Systematic examination of thermal, mechanical and dielectrical properties of aromatic polybenzoxazines

A series of bis-benzoxazines, prepared in high yield and purity using two synthetic procedures, is reported. Differential scanning calorimetry reveals similar temperatures for the onset of polymerisation (162-180 °C); the higher values representing monomers containing polar bridges or rigid backbones. Dynamic viscoelasticity data reveal glass transition temperatures for the polybenzoxazines ranging from 187 °C to 235 °C; a fluorinated polybenzoxazine consistently yields the highest Tg of the polymers studied. The latter is interesting since it is superior to many commercial benzoxazines with a relatively high Tg (235 °C), flexural modulus (5.0 GPa) and flexural strength (146.7 MPa), but coupled with a breaking strain (3.06%) that is uncharacteristically high for polybenzoxazines. The incorporation of fluorine results in a low dielectric loss properties (Dk = 3.71-4.12 at 10 MHz, Df = 0.0109 - 0.0980 at 10 MHz), which are comparable with commercial polybenzoxazines, FR4 and aerospace epoxy resins and superior to commercial bismaleimides.