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.