Reprocessability in Engineering Thermosets Achieved Through Frontal Ring-Opening Metathesis Polymerization.

While valued for their durability and exceptional performance, crosslinked thermosets are challenging to recycle and reuse. Here, inherent reprocessability in industrially relevant polyolefin thermosets is unveiled. Unlike prior methods, this approach eliminates the need to introduce exchangeable functionality to regenerate the material, relying instead on preserving the activity of the metathesis catalyst employed in the curing reaction. Frontal ring-opening metathesis polymerization (FROMP) proves critical to preserving this activity. Conditions controlling catalytic viability are explored to successfully reclaim performance across multiple generations of material, thus demonstrating long-term reprocessability. This straightforward and scalable remolding strategy is poised for widespread adoption. Given the anticipated growth in polyolefin thermosets, these findings represent an important conceptual advance in the pursuit of a fully circular lifecycle for thermoset polymers.

Switching Frontal Polymerization Mechanisms: FROMP and FRaP.

Two frontal polymerization (FP) mechanisms, frontal ring-opening metathesis polymerization (FROMP) of dicyclopentadiene and frontal radical polymerization (FRaP) of benzyl acrylate and hexanediol diacrylate, were combined for rapid manufacturing of welded thermoset materials. Leveraging the immiscibility of the two different FP resins, welded thermosets and gradient foams of varying composition were achieved by switching of FP mechanisms. The adhesion strength of the welded thermoset materials differed depending on the originating mechanism. Finally, welded thermoset foams of varying porosity and homogeneity were generated through initiation from the bottom of the two resins.

Photoexcitation of Grubbs' Second-Generation Catalyst Initiates Frontal Ring-Opening Metathesis Polymerization.

In this work, a simple method is reported for control over initiation in frontal ring-opening metathesis polymerization (FROMP). This noncontact approach uses 375 nm light to excite Grubbs' second-generation catalyst in the presence of a phosphite inhibitor. Photoinitiated FROMP of dicylcopentadiene (DCPD) displays a similar cure profile to that of its thermally initiated counterpart, yielding a robust polymer with high glass transition temperature. Furthermore, this system is applied to enhance reaction rates in conventional ring-closing metathesis reactions.

Enzymatically triggered shape memory polymers.

Cytocompatible shape memory polymers activated by thermal or photothermal triggers have been developed and established as powerful "smart material" platforms for both basic and translational research. Shape memory polymers (SMPs) that could be triggered directly by biological activity have not, in contrast, been reported. The goal of this study was to develop an SMP that responds directly to enzymatic activity and can do so under isothermal cell culture conditions. To achieve this goal, we designed an SMP with a shape fixing component, poly(ε-caprolactone) (PCL), that is vulnerable to enzymatic degradation and a shape memory component, Pellethane, that is enzymatically stable - as the shape fixing component undergoes enzymatically-catalyzed degradation, the SMP returns to its original, programmed shape. We quantitatively and qualitatively analyzed material properties, shape memory performance, and cytocompatibility of the enzymatically-catalyzed shape memory response. The results demonstrate enzymatic recovery, as contraction of tensile specimens, using bulk enzymatic degradation experiments and show that shape recovery is achieved by degradation of the PCL shape-fixing phase. The results further showed that both the materials and the process of enzymatic shape recovery are cytocompatible. Thus, the SMP design reported here represents both an enzyme responsive material capable of applying a programmed shape change or direct mechanical force and an SMP that could respond directly to biological activity. STATEMENT OF SIGNIFICANCE: Cytocompatible shape memory polymers activated by thermal or photothermal triggers have become powerful "smart material" platforms for basic and translational research. Shape memory polymers that could be triggered directly by biological activity have not, in contrast, been reported. Here we report an enzymatically triggered shape memory polymer that changes its shape isothermally in response to enzymatic activity. We successfully demonstrate enzymatic recovery using bulk enzymatic degradation experiments and show that shape recovery is achieved by degradation of the shape-fixing phase. We further show that both the materials and the process of enzymatic shape recovery are cytocompatible. This new shape memory polymer design can be anticipated to enable new applications in basic and applied materials science as a stimulus responsive material.

Ternary Polymeric Composites Exhibiting Bulk and Surface Quadruple-Shape Memory Properties.

We report the design and characterization of a multiphase quadruple shape memory composite capable of switching between 4 programmed shapes, three temporary and one permanent. Our approach combined two previously reported fabrication methods by embedding an electrospun mat of PCL in a miscible blend of epoxy monomers and PMMA as a composite matrix. As epoxy polymerization occurred the matrix underwent phase separation between the epoxy and PMMA materials. This created a multiphase composite with PCL fibers and a two-phase matrix composed of phase-separated epoxy and PMMA. The resulting composite demonstrated three separate thermal transitions and amenability to mechanical programming of three separate temporary shapes in addition to one final, equilibrium shape. In addition, quadruple surface shape memory abilities are successfully demonstrated. The versatility of this approach offers a large degree of design flexibility for multi-shape memory materials.