Solubilities and diffusivities of various gases (helium, nitrogen, carbon dioxide, argon, neon, krypton, and monochlorodifluoromethane) in molten or thermally softened polymers (polyethylene, polypropylene, polyisobutylene, polystyrene, and polymethylmethacrylate) have been correlated with structural characteristics, temperature, and pressure. Temperature dependence of both Henry's Law constants and diffusivities were of the Arrhenius equation form. No appreciable effect of pressure was found for either Henry's Law constants or diffusivities up to 300 atm. Earlier correlations for Henry's Law constants in solid polymer systems were found to be inapplicable for molten and thermally softened polymers. New correlations were developed individually for the latter systems. The correlating factor used was the gos Lennard-Jones force constant. Existing correlations for diffusivities were also found not to apply to molten and thermally softened systems. New correlations were again developed on an individual polymer basis. These related diffusivity to gas Lennard-Jones collision diameter or molecular diameter. Generalized correlations were also developed that held for a number of polymers.
These were for both Henry's Law constants and diffusivities.
In an earlier paper (1) solubility and diffusivity data were presented for gases absorbed into molten or thermally softened polymer systems. The intent of this paper is to use these data together with other literature information ( 2 to 10) to correlate solubilities and difFusivities with temperature, pressure, and gas and polymer structural characteristics for molten or thermally softened polymer systems.
EFFECT OF PRESSURE ON GAS SOLUBILITIES AND DIFFUSIVITIES
It was shown previously (1) that Henry's Law held for pressures up to 20 atm. for a large number of gas-molten polymer or gas-thermally softened polymer systems. Included were data for sorption of carbon dioxide, nitrogen, helium, and argon in polyethylene, polypropylene, polyisobutylene, polstyrene, and polymethylmethacrylate. Additional data for monochlorodifluoromethane in polyethylene, polypropylene and polystyrene as well as krypton and neon in polyisobutylene and polymethylmethacrylate showed an adherence to Henry's Law up to 20 atm. Other investigators ( 2 to 4 ) found that Henry's Law held up to at least 100 atm. (nitrogen, methane with polyethylene) and possibly ( 5 ) up to 300 atm. (nitrogen, hydrogen with polystyrene). Likewise, no appreciable effect of pressure on diffusivities was found for the foregoing systems up to 300 atm.