Polybenzoxazines containing borosiloxane structures as high-temperature resistance (T_g > 300 °C) and environment-friendly flame-retardant materials

Abstract

A series of borosiloxane structures-containing polybenzoxazines (PBZs) with intrinsic environment-friendly flame-retardant properties and high-temperature resistance are investigated in this study. Initially, borosiloxane structures-containing benzoxazine macromonomers (BZ-BSiO-X) were synthesized through a condensation reaction between silicon ethoxy groups-containing benzoxazine monomers (P-mdes), boric acid (BA) and diphenyldimethoxysilane (DPDMS) with varying feed ratios. Subsequently, the benzoxazine groups in BZ-BSiO-X underwent ring-opening polymerization at elevated temperatures to produce poly(BZ-BSiO-X). The properties of poly(BZ-BSiO-X) were evaluated using Dynamic Mechanical Analysis, Thermogravimetric Analysis and an Oxygen Index instrument. The results show that the heat resistance of poly(BZ-BSiO-X) is enhanced by the cross-linking structures formed by the P-mdes segment and B-N coordination interaction, leading to their glass transition temperatures (T_g, tan δ) exceeding 300 °C. The thermal stability and flame-retardant properties of poly(BZ-BSiO-X) are reinforced via the borosiloxane structures formed through DPDMS and BA, resulting in a 5% weight loss temperatures (T_d5) around 400 °C and limiting oxygen index (LOI) values above 30. These polymers, containing environment-friendly flame-retardant boron (B) and silicon (Si) elements, exhibit potential as alternatives to halogen- or phosphorus-containing flame-retardant materials and are expected to be used in various fields as environment-friendly flame-retardant materials.

Graphical Abstract

Keywords:

• Borosiloxane structures
• ring-opening polymerization
• polybenzoxazines
• high-temperature resistance
• environment-friendly flame-retardant properties

Acknowledgments

Authors are greatly thankful for the financial support from National Natural Science Foundation of China, Natural Science Foundation of Shandong Province, Talent research project of Qilu University of Technology (Shandong Academy of Sciences) and Wynca Chemicals Group.

Authors’ contribution

Sheng Gao: conceptualization, funding acquisition, methodology, resources, supervision, and writing original draft. Lin Zhang: data curation and formal analysis. Bin Wang: data curation and formal analysis. Mingxing An: conceptualization and funding acquisition.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by National Natural Science Foundation of China (52103114), Natural Science Foundation of Shandong Province (ZR2021QE140), Talent research project of Qilu University of Technology (Shandong Academy of Sciences) (2023RCKY001) and Wynca Chemicals Group.