Abstract: A fluorogenic sensory film, or dense membrane, capable of detecting Cr(VI), Fe(III), and Hg(II) in water was prepared. The film was prepared by a bulk radical polymerization of different comonomers, one of which contained a piperazinedione motif as sensory fluorophore. The film exhibited gel-like behavior and was highly tractable, even after being swollen in water. The sensing conditions were chosen to overcome interference from iron and mercury cations, giving rise to a material with a detection limit of 1 ppb for Cr(VI).
Abstract: The preparation of a fluorogenic sensory material for the detection of biomolecules is described. Strategic functionalisation and copolymerisation of a water insoluble organic sensory molecule with hydrophilic comonomers yielded a crosslinked, water-swellable, easy-to-manipulate solid system for water ââdip-inââ fluorogenic coenzyme A, cysteine, and glutathione detection by means of host-guest interactions. The sensory material was a membrane with gel-like behaviour, which exhibits a change in fluorescence behaviour upon swelling with a water solution of the target molecules. The membrane follows a âturn-onâ pattern, which permits the titration of the abovementioned biomolecules. In this way, the water insoluble sensing motif can be exploited in aqueous media. The sensory motif within the membrane is a chemically anchored piperazinedionederivative with a weakly bound Hg(II). The response is caused by the displacement of the cation from the membrane due to a stronger complexation with the biomolecules, thus releasing the fluorescent sensory moieties within the membrane.
Abstract: Our work investigates the tuning of the solvatochromic characteristics of the inorganic oligomer [Au2Ag2(C6F5)4(tht)2]n. This orange solid product gives rise to a colourless solid upon exposure to acetone vapour or to a transparent colourless solution when dissolved in acetone. Furthermore, upon removal of the acetone, the orange-coloured solid is recovered, which indicates that this compound is an excellent acetone chromogenic sensor even in a mixture of solvents or in the gas phase. Upon its incorporation into an organic membrane, the compoundâs sensing behaviour changes depending on the organic microenvironment surrounding the inorganic oligomers. Thus, we have incorporated the inorganic oligomers into different, dense organic membranes to yield hybrid inorganic-organic membranes; the dry materials are perfectly colourless and transparent, in contrast to the orange colour of the dry inorganic compound. Moreover, in aqueous environments, the hybrid inorganic-organic materials exhibited different colours depending on the composition of the organic membrane, and certain hybrids behaved as chromogenic water sensors. The water-swelled hybrid materials showed photoluminescent behaviour depending on the membrane composition. In summary, we have incorporated an inorganic, solvatochromic compound in creasable, transparent organic membrane films to obtain tunable luminescent and solvatochromic materials. The luminescent and solvatochromic properties could be selectively modified by the macromolecule environment.
Abstract: Linear water soluble polymers and nets with gel-like behavior were prepared for use as colorimetric sensors and selective extracting agents for naked eye detection and solid-liquid removal of heavy metal cations from aqueous environments. Triazole is a well-known, heavy-metal cation host. A water insoluble methacrylamide containing a 1,2,4-triazole receptor derivative was copolymerized with highly hydrophilic and water soluble methacrylamides to yield a water soluble polymer or a cross-linked network as a powder or a dense membrane. In powder form, the material selectively removed Hg2+, Pb2+, and Ag+ from aqueous media. In the form of swelled dense membranes or films, the material acted as colorimetric sensor for Fe3+. When the membrane was soaked in a yellow aqueous solution of Fe3+, the formerly colorless, transparent membrane became reddish (but retained its transparency) and the solution became colorless. Aqueous conductivity studies confirmed that both the extraction and sensing phenomena arose from the interaction of the cations with the triazole moieties.
Abstract: This paper describes a strategy followed to achieve a sensing phenomenon in aqueous media using water-insoluble organic molecules. We have prepared a methacrylamide and a methacrylate with pendant cyanide chemosensors based on a fluorene-derivative motif, and we have fabricated highly hydrophilic membranes by means of copolymerising these hydrophobic monomers with others. Therefore, upon absorption of water in the membranes, solvated ions enter the membrane by a simple diffusion mechanism, reaching the hydrophobic chemosensor motifs and giving rise to a macroscopic sensing phenomenon. In this way, we have prepared solid materials (dense membranes or films) capable of selectively detecting cyanide, with an extremely low detection threshold, in aqueous solution by means of colour changes (naked-eye sensing) (13 ppb). Nevertheless, the key point of this research is the description of the possibilities of anchoring organic insoluble molecules (i.e., drugs, fungicides, bactericides, sensing probes, etc.) to solubilise them in water, or to prepare hydrogels, permitting the use of these molecules in aqueous media or in biological media for medical, biological or biochemical purposes.
Abstract: The synthesis and radical polymerisation of methacrylic monomers with benzo-12-crown-4, benzo-15-crown-5, benzo-18-crown-6, and their dipodal counterparts in the ester residue is described. The radical polymerisation of the monomers in solution was carried out at different temperatures, and the polymerisation kinetics curves were obtained by direct measurement of the instantaneous monomer concentrations by nuclear magnetic resonance spectroscopy (NMR). Thus, the polymerisation rate parameter (2fkp/â¹ktâºÂ½), along with the polymer stereoregularity, were obtained in terms of the molar fractions of meso and racemo diads and of syndiotactic, isotactic and heterotactic triads. The interaction of the polymers with cations was studied using polymer networks as solid phases in the solid-liquid extraction of lanthanide cations from both organic and aqueous media.
