Polymorphism of syndiotactic poly(p-fluoro-styrene)

Syndiotactic poly(p-fluoro-styrene) (s-PPFS) has been prepared with a polymerization procedure which allows reaching high average molecular masses and satisfactory yields. The polymorphic behavior of the polymer has been mainly studied by X-ray diffraction, calorimetric and infrared analyses. The main crystalline phase of s-PPFS, obtained by melt processing or cold-crystallization, exhibits trans-planar chains, is orthorhombic (a 1⁄4 9.5 Å, b 1⁄4 28.7 Å, c 1⁄4 5.1 Å) and melts at nearly 320 C. The X-ray analysis shows a strict analogy of this orthorhombic phase with the b phase of s-PS, also as for the occurrence of two limit ordered (b00) and disordered (b0) modifications, which differ for the intensity of reflections characterized by h þ k 1⁄4 2n þ 1. A metastable crystalline phase, also exhibiting trans-planar chains, has been observed for as-polymerized samples as well as for amorphous samples crystallized by sorption of toluene or 1,4-difluoro-benzene. Mainly on the basis of solvent sorption and desorption experiments, it is suggested that this metastable phase is a co-crystalline phase with the low-molecular-mass guest molecules