Herein, we report significantly enhanced mechanical properties and thermal conductivity of polyimide (PI) by incorporating a small amount (0.01 wt %) of individualized boron-doped high-quality graphene as a filler. The boron-doped expandable graphite (B-EG) was synthesized by mixing boric acid ( H3BO4) with expandable graphite (EG) and thermally treating the mixture at 2450 °C for 30 min using a graphite furnace in an argon atmosphere. The boron-doped graphene (B-g) was prepared by the solution-phase exfoliation of B-EG with an ultrasonication process, which is a method to obtain individualized graphene as well as few-layer graphene. The PI nanocomposites were prepared using the obtained graphene. The PI nanocomposites synthesized with high-quality B-graphene (B-g) showed enhanced mechanical properties and thermal conductivity compared to those of pure PI due to the doping effects and strong interfacial interactions between graphene and the PI matrix.

    Abstract
    1 Introduction
    2 Experimental
        2.1 Synthesis and preparation of boron-doped graphene
        2.2 Fabrication of graphene-reinforced PI nanocomposite film
        2.3 Characterization
    3 Results and discussion
        3.1 Characterization of exfoliated boron-doped graphene
        3.2 Characterization of B-graphenePI nanocomposites
    4 Conclusions
    Acknowledgements 
    References

• Yu‑Mi Ha(Institute of Advanced Composite Materials, Korea Institute of Science and Technology (KIST), School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST))
• Young Nam Kim(Institute of Advanced Composite Materials, Korea Institute of Science and Technology (KIST))
• Young‑O Kim(Institute of Advanced Composite Materials, Korea Institute of Science and Technology (KIST))
• Chan So(Pohang University of Science and Technology (POSTECH))
• Jae‑Suk Lee(School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST))
• Jaewoo Kim(Institute of Advanced Composite Materials, Korea Institute of Science and Technology (KIST))
• Yong Chae Jung(Institute of Advanced Composite Materials, Korea Institute of Science and Technology (KIST))