Flame retardancy and chemical degradation of epoxy containing phenylphosphonate group under mild conditions

The development of methods for recycling of thermosetting resin is difficult due to their structure. To regulate the flame retardancy and chemical degradation behavior of epoxy (EP), a phenylphosphonate based EP monomer (DGEP) was prepared and cured using 4,4-diamino diphenylmethane (DDM). For comparison, bisphenol A EP (DGEBA/DDM) was also prepared. The modes of flame retardancy and chemical degradation have been investigated. The DGEP/DDM displays a UL-94 V0 rating while the DGEBA/DDM may not be classified in the UL-94 test. Moreover, DGEP/DDM is stable in most solvents and is degraded after 40 min in a solution of methanol/sodium hydroxide (NaOH)/water (H2O) at 50 °C, while DGEBA/DDM is stable under the same conditions. Degradation occurs by hydrolysis and alcoholics of phenylphosphonate in the main chain of EP under alkaline conditions. In addition, DGEP/DDM has a similar glass transition temperature and tensile properties as those for DGEBA/DDM. The introduction of phenylphosphonate into EP may represent a useful method for the preparation of flame retardant and recyclable EP.