Abstract: This paper describes the preparation of a hydrophilic copolymer membrane with two comonomers: 1-vinyl-2-pyrrolidone (commercial) and a new water insoluble piperazinedione derivative, which is a fluorogenic mercury sensing motif. The dense membrane permitted the fluorogenic detection of Hg+2 in aqueous media. The sensitivity of the membrane to mercury was significantly high, with a detection limit of 10 ppt. This limit of detection is much lower than that of DMSO/water solutions of the sensing monomer, which is 10 ppb, and significantly lower than the maximum contaminant level (EPA) in drinking water, 2 ppb.
Abstract: The introduction of host units, also called binding sites or receptor subunits, and fluorescence or chromogenic signaling motifs into the lateral or into the main polymer chain opens the way for cutting-edge applications related to the selective interaction of these chemical sites with guest or target molecules (i.e., cations, anions or neutral molecules). Thus, the good mechanical properties of these polymers permit the design and preparation of âá la carteâ fluorogenic or colorimetric probes for sensing diverse analytes. These polymeric probes may work in organic or aqueous solutions and, most importantly, in the solid state, as finished materials, can operate in aqueous media, permitting the preparation of ânaked-eyeâ solid probes to be used by non-specialist personnel, for example, to control the concentration of analytes in chemical industries or to test whether environmental polluting chemicals exceed the legal limits.
Abstract: This paper describes a strategy followed to achieve a sensing phenomenon in aqueous media using water-insoluble organic molecules. A sensory polymeric material for the colorimetric sensing of cyanide in water has been developed based on the reactivity of this anion with a fluorene derivative.
Abstract: This work describes five novel aromatic polyamides and copolyamides containing the triazole heterocycle attached by an amine linkage to the main and lateral chains. The polyamides were found to be amorphous and soluble in polar aprotic solvents. They demonstrated a film-forming capability, exhibited good thermal resistance and had high thermal transition temperatures (up to 375 ºC). The triazole and amine groups imparted hydrophilicity to the polymers, giving rise to materials that improve their mechanical properties upon water uptake, and were efficient chelating/host units for heavy metal cations. These properties facilitated the preparation of solid polymer phases to be used for the extraction and elimination of environmentally deleterious cations from water environments. In regards to cation extraction from aqueous media with polyamide solid phases, the correct polymer structure designs led to the extraction of high percentages of HgII (neat 100%).
Abstract: Novel colorimetric polyamide model compounds for anion-sensing applications are described. Light beige solutions of one of the models (M3) in DMSO develop a red to yellow-reddish colour upon addition of some anions, including OH-, F-, HCO3-, PO43-, AcO-, benzoate-, oxalate2- and p-toluenesulfonate-. In contrast, they remain unchanged in the presence of CH2ClCO2 -, H2PO4-, CF3CO2-, Br-, methanesulfonate-, Cl- or I-. The
reddish colour caused by the addition of basic anions is due to the deprotonation of the urea groups, while the yellowish colour corresponds to modification of the electron density surrounding the urea group due to complexation. The development of the yellow colour of DMSO solutions of M3 upon addition of acetate ions and the disappearance of the red colour of solutions of M3/fluoride by displacement of the acetate ions can serve
as a novel colorimetric assay for titration of the acetate anion, with detection limits close to 1 ppb. The host:guest stoichiometry (polyamide model compound:anion complexes) and the stability constants of complexes were determined by 1H NMR.
Abstract: Wholly aromatic polyamides (aramids) are considered to be high-performance organic materials due to their outstanding thermal and mechanical resistance. Their properties arise from their aromatic structure and amide linkages, which result in stiff rod-like macromolecular chains that interact with each other via strong and highly directional hydrogen bonds. These bonds create effective crystalline microdomains, resulting in a high-level intermolecular packing and cohesive energy. The better known commercial aramids, poly(p-phenylene terephthalamide) and poly(m-phenylene isophthalamide), are used in advanced technologies and have been transformed into high-strength and flame resistant fibers and coatings, with applications in the aerospace and armament industry, bullet-proof body armor, protective clothing, sport fabrics, electrical insulation, asbestos substitutes, and industrial filters, among others. Owing to their chemical structure, they exhibit extremely high transition temperatures that lie above their decomposition temperatures, are sparingly soluble in common organic solvents and, accordingly, can only be transformed upon solution. Research efforts are therefore underway to take advantage of their properties, enhance their processability and solubility, and incorporate new chemical functionalities in the polyamide backbone or lateral structure, so that their applicability is expanded and remains on the forefront of scientific research.
Abstract: This work describes the preparation of functional aromatic polyamides with pendant fluorescent chemical structures. The preparation of a parent copolyamide with a lateral fluorene moiety anchored to the main chain through a urea group is described, along with the chemical modification of the fluorene moieties to render six copolymers with different fluorescent behaviors. The easy and clean chemical modification of the polyamide structure permits the preparation of high-performance materials with âa la carteâ fluorescence properties. The characteristics of these materials make them useful for cutting-edge technologies associated with the fluorescence of the pendant fluorene moiety and with the host behavior of the urea motif, i.e., fluorescent sensing of analytes or hybrid luminescent converter (LUCO) â LED systems. The chemical modification of the polymer structure was carried out with chemicals and conditions optimized for polyamide models. The influence of the chemical structure of the pendant fluorene core has also been addressed in terms of mechanical and thermal properties, solubility, water uptake, etc.
Abstract: This paper describes the preparation and chemical modification of pyranone-based aromatic polyethers to yield polymers that contain pyrylium rings, which permit the design of high performance materials with âa la carteâ chromogenic and fluorescence behavior. These materials can be used for innovative applications such as luminescent converter (LUCO) materials for hybrid light-emitting diodes (LEDs) or the preparation of selective chromogenic and fluorogenic sensing materials for the preparation of sensing devices. The fluorescence emission maxima of polyether films ranged from 514 to 561 nm, allowing the future development of LUCO-LED devices. Moreover, the interaction of polyether films with different amines leads to color changes and variations in the intensity and emission maxima of fluorescence, which permits the development of amine sensing materials.
