Yanxiong Pan

Poly(amic acid) (PAA) is the precursor of polyimide (PI), and the imidization from PAA to PI is a highly complex process involving the formation of a series of PAA‐PI copolymers. The molecular weight changes during this process critically impact the resulting product performance. This study applied two distinct thermal imidization methods, that is, multi‐step and isothermal heating, to (6FDA‐DMB) PAA. The structural evolution, imidization degree (ID) and molecular weight variations were monitored by Fourier transform infrared (FT‐IR) spectroscopy and gel permeation chromatography (GPC). During multi‐step thermal imidization from 80°C to 350°C, ID gradually increased to 94.6%. Specifically, ID experienced the highest rate of increase between 120°C and 200°C. Regarding the isothermal imidization at 200°C, 250°C, and 350°C, the ID initially increased over time and then stabilized. Moreover, the higher the temperature, the faster the ID reached plateau, and complete imidization was achieved by curing at 350°C for 5 min. This study revealed a two‐stage evolution of molecular weight under both multi‐step and isothermal heating conditions. The molecular weight exhibited initial decrease followed by an increase, attributed to the decomposition and recombination of PAA chains. These findings provide deeper insights into molecular weight dynamics during PAA‐PI thermal conversion.

The long-standing trade-off between enantioselectivity and permeability remains a central challenge in mem-brane-based chiral separation. Materials capable of strong chiral recognition often suffer from slow molecular transport, while highly permeable membranes generally exhibit limited enantioselectivity. Here, we show that intrinsic microporosity provides an effective route to alleviate this limitation. We construct a pair of enantio-meric polymers of intrinsic microporosity (HBIN-Is) through the one-step polymerization of BINOL and isatin. The resulting polymers combine rigid contorted backbones, permanent microporosity, and homochiral envi-ronments, enabling the formation of robust free-standing membranes. The membranes exhibit simultaneous high enantioselectivity and permeation flux toward BINOL and Br-BINOL racemates, achieving enantiomeric excess values up to 97.7% together with high fluxes around 0.38 mmol·m-2·h-1, among the highest reported for polymer-based chiral membranes. Adsorption experiments, density functional theory calculations, and non-covalent interaction analyses reveal that chiral discrimination originates from cooperative hydrogen-bonding and stereochemically matched host–guest interactions within the microporous framework. This work identifies intrinsic microporosity as a powerful design principle for integrating molecular recognition and rapid transport in chiral membranes and provides a scalable platform for energy-efficient enantiomer separation.

Poly(m-phenylene isophthalamide) (PMIA) is a high-performance meta-aramid polymer whose processing is governed by chain segmental dynamics. Herein, PMIA segmental dynamics were evaluated by combining spin-labeled PMIA and continuous-wave electron paramagnetic resonance (CW-EPR) spectroscopy. The rotational correlation time (τc) obtained from EPR simulation exhibited a sharp increase near 4.5 wt %, close to the entanglement concentration (ce) determined from rheological measurements, demonstrating the reliability of spin-label EPR in determining segmental motion and entanglement. The dissolution behavior of PMIA was monitored by EPR spectroscopy, and the solubilizing salt concentration at which τc changed abruptly closely matched that at which the solution became transparent. Additionally, τc increased rapidly at low molecular weights before leveling off at higher molecular weights, reflecting the development and saturation of entanglement. These features establish spin-label CW-EPR as a complementary tool for elucidating polymer solution behavior at the microscopic scale in systems containing additives and for guiding polymer processing optimization.

