Time-Dependent Transformation of an Electrospun Isotactic Poly(1-butene) Fibrous Membrane

Isotactic poly(1-butene) (i-PB) fibrous membranes with fiber diameters on the order of microns were prepared from polymer solutions using mixed solvents via electrospinning. As demonstrated by FE-SEM, unexpected structures such as curled, twisted ribbon fibers and hollow hemisphere (HHS) on a string appeared depending on the type of solvents used. Furthermore, it was observed that electrospun fibrous membranes and solvent cast films gave rise to different crystalline modifications even though they were formed from the same solutions. This may be due to different crystallization times and stresses induced during the electrospinning process. The electrospun fibrous membrane contained both form I (twinned hexagonal structure) and metastable form II (tetragonal structure) immediately after spinning. The metastable form II gradually transformed into the stable form I at room temperature over the span of several days. This transformation was observed to occur more rapidly with increased temperature. In comparison, solvent cast films contained a mixture of form III (orthorhombic structure) and a small amount of form I' (untwinned hexagonal structure) and was stable at room temperature. However, form III is the dominant crystal structure in the solvent cast film, as determined by WAXD. These transformations were investigated as a function of aging time by Fourier transform infrared and Raman spectroscopy as well as X-ray diffraction and differential scanning calorimetry.