Benzoxazine-based phosphinated bisphenols and their application in preparing flame-retardant, low dielectric cyanate ester thermosets

This work reveals a facile, one-pot synthesis of phosphinated bisphenols (1–2) from a nucleophilic addition of 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) to diaminophenylmethane- and diaminophenylether-based benzoxazines (P-ddm and P-oda). A reaction mechanism including active hydrogen abstraction, ring-opening, and nucleophilic addition was proposed for the synthesis. Phosphinated dicyanate esters (3–4) were prepared based on bisphenols (1–2), and were copolymerized with a commercially available dicyanate ester of bisphenol A (BACY). The properties such as glass transition temperature, coefficient of thermal expansion, thermal decomposition temperature, water absorption, and flame retardancy of the resulting thermosets were evaluated. Experimental data show that incorporating (3–4) into BACY enhances the flame retardancy, dimensional stability and dielectric properties with small penalty to the thermal properties. A thermoset with Tg 241 °C, CTE 50 ppm per °C, Dk 3.01 (1 GHz), Td (5%), N2: 407 °C, and UL-94 V-0 rating can be achieved via this approach.