Phthalonitrile functionalized resoles – use of 2,3-dicyanohydroquinone as a versatile monomer for resins with very high thermal stability

Abstract

In the aerospace industry, composite materials based on high-performance fibers and polymer matrices are widely used. Indeed, they can display very important mechanical and thermal properties with a very large density-to-stiffness balance. Usually, thermal protection systems are made from composite materials containing a char precursor for the polymer matrix. Temperature-resistant organic polymers are still quite rare and generally require very restrictive manufacturing and use processes. Recently, phthalonitriles have gained interest due to their very good thermostability and high char yield. However, phthalonitrile resins are generally solid at room temperature and often have a narrow processing window. In this work, synthesis methods allowing access to phthalonitrile resins were developed from 2,3-dicyanohydroquinone. These methods propose to consider together phenolic chemistry (phenolic reactive positions and aldehyde) and self-crosslinkable phthalonitrile chemistry (hydroxyl-mediated from phenolic and nitriles). It was thus possible to synthesize liquid resins at room temperature, leading to polymeric networks with a very high thermostability (temperature at 5% mass loss > 450 °C and char yield ≈ 70 %).