ACS Macro Letters最新文献

Positional isomerism is a key determinant of mechanical performance in polymer networks, yet its underlying molecular mechanisms remain insufficiently understood. In this work, we employ a multiscale simulation approach─integrating density functional theory with a stochastic coarse-grained reaction model─to investigate how meta- and para-substituted diamine curing agents influence the curing kinetics, network architecture, and mechanical properties of epoxy resins. Simulations reveal that the meta-substituted system exhibits higher ultimate strength and fracture toughness than its para-substituted counterpart, consistent with experimental observations. Mechanistic analysis shows that the enhanced performance of the meta-system stems from strain-induced conformational adaptation within loop structures, facilitated by progressive bond-angle relaxation. This dynamic response promotes energy dissipation and effectively suppresses void growth during deformation. In contrast, the para-system undergoes accelerated failure due to its restricted structural flexibility. Our findings highlight positional isomerism as a powerful molecular design strategy for achieving simultaneous improvements in strength and toughness in epoxy thermosets, providing a foundation for rational material design beyond empirical approaches.

Advancing the development of high-performance solid-state electrolytes is critical for realizing next-generation lithium metal batteries. Among promising candidates, polymer–succinonitrile composites have emerged as effective polymer plastic crystal electrolytes, demonstrating enhanced electrochemical performance. However, further improvements are needed to meet practical application requirements. In this study, we report a novel strategy for synthesizing electrochemically stable branched polyacrylonitrile through controlled/living branching radical polymerization, employing 2-chloroacrylonitrile as an innovative inibramer. The unique branched architecture of the resulting polymer facilitates continuous pathways, enabling rapid lithium-ion transport when incorporated in polymer plastic crystal electrolytes. Electrochemical characterization reveals substantial improvements in both ionic conductivity and stability compared to conventional linear counterparts. These findings highlight the pivotal role of polymer architectural design in optimizing ion transport within solid electrolytes, offering new opportunities for developing safer and more efficient energy storage devices.

A major challenge in cryopreservation lies in controlling ice recrystallization during freeze–thaw processes. Here, inspired by natural helical antifreeze (glyco)proteins (AF(G)Ps), helical disubstituted polypeptoids with different hydrophilic groups, hydrophobic segments, and side-chain sequences were efficiently synthesized using ring-opening polymerization and thiol–ene click reactions. Their rigid helical backbones facilitated the exposure of substituents, inducing the segregation of hydrophilic and hydrophobic domains that resemble those in AF(G)Ps. Polypeptoids with increased hydrophobic domains exhibited stronger ice-binding interactions and higher ice recrystallization inhibition (IRI) activity. Preliminary cryopreservation studies showed that the helical disubstituted polypeptoids enhanced post-thaw recovery rates of blood cells compared to the commonly used hydroxyethyl starch (HES). With facile synthesis, helical stability, structural tunability, biocompatibility, and IRI activity, disubstituted polypeptoids represent a promising platform for advanced cryopreservation materials. Moreover, the structural insights into the IRI activity of disubstituted polypeptoids pave the way for the rational design of efficient cryoprotective agents.

The heterogeneity of the microstructure for polymer materials determines the differential performance of their macroscopic properties. In this work, para-ionic homopolymers (P4VBC_n-(i)imi) and meta-ionic homopolymers (P3VBC_n-(i)imi) were prepared by reacting poly(4-vinylbenzyl chloride) and poly(3-vinylbenzyl chloride) with long-chain alkyl imidazole, respectively. Microphase separation was achieved through the dominance of long-chain crystallization, resulting in lamellar nanopatterns below 5 nm. The thermal properties of para-ionic homopolymers were higher than those of meta-ionic homopolymers in terms of polymer bulk and microphase separation structure, reflecting a significant dependence of thermal properties on the dipole orientation of the side chains. For the first time, the calculation of the Flory–Huggins parameter (χ) was introduced into the homopolymer systems, providing a simple and efficient method for investigating the effects of the side-chain dipole orientation and ionization on ionic homopolymers. Calculation results showed that the side-chain dipole orientation differentiates χ values for ionic homopolymers. These findings provided a novel research strategy for the correlation between the microstructure and macroscopic properties of homopolymer materials and offered new ideas for the design and manufacture of homopolymer patterned materials.

Granular hydrogel scaffolds (GHS) are macroporous biomaterials composed of interlinked jammed hydrogel particles, particularly microgels. Each microgel is a crosslinked polymer network, typically with nanoscale pores. Among macromolecules, proteins such as gelatin and its derivatives are commonly used in GHS research, as their physicochemical characteristics and biological properties are well established. The hierarchical architecture of gelatin-based GHS, spanning from the nanoscale macromolecular network within microgels to jammed microgels with macroscale interstitial pores, provides modular control over the structural and functional properties of scaffolds, enabling unique biomedical applications. This Viewpoint highlights how gelatin chemistry at the molecular scale, microscale hydrogel particle design, and macroscale scaffold assembly regulate the overall behavior of gelatin-based GHS. At the molecular scale, the chemical composition of gelatin-based polymers modulates crosslinking mechanisms, degradation kinetics, and bioactivity, influencing microgel stability and mechanical behavior. At the microscale, particle size, stability, shape/porosity, and stiffness are key design factors that regulate GHS pore architecture, mechanical integrity, and cell– and tissue–biomaterial interactions, which, in turn, influence the overall properties of GHS at the macroscale. The interconnected macroporous network of GHS, tuned via microgel properties, guides cell infiltration and tissue integration, enabling applications in vascularization, immunomodulation, tissue regeneration, and 3D bioprinting. By mapping structure–property relationships from macromolecules to microgel features to scaffold properties, this Viewpoint may open new opportunities for the rational design and optimization of gelatin-based GHS for broad biomedical applications.

