Arlette A. Santiago

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

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.

Ion-Exchange Membranes Based on Polynorbornenes with Fluorinated Imide Side Chain Groups

The electrochemical characteristics of cation-exchange membranes based on polynorbornenes with fluorinated and sulfonated dicarboximide side chain groups were reported. This study was extended to a block copolymer containing structural units with phenyl and 4-oxybenzenesulfonic acid, 2,3,5,6-tetrafluorophenyl moieties replacing the hydrogen atom of the dicarboximide group. A thorough study on the electrochemical characteristics of the membranes involving electromotive forces of concentration cells and proton conductivity is reported. The proton permselectivity of the membranes is also discussed.

Synthesis, characterization, and heavy metal adsorption properties of sulfonated aromatic polyamides:

This work reports on the synthesis of a series of new sulfonated fluorine-containing aromatic polyamides with increasing degree of sulfonation (DS). The chemical structure of the resulting polymers was confirmed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance (1H NMR) which evidenced the presence of amide and sulfonic groups in the proposed concentrations. Afterwards, we carried out a comparative study of heavy metal ion adsorption in membranes based on these aromatic polyamides. The main purpose was to determine the adsorption capacity of the prepared polymer membranes toward Pb2+ and Hg2+ in aqueous media at 30°C and pH neutral. The adsorption kinetics was evaluated with the pseudo-first-order and pseudo-second-order models. The adsorption kinetics in all the polyamide membranes followed the pseudo-second-order rate law for both heavy metal ions. It is observed that the adsorption capacities of all the polyamides toward Pb2+ ions are higher than those of the Hg2+ ions, and these capacities increase as the DS increases. The equilibrium adsorption amounts, q e, were 11.87 mg/g for Pb2+ and 5.17 mg/g for Hg2+ ions for the highest sulfonated polymer.