Javier de Abajo

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.

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.

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.

LC-polyimides: 5. Poly(ester-imide)s derived from N-(4-carboxyphenyl) trimellitimide and α,ω-dihydroxyalkanes

Abstract N-(4-carboxyphenyl)trimellitimide was prepared from trimellitic anhydride and 4-aminobenzoic acid and esterified with methanol. Transesterification with α,ω-dihydroxyalkanes in the melt yielded a series of poly(ester-imide)s with varying spacer lengths. These poly(ester-imide)s were characterized by elemental analyses, inherent viscosities, differential scanning calorimetry measurements, wide angle X-ray spectroscopy powder and fibre patterns, including synchrotron radiation measurements at variable temperature, optical microscopy with polarized light, and thermogravimetric analyses. Poly(ester-imide)s with even-numbered spacers can form three different kinds of solid phase, including a smectic glass and a crystalline smectic phase. Fibre patterns of melt-spun fibres indicate a high degree of order for series of subsequent layers, even when any order inside the layers is lacking. Poly(ester-imide)s with odd-numbered spacers crystallize much more slowly and can be quenched from the isotropic melt, so that isotropic glasses can be obtained.

Aromatic polyamides with benzothiazole pendent groups: synthesis, nuclear magnetic resonance structural study and evaluation of properties☆

Abstract A new family of aromatic polyamides were prepared from six aromatic diamines and a new monomer derived from isophthalic acid: 5-(2-benzothiazolyl)isophthaloyl chloride. Theoretical calculations of the reactivity of the new monomer were made by semiempirical methods. The polymers were synthesized by the solution polycondensation method at low temperature, in high yields and moderate to high inherent viscosities. The presence of pendent benzothiazole rings brought about remarkable changes in the spectral (nuclear magnetic resonance) characteristics, compared with those of the homologous unmodified polyisophthalamides. Noticeable improvements were observed also for the solubility and for the glass transition temperatures, which rose 20–30°C relative to those of the conventional polysiophthalamides. Thermogravimetric analyses showed that the new polymers have better thermal stability than the unmodified ones.

Polyisophthalamides with phenoxy pendant groups

Abstract Polyisophthalamides containing phenoxy pendant groups were prepared from 5-phenoxyisophthaloyl chloride and aromatic diamines, and their properties were compared with those of unsubstituted polyisophthalamides. The incorporation of one phenoxy group per repeating unit brought about a decrease in the glass transition temperatures of 20–30°C, while the thermal resistance (t.g.a.) remained unchanged for those polymers with aliphatic or ether linkages in the main chain, and slightly diminished for the fully aromatic polymers. Other properties investigated were mechanical resistance, solubility and water absorption.

New perylene-doped polymeric thin films for efficient and long-lasting lasers

We establish an efficient strategy to optimize the performance of dye-doped host materials consisting of analyzing in a systematic way the dependence of their Amplified Spontaneous Emission (ASE) efficiency and photostability on the composition and structure of the matrices, selected to specifically avoid the thermal and/or chemical (photooxidation) processes, main mechanisms of dye photodegradation. For this study, a number of experimental polyimides have been chosen as a host matrix and their behavior has been compared with that of poly(methyl methacrylate) (PMMA). We correlate the optical properties with the oxygen permeation and thermal properties of the different polymeric hosts doped with perylene dyes to deepen the understanding of the photodegradation mechanism predominant in these dyes and to minimize its influence. We demonstrate high efficiency and photostable ASE from waveguides based on polymeric materials doped with Perylene Orange (PO), Perylene Red (PR), and mixtures of both. This enhancement in the optical properties allows reaching high gain and long-lasting distributed feedback (DFB) laser emission based on PO doped polymer matrices, even when operating in an unoptimised resonator.

Aromatic polyamides with pendent heterocycles: 2. Benzoxazole groups

Abstract A series of polyisophthalamides (PIPAs) containing pendent benzoxazole groups was prepared from six aromatic diamines and a new monomer, 5-(2-benzoxazole)isophthaloyl chloride. These polymers, having moderate to high inherent viscosity values, were synthesized by the low temperature polycondensation method in high yields. A striking feature of these polymers is that their solubility and thermal properties were enhanced compared to the corresponding unmodified PIPAs. Thus, all of the polymers were soluble in aprotic polar solvents and glass transition and decomposition temperatures were, respectively, 15–40°C and 25–35°C higher than for the reference PIPAs. The tensile strengths were somewhat lower than those for the unmodified PIPAs.