Polymerisation of vinylidene fluoride in supercritical carbon dioxide: Formation of PVDF macroporous beads

Poly(vinylidene fluoride) (PVDF) macroporous beads with diameter in the range of hundreds of micrometers were produced by batch polymerisation of vinylidene fluoride (VDF) in supercritical carbon dioxide (scCO2) using diethyl peroxydicarbonate (DEPDC) as a free radical initiator. The rate and type of stirring were found to influence strongly the morphology of polymers, and the results indicated that the shear force was the key factor. A low shear force and a suitable monomer concentration range at 6–8 mol/l were needed for the formation of PVDF macroporous beads. Scanning electron microscopy (SEM) was employed to characterize the polymer morphology, and Brunauer–Emmett–Teller (BET) method was used to analyze the surface area of the polymer macroporous beads. In addition, polydimethylsiloxane monomethylacrylate (PDMS-ma) and poly(1H,1H,2H,2H-perfluorooctyl methacrylate) (PFOMA) were found to be able to control the size of PVDF macroporous beads. We propose that the formation of PVDF macroporous beads results from the aggregation of semi-crystalline PVDF primary particles.