truly multistimuli, multiresponsive are discussed, and an outlook on possible directions that future work in the field may take is presented.

Combining Chemistry, Materials Science, Inspiration from Nature, and Serendipity to Develop Stimuli‐Responsive Polymeric Materials

“…The use of electrical or magnetic stimuli are also options but there is a lot less work using these . Recently, researchers have focused on multi‐stimuli, multi‐responsive polymers, which respond to different stimuli with distinct responses . Somewhat like living systems, although in a much less sophisticated way, such materials can offer a broad range of complex properties and (emergent) functions.…”

“…In fact, most materials used by biological systems have a high level of complexity and are able to achieve more than one response. Even though the field of synthetic stimuli‐responsive polymers has transformed from its roots over thirty years ago to a point where it is now possible to program materials that display multiple functions, each of which can be triggered by exposure to a given stimulus, synthetic materials are still far away from the complexity of many of nature's materials . Maybe we have to think differently about materials design.…”

Investigation of the swelling behavior of hydrogels derived from high‐molecular‐weight poly(2‐ethyl‐2‐oxazoline)

“…Smart or responsive materials react to external stimuli by changing at least one of their properties, such as shape, stiffness, or optical properties . One way to obtain stimuli‐responsive materials is chemical cross‐linking of linear polymers with high molecular weight.…”

Glass‐transition temperature governs the thermal decrosslinking behavior of Diels–Alder crosslinked polymethacrylate networks

“…The effect of T g on bond exchange reactions in dynamic‐covalent systems, particularly in healable materials, is a significant consideration . Specifically, the requirement for healable systems to possess a sufficiently low T g in order to render the polymer chains adequately mobile for reactive functionalities to undergo bond exchange is one of the most important aspects of designing self‐healing networks .…”