Vibrational spectrum of syndiotactic polypropylene. Raman tacticity bands and local structures of iso- and syndiotactic polypropylenes

New Raman spectra of syndiotactic polypropylene (form I) are presented together with the infrared spectrum in the low energy region. Depolarization ratios of an optically transparent, solid block of polymer are also given. The vibrational assignments are re-discussed in combination with the results of normal coordinate calculations of other authors. The meaning and validity of the 'Syndiotacticity Index' proposed by other authors is discussed in terms of the concept of regularity bands. Raman bands characteristic of the stereoregularity of iso- and syndiotactic polypropylene are proposed. Their existence suggests the interesting fact that in the molten state stereo-regular diads or triads may exist which are locked into an average conformation which has to be the same as that taken up by the polymer chain upon crystallization.