Effect of reactor size on plasma polymerization of perfluoropropene

Abstract

Effects of the reactor size on the deposition characteristics and the chemical structure of deposited polymers during the plasma polymerization of perfluoropropene were investigated. A 132 cm long glass tube with a diameter of 1.8, 3.3, or 4.7 cm was chosen for a small, medium, or large reactor, respectively. Plasma was formed by a capacitively coupled 13.56 MHz rf power generator. Deposition rate profiles along the reactor tube showed that the dependence of the deposition rate on the operating conditions depended on the reactor size. As the size (diameter) of a tubular reactor decreases, the dissipation of energy to the reactor wall increases since the surface to volume ratio of a tubular reactor increases. Therefore, the plasma polymerization domain changes from the monomer deficient to the energy deficient domain as the reactor size decreases under the same (externally controllable) operating conditions. Electron spectroscopy for chemical analysis was used to analyze the chemical composition and structures of deposited polymers. The chemical composition and structures were varied depending on the reactor size which were also due to the change of the plasma polymerization domain. The plasma polymers prepared in the monomer deficient domain showed a similar composition and structures regardless of the reactor size or the operating conditions. Generally, large amounts of CF3 and CF2 groups were present in the polymer prepared in the monomer deficient domain, and the F/C ratios were approximately 1.6. As the W/FM (energy input per unit mass of monomer) value decreased to the energy deficient domain, the composition and the structures were changed sensitively but following a complicated pattern according to the change of operating conditions.