RHEOOPTICAL RAMAN-STUDY OF CHAIN DEFORMATION IN UNIAXIALLY STRETCHED BULK ISOTACTIC POLYPROPYLENE

A rheo-optical system was used to analyse the nature of the structural changes, other than the well known chain orientation, which can appea r during uniaxial drawing of bulk isotactic polypropylene samples with a spherullitic structure. The stretching was performed at room temper ature and Raman spectra were simultaneously collected along with stres s and strain data to gain insight into the molecular basis of the prop erties involved in the mechanical process. Some degree of backbone cha in deformation is suggested based on observations of the wavenumber sh ift of some Raman bands, especially those with high contributions of s keletal vibrations. The dependence of the band shift on the applied st ress was not linear. and this is interpreted in terms of the different average orientation that the polymer shows during the stretching. The band shift and its associated phenomena were reversible as the load w as removed.