CHEMICAL-REACTIONS OCCURRING IN THE THERMAL-TREATMENT OF POLYMER BLENDS INVESTIGATED BY DIRECT PYROLYSIS MASS-SPECTROMETRY - POLYCARBONATE POLYBUTYLENETEREPHTHALATE

The chemical reactions occurring in the thermal treatment of polycarbonate/polybuthyleneterephthalate (PC/PBT) blends have been investigated by gradual heating (10-degrees-C/min) using thermogravimetry and direct pyrolysis into the mass spectrometer. Exchange reactions occur already in the temperature range below 300-degrees-C but the transesterification equilibrium is affected by the evolution of thermal degradation products. Buthylenecarbonate, was detected in the first decomposition stage (320-380-degrees-C), which is evolved together with a series of cyclic compounds containing units of PC and PBT, in varying ratios. The overall thermal reaction evolves towards the formation of the most thermally stable polymer, i.e., a totally aromatic polyester (polymer III, Table I), which was found to be the end-product of the thermal processes occurring in the system investigated. The thermal decomposition products obtained from the PC/PBT blends in the range 320-600-degrees-C have mass sufficiently high to be structurally significant, since they contain at least one copolymer repeating unit. The reactions occurring in the thermal treatment of the PC/PBT blend are discussed in detail.