Characterization of fire retardant polymer blends by temperature resolved in-source pyrolysis mass spectrometry

The characterization of fire retardant polymer blends by temperature resolved in-source pyrolysis mass spectrometry (PYMS) is demonstrated with a few examples. Electron impact (EI) and electron capture negative ionization (ECNI) were used to identify the thermal degradation products of polymer blends containing brominated fire retardants. PYMS (EI mode) offers an analytical instrument for a fast analysis of unknown mixtures of polymers and for the presence of fire retardant additives. Under electron impact conditions, in vacuo, low-molecular weight additives like fire retardants mainly evaporate from the polymer matrix. PYMS (EI mode) has been used for the characterization of addition polymers like polystyrene and acrylonitrile-butadiene-styrene copolymer, and for condensation polymers like the polyester poly(butylene terephthalate). Applying electron capture negative ionization, at low argon pressure in the ionization chamber, a more realistic pyrolysis situation is created because the premature loss of volatile additives is suppressed. The selectivity of ECNI for electron accepting groups like bromine makes it possible to study the influence of brominated compounds on the degradation processes in the melt. This is demonstrated by our studies on polystyrene and acrylonitrile-butadiene-styrene copolymer. High-molecular weight pyrolysis products in the m/z range of 1000 - 2000 are detected for p-bromopolystyrene and for a blend of high impact polystyrene with the fire retardant system decabromodiphenyl ether/antimony(III) oxide. In addition to the formation of antimony bromides shown in earlier studies, the emission of the synergist antimony(III) oxide as a dimeric cluster (Sb₄O₆) or as a reduced Sb₄ cluster is observed under PYMS conditions.