ACS Applied Polymer Materials最新文献

The development of high-performance nickel catalysts, which exhibit high thermal stability and facilitate the mediation of high-temperature ethylene (co)polymerization with polar monomers, remains a significant challenge in the field of olefin polymerization. In this contribution, a series of cationic α-imino ketone single-component nickel catalysts with N-substituents were synthesized and characterized for their sterically open nature. These thermostable nickel catalysts demonstrated high catalytic activity (10⁷ g mol^–1 h^–1) in ethylene polymerization at temperatures as high as 150 °C. Moreover, they enabled the synthesis of semicrystalline UHMWPE with high molecular weights (up to 153.7 × 10⁴ g mol^–1) and melting points up to 128.3 °C. It is particularly interesting that the high-temperature ethylene polymerization process selectively favors the formation of methyl branches, which are derived exclusively from ethylene and hold potential for commercial applications. Most importantly, successful large-scale polymerization experiment on the synthesis of high molecular weight polyethylene in n-heptane using Ni4 at 150 °C, the relative activity is further increased to up to 1.45 × 10⁷ g mol^–1 h^–1, maintaining high catalytic activity indicate their potential practical applications. These catalysts also demonstrated remarkable competence in ethylene copolymerization with various polar monomers (including methyl 10-undecenoate, vinyltrimethoxysilane, methyl 5-norbornene-2-carboxylate, and acrylates) to produce methyl-branched high-molecular-weight copolymers with high comonomer incorporation levels (up to 19.4 mol %), demonstrating promising potential in polyolefin functionalization. Notably, the resultant high-molecular-weight copolymers exhibited favorable mechanical properties, thereby expanding their application prospects.

Thermoresponsive polymer nanofibers are promising candidates for viscosity modifiers in various applications such as oil lubricants and thixotropic agents, offering great control over fluid behavior in response to temperature via the reversible glass transition of the nanofibers. In this study, thermoresponsive polymer nanofibers with diameters of 40–60 nm are synthesized using styrene and butyl acrylate as core-forming blocks via reversible addition–fragmentation chain transfer (RAFT) aqueous emulsion polymerization. It is found that the thermoresponsivity is governed by the glass-transition temperature (T_g) of the nanofibers, which can be finely tuned via the composition of the nanofibers. The nanofibers are prepared by the self-assembly of amphiphilic block copolymers, and the T_g can be varied between −53 and 100 °C by simply adjusting the monomer ratio. Aqueous dispersions of the nanofibers exhibit reversible viscosity change (by more than an order of magnitude) in response to temperature without morphology disintegration. Consequently, these nanofibers can achieve the desired effect at lower concentrations, making them highly promising as viscosity modifiers.

Epoxy resin and amine curing agents containing CaCO₃ (epoxy resin AB colloids) have been widely utilized in electronic device manufacturing and other engineering fields, owing to their high glass transition temperature (T_g), exceptional mechanical strength, and excellent dielectric properties, serving as a key molding and sealing agent. However, over time and under the influence of the environment, epoxy resin will undergo aging, leading to a decline in its performance and a shortened lifespan. The focus of this work is on the aging processes and mechanisms of epoxy AB colloids from the perspective of mechanics and electricity under extreme conditions. The degradation behavior and deterioration mechanisms of the structural, mechanical, and electrical properties of epoxy resin AB colloids at aging temperatures are discussed in depth. It shows that the glass transition temperature of the resin increases after low-temperature aging, while it decreases after high-temperature aging. At the same time, after high-temperature aging, the C–OH bonds inside the resin break, and chemical water absorption occurs, with the water absorption rate following Fick’s second law. Surface peeling and holes also appear, while the resin after low-temperature aging does not absorb water or break chemical bonds, only reducing the free volume. Taking all these factors into account, the resistivity, contact angle, and mechanical properties of the resin are degraded, especially samples after high-temperature aging, degrading more severely. Furthermore, after high-temperature aging, the dielectric constant and dielectric loss of the resin increase while the internal dipole chain segments are more easily polarized, making it easier to store and release charges, whereas the changes in resin after low-temperature aging are the opposite.

