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. Two kinds of (GE-MDI/HBPEI) nanocomposites with highly enhanced thermal, mechanical and gas barrier properties, were prepared via in situ solution polymerization, as well as subsequent synchronous thermal imidization and reduction.