Angel E. Lozano

Synthesis and characterization of novel polyimides with bulky pendant groups

New dianhydrides containing t-butyl and phenyl pendant groups have been synthesized and used as monomers, together with commercial diamines, to prepare novel polyimides. The influence of the chemical structure of the monomers on their reactivity has been studied by quantum semiempirical methods. The polyimides have been characterized by FTIR and by NMR in the case of soluble polymers. The presence of pendant groups and the method used to imidize polyimide precursors greatly affected polymer properties such as solubility, glass transition temperature, thermal stability, and mechanical properties. As a rule, the novel polyimides showed better solubility in organic solvents than the parent polyimides. Glass transition temperatures in the range 250 -270°C and decomposition temperatures over 520°C were observed for the set of current polymers. Tensile strengths up to 135 MPa and mechanical moduli up to 3.0 GPa were measured on films of the current polyimides.

Gas separation properties of aromatic polyimides

A series of aromatic polyimides have been investigated for their permeation properties to oxygen, nitrogen, helium, carbon dioxide and methane. The polymers are soluble, film-forming polyimides based on new anhydride monomers containing carbonyl groups as connecting linkages of phenyl rings and bulky side groups like phenyl and t-butyl. To assist in explaining the experimental results, molecular modeling was performed to calculate density, free volume and chain parameters that could account for the behavior of the polymers as selective barriers for gas penetrants. High values of O2/N2 selectivity and good permeabilites were observed for some polymers; their properties lie near the upper bound for this gas pair. Gas permeability typically increased with increasing free volume, and, in general, free volume could be related to the chemical composition of the polymer backbone and to the nature of the pendent groups.

Synthesis and characterization of new soluble aromatic polyamides derived from 1,4-Bis(4-carboxyphenoxy)-2, 5-di-tert-butylbenzene

Aromatic polyamides based on a novel bis(ether-carboxylic acid) were synthesized by the direct phosphorylation condensation method. 1,4-Bis(4-carboxyphenoxy)-2,5-di-tert-butylbenzene was combined with various diamines containing flexible linkages and side substituents to render a set of eight novel aromatic polyamides. The polymers were produced with high yields and moderate to high inherent viscosities (0.49–1.32 dL/g) that corresponded to weight-average and number-average molecular weights (by gel permeation chromatography) of 31,000–80,000 and 19,000–50,000, respectively. Except for a single example, the polyamides were essentially amorphous and soluble in a variety of common solvents such as cyclohexanone, dioxane, and tetrahydrofuran. They showed glass-transition temperatures of 250–295 °C (by differential scanning calorimetry) and 10% weight loss temperatures above 460 °C, as revealed by thermogravimetric analysis in nitrogen. Polymer films, obtained by casting from N,N-dimethylacetamide solutions, exhibited good mechanical properties, with tensile strengths of 83–111 MPa and tensile moduli of 2.0–2.2 GPa.

Synthesis and characterization of new soluble aromatic polyamides based on 4‐(1‐adamantyl)‐1, 3‐bis(4‐aminophenoxy)benzene

A set of new aromatic polyamides were synthesized by the direct phosphor- ylation condensation of 4-(1-adamantyl)-1,3-bis-(4-aminophenoxy)benzene with various diacids. The polymers were produced with high yields and moderate to high inherent viscosities (0.43-1.03 dL/g), and the weight-average molecular weights and number- average molecular weights, determined by gel permeation chromatography, were in the range of 37,000 -93,000 and 12,000 -59,000, respectively. The polyamides were essen- tially amorphous and soluble in a variety of solvents such as N,N-dimethylacetamide (DMAc), cyclohexanone, and tetrahydrofuran. They showed glass-transition tempera- tures in the range of 240 -300 °C (differential scanning calorimetry) and 10% weight- loss temperatures over 450 °C, as revealed by thermogravimetric analysis in nitrogen. All the polymers gave strong films via casting from DMAc solutions, and these films exhibited good mechanical properties, with tensile strengths in the range of 77-92 MPa and tensile moduli between 1.5 and 2.5 GPa.

Sulfonated poly(ether ether sulfones): Characterization and study of dielectrical properties by impedance spectroscopy

In this work, three samples of sulfonated polysulfones of different sulfonation degree have been characterized, and the electrical properties of dense membranes based on them have been evaluated. The polymers were characterized spectroscopically, and by their inherent viscosity, and water absorption. Electrical characterization of membranes was carried out on dense membranes in contact with NaCl solutions, by impedance spectroscopy (IS) measurements using equivalent circuits as models. The results showed how the sulfonation clearly affected the membrane electrical characteristics, strongly reducing the membrane resistance, and also changing the type of circuit associated to the membrane, which could be related to the increase of electrolyte taken by the membrane when the sulfonation degree increased. Concentration dependence of the electrical parameters was also studied.

Tuning microcavities in thermally rearranged polymer membranes for CO2 capture.

