Quadruple Hydrogen Bonding Supramolecular Elastomers for Melt Extrusion Additive Manufacturing

Abstract

This manuscript describes the versatility of highly directional, noncovalent interactions, i.e., quadruple hydrogen bonding (QHB), to afford novel polyurea segmented supramolecular polymers for melt extrusion three-dimensional (3D) printing processes. The molecular design of the polyurea elastomers features (1) flexible polyether segments and relatively weak urea hydrogen-bonding sites in the soft segments to provide elasticity and toughness, and (2) strong ureido-cytosine (UCyt) QHB in the hard segments to impart enhanced mechanical integrity. The resulting polyureas were readily compression-molded into mechanically-robust, transparent, and creasable films. Optimization of polyurea composition offered a rare combination of high tensile strength (95 MPa), tensile elongation (788% strain), and toughness (94 MJ/m3), which are superior to a commercially available Ninjaflex elastomer. The incorporation of QHB facilitated melt processability, where hydrogen bonding dissociation provided low viscosities at printing temperatures. During cooling, directional self-assembly of UCyt QHB facilitated the solidification process and contributed to part fidelity with the formation of a robust physical network. The printed objects displayed high layer fidelity, smooth surfaces, minimal warpage, and complex geometries. The presence of highly directional QHB effectively diminished mechanical anisotropy, and the printed samples exhibited comparable Young’s moduli along (x–y direction, 0°) and perpendicular to (z-direction, 90°) the layer direction. Remarkably, the printed samples exhibited ultimate tensile strains approaching 500% in the z-direction prior to failure, which was indicative of improved interlayer adhesion. Thus, this design paradigm, which is demonstrated for novel polyurea copolymers, suggests the potential of supramolecular polymers with enhanced mechanical performance, melt processability, recyclability, and improved interlayer adhesion for melt extrusion additive manufacturing processes.

Autonomous Self‐Healing Elastomers with Unprecedented Adhesion Force

“…[ 46–48 ] For example, self‐healing polymers based on 2‐ureido‐4[1 H ]‐pyrimidinone (UPy) [ 47 ] exhibited some adhesive property owning to the presence of strong quadruple‐hydrogen‐bonding UPy units. [ 49,50 ] However, their adhesion strength is too weak (<1 N m −1 ) to have practical applications. Notable progress was made by Hayes and co‐workers in 2016 as they synthesized a polyurethane‐based elastomer capable of fully self‐healing at body temperature and achieved strong adhesion to animal skin (peel strength of 1600 N m −1 ).…”

Quadruple Hydrogen Bond-Containing A-AB-A Triblock Copolymers: Probing the Influence of Hydrogen Bonding in the Central Block

“…In contrast to chemically crosslinked thermoset rubbers, thermoplastic elastomers (TPEs) consist of thermoreversible physical crosslinks, which allow for recycling and reprocessing through melt-extrusion and injection-molding [1,2]. Poly(styrene-b-butadieneb-styrene) (SBS) triblock copolymers as well as isoprene analogs and hydrogenated versions collectively serve as prominent TPEs in the automotive industry and common consumer products such as asphalt additives.…”

“…Thus, the SBS TPE exhibits a wide working-temperature window between the two T g s. However, the triblock copolymer flows below 100 • C due to the partially miscible styrene and butadiene blocks, limiting the upper service temperature [4,5]. Alternatively, supramolecular strategies including H-bonding, electrostatic interactions, and pi-pi stacking offer routes to extend the upper service temperature due to the introduction of additional physical crosslinks into the hard domain [2,6,7]. Moreover, these specific noncovalent interactions, which impart enhanced non-covalent bond strengths compared to only van der Waals forces, improved the stiffness of polymers [8,9].…”

Three‐dimensional chemical reactors: in situ materials synthesis to advance vat photopolymerization

“…This concept has been demonstrated in other AM techniques, particular in material extrusion processes, and has been shown to be effective in reducing anisotropy in their fabricated parts. [200][201][202] In VP, the use of supramolecular functionality has largely focused on its biological applications, 203 with less emphasis on its impact on interlayer adhesion strength. However, recent work by Wilts et al has hinted at its utility: hydrogels fabricated via the DLP printing of trimethylammonium ethyl acrylate chloride and N-vinyl pyrrolidone did not exhibit any layering, suggesting that the physical ionic crosslinking in the polymer allowed for blending of the layers during the printing process (Fig.…”