RHEOOPTICAL FOURIER-TRANSFORM RAMAN-STUDY OF THE CONFORMATIONAL-CHANGES IN UNIAXIALLY STRETCHED AMORPHOUS BULK POLY(ETHYLENE-TEREPHTHALATE)

Different types of poly(ethylene terephthalate) (PET) films suffering a deformation process have been studied at the molecular level by diff erent groups using FTIR spectroscopy in a rheo-optical system. However , there is a clear lack of knowledge about the real-time behaviour at a molecular level of the deformation process of bulk samples. The subs titution of the FTIR system by the more recently developed FT-Raman sp ectroscopy has allowed the study of such samples. Amorphous bulk PET s amples were stretched at different temperatures below and above the gl ass transition temperature (T-g) and three different mechanical behavi ours were found with three corresponding behaviours at molecular level s. At temperatures below T-g, there is a gauche to trans conformationa l transition in the C-C bond of the ethylene glycol fragment. At tempe ratures around T-g this conformational transition is lost and no confo rmational changes were observed. At higher temperatures the gauche to trans transition is again present. The molecular behaviour was analyse d in terms of the mobility of the chains, which suffered temperature-i nstigated increases and decreases when thermal crystallization took pl ace on the sample.