Abstract: This work describes the synthesis and characterization of polyamides, copolyamides, and polyamide blends containing cation- and anion-selective host units in the pendant structure and their application to the extraction of environmentally polluting cations from aqueous media. The cation host unit consists of a crown ether subunit and the anion receptor is a urea group. The preparation of the copolymers involves the copolymerization of two isophthalic acid derivatives - one containing a lateral urea group and the other a crown ether moiety - with m-phenylenediamine. The molar ratio of crown ether to urea subunits is varied from 1/1 to 1/2 and 1/3 to fit the ion and counterion ratio of metals with valences I, II, and III. The extraction effectiveness and selectivity is related to the composition of the copolymer or the polymer blend, and thus formally to the cation to anion host units ratio, which therefore permits the á la carte design of materials to be used in the decontamination and elimination of polluting cations. With regard to the cation extraction from aqueous media with polyamide solid phases, the polymer structure design leads to the extraction of high percentages of HgII (almost 100%) and moderate extraction of PbII and CrIII.
Abstract: A colorimetric diacid monomer for aromatic diamine sensing containing the urea binding site has been synthesised and characterised. A colour development from colourless to blue, brown or yellow was observed upon addition of metha, para or ortho-phenylenediamine, respectively, to polar aprotic organic solvent solutions of the monomers. The solutions remained colourless upon addition of other amines or diamines. The model polyamide compound derived from the diacid monomer maintains the colorimetric sensing selectivity towards the aromatic diamines; so the polyamides derived from the diacid monomer described herein are supposed to retain the ability to interact selectively with the aromatic diamines; hence cheap future sensing devices could be built by means of easy-to-use naked eye polyamide film chemosensor or by incorporating a polyamide coating in the end of an optic fibre connected to a portable diode array visible detector.
Abstract: Aromatic polyamides are high performance materials with superior thermal and mechanical properties which make them extremely useful for advanced technologies. These polymers can be transformed into high-tensile strength synthetic fibers and into flame and cut-resistant materials that have technological applications in the field of coatings and fillers in the aerospace and armaments industry, in asbestos substitutes, electrical insulation, bullet-proof body armor, industrial filters, and sports fabrics, among others. This article sets out to review the existing literature and recent patent claims that describe the design, the preparation and the applications of wholly aromatic polyamides, semiaromatic polyamides and poly(amide imide)s.
Abstract: A series of aromatic polyisophthalamides containing mono-, di- and tri-nitroiminobenzoyl pendant groups were prepared from aromatic diamines and different 5-iminonitrobenzoylisophthalic acids. Interesting property relationships were revealed when evaluating the influence of the number and the position of the nitro groups in the benzoyl ring. Semi-empirical methods were used to obtain quantitative structure-property relationships (QSPR), which correlated the parameters obtained by molecular modeling with water uptake, thermal stability and C-13 and H-1 NMR chemical shifts. Moreover, by modifying the Bicerano method for aromatic polyamides, the predicted glass transition temperature (T-g) values showed a high degree of correlation with the measured data. The polyamides registered high Tg values of up to 343 degrees C, good thermal and mechanical properties, enhanced solubility in polar aprotic solvents, and their water uptake was as high as 19% (w/w) at 100% relative humidity.
Abstract: This work describes eight novel aromatic and aliphatic-aromatic poly(amide urea)s. These polyamides are semicrystalline and are soluble in polar aprotic solvents. They also demonstrate a film-forming capability, they exhibit moderate thermal resistance and the decomposition temperature is similar in oxidizing and inert atmosphere. The urea group imparts hydrophilicity to the polymers and is an efficient host unit for anions, which facilitates the preparation of solid polymer phases to be used as extractants for the extraction/elimination of environmentally toxic cations from aqueous environments. These systems give moderate but promising results in the extraction of different Pb-II and Hg-II salts from aqueous solution. (C) 2008 Elsevier Ltd. All rights reserved.
Abstract: This work describes six novel fluorescent aromatic polyamides with bulky dansyl or fluorene pendant groups or with the fluorene moiety in the main chain. The fluorescent signaling dansyl or fluorene moieties are chemically connected to, or within, the main polymer chains through a urea group, a well-known binding site in supramolecular chemistry. These polyamides are amorphous and soluble in polar aprotic solvents and demonstrate a film-forming capability. They also show yellowish-green or blue fluorescence in solution and in the solid state depending on the signaling unit, with the former corresponding to the dansyl and the latter to the fluorene residue. The water uptake and the thermal behavior have also been evaluated and related to the chemical structure. The polar amide, urea, and sulfonamide groups give rise to a high water sorption of up to 3.8 water molecules per repeating unit. The thermal behavior has been investigated by means of DSC and TGA. The glass transition temperatures of the polymers are high (up to 331 °C) and the decomposition temperatures (around 300 °C) are due to the moderate thermal stability of the urea group.
Abstract: This work describes the interaction of alkaline, alkaline earth, transition metal, heavy metal, and lanthanide cations from nitrate solutions with synthetic polyamides. The polyamides have pendant structures acting as cation host moieties. The host subgroups are benzo-12-crown-4, benzo-15-crown-5, benzo-18-crown-6, and the three dipodal counterparts of the three benzo-crown units. This interaction has been analyzed in terms of competitive polyamide solid-phase extraction of nitrate cations from aqueous or acetronitrile solutions. The solid-phase extraction of water or acetonitrile solutions of alkaline, alkaline earth, transition metal, heavy metal, and lanthanide ions using solid-phase polyamides is performed with a degree of selectivity. Higher selectivity is observable in the extraction of Pb(II) from a set of heavy metal ions inwater and acetonitrile solutions, and the extraction of Cr(III) from a set of transition metals in acetonitrile solutions. It is a noteworthy result, which along with the reusability of the solid-phase polyamides points to potentially successful applications in the field of environmental chemistry: the decontamination and elimination of poisoning cations, the separation and modification of cation mixtures, and the development of fixed-site carrier membranes for selective transport or manufacture of cation-sensitive sensors. (c) 2007 Wiley Periodicals, Inc.
