Synthesis and gas transport properties of new polynorbornene dicarboximides bearing trifluoromethyl isomer moieties

Abstract

This work reports on the synthesis and ring-opening metathesis polymerization (ROMP) of new structural isomers based on norbornene dicarboximides bearing trifluoromethyl moieties, specifically, N-2-trifluoromethylphenyl- exo- endo-norbornene-5,6-dicarboximide (2a) and N-3-trifluoromethylphenyl- exo- endo-norbornene-5,6-dicarboximide (2b) using tricyclohexylphosphine [1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzylidene] ruthenium dichloride (I), bis(tricyclohexylphosphine) benzylidene ruthenium (IV) dichloride (II), and bis(tricyclohexylphosphine) p-fluorophenylvinylidene ruthenium (II) dichloride (III). It is observed that the –CF3 moiety attached to the ortho position of the aromatic ring increases the thermal and mechanical properties of the polymer, whereas the meta substitution has the opposite effect. A comparative study of gas transport in membranes based on these fluorinated polynorbornenes showed that the –CF3 ortho substitution increases the permeability of the polymer membrane as a consequence of the increase of both the gas solubility and the gas diffusion. In contrast, the gas permeability coefficients of the meta-substituted polymer membrane are rather similar to those of the non-fluorinated one attributed to a lower fractional free volume. The meta-substituted polymer membrane besides showing the largest permselectivity coefficients of all the isomers studied here was also found to have one of the largest permselectivity coefficients reported to date for separating hydrogen/propylene in glassy polynorbornene dicarboximides.