SYNTHESIS, GAS-PERMEABILITY, AND GAS SORPTION PROPERTIES OF FLUORINE-CONTAINING NORBORNENE POLYMERS

Two fluorine-containing glassy polynorbornenes were synthesized, and t heir properties (permeability (P), diffusion (D), and solubility (S) c oefficients, sorption isotherms, and lifetime positron annihilation sp ectra) were studied. Both polymers, y[5,5-difluoro-6,6-bis(trifluorome thyl)norbornene] (PFMNB) and [5,5,6-trifluoro-6-(heptafluoropropoxy)no rbornene] (POFPNB), were demonstrated to be highly permeable materials having P values much larger than the P value of nonsubstituted polyno rbornene. Positron annihilation analysis and density measurements show ed that these polymers have high free volumes. However, the reasons fo r the high permeabilities of these two materials were different. The p ermeability of PFMNB (T(g) = 169-degrees-C) is related to its very hig h solubility coefficients while that of POFPNB (T(g) = 77-degrees-C) a ppears to be caused by both its diffusion and solubility coefficients. Sorption isotherms have the form expected for materials behaving acco rding to the dual-mode sorption model. The parameters for this model w ere determined by a least squares analysis of the isotherms. It was sh own that the Henry's law solubility coefficient k(D) is enhanced in th ese fluorine-containing polymers compared to other polynorbornenes. On the other hand, the Langmuir capacity parameter C'H, which characteri zes the nonequilibrium state of a polymer, also correlates with the T( g) values of these norbornene polymers. Hence, both equilibrium and no nequilibrium factors appear to be responsible for the enhanced solubil ity and permeability seen for these fluorine-containing norbornene pol ymers.