Abstract: A new model polyamide compound that has a benzo-18-crown-6 moiety in the pendant structure is described. This model interacts with metal cations in the alkaline, earth alkaline, transition metal and heavy metal series. The interaction has been analyzed in terms of competitive cation extraction from aqueous solution by liquid model/dichloromethane phase. In each cation series, K(I), Ba(II), Cr(III), and Hg(II) have been selectively extracted by liquid model polyamide phases. The interaction of a dense composite model polyamide-cellu lose acetate membrane with lead(II) has been studied through its adsorption isotherm, infrared spectra and scanning electron microscopy study of the membranes before and after Pb(II) adsorption. The transport of lead nitrate through the membrane together with that of sodium chloride (for comparison), have been evaluated. (C) 2007 Elsevier Ltd. All rights reserved.
Abstract: Four novel A-B condensation monomers containing an amine and a carboxylic acid function are described, along with their polymerization to give main chain aromatic poly(amide urea)s. The monomers, and the polymer structural unit, are N,N'-diphenylurea derivatives. When comparing wholly aromatic polyamides, or aramids, with the poly(amide urea)s described herein, we find that the chemical resistance to hydrolysis of the later polymers increases and their thermal resistance is diminished due to the main chain urea groups, whereas their water uptake is not greatly modified. The most striking result of the new poly(amide urea)s is their outstanding mechanical resistance: their Young's modulus rises as high as 5.5 GPa and their tensile strengths as high as 170 MPa for unoriented films prepared at laboratory scale by casting. (c) 2007 Wiley Periodicals, Inc.
Abstract: This paper describes certain wholly aromatic polyamides based on 1,3-diamino-4-halobenzenes and 1,3-diamino-4,6-dihalobenzenes, and on isophthaloyl and terephthaloyl chloride by means of low temperature solution polymerization. We set out to study the influence of the kind of halogen (F, Cl or Br) and the type of substitution (mono or di) in the diamine moiety with regard to solubility, water uptake and thermal and mechanical properties. The materials are characterized with respect to chemical structure and purity by elemental analysis, infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopic techniques, and special attention is paid to the sequence distribution (constitutional order) of polymers derived from non-symmetric monohalogen-substituted diamines, and their influence on the above-mentioned properties.
Abstract: The interaction between trivalent lanthanide ions and poly(1,4,7,10,13-pentaoxacyclopentadecan-2-yl-methyl methacrylate), PCR5, in aqueous solution and in the solid state have been studied. In aqueous solution, evidence of a weak interaction between the lanthanides and PCR5 comes from the small red shift of the Ce(III) emission spectra and the slight broadening of the Gd(III) EPR spectra. From the Tb(III) lifetimes in the presence of H2O and D2O the loss of one or two water coordinated molecules is confirmed when Tb(Ill) is bound to PCR5. An association constant of the order of 200 M-1 was obtained for a 1:1 (lanthanide: 15-crown-5) complex from the shift of the polymer NMR signals induced by Tb(III). A similar association constant is obtained from the differences of the molar conductivity of Ce(Ill) solution at various concentrations in presence and absence of PCR5. When Tb(III) is adsorbed on PCR5 membranes, lifetime experiments in H2O and D2O confirm the loss of 5 or 6 water coordinated molecules indicating that in solid state the lanthanide(III)-PCR5 interaction is stronger than in solution. The adsorption of Ce(III) in PCR5 membranes shows a Langmuir type isotherm, from which an equilibrium constant of 39 M-1 has been calculated. SEM shows that the membrane morphology is not much affected by lanthanide adsorption. Support for lanthanide ion-crown interactions comes from ab initio calculations on 15-crown-5/La(III) complex. (c) 2007 Wiley Peiiodicals, Inc.
Abstract: Polymeric films containing pyrylium derivatives showing a selective color modulation from yellow to red in the presence of the poorly coordinating hydrogen carbonate anion in water at neutral pH have been developed.
Abstract: This work describes six novel aromatic polyamides with bulky pendant groups, each having a polyisophthalamide backbone substituted with different urea groups in ring position 5 of the diacid or the diamine residue. Thus, one of the nitrogen atoms of the urea is chemically anchored to the main rigid polyamide chain, while the other nitrogen atom is substituted by phenyl, nitrophenyl, naphthyl, and phenylureidophenyl groups. The polyamides are amorphous and soluble in polar aprotic solvents. They demonstrate a film-forming capability with outstanding mechanical properties, and exhibit moderate thermal resistance in nitrogen and oxygen atmospheres. The urea group imparts hydrophilicity to the polymers, and facilitates the future preparation of specialty polymers through the easy chemical modification of this group. (C) 2007 Wiley Periodicals, Inc.
Abstract: This article describes the synthesis and characterization of two diacid monomers, each containing a benzo-15-crown-5 subunit or its dipodal counterpart. Both novel monomers were reacted with technical aromatic diamines with Yamazaki's direct polyamidation method to render modified polyisophthalamides with high molecular weights containing side moieties of cyclic and acyclic ethylene oxide sequences. All the polymers were soluble in aprotic polar solvents and showed high glass-transition temperatures in the range of 190-345 degrees C. The polymers with side crown ethers showed much higher glass-transition temperatures than those with acyclic linear side ethylene oxide arms. The chemical composition, particularly with respect to the diamine and the open or closed character of the pendent ethylene oxide sequence, also affected other general properties such as the mechanical resistance, mechanical modulus, or water absorption. (c) 2006 Wiley Periodicals, Inc.