Super-tough poly(lactic acid) (PLA) composites with an excellent balance between stiffness and toughness were successfully developed by incorporating core-shell particles comprising a rigid silica (SiO2) core and an elastomeric poly(ether-block-amide) grafted with a glycidyl methacrylate (PEBA-GMA) shell. Morphological observations confirmed the formation of a well-defined core-shell structure within the PLA matrix. The effects of SiO2 particle size (100–800 nm) and core-shell mass ratio (1:3 to 3:1) on mechanical properties were systematically investigated. The results indicate that smaller SiO2 core particles (100 nm) led to severe agglomeration and poor dispersion, resulting in ineffective toughening. The optimal performance was achieved with PLA composites containing 500 nm SiO2 at a core-shell ratio of 1:3 and a total modifier content of 20 wt %, which exhibited a notched Izod impact strength of 70.6 kJ/m2─a significant enhancement over binary PLA/PEBA-GMA composites. Furthermore, this composite maintained ductile fracture behavior even at a high SiO2 content, with an impact strength of 33.9 kJ/m2 at a SiO2:PEBA-GMA core-shell ratio of 3:1. The flexural modulus of this optimized composite was retained at 87% of that of pure PLA, demonstrating an excellent balance between stiffness and toughness. This work presents an effective strategy for developing high-performance PLA materials with tailored mechanical properties, offering promising potential for advanced biodegradable applications.

As the phase morphology of polypropylene composites is highly sensitive to processing conditions and considerably determines the final properties, fabricating composites with controllable phase morphology and macroscopic properties remains an ongoing task. In this study, to achieve an optimal balance between stiffness and toughness in composites, SiO2 and POE (polyolefin elastomer) were selected as modifiers, and the effects of mixing time, rotational speed, and mixing sequence of PP/SiO2/POE (70/15/15) composites on phase morphology and material performance were systematically investigated. From the perspective of mixing time, samples prepared within 6-8 minutes exhibited a higher number of uniformly distributed core-shell structure, resulting in excellent mechanical properties. When the rotational speed was set at 60 rpm, the optimal performance was achieved. Considering the mixing sequence, the one-step method provided favorable core-shell morphology and desirable mechanical performance,. Under the aforementioned conditions, a polypropylene composite with an excellent balance of stiffness (1245 MPa) and toughness (57.19 kJ/m2) was successfully fabricated. Notably, SEM and the spreading coefficient theory analysis revealed that SiO2 and POE tend to form a core-shell structure within the composite. However, the stability of this structure varies with processing conditions. Mechanical testing further confirmed that the presence of the SiO2/POE core-shell structure contributes to a balanced stiffness-toughness, while variations of the structure lead to corresponding changes in the macroscopic properties of composites. The relationship between phase morphology and performance was further elucidated through DMA and DSC analyses. Morphological examination of impact-fractured surfaces indicated that in highly tough composites containing core-shell structures, energy dissipation primarily occurs through shear yielding and plastic deformation, revealing the underlying toughening mechanism.

As the phase morphology of polypropylene composites is highly sensitive to processing conditions and considerably determines the final properties, fabricating composites with controllable phase morphology and macroscopic properties remains an ongoing task. In this study, to achieve an optimal balance between stiffness and toughness in composites, SiO2 and POE (polyolefin elastomer) were selected as modifiers, and the effects of mixing time, rotational speed, and mixing sequence of PP/SiO2/POE (70/15/15) composites on phase morphology and material performance were systematically investigated. From the perspective of mixing time, samples prepared within 6-8 minutes exhibited a higher number of uniformly distributed core-shell structure, resulting in excellent mechanical properties. When the rotational speed was set at 60 rpm, the optimal performance was achieved. Considering the mixing sequence, the one-step method provided favorable core-shell morphology and desirable mechanical performance,. Under the aforementioned conditions, a polypropylene composite with an excellent balance of stiffness (1245 MPa) and toughness (57.19 kJ/m2) was successfully fabricated. Notably, SEM and the spreading coefficient theory analysis revealed that SiO2 and POE tend to form a core-shell structure within the composite. However, the stability of this structure varies with processing conditions. Mechanical testing further confirmed that the presence of the SiO2/POE core-shell structure contributes to a balanced stiffness-toughness, while variations of the structure lead to corresponding changes in the macroscopic properties of composites. The relationship between phase morphology and performance was further elucidated through DMA and DSC analyses. Morphological examination of impact-fractured surfaces indicated that in highly tough composites containing core-shell structures, energy dissipation primarily occurs through shear yielding and plastic deformation, revealing the underlying toughening mechanism.