WAXD and FTIR spectroscopy studies on phase behavior of syndiotactic polystyrene/1,1,2,2-tetrachloroethane complexes

Crystal polymorphism, conformation, and transformation of syndiotactic polystyrene (sPS) thin films cast from 1,1,2,2-tetrachloroethane were investigated via wide angle X-ray diffraction, transmission electron microscopy, electron diffraction, differential scanning calorimetry, and Fourier-transform infrared spectroscopy (FT-IR). The solvent-induced crystallization of sPS yielded an ordered crystalline γ-form packed with a helical conformation of lower degrees of perfection. The 1,1,2,2-tetrachloroethane solvent was unique in that, instead of forming a meso crystalline δ-form (which is a polymer-solvent complex) for most other solvents, it could induce sPS to develop a crystalline γ-form. The unique behavior was attributed to the discrepancies in the location of solvent molecules after solvent casting. As evidenced by FT-IR characterization, the solvent molecules within the polymer-solvent complex were identified being mainly trapped in the non-crystalline/amorphous phase. The solvent-induced crystalline γ-form exhibited a crystalline morphology having small crystal aggregates with an average size less than 100 nm. Upon heating, the crystalline γ-form gradually grew into much perfect packing, and finally went through a γ → α′ transformation at temperature of 200°C.