Fine fibers constitute significant applications in advanced materials engineering. However, the development of absorbable ultrathin fibers as sutures (<0.05 mm diameter, USP 10–0 gauge) has been hindered by the inherent limitations of biodegradable polymers, particularly their insufficient mechanical strength and thromboresistance. To overcome these challenges, we developed a novel heparin-conjugated polycaprolactone-based ultrathin fiber through a bioinspired two-step stretching process employed by spiders. This approach enabled a diameter adjustment while inducing strain-induced crystallization and molecular orientation, resulting in exceptional mechanical properties, tensile strength of 916.89 ± 81.24 MPa and toughness reaching 203.97 ± 22.17 MJ/m³, all exceeding biodegradable ultrathin surgical suture requirements, and concurrently provided outstanding thromboresistance without compromising biocompatibility or biodegradability. This study advances absorbable ultrathin suture technology at the polymer physics–biomaterials interface, which demonstrates its significant potential for cardiovascular microsurgery and other delicate reconstructive procedures.

We report the phase behavior of twenty-three poly(ethylene-alt-propylene)-b-poly(d,l-lactide)-b-polystyrene (PEP-b-PLA-b-PS) bottlebrush block terpolymers based on small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) measurements. Polymers were synthesized by sequential ring-opening metathesis polymerization (ROMP) of norbornene end-capped macromonomers with PEP and PS number-average molecular weights M_n = 4.7 and 3.9 kg/mol, respectively, and M_n = 1.5 kg/mol PLA. These architecturally asymmetric block terpolymers produce morphological packing frustration due to the sequence of segment–segment interactions χ_PEP–PLA > χ_PLA–PS ≈ χ_PEP–PS. SAXS and TEM reveal the expected ordered hexagonal and lamellar (both “two-color” and “three-color”) morphologies, but additionally, there is an unanticipated bicontinuous disordered morphology across a significant range of the compositional space. Larger PEP and PS side chain lengths relative to PLA, i.e., a “dumbbell” shape, combined with packing frustration due to the higher interfacial energies of the mandatory PEP/PLA interfaces compared to PEP/PS and PLA/PS, apparently stabilize an equilibrium disordered bicontinuous structure even at relatively strong segregation. This study expands the diverse phase behavior available with ABC bottlebrush block terpolymers, while revealing a new approach for producing cocontinuous materials attractive for various applications.

Debondable adhesives have emerged as a promising alternative for industries such as automotive and electronics, offering strong, yet reversible bonding. The limitations of conventional debondable adhesives include the harsh conditions required and the residue left behind upon removal that necessitates additional cleaning steps. Herein, we report water-debondable adhesives based on polyester-cross-linked hyperbranched polyglycerols (HPGs), which afford high adhesion strength and yet are debondable upon exposure to water. The advantages of HPG as adhesive precursors are the high valency of hydroxyl functionalities, low T_g, low viscosity, and the reversibility of the hydrogen bonding interactions that enable strong surface adhesion. HPG and pyromellitic dianhydride (PMDA) were cast and thermally cured to adhere aluminum substrates with an adhesion strength over twice that of a commercial epoxy adhesive. This high adhesion strength was maintained for 3 days under ambient conditions, after which the adhered samples were debonded after immersion in water at 90 °C. Thus, these adhesives exhibit both a high adhesion strength and a simple mechanism for debonding and could find utility in future sustainable manufacturing practices.

Molecular recognition of chemically inert gases like SF₆ is often challenged by their inherently weak and nonspecific interactions with traditional adsorbents. Here, we synthesized a fluorinated nanoporous polyketaminal network, PKAN-1, engineered with a triad of synergistic binding sites (triazine, ketaminal, and fluorine). This architectural synergy creates an exceptionally specific trap, achieving a record SF₆/N₂ selectivity (113) and high SF₆ uptake (2.40 mmol·g^–1). A high isosteric heat of adsorption (−29.3 kJ·mol^–1), corroborated by molecular simulations, provides definitive evidence for this cooperative binding mechanism. This work validates cooperative recognition as a powerful principle for designing adsorbents for challenging molecular targets.

The crystallization pathway of long and flexible polymer chains is debatable because of the lack of an initial melt/glass structure. To identify the crystallization pathway, we focus on two binary blends of poly(lactic acid) racemates that form stereocomplex crystals (SCCs). NMR crystallography is used to identify the stereocomplex (SC) structure and SC fraction with or without long-range order. There are significant structural analogies between glass and crystals for both high-molecular-weight (M) and low-M racemates. The observed analogies and kinetics of crystallization indicate that polymer crystallization proceeds via chain segments moving the least possible distance (“freezing in” mechanism) and that topological constraints govern nucleation barriers.