In this study, we developed a photocurable hydrogel resin incorporating a polyelectrolyte complex (PEC) for 3D printing. Acrylamide-based monomers were formulated with varying PEC contents (0–15 wt %) in an aqueous KBr medium to fabricate patterned porous hydrogel structures. The morphology of printed hydrogels was characterized by field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. Notably, the PEC5 and PEC10 formulations exhibited optimal thermal stability and compressive properties, attributed to the homogeneous distribution of PEC domains within the hydrogel matrix. Furthermore, dye adsorption experiments demonstrated excellent removal efficiency, highlighting the potential of PEC-containing hydrogels for environmental remediation applications, particularly in the treatment of dye-contaminated wastewater.

Inherent flammability is a major limitation of polylactic acid (PLA) in industrial applications. Several flame retardants (FRs) have been explored to address this, but many undergo complicated synthesis routes, often accompanied by toxic chemical use. Moreover, these FR systems negatively affect the biodegradability of PLA. In this study, epoxidized tannic acid (ETA) and a phytic acid-lysine (PALys) biobased FR were used. The former has two functions: an anchor and a carbon source, while the latter functions as a synergistic phosphorus–nitrogen (P–N) FR. The anchoring process of PALys to the PLA end groups using ETA was accomplished through melt blending. The heat and shear allow the epoxy groups in ETA to react to OH groups in PALys and PLA. The addition of 1 wt % ETA and 5 wt % PALys improved PLA thermal stability by reducing the weight loss rate from 40.69 to 2.99 wt %/min. Moreover, microscale combustion calorimeter (MCC), limiting oxygen index (LOI), UL-94, and cone calorimeter tests were performed to evaluate the efficacy of the FR system. PLA/1ETA/5PALys achieved a high LOI value of 34% vol, a UL-94 V-0 rating, and 50% reduction in the flame out time. Char formation was also observed during the combustion tests. Additionally, the FR mechanism was evaluated using scanning electron microscopy–energy-dispersive spectroscopy and thermogravimetry–mass spectrometry. The latter established the gas-phase action by the emission of noncombustible gases, such as ammonia, CO₂, and H₂O, from the decomposition of lysine and ETA, which reduces the combustible gas concentration. Furthermore, phosphorus from PALys was able to dehydrate ETA and PLA to catalyze the formation of stable aromatic and phosphorus-containing char.

Borate-cross-linked guar gum gels exhibit complex viscoelasticity driven by reversible covalent interactions between borate ions and cis-diol groups. Despite their widespread industrial use, limited knowledge of their thermorheological behavior makes it difficult to predict their performance at high temperatures. Here, 0.50 wt % guar gum dispersions with borax-to-guar ratios ranging from 1:1 to 1:8 (i.e., 0.5000−0.0625 wt % borax) were characterized from 25 to 140 °C using oscillatory rheometry. At 25 °C, gels displayed predominantly elastic behavior (G′ ≫ G″); above 120 °C, viscous behavior dominated due to thermally induced cross-link dissociation. Time−temperature superposition was valid up to 120 °C, and Arrhenius analysis yielded activation energies of 72−85 kJ mol⁻¹ for junction relaxation and −10 to −21 kJ mol⁻¹ for modulus decay. A borax threshold near 0.1250 wt % delineated weak from strong gel regimes. Steady shear measurements revealed a three-region flow curve, including shear-thickening and shear-thinning regions that depended on temperature and cross-link density. All formulations deviated from the Cox−Merz rule at high shear. These findings support predictive design of thermoresilient borate-guar gels for energy and high-temperature applications.

Passive radiative cooling, which dissipates heat to outer space (∼3 K) through the atmospheric transparency window (ATW), has attracted significant attention due to its potential for subambient cooling. The key feature of radiative cooling materials lies in their high emissivity within the atmospheric transparent window. Current material designs primarily focus on either broadband high emissivity or selective emitters dominated by the 8–13 μm range (defined as the first ATW). However, another band of the ATW is frequently overlooked (defined as the second ATW), leaving its cooling potential underutilized. Herein, we fabricate a dual-selective radiative cooling film (DS-F) composed of poly(ethylene oxide) (PEO) and polytetrafluoroethylene (PTFE) via electrospinning, demonstrating exceptional daytime radiative cooling performance. The molecular vibrations of PEO and PTFE synergistically contribute to achieving an infrared emissivity of 94.2% in the first atmospheric transparency window (8–13 μm) and 66.5% in the second window (16–25 μm). The micronanostructured fibrous architecture endows the film with a remarkable solar reflectance of 94.8%. Consequently, the DS-F achieves a subambient temperature reduction of 10.3 °C, outperforming both single-selective and nonselective radiative coolers. Numerical simulations under arid climate conditions reveal an effective cooling performance of 4.99 °C, suggesting promising potential for broader applications of dual-selective thermal emitters in energy-efficient cooling technologies.

