Surface evolution of polycarbonate/polyethylene terephthalate blends induced by thermal treatments (original) (raw)

Bisphenol-A polycarbonate (PC) and polyethyleneterephthalate (PET) blends are known to undergo, upon thermal treatment (melt mixing), exchange reactions leading to the formation of copolymers having a ®nal structure that is also affected by consecutive reactions involving CO 2 and ethylene carbonate losses. In this work we followed the evolution of the surface composition of this system during the melt mixing at 270 8C, both with and without catalysts, by means of time-of-¯ight secondary ion mass spectroscopy (ToF-SIMS). The static SIMS spectra obtained at different treatment times show the appearance of peaks related to newly formed structures and also the modi®cation of the relative intensities of peaks characteristic of both the initial constituents of the blend. From the variation of the relative intensities of peaks related to the bisphenol-A unit of PC and to the phthalate structure of PET, it is shown that after the ®rst stages of melt mixing the surface is PC enriched and that with the progressive formation of a random copolymer the phthalate units increase their concentration at the surface of the system. Hence, as ®nal result of the melt mixing process, the surface composition tends to re¯ect the relative amount of the repeating units in the bulk.