Abstract: We report the synthesis and characterization of 10 novel polyamides containing the benzo-18-crown-6 subunit and its dipodal counterpart, along with their properties, and a comparison with homologous polyamides bearing benzo-12-crown-4, benzo-15-crown-5, and the corresponding dipodal systems. The anomalous polymerization of some of the diacid monomers, that leads to insoluble gels under standard Yamazaki polymerization conditions, is described. The gel formation has been attributed to the threading of cyclic oligoamides with a growing polyamide chain to yield rotaxanes, polyrotaxanes, catenanes, or polycatenanes. Polyamide macrocycles have been characterized with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. A route to avoid gel formation, consisting of a lower initial monomer concentration, is also described, along with the polymer properties of the polyamides obtained, including the chemical characterization, mechanical behavior, water sorption, morphology, diffusion data, and permeability of membranes prepared with these polymers. (c) 2006 Wiley Periodicals, Inc.
Abstract: Two novel isoplithalic diacid-based monomers have been synthesized by inclusion in ring position 5 of a functionalized benzoylamine moiety. The functionalization includes a 12-crown-4 ether group fused with the benzene subunit and a dipodand substructure, formally a disubstitution of the benzene ring, with two sequences of ethyl-terminated ethylene oxide units, which represent the open-chain counterpart of the alicylic crown moiety. The polycondensation of the two diacids with five aromatic diamines yielded 10 new polyamides with crown or podand pendant substructures. The polyamides had previously been chemically characterized by NMR, IR, and elemental analysis. The polymers showed high glass transition temperatures of up to 349 degrees C, good thermal stability (T-d (onset), (N2) approximate to 400 degrees C), and improved solubility in organic solvents. The presence of acyclic or alicyclic oxyethylene sequences as crown ether or podand substructures and an additional amide side group per repeat unit made the polymers essentially amorphous and improved their water absorption ability in comparison with nonsubstituted polyamides. Water uptake values as high as 12% were observed at 65% relative humidity. All the polyamides showed a good film-forming ability, and the mechanical properties of these films are considered to be satisfactory for experimental aromatic polyamides. (c) 2006 Wiley Periodicals, Inc.
Abstract: The oxygen permeability and diffusion coefficients of hydrogel membranes prepared with copolymers of 2-ethoxyethyl methacrylate (EEMA)/2,3-dihydroxypropylmethacrylate (MAG) with mole fraction of the second monomer in the range between 0 and 0.75 are described. Values of the permeability and diffusion coefficients of oxygen are determined by using electrochemical procedures involving the measurement of the steady-state current in membranes prepared by radical polymerization of the monomers. The results obtained for the transport properties were analyzed taking into account the fractional free volumes, the cohesive energy densities and the glass transition temperatures of the hydrogels. (C) 2004 Elsevier Ltd. All rights reserved.
Abstract: New polyamides, containing a benzimidazole side group and ethylene oxide moieties in the structural repeat unit, were synthesized by low-temperature polycondensation. The aim of this design was to obtain polyamides that were more soluble in common organic solvents and hence had better processability than benzimidazole polyamides while maintaining the water sorption properties characteristic of the latter. The results showed that the number of ether linkages of the repeat unit played an important role in the glass-transition temperature and in the water sorption properties, the polyamides with one or two ethylene oxide units being more hydrophilic than benzimidazole polyamides. However, the length of the ethylene oxide chain played a minor role in the solubility because the second member of the series, with two ether linkages (i.e., one ethylene oxide unit), reached the same level of solubility as those polyamides with more ethylene oxide moieties. No crystallinity was observed by X-ray and calorimetric measurements for the new polymers. (C) 2004 Wiley Periodicals, Inc.
Abstract: A sensory polymeric material for the colorimetric sensing of cyanide in water has been developed based on the reactivity of this anion with the pyrylium cation.
Abstract: The interaction between trivalent lanthanide ions and the polymer poly(1,4,7,10-tetraoxacyclododecan-2-ylmethyl methaerylate) (PCR4) containing pendant 1,4,7,10-tetraoxacyclododecane (12-crown-4) groups has been studied by various spectroscopic techniques, calorimetry and theoretical calculations. Evidence for the binding of Eu(III), Tb(III), and Ce(III) ions and PCR4 in solution was obtained by the lanthanide-induced III and C-13 NMR shifts and the decay of Tb(III) luminescence. From the isotope effect observed on the decay of luminescence of Th(III) bound to PCR4 in H2O and D2O solutions, it is suggested that complexation leads to a decrease in the number of water molecules from 8 or 9 to 7. In the solid state, studies by differential scanning calorimetry (DSC) show that the interaction between Ce(III), Tb(III), and Li(I) ions and PCR4 leads to an increase in the glass transition temperature (T-g) of the polymer. Electron paramagnetic resonance (EPR) spectra of Gd(III) in the presence of the polymer are quite similar to those in aqueous solution, while Tb(III) emission is quenched by Ce(III) with nearly the same rate constants in water and aqueous PCR4 solutions, and the Ce(III) emission maxima are only very slightly shifted in the presence of the polymer, all suggesting relatively weak dynamic interaction between the cations and the crown ether. However, isotope effects on the Tb(III) luminescence lifetime confirm complexation. From the lanthanide-induced H-1 and C-13 NMR shifts the stability constants of the 1:1 complexes formed have been calculated for both Tb(III) and Eu(III), yielding values 22.5 and 1.9, respectively. The agreement between the constants calculated from H-1 and C-13 NMR shifts are very good and the low values of the calculated stability constants confirm the weak binding of the lanthanide ions by the crown ether. Results of ab initio calculations are also reported, where the interactions are modeled for 12-crown-4/La(III) complex and bond energies determined.
