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Controlling the molecular structure of amorphous cross-linked polymeric materials is a longstanding challenge. Herein, we disclose a general strategy for precise tuning of loop defects in covalent polymer gel networks. This “loop control” is achieved through a simple semibatch monomer addition protocol that can be applied to a broad range of network-forming reactions. By controlling loop defects, we demonstrate that with the same set of material precursors it is possible to tune and in several cases substantially improve network connectivity and mechanical properties (e.g., ∼600% increase in shear storage modulus). We believe that the concept of loop control via continuous reagent addition could find broad application in the synthesis of academically and industrially important cross-linked polymeric materials, such as resins and gels. [ABSTRACT FROM AUTHOR]

The functionality inherent in lignin-derivable aromatics ( e.g. , polar methoxy groups) can provide a potential opportunity to improve the hydrophilicity of polysulfones (PSfs) without the need for the additional processing steps and harsh reagents/conditions that are typically used in conventional PSf modifications. As determined herein, lignin-derivable PSfs without any post-polymerization modification exhibited higher hydrophilicity than comparable petroleum-based PSfs (commercial/laboratory-synthesized) and also demonstrated similar hydrophilicity to functionalized BPA-PSfs reported in the literature. Importantly, the lignin-derivable PSfs displayed improved thermal properties relative to functionalized BPA-PSfs in the literature, and the thermal properties of these bio-derivable PSfs were close to those of common non-functionalized PSfs. In particular, the glass transition temperature ( T g ) and degradation temperature of 5% weight loss ( T d5% ) of lignin-derivable PSfs ( T g ∼165-170 °C, T d5% ∼400-425 °C) were significantly higher than those of typical functionalized BPA-PSfs in the literature ( T g ∼110-160 °C, T d5% ∼240-260 °C) and close to those of unmodified, commercial/laboratory-synthesized BPA-/bisphenol F-PSfs ( T g ∼180-185 °C, T d5% ∼420-510 °C)., Competing Interests: M. D. G. is co-founder of NuAria, LLC and owns 50% equity interest in the company. The work of this manuscript is not directly related to the activities of the company., (This journal is © The Royal Society of Chemistry.)

Lignin-derivable bisguaiacols/bissyringols are viable alternatives to commercial bisphenols; however, many bisguaiacols/bissyringols (e.g., bisguaiacol F [BGF]) have unsubstituted bridging carbons between the aromatic rings, making them more structurally similar to bisphenol F (BPF) than bisphenol A (BPA) - both of which are suspected endocrine disruptors. Herein, we investigated the estrogenic activity (EA) and developmental toxicity of dimethyl-substituted bridging carbon-based lignin-derivable bisphenols (bisguaiacol A [BGA] and bissyringol A [BSA]). Notably, BSA showed undetectable EA at seven test concentrations (from 10 -12  M to 10 -6  M) in the MCF-7 cell proliferation assay, whereas BPA had detectable EA at five concentrations (from 10 -10  M to 10 -6  M). In silico results indicated that BSA had the lowest binding affinity with estrogen receptors. Moreover, in vivo chicken embryonic assay results revealed that lignin-derivable monomers had minimal developmental toxicity vs. BPA at environmentally relevant test concentrations (8.7-116 μg/kg). Additionally, all lignin-derivable compounds showed significantly lower expression fold changes (from ∼1.81 to ∼4.41) in chicken fetal liver tests for an estrogen-response gene (apolipoprotein II) in comparison to BPA (fold change of ∼11.51), which was indicative of significantly reduced estrogenic response. Altogether, the methoxy substituents on lignin-derivable bisphenols appeared to be a positive factor in reducing the EA of BPA alternatives., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

We report a depolymerization strategy to nearly quantitatively regenerate isocyanates from thermoplastic and thermoset polyurethanes (PUs) and then resynthesize PUs using the recovered isocyanates. To date, chemical/advanced recycling of PUs has focused primarily on the recovery of polyols and diamines under comparatively harsh conditions ( e.g., high pressure and temperature), and the recovery of isocyanates has been difficult. Our approach leverages an organoboron Lewis acid to depolymerize PUs directly to isocyanates under mild conditions ( e.g., ∼80 °C in toluene) without the need for phosgene or other harsh reagents, and we show that both laboratory-synthesized and commercially sourced PUs can be depolymerized. Furthermore, we demonstrate the utility of the recovered isocyanate in the production of second-generation PUs with thermal properties and molecular weights similar to those of the virgin PUs. Overall, this route uniquely provides an opportunity for circularity in PU materials and can add significant value to end-of-life PU products., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Inspired by spider silk's hierarchical diversity, we leveraged peptide motifs with the capability to tune structural arrangement for controlling the mechanical properties of a conventional polymer framework. The addition of nanofiller with hydrogen bonding sites was used as another pathway towards hierarchical tuning via matrix-filler interactions. Specifically, peptide-polyurea hybrids (PPUs) were combined with cellulose nanocrystals (CNCs) to develop mechanically-tunable nanocomposites via tailored matrix-filler interactions (or peptide-cellulose interactions). In this material platform, we explored the effect of these matrix-filler interactions on the secondary structure, hierarchical ordering, and mechanical properties of the peptide hybrid nanocomposites. Interactions between the peptide matrix and CNCs occur in all of the PPU/CNC nanocomposites, preventing α-helical ordering, but promoting inter-molecular hydrogen bonded β-sheet formation. Depending on peptide and CNC content, the Young's modulus varies from 10 to 150 MPa. Unlike conventional cellulose-reinforced polymer nanocomposites, the mechanical properties of these composite materials are dictated by a balance of CNC reinforcement, peptidic ordering, and microphase-separated morphology. This research highlights that leveraging peptide-cellulose interactions is a strategy to create materials with targeted mechanical properties for a specific application using a limited selection of building blocks.

