Pure-Gas and Vapor Permeation and Sorption Properties of Poly[1-phenyl-2-[<i>p</i>-(trimethylsilyl)phenyl]acetylene] (PTMSDPA)

Abstract

The pure-gas permeation and sorption properties of poly[1-phenyl-2-[ p -(trimethylsilyl)phenyl]acetylene] [PTMSDPA] are presented and compared to those of poly(1-trimethylsilyl-1-propyne) [PTMSP], poly(4-methyl-2-pentyne) [PMP], and poly(1-phenyl-1-propyne) [PPP]. PTMSDPA is more permeable to large, condensable vapors (e.g., n -butane) than to small, permanent gases (e.g., hydrogen). Such behavior is also observed in PTMSP and PMP but not in PPP. PTMSDPA has lower fractional free volume (0.26) and gas permeabilities than PTMSP and PMP. However, relative to conventional glassy polymers, PTMSDPA is a highly permeable, high free volume, glassy material. For example, the oxygen permeability coefficient of PTMSDPA is 1200 × 10 -10 cm 3 (STP)·cm/(cm 2 ·s·cmHg) at 25 °C. As temperature increases, the permeability in PTMSDPA increases for light gases (helium, hydrogen, and nitrogen) and decreases for more condensable gases. In contrast, the permeabilities of PTMSP and PMP decrease with increasing temperature for both light gases and more condensable hydrocarbons. n -Butane and propane sorption isotherms for PTMSDPA are concave to the penetrant relative pressure axis, consistent with dual-mode sorption behavior. Hydrocarbon sorption levels decrease in the order PTMSP > PMP > PTMSDPA > PPP, in agreement with the ranking of the fractional free volumes of the materials.