Raman Vibrational Studies of Syndiotactic Polystyrene. 1. Assignments in a Conformational/Crystallinity Sensitive Spectral Region

Abstract

A detailed analysis of the Raman spectrum of syndiotactic polystyrene, sPS, in the region 600−850 cm -1 has been undertaken. As sPS exhibits considerable polymorphism, spectra of various preparations including melt-crystallized sPS (α/β form), solvent-crystallized sPS (γ/δ forms), and quenched glassy material were studied. The ν 1 vibration of the phenyl ring (ring breathing mode) has been shown to manifest itself through the presence of two peaks resulting from local conformational changes in the alkyl backbone. The peak centred around 773 cm -1 has been assigned to an all-trans backbone sequence whereas the higher frequency feature at ∼798 cm -1 is attributed to mixed trans/gauche conformations. For comparison the spectrum of atactic polystyrene was also studied, and the presence of a weak shoulder is assigned to a syndiotactic all-trans component within the polymer. Further study of a cross section of molded material exhibiting a skin/core structure reveals the continuous way in which the relative size, position, width, and intensity of these features vary with changing crystallinity.