Yichun Ding

Highly strong and highly tough electrospun polyimide/polyimide composite nanofibers from binary blend of polyamic acids

Electrospun blend-polyimide (blend-PI) nanofibers with high tensile strength and toughness are highlighted in this article. The blend-PI nanofibers were prepared by electrospinning the binary blend of rigid and flexible polyamic acids, followed by thermal imidization. The method is simple and can be extended to other kinds of polyamic acids. The morphologies and structures of the blend-PI nanofibers were investigated by scanning electron microscopy (SEM) and wide-angle X-ray diffraction (XRD). The mechanical properties, thermal properties and miscibility of the blend-PI nanofibers were studied by a tensile test, thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The mechanical properties of the blend-PI nanofibers, including tensile strength, modulus, elongation at break and toughness, could be well-tuned by modifying the molar ratio of the rigid component (B-PI) and the flexible component (O-PI). The blend-PI nanofibers with B-PI/O-PI molar ratio of 4/6 had an ultra-high strength of 1.3 GPa with an excellent toughness of 82 J g−1. All the blend-PI nanofibers showed thermal stability to above 500 °C. The presence of only one glass transition temperature (Tg) suggested the good miscibility of the binary PIs in the blend-PI nanofibers. This study would provide completely new opportunities for modifying the properties of electrospun PI nanofibers.

Thermal, mechanical and thermomechanical properties of tough electrospun poly(imide-co-benzoxazole) nanofiber belts

Mechanically strong electrospun nanofibers at high temperature are highly desired in the aerospace industry, high temperature filtration and fire protection clothing. In the present work, highly tough poly(imide-co-benzoxazole) (PI-co-PBO) nanofiber belts with excellent thermal stability, mechanical properties and thermomechanical properties were produced from the highly viscous methoxy-containing polyamic acid (MeO-PAA) solution by electrospinning followed by thermal rearrangement. The chemical structures of the polymer nanofibers and the corresponding thermal rearrangement were confirmed by 1H-NMR, FT-IR and TGA. The mechanical properties and thermomechanical properties were characterized by a tensile test and thermomechanical analysis (TMA). The aligned nanofiber belts heat-treated at 450 °C (ANF-450) had the highest tensile strength of 559 MPa, a modulus of 11.2 GPa and a toughness of 12.0 J g−1, respectively, which were much higher than those of the pure PBO films made by thermal rearrangement. The TMA test showed that the ANF-450 exhibited a high tensile strength retention of 90% and a modulus retention of 94% at a high temperature of 200 °C. These excellent thermomechanical properties make electrospun PI-co-PBO nanofibers promising candidates in high temperature areas.

Polyimide complexes with high dielectric performance: toward polymer film capacitor applications

Novel polyimide–copper complexes (PICuCs) with a high dielectric constant of up to 133 were prepared by polymerization, complexation and imidization of a newly synthesized bipyridine-containing diamine monomer. The PICuCs showed high dielectric constant because of the enhanced electronic depolarization. Moreover, the PICuCs presented better mechanical and thermal properties than neat PI, which are promising materials for polymer film capacitors.

Facile synthesis, characterization and application of highly active palladium nano-network structures supported on electrospun carbon nanofibers

Palladium nano-network structures supported on electrospun carbon nanofibers (Pd-NNSs-ECNFs) were successfully prepared through a novel K2PdIICl4/K4FeII(CN)6 cyanogel method. The Pd-NNSs have the features and properties of small particle size, low dimensionality, quantum effects and high stability. SEM, TEM and XPS were used to characterize the Pd-NNSs-ECNFs. The Pd-NNSs-ECNFs were used as a catalyst in different types of Suzuki coupling reactions to evaluate the catalytic abilities. The results showed that the heterogeneous catalyst (Pd-NNSs-ECNFs) had a high catalytic activity (high yields to the products) to the Suzuki coupling reactions in an environmentally friendly solvent system (ethanol/H2O). The catalyst can be recycled by filtration, and reused seven times without losing the catalytic activity. This research opens new applications of Pd-NNSs-ECNFs in the area of green chemistry.

Synthesis and properties of a high dielectric constant copolymer of a copper phthalocyanine oligomer grafted to amino-capped polyimide

A novel high dielectric constant all-organic polymer film of a copper phthalocyanine oligomer grafted to polyimide (CuPc–PI) was successfully synthesized via a polycondensation between a copper phthalocyanine anhydride oligomer (o-CuPcA) and amino-capped polyamic acid (PAA), followed by thermal treatment (i.e., thermal imidization).