Microporous materials have a great importance in catalysis, delivery, storage and separation in terms of their performance and efficiency. Most microporous materials are comprised of inorganic frameworks, while thermally rearranged (TR) polymers are a microporous organic polymer which is tuned to optimize the cavity sizes and distribution for difficult separation applications. The sub-nano sized microcavities are controlled by in situ thermal treatment conditions which have been investigated by positron annihilation lifetime spectroscopy (PALS). The size and relative number of cavities increased from room temperature to 230 °C resulting in improvements in both permeabilities and selectivities for H(2)/CO(2) separation due to the significant increase of gas diffusion and decrease of CO(2) solubility. The highest performance of the well-tuned TR-polymer membrane was 206 Barrer for H(2) permeability and 6.2 of H(2)/CO(2) selectivity, exceeding the polymeric upper bound for gas separation membranes.

Gas separation properties of aromatic polyamides containing hexafluoroisopropylidene groups

Abstract The synthesis and gas transport properties of aromatic polyisophthalamides (PIPAs), based on isophthaloyl chloride derivatives bearing pendent groups and hexafluoroisopropylidene (6F) linkages in the main chain, are reported and compared with properties of a similar series of PIPAs containing sulfonyl (SO2) rather than 6F in the main chain. All of those polymers exhibit high glass transitions temperatures. The polymers containing 6F groups were markedly more permeable and somewhat less selective than their sulfonyl analogs. Polymers containing a t-butyl pendent group at the 5 position of the isophthaloyl linkage were much more permeable than those bearing only a hydrogen atom at this position, although a strong decrease in permselectivity accompanied the large increase in permeability. CO2/CH4 solubility selectivity values of the 6F-containing polymers were similar to values reported for other polymetric and non-polymeric organic materials with similar concentrations of polar carbonyl linkages. In contrast, the CO2/CH4 solubility selectivity in SO2-containing variants of these polymers was substantially lower than expected based on total polar group concentration. The low CO2/CH4 solubility selectivity is believed to be related to the extremely efficient chain packing in the SO2-containing polymers, which may lead to strong amide-amide linkage interaction, thereby inhibiting carbonyl groups in the amide linkage from interactions with CO2 molecules to increase CO2/CH4 solubility selectivity.

New liquid absorbents for the removal of CO2 from gas mixtures

New liquid absorbents (LA) consisting of water solutions of CO2-complexing agents have been developed and tested in an experimental lab-scale to be used in CO2 separation from gas mixtures. The results here presented concern the preparation of these amino acid based new liquid absorbents and the studies carried out to determine their performance as CO2 scrubbers. The novel systems show good performance in terms of sorption and stability compared to the standard alkanolamines. Moreover, the experimental results have shown that among the studied carriers, arginine and ornithine are the natural amino acids with greater affinity towards CO2 and that some of the here synthesized amino acids show outstanding absorption capacities, superior to MEA or any other amino acid tested. The developed materials have a direct use as mobile carrier membranes for facilitated transport and present a great potential for application in gas separation processes. Computational (DFT) and spectroscopic (1H and 13C-NMR) methods have been applied to make clear the mechanism of carbamate formation from the amine group of amino acids and CO2.

Gas separation properties of aromatic polyamides with sulfone groups

Abstract The gas transport properties of three aromatic polyisophthalamides based on isophthaloyl chlorides and 4,4′-diaminodiphenylsulfone are reported at 35°C. The effects of bulky t-butyl and phthalimide substituents, at the 5 position of the isophthaloyl chloride moiety, on CO 2 , CH 4 , O 2 , N 2 , H 2 and He permeability, solubility and diffusivity were determined and correlated with chain packing and thermal properties of the polymers. Gas permeability was higher in substituted polyisophthalamides than in the unsubstituted analogue. Polymers containing the pendent t-butyl substituent have substantially higher permeability than polymers bearing the phthalimide substituent, despite the fact that the phthalimide substituent appears to be more bulky than the t-butyl group, based on van der Waals volume estimations. The strong polarity of the phthalimide moiety may act to increase chain-chain cohesive forces, which would tend to enhance chain packing, thereby reducing the packing-disrupting ability of the bulky phthalimide group. The permeability increase of the substituted polymers was accompanied by a permselectivity decrease.

Gas separation properties of pendent phenyl substituted aromatic polyamides containing sulfone and hexafluoroisopropylidene groups

Abstract The synthesis and gas transport properties of aromatic polyisophthalamides (PIPAs) based on isophthaloyl chloride (IPC) derivatives bearing a pendent phenyl group and a hexafluoroisopropylidene (6F) linkage in the main chain are reported. The properties of these polymers are compared with the properties of similar PIPAs containing sulfonyl (SO2) rather than 6F in the main chain. Polymers containing a phenyl pendent group at the five position of the isophthaloyl linkage are more permeable than those bearing only a hydrogen atom at this position, although increases in permeability are generally accompanied by decreases in selectivity. In the SO2-bearing polymer, the addition of a phenyl pendent group hinders chain packing more than in the 6F containing PIPAs. Consequently, permeability coefficients increase more upon addition of a pendent phenyl group in SO2-containing rather than 6F-containing PIPAs. The effect of amide linkage reversal on the gas transport properties of a polymer containing 6F linkages in the chain backbone and a hydrogen atom at the five position of the isophthaloyl linkage was minimal. All the PIPAs considered in this study were more permeable to nitrogen than to methane, some with nitrogen/methane selectivities of more than two.