Synthesis and characterization of a cyclic 9,9-bis(4-hydroxyphenyl)fluorine (phenylene phosphonate) oligomer and its flame retardancy application

Abstract

A novel solid flame retardant cyclic 9,9-bis(4-hydroxyphenyl)fluorine (phenylene phosphonate) (CPFP) oligomer was synthesized in high yields by the reaction of phenylphosphonic dichloride with 9,9-bis(4-hydroxyphenyl)fluorine under pseudo-high-dilution conditions via polycondensation. Detailed structural characterizations of this oligomer were conducted by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), ¹H NMR, ³¹P NMR and FTIR. Furthermore, the flame-retardant efficiency of this oligomer in polybutylene terephthalate (PBT) was studied using limiting oxygen index (LOI) and UL-94 tests. After the addition of CPFP, the LOI increased and the UL-94 V-0 rating was achieved. The occurrence of an interaction between CPFP and PBT was elucidated by thermogravimetric analysis (TGA), FTIR and pyrolysis/GC/MS. The results showed that the CPFP oligomer could change the degradation path of PBT and improves the char formation of the PBT/CPFP system. The residual morphologies of residues of the PBT/CPFP25% system were investigated by scanning electron microscopy (SEM). SEM investigations revealed that the residual chars contained polyphosphoric or phosphoric acid, which plays an important role in the process of carbonization.