Abstract: A series of methacrylic copolymers was prepared by radical polymerization of the monomers 2-ethoxyethyl methacrylate and 2-hydroxyethyl methacrylamide and a small quantity of a cross-linking agent ethylene glycol dimethacrylate. Water swelling of the membranes, mechanodynamical analysis, density measurements, and ATR-FTIR studies were performed on the copolymers. High vacuum pressure techniques were used to evaluate the flow of He, O-2, N-2, CO2, CH4, CH3CH3, and CH2CH2 through these membranes, and solubility, diffusivity, and permeability coefficients were determined. The effect of the increase of the amount of methacrylamide in the copolymer on transport properties, glass transition, fractional free volume, cohesive energy density, and specific interactions has been studied and is reported in this work.
Abstract: The synthesis and radical polymerization of 1,4,7,10-tetraoxacyclododecan-2-ylmethylmethacrylate (CR4MA) is described. The polymerization reactions of CR4MA were carried out at different temperatures and the kinetic curves of monomer depletion against time were obtained by direct measurements of the instantaneous monomer concentrations by using nuclear magnetic resonance (NMR) spectroscopy. At the same time electron paramagnetic resonance (EPR) spectroscopy was used to determine the actual polymer radical concentration during all the reaction time. The conjunction of both techniques (NMR and EPR) allowed the determination of the polymerization rate parameter (2fk(p)/<k(t)>(1/2)) and separately of k(p) and <k(t)>/f, where f, k(p) and <k(t)> are, respectively, the initiator efficiency factor and the overall averages of propagation (kp is considered to be practically independent of the chain length) and termination rate constants. The values found for this ratio and for k(p) were comparatively higher than those recently reported in the literature for its lateral open chain counterpart, the methacrylic monomer with equal number of oxyethylene units in the residue ester (TTEMA). However, the <k(t)> values were similar for the polymerization of both monomers CR4MA and TTEMA. The polymer, PCR4MA, is soluble in water as its open chain homologous, and exhibits a glass transition temperature in the vicinity of the ambient temperature (about 35 degreesC), much higher than the value found for the homologous polymethacrylate derived from the TTEMA. (C) 2003 Elsevier Ltd. All rights reserved.
Abstract: The syntheses of methacrylic monomers of the general structure [GRAPHICS] where n is 3, 4, 5, or 6, were performed by the reaction of the corresponding alcohol ethers with methacryloyl chloride. The alcohol ethers were previously prepared by different synthetic procedures involving the monoetherification of the starting glycols. The polymerizations kinetics of the monomers were examined at several temperatures in the bulk and in dioxane solutions. NMR spectroscopy and electron paramagnetic resonance techniques were used to study the kinetics of polymerization. The polymerization rate parameter, expressed as (2f)(1/2)k(p)/<k(t)>(1/2), and the values of the propagation rate coefficient k(p) and the termination rate coefficient <k(t)>/f, where f is the efficiency factor of the initiator, were determined. The reactivity of the monomers depended on the size of the ester residue in such a way that the longer the lateral chain was, the higher the polymerization rate was and the lower the termination rate coefficient was. On the contrary, the dependence of k(p) on the chemical structure was very small. In the solution polymerizations of all these monomers (monomer concentration = 1 mol L-1), the radical concentrations remained almost constant until very high conversions, whereas in the bulk, a different behavior was observed that depended on the number of oxyethylene units in the side chain of the monomer. In this sense, for n = 4, 5, or 6, the radical concentration remained almost invariable with the reaction time, whereas for n = 3, a moderate increase occurred at low conversions, contrasting with the important increase observed at similar conversions for n = 1. This showed that the gel effect in these methacrylic monomers was greatly dependent on the number of bonds of the lateral chain. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polyrn Chem 41: 1567-1579, 2003.
Abstract: Polymer membranes were prepared by radical polymerization of the 1,4,7,10-(tetraoxacyclododecan-2-yl) methyl methacrylate (CR4MA) monomer and a small quantity of a cross-linking agent ethyleneglycoldimethacrylate. High vacuum pressure techniques were used to evaluate oxygen and helium transport through these membranes at temperatures below and above its glass transition temperature, between 0 and 50 degreesC. The apparent values of both the permeability and diffusion coefficients are unusually low because of the high packing degree of these polymeric membrane materials. The results obtained were also compared with those deter-mined for polymer membranes derived from their open chain counterparts, the polymer derivatives from methacrylate monomers with a number of oxyethylene units in the ester residue variable between 2 and 6, and with a set of other polymers. (C) 2003 Published by Elsevier Ltd.
Abstract: The diffusion of He, Ar, O-2, N-2, CO2, CH4, CH3CH3 and CH2CH2 has been determined in three polymethacrylates with one, two and three oxyethylene units as side chains. For these three rubbery polymers we have used the acronyms PEEMA, PDEMA and PTEMA, respectively. The results have been compared to those of poly(ethyl methacrylate) on one hand, and on the other with previous results on methacrylates of varying length alkyl side chains. It has been found that the oxyethylene units side chains methacrylates show diffusion coefficients which are slightly lower than those methacrylates bearing alkyl side chain, when comparing polymers with the same number of atoms in the side chain. These diffusion data are put in relation to relevant structural features such as the glass transition temperature and the fractional free volume of both families of rubbery methacrylates. (C) 2003 Elsevier Science Ltd. All rights reserved.
