Flame-retarding behaviors of novel spirocyclic organo-phosphorus compounds based on pentaerythritol

In order to find effective flame retardant for charrable polycarbonate (PC) and non-charrable acrylonitrilebutadiene- styrene copolymer (ABS), a series of novel organo-phosphorus compounds derived from 4-(hydroxymethyl)- 1-oxido-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane (HPO) flame retardant (FR) were synthesized and their flame retardancies were investigated for the mixtures containing PC or ABS. The successful synthesis of high purity FRs was verified by spectroscopic analysis, 1H and 31P nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FTIR). In an attempt to provide a basis to understand the flame retardancy behaviors of synthesized FRs, various other techniques such as thermal analysis and micro-scale calorimetry were employed. The flame retardancies were determined by UL-94 vertical test methods. The results show that V-0 ratings are achieved at 3-5 wt% loadings of FR for PC and V-1 rating at 30 wt% for ABS. This big difference is believed to be resulted from the fact that the main mechanism of flame retardancy is based on the condensed phase in the case of PC. Nevertheless, effective gas phase acting FR is needed for ABS containing mixtures. Both peak heat release rate obtained from micro-calorimeter experiments and the decomposition activation energy determined from differential scanning calorimetry (DSC) results are greatly reduced for the PC/FR mixtures, indicating that a stable insulating barrier is formed between fire and charrable PC containing substrate. On the other hand, ABS is a non-charrable polymer and the flame retardant acting in the gas phase is more desirable. The findings obtained in this study clearly implies that it would not be easy to find a promising phosphorus based FR which is good not only in flame retardancy but also in other properties such as hydrolytic and thermal stability for non-charrable polymer like ABS.