Synthesis, Gas Permeability, and Gas Sorption Properties of Fluorine-Containing Norbornene Polymers

Abstract

Two fluorine-containing glassy polynorbornenes were synthesized, and their properties (permeability (P), diffusion (D), and solubility (S) coefficients, sorption isotherms, and lifetime positron annihilation spectra) were studied. Both polymers, poly(5,5-difluoro-6,6-bis(trifluoromethyl)norbornene) (PFMNB) and poly(5,5,6-trifluoro-6-(heptafluoropropoxy)norbornenel (POFPNB), were demonstrated to be highly permeable materials having Pvalues much larger than the Pvalue of nonsubstituted polynorbornene. Positron annihilation analysis and density measurements showed that these polymers have high free volumes. However, the reasons for the high permeabilities of these two materials were different. The permeability of PFMNB (Tg = 169 C) is related to its very high solubility coefficients while that of POFPNB (Tg = 77 C) appears to be caused by both its diffusion and solubility coefficients. Sorption isotherms have the form expected for materials behaving according to the dual-mode sorption model. The parameters for this model were determined by a least squares analysis of the isotherms. It was shown that the Henry's law solubility coefficient ko is enhanced in these fluorine-containing polymers compared to other polynorbornenes. On the other hand, the Langmuir capacity parameter C'H, which characterizes the nonequilibrium state of a polymer, also correlates with the Tgvalues of these norbornene polymers. Hence, both equilibrium and nonequilibrium factors appear to be responsible for the enhanced solubility and permeability seen for these fluorine-containing norbornene polymers.