Estimation of crystallinity of isotactic polypropylene using Raman spectroscopy

A method to estimate the degree of crystallinity in isotactic polypropylene has been developed. The method is based on integrated intensities of the Raman bands at 808 and 841 cm⁻¹. From the observation of correlation splitting, Raman bands related to different conformational states were identified. This analysis indicates the existence of three different conformational states. The 808 cm⁻¹ band was assigned to helical chains within crystals. The 840 cm⁻¹ band was shown to be composed of a band at 840 cm⁻¹, assigned to shorter chains in helical conformation, and a broader band at 830 cm⁻¹ assigned to chains in non-helical conformation. In order to establish a quantitative relation between Raman scattering intensity and crystallinity samples subjected to different cooling rates and crystallisation temperatures were analysed. These results correlate well with those of differential scanning calorimetry.