Deterioration of microwave dielectric properties of low-loss thermosetting polyphenylene oxide/hydrocarbon resin induced by short-term thermo-oxidative aging

•Thermosetting polyphenylene oxide/hydrocarbon resin with ultra-low dielectric loss is prepared.•Oxidative aging of ultra-low loss resin material causes a rapid increase in high frequency dielectric loss.•Oxidative crosslinking of 1,2-polybutadiene segments is the primary cause of material aging.•High frequency dissipation factor of the material is a reliable indicator of the aging degree and polar oxidation products.