Boron-containing Phthalonitrile Resin: Synthesis, Curing Behavior, and Thermal Properties

A novel boron-containing monomer, (4-(3,4-dicyanophenoxy)phenyl)boronic acid (BPhPN) was synthesized and used to promote the curing process of phthalonitrile monomer 1,3-bis(3,4-dicyanophenoxy)benzene (MPN). Differential scanning calorimetry and rheological analysis were used to study the curing behaviors of BPhPN/MPN (namely B-MPN), and results suggested that B-MPN systems have better processibility. FTIR spectra and solid-state C-13-NMR exhibited triazine and isoindoline have been formed in the curing process. Boron-containing Lewis acid curing mechanism was preliminarily speculated and verified by two model compounds with different boron chemical environments. The thermogravimetric analysis and dynamic mechanical analysis demonstrated that the cured B-MPN polymers showed excellent thermal stability and heat resistance, which were comparable with conventional catalytic systems for phthalonitrile resins. This study not only presented a novel curing system for phthalonitrile resins, but also shed light on future design of high temperature thermosets.