Sorption and transport of organic vapors in poly[1-(trimethylsilyl)-1-propyne

Abstract

Sorption kinetics and apparent equilibrium isotherms were determined gravimetrically at 35°C for organic vapors in glassy poly[1-(trimethylsilyl)-1-propyne] (PMSP). The sorption kinetics are characterized by diffusion coefficients on the order of 10 −8 cm 2/sec for the normal hydrocarbons (C 3-C 9). These diffusivities are more than one million times larger than corresponding diffusivities characterizing the transport of corresponding penetrants in conventional glassy polymers such as polystyrene, poly(vinyl chloride), and poly(methyl methacrylate). The sorption capacity of this polymer is also quite high compared with values observed for more conventional polymeric glasses. The sorption isotherms of the organic vapors in PMSP follow a generalized dual mode behavior which is often observed for vapors in polymeric glasses. Specifically, at low activities the isotherms are concave toward the activity axis, then become convex to the activity axis at higher activities. The transition separating these two portions of the isotherms does not become evident until the sorption level in PMSP reached more than 30 weight percent, compared with less than 10 weight percent for other glassy polymers. These unusual properties can be related to the low packing density of PMSP. However, the results also reveal that although the quantitative values of diffusivities and solubilities are extraordinary, the qualitative behavior regarding sorption and diffusion is consistent with comparable observations on conventional glassy polymers.