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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.

Dynamic covalent networks comprised of tunable thia-Michael bonds result in phase separated networks with tailorable mechanical and adaptive properties.

A series of strong, rebondable polydisulfide nanocomposite adhesive films have been prepared via the oxidation of a thiol-endcapped semicrystalline oligomer with varying amounts of thiol-functionalized cellulose nanocrystals (CNC-SH). The nanocomposites are designed to have two temperature-sensitive components: (1) the melting of the semicrystalline phase at ca. 70 °C and (2) the inherent dynamic behavior of the disulfide bonds at ca. 150 °C. The utility of these adhesives was demonstrated on different bonding substrates (hydrophilic glass slides and metal), and their bonding at both 80 and 150 °C was examined. In all cases, stronger bonding was achieved at temperatures where the disulfide bonds are dynamic. For high surface energy substrates, such as hydrophilic glass or metal, the adhesive shear strength increases with CNC-SH content, with the 30 wt % CNC-SH composites exhibiting adhesive shear strengths of 50 and 23 MPa for hydrophilic glass and metal, respectively. The effects of contact pressure and time of bonding were also investigated. It was found that ca. 20-30 min bonding time was required to reach maximum adhesion, with adhesives containing higher wt % CNCs requiring longer bonding times. Furthermore, it was found that, in general, an increase in contact pressure results in an increase in the shear strength of the adhesive. The rebonding of the adhesives was demonstrated with little-to-no loss in adhesive shear strength. In addition, the 30 wt % nanocomposite adhesive was compared to some common commercially available adhesives and showed significantly stronger shear strengths when bonded to metal.