Using Raman spectroscopy to determine the structure of copolymers and polymer blends

We present Raman structural study of two grades of random propylene/1-octene copolymers with low and high molecular weights and the 1-octene content up to 4.5 mole %. The copolymer spectra are compared with the spectra of the alpha,gamma, and smectic modifications of isotactic polypropylene. Raman investigation has showed that the degree of crystallinity and conformational order of the copolymer macromolecules slightly decrease with the growth of the 1-octene content. The degree of crystallinity is slightly higher for the samples of the high-molecular-weight grade compared to the low-molecular-weight one. Furthermore, we present Raman spectra of polyethylene/polypropylene (90/10) blends, mixed in the polyethylene melt at three different temperatures, corresponding to three different states of polypropylene macromolecules. It was concluded that the degree of crystallinity and conformational order of the polyethylene macromolecules in the blends are the highest for the temperature, at which polypropylene macromolecules have lost their packing and conformational order.