Abstract: Polyamides from isophthaloyl chloride and 1,3-diamino-4-chlorobenzene with diverse constitutional order were obtained in a one-stage synthesis varying the polymerization temperature and the monomer mixing modes. The constitutional order was calculated by H-1 and C-13 NMR spectroscopies. A model to determine the constitutional isomerism in these polycondensates was applied with the relevant kinetic reaction parameters obtained from the model reactions. The Monte Carlo technique was used to model the constitution along the polycondensation reaction as a function of the average polymerization degree. Constitution was determined by kinetic factors and not by thermodynamic ones. (C) 2003 Wiley Periodicals, Inc.
Abstract: Polymerization kinetics at several temperatures of 2-ethoxyethyl methacrylate (EEMA) and 2(2-ethoxyethoxy) ethyl methacrylate (DEMA) in bulk and in dioxane solutions are described. The gel effect was never detected at monomer concentrations equal to or lower than 1 mol L-1, although in the bulk polymerization both monomers display the gel effect at very low conversions. Because of the influence of the efficiency factor f on the polymerization rate, a theoretical kinetic interpretation of the changes in f with monomer and initiator concentrations and kinetic parameters was performed to achieve a better understanding of the mechanisms involved in radical polymerization. (C) 2002 Wiley Periodicals, Inc.
Abstract: Two new monomers, cis-(2-phenyl-1,3-dioxan-5-yl) methacrylate (CPDM) and trans-(2-phenyl-1,3-dioxan-5-yl) methacrylate (TPDM), have been synthesized. The stereochemical configuration in both monomers was unequivocally assigned by correlation H-1-C-13 NMR experiments. The radical polymerization reactions of both monomers were studied by ultraviolet spectroscopy and electron paramagnetic resonance spectroscopy to determine the polymerization rate parameter k(p)/k(t)(1/2) and the absolute propagation and termination rate constants (k(p) and k(t)) at different temperatures. The values of k(p)/k(t)(1/2) lie in the range 0.40-0.55 L-1/2/(mol(1/2) s(1/2)) for CPDM and 0.29-0.37 L-1/2/(mol(1/2) s(1/2)) for TPDM at temperatures between 45 and 70 degreesC, showing that the polymerization rate of the cis monomer with the substituents in equatorial-axial positions on the dioxane ring is higher than that of its trans counterpart with the phenyl and ester residue in equatorial positions on the dioxane ring. Using EPR measurements of the polymer radical concentrations, similar values for hp were obtained for both trans and cis monomers, whereas the termination rate constant of the trans monomer was about twice that of the cis monomer at the same temperature.
Abstract: A new oxypyrone diamine, 2,6-bis(4-aminophenyl)-3,5-dimethyltetrahydro-4H-pyran-4-one (DAPP), was prepared from 4-nitrobenzaldehyde and 3-oxa-n-pentane in a two-step reaction with a high yield and a high purity. Aromatic polyamides were obtained from this novel condensation monomer and several diacid chlorides through the conventional low-temperature solution method in iv,N-dimethylacetamide. Polycondensation results were consistent with a high reactivity for DAPP because high yields and high molecular weight polyamides were obtained with inherent viscosities up to 1.8 dL/g, The reactivity of DAPP was also estimated with theoretical calculations from computer programs for molecular simulation, with orbital and charge factors considered. The polymers showed improved solubility in organic solvents, relative to conventional wholly aromatic polyamides, and high glass-transition temperatures (from differential scanning calorimetry) over 270 degreesC. However, the thermal resistance, as estimated by thermogravimetric analysis, was lower than that of conventional aromatic polyamides; nevertheless, decomposition temperatures well beyond 300 degreesC were observed in nitrogen and air. (C) 2001 John Wiley & Sons, Inc.
Abstract: The synthesis of poly[(2,2-dimethyl-1,3-dioxolan-4-yl) methyl acrylate] (PACCA) and poly[(2,2-dimethyl-1,3-dioxolan-4-yl) methyl methacrylate] (PMCGA) is reported. Both polymers present dielectric and mechanical beta subglass absorptions at -128 and -115 degreesC, respectively, at 1 Hz, followed by ostensible glass-rubber or or relaxations centered in the vicinity of 0 and 67 degreesC, respectively, at the same frequency. The values of the activation energy of both the mechanical and dielectric beta absorptions lie in the vicinity of 10 kcal mol 1. The critical interpretation of the relaxation behavior of PMCGA suggests that dipolar intramolecular correlations play a dominant role in the response of the polymer to an electric field. The subglass relaxations of PACGA and PMCGA are further compared with the relaxation behavior of poly(1,3-dioxane acrylate), poly(1,3-dioxane methacrylate), and other polymers in the glassy state. The strong conductive processes observed in PMCGA at low frequencies and high temperatures were studied under the assumption that that these processes arise from Maxwell-Wagner-Sillars effects occurring in the bulk combined with Nernst-Planckian electrodynamic effects caused by interfacial polarization in the films. (C) 2000 John Wiley & Sons, Inc.