Nature-inspired stimuli-responsive hydrogels hold great potential for advanced functional applications in soft robotics, tissue engineering, and bionic systems. Here, we report anisotropic poly(N-isopropylacrylamide)-based hydrogel actuators incorporating polydopamine-coated cellulose nanocrystals (PDACNCs) for simultaneous photothermal conversion and mechanical reinforcement combined with a two-step metal ion cross-linking strategy targeting carboxylate groups in the network. Uniform Al³⁺ cross-linking enhanced the stiffness and toughness of the hydrogels, while controlled Fe³⁺ diffusion produced cross-linking density gradients that induced anisotropic swelling and deswelling. Optimizing the Al³⁺ and PDACNC contents yielded the best balance between mechanical robustness and actuation speed. Under thermal stimulation, the actuators achieved bending angles of up to 280° within 0.3 min, whereas higher Al³⁺ or PDACNC levels slowed the response and reduced the deformation. Patterned Fe³⁺ diffusion enabled diverse programmable deformation modes including bending, twisting, and folding. Moreover, the photothermal effect of PDACNCs facilitated rapid, remote actuation under near-infrared irradiation. This work presents a versatile design platform for dual-responsive hydrogel actuators with tunable performance and complex, programmable shape transformations.

In recent years, the development of flexible wearable materials and electromagnetic shielding materials has progressed rapidly. The demand for monitoring movement data and providing protection against electromagnetic waves has also increased significantly. However, there is currently a lack of materials suitable for applications in high-humidity and underwater environments, which limits their ability to meet the needs of users in special conditions. In this study, we designed an aerogel sensor based on MXene and bacterial cellulose (BC) capable of monitoring movement in both dry and wet states while also exhibiting good electromagnetic wave absorption properties.The sensor showed a sensitivity of −6.43 with excellent linearity (99.8%) and stability. The sensor exhibits a high compressive strength of up to 15 kPa in the dry state, with a resistance change rate reaching 50% under 8% strain, and can undergo 710 cycles, demonstrating high sensitivity and stability. Under water-induced conditions, the sensor demonstrates high flexibility, shape-memory performance, and a wide strain range (0–80%) as a wet-state sensor, maintaining good structural stability and sensing performance throughout the dry–wet transition process. The BCNF/MXene sensor also demonstrates good resistance to electromagnetic interference. The RLmin of the BCNF/MXene-30% sensor reaches −45.60 dB, with an electromagnetic wave absorption rate of 99.99% and a relatively broad effective absorption bandwidth (4 GHz). This resistive sensor can be applied in electronic skins, human–machine interactions, smart wearable devices, and personalized health monitoring. Our work successfully demonstrated the application of water-sensitive shape-memory materials in electronic skins, health monitoring components, and electromagnetic wave protection.

Fluorescent hydrogels hold significant promise for information encryption, yet often suffer from signal instability under environmental fluctuations or limited responsive modes. Here, a fluorescent hydrogel with antiswelling properties was fabricated via micellar copolymerization of acrylic acid (AAc) and lauryl methacrylate (LMA), incorporating the pH-responsive aggregation-induced emission (AIE) agent tetra-(4-pyridylphenyl) ethylene (TPE-4Py). The reversible protonation/deprotonation of TPE-4Py, coupled with dynamic structural changes in the polymer network during hydration/dehydration cycles, enabled the fluorescent hydrogel to exhibit a reversible fluorescence wavelength shift from 545 to 508 nm, accompanied by significant intensity variations. Furthermore, the fluorescent hydrogel displayed distinct fluorescence responses to different metal cations. By leveraging specific metal cations, their concentrations, and environmental humidity, the hydrogel allowed flexible information encryption, enhancing data security. This multidimensional strategy effectively overcame the limitations of conventional static or single-mode encryption. This platform provided a reliable and interference-resistant solution for advanced dynamic anticounterfeiting technologies and secure information storage.