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.

This manuscript describes the structure–property–morphology relationships of doubly charged 1,4-diazabicyclo[2.2.2]­octane (DABCO) salt-containing ABA triblock ionomers. The triblock copolymers consist a soft poly­(n-butyl acrylate) (PnBA) central block and two external styrenic hard blocks bearing amphiphilic pendant C18-alkyl groups and doubly charged salt units. Surprisingly, the DABCO salt-containing ABA block copolymers preserved the thermomechanical integrity until degradation, which indicated the formation of a reinforcing physical network compared to the corresponding doubly charged random copolymers and singly charged block copolymer analogs. Small-angle X-ray scattering data revealed that the DABCO-based ABA block copolymers self-assembled into highly ordered hierarchical microstructures, in which the soft and hard domain of the block copolymers phase-separated into highly ordered lamellar morphologies. Moreover, a secondary structure that originated from the ordering of the amphiphilic pendant groups formed within the lamellar hard domain. The interesting thermal, thermomechanical, and morphological properties of doubly charged ionic block copolymers open promising avenues for the synthesis of novel thermoplastic elastomers.

Lignin is one of the most abundant biopolymers in nature. Although lignin-derived hard carbon (L-HC) has potential to be used as a sodium-ion battery (SIB) anode but is limited by its poor electrochemical performance. In nature, lignin normally coexists with cellulose and hemicellulose in agricultural biomass, and studies have applied different agricultural biomasses to make SIB anodes; however, the underlying mechanism, especially the functionality of each component, is still unclear. In this study, we aim to combine lignin with cellulose and/or hemicellulose to produce hard carbons with outstanding electrochemical performance and low cost, and more importantly, unveil the underlying mechanisms. We found that the poor electrochemical performance of L-HC was mainly due to its large surface area with high amount of oxygen-containing functional groups and its unique physical structure that inhibit effective Na diffusion. Combining lignin with either cellulose or hemicellulose led to significantly improved electrochemical performance of the resulting hard carbon, with cellulose mainly contributing to the increase of capacity and hemicellulose mainly contributing to the stability of capacity during cycling and at high current density. Based on the comprehensive consideration of both electrochemical performance (half and full cells) and economic perspectives, lignin combined with cellulose showed great potential. Our study shed light on the contributions of each major biomass component on physical and electrochemical properties of resulting hard carbon and designed a unique way to improve L-HC.

This manuscript describes a synthetic strategy and structure–property investigation of unprecedented phosphonium-based zwitterionic homopolymers (polyzwitterions) and random copolymers (zwitterionomers). Free radical polymerization of 4-(diphenylphosphino)­styrene (DPPS) provided neutral polymers containing reactive triarylphosphines. Quantitative postpolymerization alkylation of these pendant functionalities generated a library of polymers containing various concentrations of neutral phosphines, phosphonium ions, and phosphonium sulfobetaine zwitterions. The zwitterionic homo- and copolymers exhibited significantly higher glass transition temperatures (T g) and enhanced mechanical reinforcement in comparison to neutral and phosphonium analogues. These changes in T g and mechanical properties were attributed to nanoscale morphological domains, which formed due to electrostatic interactions between zwitterionic groups, as revealed by X-ray scattering and broadband dielectric spectroscopy (BDS). BDS revealed increased static dielectric constants (>25) for the phosphonium zwitterionomers compared to ionomeric or neutral analogues. These high static dielectric constants for the solvent-free polyzwitterions supported their stronger polarization response in comparison with polymers containing neutral phosphines and phosphonium ions, and these interactions accounted for morphological differences and enhanced mechanical behavior. This work describes a versatile strategy for modulating electrostatic interactions with tunable mechanical properties for an unprecedented family of zwitterionic polymers.

The aspect ratio (AR) of filler particles is one of the most critical determinants for the mechanical properties of particlereinforced polymer composites. However, it has been challenging to solely study the effect of particle AR due to the difficulties of controlling AR without altering the physical and chemical properties of the particle. Herein, we synthesized PCN-222, a zirconium-based porphyrinic metal−organic framework (MOF) with preferential longitudinal growth as a series of particles with ARs increasing from 3.4 to 54. The synthetic MOF conditions allowed for the chemical properties of the particles to remain constant over the series. The particles were employed as reinforcers for poly(methyl methacrylate) (PMMA). MOF−polymer composite films were fabricated using doctor-blading techniques, which facilitated particle dispersion and alignment in the PMMA matrix, as revealed by optical microscopy and wide-angle X-ray diffraction. Mechanical measurements showed that both elastic and dynamic moduli increased with particle AR and particle concentrations but started to decrease as particle loading increased beyond 0.5 wt % (1.12 vol %). The data obtained at low particle loadings were fitted well with the Halpin−Tsai model. In contrast, the percolation model and the Cox model were unable to adequately fit the data, indicating the mechanical reinforcement in our system mainly originated from efficient load transfer between particles and the matrix in the particle orienting direction. Finally, we showed that the thermal stability of composite films increased with the addition of MOF particles because of the high thermal degradation temperature and restricted polymer chain mobility.