Weder’s early research activities in the 1990s focused on polymers with special optical properties. This involved the development of nonlinear optical polymers and investigations of the structure-property relationships of photoluminescent poly(p-phenylene ethynylene)s. He demonstrated the usefulness of these semiconducting polymers as the active layer in polymer-based light-emitting diodes. His group also exploited the possibility to orient such rod-like molecules to create fluorescent materials that display linearly polarized absorption and emission. Such materials formed the basis of security features that Weder’s group developed, which were used as an anti-counterfeiting element in security paper. His team also discovered a light-polarizing energy transfer effect that can be used to produce highly efficient fluorescent polarizers. Such elements are useful in display and other applications.
Weder’s research focus turned to stimuli-responsive polymers shortly after he moved to CWRU in 2001. In 2002, Weder’s research lab developed a novel method to create polymeric materials that change their fluorescence color upon deformation. Recognizing the potential for practical applications this effect had, Weder established a research program to develop polymers that translate mechanical forces into optical signals, which is still active today, and shortly thereafter, mechanochromic polymers began to attract widespread interest. Most of the mechanochrochromic materials reported by Weder’s group in the following two decades operate on the basis of the same general transduction principle, which involves changing the interactions among optically active motifs in response to mechanical deformation. Recent discoveries include the development of new mechanically responsive motifs or “mechanophores” based on rotaxanes and loop-forming dye pairs.
Controlling the interactions between molecular or nanoscale building blocks through an external stimulus has become one of Weder’s main design tools for the creation of stimuli-responsive polymers. In 2008, in collaboration with his colleague Stuart Rowan, Weder introduced stimuli-responsive mechanically adaptive polymer nanocomposites whose architecture and function was inspired by sea cucumbers. The mechanical properties of these materials, which were made by incorporating nanocellulose crystals as a reinforcing filler into polymer matrices, depend on the interactions among the cellulose nanocrystals (CNCs), and can be regulated by an external stimulus. The approach was initially used to create mechanically morphing implant materials, which soften upon exposure to physiological conditions. This work led to sustained research efforts in Weder’s group on bio-inspired mechanically morphing polymers, the development of protocols for the processing of CNC/polymer nanocomposites, and the development of new cellulose-based nanocomposites. Adaptive polymers that show such mechanical morphing upon exposure to physiological conditions were reported to increase the functionality of cortical implants.
The possibility to heal defects in polymeric materials can increase the reliability and durability of polymer products. In 2011, also in collaboration with Rowan, Weder demonstrated that the UV-light induced temporary disassembly of metallosupramolecular polymers can be used to heal defects in these materials. Expanding on this concept, Weder’s team introduced light healable nanocomposites, and modified the structure to include different binding motifs and architectures, for example glassy hydrogen-bonded supramolecular polymer networks. His group also used this approach to develop adhesives with the capability to bond or debond on demand. Weder’s group sought to push the mechanical properties of supramolecular polymers towards those of conventional thermoplastics. In 2019, his team demonstrated that it is possible to toughen stiff but brittle glassy supramolecular polymer networks by forming blends with a rubbery component. More recent versions of such materials were shown to be healable and to display property combinations that are comparable to some conventional plastics.