Solvent-Induced Crystallization of Poly(phenylene sulfone)

Crystallization of poly(phenylene sulfone) (PPSU) occurs given that the solvent quality is low. This may be the case through adding a nonsolvent to a good solvent like N-methyl-2-pyrrolidone (NMP) or by choosing a poor solvent like N,N'-dimethylacetamide (DMAc) or N,N'-dimethylformamide (DMF). Wide-angle X-ray scattering (WAXS) investigations revealed the degree of crystallinity of PPSU in DMF and DMAc, and the lattice spacing for the structures was calculated to be 5.30 and 5.24 angstrom, respectively. Poly(phenylene sulfone) in DMAc formed well-defined banded spherulites with typical maltese crosses as observed by polarized light microscopy. For PPSU in DMF, crystalline plates were found by means of atomic force microscopy (AFM) with a thickness of 21 nm for a single plate. Both structures consist of lamellar fibrils with a thickness of 10 nm and a length in the order of 100-150 nm. The authors propose the reason for the crystallization to be pi-pi stacking of the rather stiff biphenylene groups.