Polymorphism in Syndiotactic Polystyrene: An 1H NMR Relaxation Study

A marked shortening of T, relaxations in solid aromatic polymers can be attributed to O2 adsorbed on the aromatic rings. This effect, observed as a function of temperature, is modulated by the amount of adsorbed O2, Which, in turn, varies according to the molecular packing and crystalline/amorphous ratio. Within the temperature range 77-400 K, semicrystalline syndiotactic polystyrenes (s-PS) in the alpha, beta, and gamma-polymorph modifications were studied by pulse H-1 NMR at 30 MHz. Due to the presence of many relaxation components, 1,2,2-trideuterio-s-PS was synthesized, crystallized, and characterized by X-ray powder diffraction. At low temperature, when both the O2 diffusion and the spin-diffusion processes are slow enough, the backbone-deuteriated polymers exhibit multiple T1 relaxations: three for alpha and beta s-PS and two for gamma s-PS. These T1 components are attributed to crystalline and amorphous phases. From the study of these components as a function of temperature and from direct comparison of T1 values in the different phases, the following conclusions were drawn: (i) Clear differentiation was possible between different s-PS polymorphs. (ii) Determination of the crystalline vs amorphous ratio fully consistent with X-ray diffraction data was achieved. (iii) The amorphous component of different semicrystalline s-PS polymorphs could be distinguished.