Characterisation and identification of fluorescent hydroxylated terephthalate species in the thermal and UV degradation of poly(ethylene-co-1,4-cyclohexanedimethylene terephthalate) (PECT)

Poly(ethylene-co-1,4-cyclohexanedimethylene terephthalate) (PECT) doped with mono and dihydroxyterephthalate esters has been characterised by fluorescence analysis in solution and the solid state (reflectance method). The fluorescence excitation and emission spectra of mono and dihydroxyterephthalate chromophores show that they are initially present in low levels in processed polymer material. The monohydroxy species exhibits emission bands at 380 and 460 nm with a corresponding excitation at 330 nm while the dihydroxy species exhibits emission bands at 450 and 550 nm and a corresponding excitation at 260 and 390 nm. In the solid polymer there is an indication that these units may form associated aggregates with either themselves or the polymer. On thermal and UV degradation/oxidation of the PECT three reactions are evident from this type of analysis. In thermal degradation smaller chain fragments are primarily formed giving rise to aggregates coupled with the formation of low concentrations of mono and dihydroxylated species. On the other hand on UV degradation small chain fragments and restructuring to form aggregates also occurs but, in this case, the reaction is dominated by monohydroxylation. Some dihydroxylation is also evident but its contribution is minor. (C) 2000 Elsevier Science Ltd. All rights reserved.