Using structure property relationships in the understanding and molecular design of inherently tough polybenzoxazines

Bisbenzoxazines form highly crosslinked, network structures with relatively high Tg (180oC+) and thermal oxidative stability but inherent brittleness (G1C = 168 J/m2) - limiting their applications. We have used synthetic polymer chemistry and molecular simulation to probe the structure/property relationships in model and commercial systems with the aim of understanding the factors governing toughness in these materials. Our previous experience, gained over 20 years, leads us to ensure that the molecular model represents as accurately as possible the real network, e.g. incorporating molecular defects derived from empirical data. We report the preparation and characterisation of selected bisbenzoxazine monomers chosen to exemplify both brittle and tough behaviour to provide a wide spectrum of mechanical characteristics and produce a wider understanding of the factors affecting brittleness. This enables us to design and execute the synthesis of new monomers with the potential for enhanced fracture toughness based on rational molecular design.