Abstract

Gas permeation, sorption, and structural properties of two highly branched polyacetylenes, poly[1-phenyl-2-[p-(triphenylsilyl)phenyl]acetylene] (PPhSiDPA) and poly[1-phenyl-2-[p-(triisopropylsilyl)phenyl]acetylene] (PPrSiDPA), are reported. Structurally, both polymers have much in common; however, their transport properties are quite different. PPhSiDPA has dramatically lower permeability coefficients than PPrSiDPA. For example, the O2 permeability coefficients of PPhSiDPA and PPrSiDPA are 12 × 10-10 and 230 × 10-10 cm3 (STP) cm/(cm2 s cmHg), respectively, at 22 °C. Gas solubility is very high in PPrSiDPA, similar to that observed in poly(1-trimethysilyl-1-propyne) (PTMSP), the most permeable polymer known. Gas solubility coefficients of PPhSiDPA are 2−3 times lower than those of PPrSiDPA. Free volume size and size distribution were characterized using positron annihilation lifetime (PAL) spectroscopy. Results from these studies (i.e., a bimodal size distribution of free volume elements and large free vol...

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