Crystallization from the amorphous form of the nanoporous ɛ form of syndiotactic polystyrene

The recently discovered channel-shaped nanoporous ɛ crystalline form of syndiotactic polystyrene (s-PS) is generally obtained by a chloroform-induced recrystallization of samples exhibiting the helical γ crystalline form, followed by chloroform desorption in suitable conditions. This nanoporous ɛ crystalline form can be also obtained by crystallization of amorphous samples as induced by the same chloroform sorption–desorption procedure. This procedure, which does not affect β form samples, when applied to samples exhibiting the trans-planar α form instead leads to a recrystallization into the cavity-shaped nanoporous δ form. Both nanoporous crystalline forms (δ and ɛ) are obtained, by this chloroform treatment on uniaxially stretched amorphous films. In particular, polarized FTIR microscopy clearly shows that δ and ɛ crystalline forms prevail in central and lateral film regions, respectively. In fact, in the film central regions, higher polymer draw ratios are reached that lead to higher degrees of trans-planar crystallinity, whose chloroform-induced crystallization leads to δ form formation.