A technique has been developed that determines simultaneously solubilities and diffusivities of gases in molten or thermally softened polymers. Henry's low was found to hold up to 20 atm. In addition it was found that pressure had no appreciable effect on diffusion coefficients up to 20 atm. Solubilities and diffusivities were determined for systems involving nitrogen, helium, carbon dioxide, and argon in polyethylene, polyisobutylene, and polypropylene. In addi. tion, solubilities were also determined for the preceding gases in polystyrene and polymethylmethacrylate. Other data were also obtained for neon, krypton, and monochlorodiflouromethane in various polymers.and diffusivity data for gases in softened or chemical engineer. Such data are of particular interest in polymer finishing processes, where the molten polymer is blanketed with inert gas; in certain specialized operations such as foam extrusion and fluidized-bed coating; and finally in the production of condensation polymers, where the small molecule split out in the condensation reaction must be continuously removed from the polymer melt in order to achieve a high degree of polymerization.The only studies found in the literature that considered solubilities and diffusivities of gas in softened or molten polymers were those of Lundberg, Wilk, and Huyett (1 to 3 ) and Newitt and Weale ( 4 ) . The fonner investigators considered the systems nitrogen-polyethylene, methanepolyethylene, and methane-polystyrene. Their polymer samples were constrained in a sintered steel cylinder placed within a pressure vessel. The principal deficiency in their work was that they assumed their data to hold for the average of their initial and final pressures even though pressure ranges were sizable.Newitt and Weale ( 4 ) studied the solution and diffusion of hydrogen, nitrogen, carbon dioxide, and ethylene in polystyrene. These workers used sosption experiments and diffusivity measurements by movement of a color boundary to determine their data. A defect in their procedure was their failure to preheat the gases used in the experimental work.The present work was undertaken to determine simultaneously solubility and diffusivity data for a number of gas-polymer systems.The apparatus (Figure 1) used permitted the simultaneous determination of solubility and diffusion coefficient in a single sorption experiment. In principle, the equipment and procedure were similar to those of Lundberg, Wilk, and Huyett and of Newitt and Weale.The diffusion cells (Figure 2 ) were constructed from 2?4-in. cold-rolled bar stock. The premolded polymer samples were contained in a cylindrical 1 in. by 1 in. diffusion cell cavity so that diffusion of gas occurred downward through the surface of the sample. The solid samples were molten sO1ubiliY poymers are of considerable importance to the Preston L. Durrill is at Radford College, Radford, Virginia.generally about 3/4 in. in height and slightly less than 1 in. in diameter.The diffusion cells were heated in a fluidized bed which was both fluidized and...

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 LennardJones 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.