Polymorphism of syndiotactic polystyrene: γ phase crystallization induced by bulky non-guest solvents

The crystallization of amorphous syndiotactic polystyrene (s-PS) films when induced by bulky solvents, whose molecules are too big to be enclosed as guest of s-PS clathrate phases, generally leads to the formation of γ-phase. This kind of solvent induced crystallization in amorphous films generates a preferential (200) uniplanar orientation of the γ-crystalline phase. Moreover, the presence of highly boiling solvents in the amorphous phase of these γ-form samples can induce a γ→β phase transition, as a consequence of thermal annealing procedures at atmospheric pressure. A comparison with literature data suggests that the formation of the thermodynamically stable β-phase is generally favored with respect to the formation of the kinetically favored α-phase, by any s-PS dilution.