Xiangling Ji

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.

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.

Looped polymer brushes lacking chain terminals exhibited unique topological structures and associated properties. Looped polymer brushes in solution have been extensively studied, although the topology and corresponding performances of the thermal-responsive polymer upon grafting onto nanoparticle surfaces have been hardly reported. In this work, gold nanoparticles (AuNPs) were modified using poly(N-isopropyl acrylamide) (PNIPAAm) terminated with one thiol and two thiol groups to prepare linear and looped PNIPAAm brush-coated AuNPs, respectively. The effect of the topology of PNIPAAm brushes on thermal-responsive behavior, colloidal stability and release performances was evaluated in detail. Compared to the linear counterparts, the looped polymer exhibits relatively higher colloidal stability and rapid thermal-responsive behavior during heating–cooling temperature cycling. This resulted in a more pronounced release of dye molecules triggered by the looped one upon temperature change, and even if the release is first saturated at 25 °C, it is triggered again by raising the temperature to 45 °C. In contrast, the linear polymer brushes did not show significant triggering behavior due to chain entanglement. This work demonstrated how the polymer brush topology affected thermal-responsive nanoparticles’ stability and temperature-responsive behavior, which may provide new opportunities for surface modification of looped polymer brushes with temperature-sensitive properties.

Binary superlattices can be prepared via the self-assembly of polystyrene tethered spherical gold nanoparticles of two kinds, and the unique configurations of the BNSLs are controllable by tuning the sizes and number ratios of the NPs.

Shape transformation of polymer particles is generally a nonequilibrium dynamics process. Controlling the shape transformation of polymers is increasingly attractive and challenging for scientists due to their extensive use in drug delivery and cancer therapy. Herein, we investigated the UV-triggered shape transformation pathway of polymeric vesicles assembled from Polystyrene-block-poly(4-vinylpyridine) and 4-hydroxyazobenzene (PS-b-P4VP(Azo-OH)) and the direct assembly pathway of UV-irradiated PS-b-P4VP(Azo-OH) homogeneous solution. In the shape transformation process, well-assembled vesicles can be transformed into toroid, cylindrical, rod-like, and spherical micelles. In the direct assembly pathway, rod-like and spherical micelles can be obtained. Interestingly, the toroid micelles can be obtained only from the UV-triggered shape transformation pathway. Contrasting the two pathways reveals the pathway dependence of PS-b-P4VP(Azo-OH) assembly, suggesting that the final assembly morphology is determined by the initial state and dynamic process. The speed of UV-triggered shape transformation and the final morphology of assemblies can be tuned easily by adjusting the UV illuminance, time, and content of Azo-OH addition. Moreover, the light-responsive polymeric vesicles can be used as drug carriers and have the potential to release drugs precisely.