Joel Vargas

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.

Halogenated Olefins as Chain Transfer Agents in the Synthesis of Telechelic Polynorbornenes Using Ruthenium Alkylidene Catalysts. Computational and Experimental Studies

Ring-opening metathesis polymerization (ROMP) of norbornene (NB) and its derivatives N-adamantyl-exo- endo-norbornene-5,6-dicarboximide (AdNDI) and N-cyclohexyl-exo-endo-norbornene-5,6-dicarboximide (CyNDI) in the presence of cis-1,4-dichloro-2-butene (2a) and cis-1,2-dichloro-ethylene (2b) as chain transfer agents (CTAs) using a (1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazolilydene) (PCy3)Cl2Ru=CHPh (I) has been studied. � Halogenated ole- fin 2b shows no activity as a CTA whenhalogenated olefin 2a is readily cross-metathesized with NB and norbornene dicarboximides. The chain transfer reaction pathways during the ROMP of NB to 2b using a (1,3-diphenyl-4,5- dihydroimidazol-2-ylidene) (PCy3)Cl2Ru=CHPh (1) have been studied at B3LYP/LACVP* level of theory. The calcula- tions show that 2b is a poor substrate for the metathesis reaction due to the steric effect produced by chlorine atoms di- rectly linked to the double bond. The calculated Gibbs free activation energy of a chain transfer reaction from ring-opened NB to 2b was 25.1 kcal/mol.

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.

Research on Polymer Membranes and Teaching Performed in UNAM Campus Morelia

In the newly established Morelia Unit of the Materials Research Institute (IIM) of the National Autonomous University of Mexico (UNAM) several investigations on polymeric materials with applications in membrane technology are being conducted. The new materials developed via ring-opening metathesis polymerization (ROMP) as well as polycondensation have potential environmental and energy applications such as gas separation (Scheme 16.1), proton exchange membranes for low temperature fuel cells, (Scheme 16.2), and the recovery of heavy metals from aqueous solutions (Scheme 16.3), among others. In the short term, the research will focus on generating more sustainable routes for producing polymers from renewable raw materials (Scheme 16.4). In particular, the inclusion of natural sources such as vegetable oil derivatives for obtaining new or already known polymeric materials will be considered.

The Solubility of Hydrocarbon Gases in Glassy Polymers: Fractal Modeling

This work describes the fractal modeling of the solubility of n-alkanes, n-alkenes, methylacetylene, allene, ethylacetylene, and butadiene hydrocarbon gases in glassy poly(vinyltrimethylsilane) (PVTMS). The proposed equation represents satisfactorily the solubility coefficients of the hydrocarbon gases in glassy PVTMS as a function of the fractal dimension of the polymer and the effective diameter of a gas penetrant molecule. It is found that the calculated solubility coefficients have a good correlation with the experimental data. The proposed model can predict the solubility of hydrocarbon gases in glassy polymers.