This investigation highlights the potential for electrospun nanofiber mats and self-assembled nanofiber networks to be interfaced synergistically to induce hygromorphic behaviour. Control poly(vinyl alcohol) (PVA) electrospun active layers and 1,3:2,4-di-p-methylbenyliedene sorbitol (MDBS) self-assembled passive layers encapsulated in an ethylene oxide-epichlorohydrin (EO-EPI) copolymer matrix were fabricated to examine the influence of composition on the properties guiding hygromorphism, such as water transport, layer thickness, and layer modulus. Experimentally determined material constants were utilized in conjunction with mathematical modeling to determine ideal layer properties. It was revealed that the active layer with the highest PVA content exhibited the fastest water transport, and the passive layer with the highest MDBS content displayed the slowest water transport. However, the hygromorphic bilayer fabricated utilizing the lowest PVA content and the highest MDBS fraction was predicted to induce the highest change in curvature due to the lower modulus and thickness of the PVA nanofiber active layer. Decreasing the MDBS content reduced the passive layer modulus while increasing water transport, which theoretically reduced the overall bilayer curvature. The hygromorphic bilayer composites fabricated using these ideal control layers exhibited folding bias and response variations dependent upon active layer composition and imposed folding directions. By utilizing the favorable force balances between the active layer with the lower PVA content and the passive layer with the highest MDBS amount in conjunction with folding bias in a non-preferential direction, it was possible to achieve hygromorphic unfolding and refolding with hydration. Through modelling and individual layer examination, a unique platform built on two independent fiber networks has been designed to achieve biomimetic hygromorphism in synthetic bilayer composites.

The effect of confinement on the deformation behavior of poly(ethylene oxide) (PEO) was studied using melt processed coextruded poly(ethylene-co-acrylic acid) (EAA) and PEO multilayer films with varying PEO layer thicknesses from 3600 to 25 nm. The deformation mechanism was found to shift as layer thickness was decreased between 510 and 125 nm, from typical axial alignment of the crystalline fraction, as seen in bulk materials, to nonuniform micronecking mechanisms found in solution-grown single crystals. This change was evaluated via tensile testing, wide-angle X-ray diffraction (WAXD), atomic force microscopy (AFM), and differential scanning calorimetry (DSC). With the commercially relevant method of melt coextrusion, we were able to overcome the limitations to the testing of solution-grown single crystals, and the artifacts that occur from their handling, and bridged the gap in knowledge between thick bulk materials and thin single crystals.

Stimuli-responsive materials are desired for a wide range of applications. Here, we report the design and fabrication of all-organic, stimuli-responsive polymer composites using electrospun nanofibers as the filler. The incorporation of 4 wt % of filler into the polymer matrix increased the tensile storage modulus by 2 orders of magnitude. Upon exposure to water, the filler fibers plasticize and no longer provide mechanical reinforcement. The tensile storage modulus subsequently diminishes 2 orders of magnitude to the value of the neat matrix polymer.

Forced assembly processing provides a unique opportunity to examine the effects of confinement on block copolymers (BCPs) via conventional melt processing techniques. The microlayering process was utilized to produce novel materials with enhanced mechanical properties through selective manipulation of layer thickness. Multilayer films consisting of an elastomeric, symmetric block copolymer confined between rigid polystyrene (PS) layers were produced with layer thicknesses ranging from 100 to 600 nm. Deformation studies of the confined BCP showed an increase in ductility as the layer thickness decreased to 190 nm due to a shift in the mode of deformation from crazing to shear yielding. Postextrusion annealing was performed on the multilayer films to investigate the impact of a highly ordered morphology on the mechanical properties. The annealed multilayer films exhibited increased toughness with decreasing layer thickness and resulted in homogeneous deformation compared to the as-extruded films. Multilayer coextrusion proved to be an advantageous method for producing continuous films with tunable mechanical response., (© 2011 American Chemical Society)