Dissociative Carbamate Exchange Anneals 3D Printed Acrylates.

Relative to other additive manufacturing modalities, vat photopolymerization (VP) offers designers superior surface finish, feature resolution, and throughput. However, poor interlayer network formation can limit a VP-printed part's tensile strength along the build axis. We demonstrate that the incorporation of carbamate bonds capable of undergoing dissociative exchange reactions provides improved interlayer network formation in VP-printed urethane acrylate polymers.

Reprocessing Postconsumer Polyurethane Foam Using Carbamate Exchange Catalysis and Twin-Screw Extrusion.

Cross-linked polyurethane (PU) is extensively used as thermoset foam; however, methods to directly reprocess PU foam waste derived from commercial sources into similar value materials have not been developed. We demonstrate that introducing dibutyltin dilaurate (DBTDL) into cross-linked PU foams and films enables their reprocessing at elevated temperatures via dynamic carbamate exchange reactions. Both model and commercial cross-linked PU foams were continuously reprocessed using twin-screw extrusion to remove gaseous filler and produce PU filaments or films with elastomeric or rigid thermoset mechanical properties.

Mechanistic Study of Stress Relaxation in Urethane-Containing Polymer Networks.

Cross-linked polymers are used in many commercial products and are traditionally incapable of recycling via melt reprocessing. Recently, tough and reprocessable cross-linked polymers have been realized by incorporating cross-links that undergo associative exchange reactions, such as transesterification, at elevated temperatures. Here we investigate how cross-linked polymers containing urethane linkages relax stress under similar conditions, which enables their reprocessing.

Rapidly Reprocessable Cross-Linked Polyhydroxyurethanes Based on Disulfide Exchange.

Polymer networks that are cross-linked by dynamic covalent bonds often sacrifice the robust mechanical properties of traditional thermosets in exchange for rapid and efficient reprocessability. Polyurethanes are attractive materials for reprocessable cross-linked polymers because of their excellent mechanical properties, widespread use, and ease of synthesis, but their syntheses typically rely on harmful isocyanate precursors. Polyhydroxyurethanes (PHUs), derived from amines and cyclic carbonates, are promising alternatives to traditional polyurethanes.

Mechanically activated, catalyst-free polyhydroxyurethane vitrimers.

Vitrimers are polymer networks whose cross-links undergo associative exchange processes at elevated temperature, usually in the presence of an embedded catalyst. This design feature enables the reshaping of materials with mechanical properties similar to thermoset resins. Here we report a new class of vitrimers consisting of polyhydroxyurethanes (PHUs) derived from six-membered cyclic carbonates and amines.

Cation-Dependent Stabilization of Electrogenerated Naphthalene Diimide Dianions in Porous Polymer Thin Films and Their Application to Electrical Energy Storage.

Porous polymer networks (PPNs) are attractive materials for capacitive energy storage because they offer high surface areas for increased double-layer capacitance, open structures for rapid ion transport, and redox-active moieties that enable faradaic (pseudocapacitive) energy storage. Here we demonstrate a new attractive feature of PPNs--the ability of their reduced forms (radical anions and dianions) to interact with small radii cations through synergistic interactions arising from densely packed redox-active groups, only when prepared as thin films. When naphthalene diimides (NDIs) are incorporated into PPN films, the carbonyl groups of adjacent, electrochemically generated, NDI radical anions and dianions bind strongly to K(+), Li(+), and Mg(2+), shifting the formal potentials of NDI's second reduction by 120 and 460 mV for K(+) and Li(+)-based electrolytes, respectively.