Wenqiu Chen

In situ solution polymerization for preparation of MDI-modified graphene/hyperbranched poly(ether imide) nanocomposites and their properties

Firstly, fully exfoliated graphene oxide (GO) colloidal dispersion in N-methyl-2-pyrrolidone (NMP) with high concentration is obtained by a solvent-exchange method and further used to prepare superior GO-MDI with free isocyanato groups by chemical modification. Then, the yielded GO-MDI is employed to prepare two kinds of MDI-modified graphene/hyperbranched poly(ether imide) (GE-MDI/HBPEI) nanocomposites via in situ random solution co-polycondensation or crosslinking reaction, followed by synchronous thermal imidization and reduction. The chemical modification of GO endows GO-MDI with good solubility in organic solvents to prepare GE-MDI/HBPEI nanocomposites with high filler content. GO-MDI is further used as a multi-functional co-monomer or crosslinker to be introduced into the HBPEI backbone with full compatibility of the guest and host at the molecular level. Finally, the performance tests show that the heat resistance, thermal stability, mechanical strength and modulus, and gas barrier properties of the obtained two kinds of nanocomposites are significantly improved or enhanced compared with pure HBPEI, and the impacts become more and more significant with the increase of GO-MDI content, but their mechanical toughness show trends of increase at first then decrease with the increase of GO-MDI content. Comparisons also show that at the same GO-MDI content, the heat resistance, thermal stability, mechanical strength and modulus of the nanocomposites obtained by in situ random solution co-polycondensation are all superior to those obtained by in situ random solution crosslinking reaction, except the mechanical toughness and gas barrier properties of the former are less than the latter. This effective approach provides a possibility for enriching and developing high performance PEI-based composites with various forms of GE for advanced engineering or functional materials.

Synthesis and characterization of thermally stable, hydrophobic hyperbranched polyimides derived from a novel triamine

A novel aromatic triamide 1,3,5-tri[4-(4-aminophenoxy)phenyl] benzene (TAPOPB) with prolonged chain segments and ether bonds was successfully prepared through a three-step reaction. Then a series of hyperbranched polyimides (HBPIs) were synthesized using A2 + B3 polycondensation from various commercial aromatic dianhydrides and TAPOPB. The HBPIs showed good solubility, thermal stability with glass transition temperatures (T g) between 218°C and 320°C, and temperature at 10% weight loss of 502.1–561.7°C in nitrogen atmosphere. Meanwhile, they had decent mechanical properties whose tensile strength and modulus were higher than 72.37 MPa and 1.039 GPa, respectively. Water uptake of less than 0.96% was obtained. The truncation wavelengths of the films were all greater than 400 nm with a good application prospect in UV protective coating. Most contact angles were more than 90°, promising to be used as hydrophobic material.

Optical Transparency and Light Colour of Highly Soluble Fluorinated Polyimides Derived from a Novel Pyridine-Containing Diamine m, p-3FPAPP and Various Aromatic Dianhydrides

A novel pyridine-containing aromatic diamine monomer, 4-(4-trifluoromethylphenyl)-2,6-bis[3-(4-aminophenoxy)phenyl]pyridine (m,p-3FPAPP), was successfully synthesized by a modified Chichibabin reaction of 4-trifluoromethylbenzaldehyde and a substituted acetophenone, 3-(4-nitrophenoxy)acetophenone (m,p-NPAP), followed by a reduction of the resulting dinitro compound 4-(4-trifluoromethylphenyl)-2,6bis[3-(4-nitrophenoxy)phenyl] pyridine (m,p-3FPNPP) with Pd/C and hydrazine monohydrate. The aromatic diamine was employed to synthesize a series of pyridine-containing polyimides by polycondensation with various aromatic dianhydrides in N,N-dimethylformamide (DMF) via the conventional two-step method, and further thermal or chemical imidization forming polyimides. The inherent viscosities of the resulting poly(amic acid)s and polyimides were 0.62–0.89 and 0.58–0.69 dl/g, and most of the polyimides obtained by chemical imidization were readily soluble in common organic solvents such as DMF, N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP) and tetrahydrofuran (THF). Meanwhile, strong and flexible polyimide films were obtained, which had good thermal stability, with a glass transition temperature (T g) of 234.4–246.6°C and the temperature at 10% weight loss of 561.4–600.6°C in nitrogen atmosphere, and good optical transparency with the cut-off wavelengths of 369–378 nm, as well as outstanding mechanical properties with tensile strengths of 89.5–96.4 MPa, a tensile modulus of 1.52–1.63 GPa and elongation-at-break of 7.2–8.7%. The polyimide films also were found to possess low water uptake (0.61–0.79%).