The effect of fluorine atoms on gas transport properties of new polynorbornene dicarboximides Joel Vargas a , Araceli Martı ´nez a , Arlette A. Santiago a , Mikhail A. Tlenkopatchev a, *, Rube ´ n Gavin ˜o b , Manuel Aguilar-Vega c, * a Instituto de Investigaciones en Materiales, Universidad Nacional Auto ´noma de Me ´xico, Apartado Postal 70-360, CU, Coyoaca ´n, Me ´xico DF 04510, Mexico b Instituto de Quı´mica, Universidad Nacional Auto ´noma de Me ´xico, CU, Coyoaca ´n, Me ´xico DF 04510, Mexico c Centro de Investigacio ´n Cientı´fica de Yucata ´n A.C., Unidad de Materiales, Calle 43 No. 130, Col. Chuburna ´ de Hidalgo, C.P. 97200, Me ´rida, Yuc., Mexico 1. Introduction Fluorine containing polymers have attracted much attention due to their outstanding properties. These kinds of polymer exhibit high thermostability, chemical inertness and good hydrophobicity. It is important to note that low intermolecular and intramolecular interactions in fluorine containing polymers are important factor for gas permeability properties of membranes. Thus, we have already reported gas transport properties of polynorbornenes containing adamantyl, cyclohexyl and cyclopentyl imide side chain groups [1– 5]. These glassy polynorbornene dicarboximides showed high T g and good physical and mechanical properties. For example, poly(N- adamantyl-norbornene-5,6-dicarboximide) (P-AdNDI) showed a T g of 271 8C [6]. Even though polynorbornene dicarboximides, such as P-AdNDI, have bulky pendant groups, their gas permeability coefficients are not high but similar to those of amorphous polyesters or polyamides [7–9]. It is well known, that in many cases higher permeabilities are found for glassy polymers with higher glass transition temperature [10–12]. However, this is not the case for polynorbornene with imide side chain groups. Membranes prepared from these polymers show an enhancement of the selectivity, though the permeability remains low and does not depend on the bulk of side chain groups. The low gas permeability of these membranes is due to strong intermolecular interactions of polar C O and C–N bonds in polynorbornene dicarboximides. It is expected that the introduction of fluorine atoms into polynorbornene dicarboximides will decrease interchain interactions between polar imide side chain groups and this effect will increase the gas permeability across them without detriment to the selectivity. The ROMP of norbornene derivatives with various fluorine-containing units is well established [13–16]. With the aim of investigating the effect of fluorine atoms on gas permeability of polynorbornene dicarboximides, the new poly(N- 4-trifluoromethylphenyl-exo-endo-norbornene-5,6-dicarboxi- mide) (Poly-2a) was synthesized and gas transport properties of membranes prepared from this polymer were studied. 2. Results and discussion Monomers 2a and 2b were prepared in high yields. 4- Trifluoromethyl aniline and 3,5-bis(trifluoromethyl) aniline Journal of Fluorine Chemistry 130 (2009) 162–168 ARTICLE INFO Article history: Received 6 August 2008 Received in revised form 20 September 2008 Accepted 22 September 2008 Available online 2 October 2008 Keywords: Fluorinated polynorbornene dicarboximide Ring opening metathesis polymerization Gas transport properties ABSTRACT The new N-4-trifluoromethylphenyl-norbornene-5,6-dicarboximide (2a) and N-3,5-bis(trifluoro- methyl)phenyl-norbornene-5,6-dicarboximide (2b) mixtures of exo and endo monomers were synthesized and polymerized via ring opening metathesis polymerization (ROMP) using bis(tricyclo- hexylphosphine) benzylidene ruthenium(IV) dichloride (I) and tricyclohexylphosphine [1,3-bis(2,4,6- trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzylidene] ruthenium dichloride (II) to produce the corresponding polynorbornene dicarboximides Poly-2a and Poly-2b, respectively. The transport of five gases He, N 2 ,O 2 , CO 2 and CH 4 across membranes prepared from Poly-2a was determined at 35 8C using a constant volume permeation cell. The gas transport properties of the fluorine containing polymer Poly- 2a were compared with those found for membranes from non-fluorinated poly(N-phenyl-exo-endo- norbornene-5,6-dicarboximide) (P-PhNDI). Gas permeability, diffusion and solubility coefficients of the fluorine containing polynorbornene Poly-2a were up to an order of magnitude larger than those of the non-fluorinated one. Poly-2a was found to have one of the largest gas transport coefficients reported to date in glassy polynorbornene dicarboximides. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +52 5556224586; fax: +52 5556161201. E-mail address: tma@servidor.unam.mx (M.A. Tlenkopatchev). Contents lists available at ScienceDirect Journal of Fluorine Chemistry journal homepage: www.elsevier.com/locate/fluor 0022-1139/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jfluchem.2008.09.011