Tailoring thermosetting benzoxazoles for optimal performance: Balancing thermal stability, dielectric properties, and processability

Abstract

Polybenzoxazole (PBO) has excellent heat resistance and dielectric properties. However, it lacks a distinct melting point and is only soluble in sulfuric and methyl sulfonic acids. This limited solubility significantly hinders its practical application due to poor processability. In order to improve the processability of PBO while preserving its thermal stability and dielectric properties, this paper investigates the impact of introducing bridging structures between benzoxazole groups and employing cross-linking groups at the chain ends. The study primarily focuses on assessing the effects of these modifications on the thermosetting PBO properties, including heat resistance, dielectric properties, and processability. The results indicate that the cured polymer exhibits high thermal stability when a biphenyl group is used as bridging structure and a cyano group as the end group. Among these thermosetting monomers, p-LARBCN has the best overall performance. The 5 % thermal decomposition temperature (Td5) of cured p-LARBCN is 612 °C, which is very similar to PBO. The dielectric constant of the cured p-LARBCN is below 2.7, and the dielectric loss is below 0.02. The dielectric performance is close to that of PBO. In addition, p-LARBCN shows good solubility in solvents like DMSO, DMF, and DMAc, which greatly improves its processability compared to PBO. This study presents a modified thermosetting PBO resin that combines high thermal stability with improved processability. This resin holds promise for applications in the aviation and aerospace fields, particularly as a high-temperature-resistant material.