Abstract: Unsaturated monomers containing none, one, or two hydroxy groups were obtained by the reaction of glycerol (1,2,3-trihydroxypropane) with acrylic and methacrylic chloride. The experimental values of the mole fractions of the different monomers were compared with those theoretically obtained by considering different mechanisms involving two or seven kinetic constants. Agreement between the theoretical and experimental results could only be achieved by assuming that the reactivity of the hydroxyl groups changed with the presence of the substituents. The investigation of the radical polymerizations 2,3-dihydroxypropylacrylate (GA) and 2,3-dihydroxypropylmethacrylate (GM) was carried out at several temperatures in water-dioxane solutions. Ultraviolet spectroscopic techniques were used to determine the kinetic constants, and the results were compared with those obtained in the same conditions for methyl acrylate, methyl methacrylate, 2-hydroxyethylmethacrylate, and 2-hydroxyethylmethacrylate. The values of the ratio k(p)/k(t)(1/2) for the methacrylic monomer GM were higher than 0.5 L-1/2 mol(-1/2) s(-1/2) at temperatures between 50 and 65 degreesC. These values exceeded 2 L-1/2 mol(-1/2) s(-1/2) for the acrylic monomer GA, perhaps the highest values reported for this kind of monomer. Electron paramagnetic resonance spectroscopy was also used to study the polymerization of GM. All the polymers were soluble in the reaction mixture until very high conversions, and the gel effect was never detected at monomer concentrations equal to or lower than 1 mol L-1. (C) 2001 John Wiley & Sons, Inc.
Abstract: 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. (C) 2000 Elsevier Science B.V. All rights reserved.
Abstract: The synthesis of two new isomeric monomers, cis-(2-cyclohexyl-1,3-dioxan-5-yl) methacrylate (CCDM) and trans-(2-cyclohexyl-1,3-dioxan-5-yl) methacrylate (TCDM), starting from the reaction of glycerol and cyclohexanecarbaldehyde, is reported. The process involved the preparation of different alcohol acetals and esterification with methacryloyl chloride of the corresponding cis and trans 5-hydroxy compounds of 2-cyclohexyl-1,3-dioxane. The radical polymerization reactions of both monomers, under the same conditions of temperature, solvent, monomer, and initiator concentrations, were studied to investigate the influence of the monomer configuration on the values of the propagation and termination rate constants (k(p) and k(t)). The values of the ratio k(p)/k(t)(1/2) were determined by UV spectroscopy by the measurement of the changes of absorbance with time at several wavelengths in the range 275-285 nm, where an appropriate change in absorbance was observed. Reliable values of the kinetics constants were determined by UV spectroscopy, showing a very good reproducibility of the kinetic experiments. The values of k(p)/k(t)(1/2), in the temperature interval 45-65 degrees C, lay in the range 0.40-0.50 L-1/2/mol(1/2)s(1/2) and 0.20-0.30 L-1/2/mol(1/2)s(1/2) for CCDM and TCDM, respectively. Measurements of both the radical concentrations and the absolute rate constants k(p) and k(t) were also carried out with electron paramagnetic resonance techniques. The values of k(p) at 60 degrees C were nearly identical for both the trans and cis monomers, but the termination rate constant of the trans monomer was about three times that of the cis monomer at the same temperature. (C) 2000 John Wiley & Sons, Inc.
Abstract: The reduction of some substituted divinylketones under Luche conditions (sodium borohydride and cerium trichloride) using different alcohols as solvents affords rearranged polyenyl alkyl ethers in good yields. (C) 1999 Elsevier Science Ltd. All rights reserved.
Abstract: The evolution of the ol-relaxation during an isothermal crystallization process of a series of flexible copolyesters of hydroxybutyrate (HB) and hydroxyvalerate (HV) has been followed in real-time by wide-angle X-ray scattering and dielectric complex permittivity measurements. The change of the dielectric parameters with crystallization time can be phenomenologically described in terms of the Havriliak-Negami equation. The dielectric strength follows a sigmoidal-shaped pattern similar to that shown by the crystallinity. A reduction of the overall mobility with crystallization time of the polymeric chains in the amorphous phase has been observed. This slowing down effect depends on the HV molar content. The influence of the chain flexibility on the crystalline-induced restriction has been discussed in the light of similar studies carried out with more rigid polymers. Dielectric experiments suggest that the progressive immobilization of polymer segments as crystallization proceeds cannot be exclusively associated with the amount of crystalline material. Differences in microstructure, depending on the HV molar content, seem to be responsible for the observed behavior. The progressive broadening and symmetrization of the ol-relaxation with increasing crystallization time has been explained as due to a restriction of the large-scale motions of the polymeric chains, as the material is being filled in with crystals. (C) 1999 John Wiley & Sons, Inc.
Abstract: The thermal properties of a set of experimental aliphatic-aromatic polyamides containing ether linkages were examined as a function of their chemical structure. Variations of the glass transition temperature (T-g) and melting temperature (T-m) could be correlated with the length of the aliphatic spacers and with the orientation of the phenylene rings. Polymers with a high concentration of p-oriented phenylene units showed a higher T-g than those containing mainly m-oriented ones; T-g values ranged from 110 to 155 degrees C. Surprisingly, a negligible dependence of T(g)s on the nature of flexible spacers was observed. For all of the polymers, the thermal stability was virtually the same, about 440 degrees C, when tested by dynamic thermogravimetric analysis (TGA). However, quite different levels of thermal stability were found by isothermal TGA analysis for polyamides with different flexible spacers. Moreover, the poly(ether-amide)s described here compare fairly well with wholly aromatic polyamides when measured by dynamic TGA; but isothermal TGA measurements clearly demonstrated that they decompose faster than aromatic polyamides. Treatment of the TGA curves by the method of McCallum provided kinetic data that confirmed a better long-term stability for poly(ether-amide)s with a higher proportion of para-oriented phenylene rings. (C) 1998 John Wiley & Sons.
Abstract: The effects of chemical structure on the values of different electrical parameters measured with novel aromatic polyamide (aramid) membranes were studied. Poly(isophthalamides) containing pendant groups were considered since they can be transformed into dense membranes, suitable for the determination of characteristic transport parameters such as ion transport numbers, electrical resistances and capacitances. Measurements were carried out with the membranes in contact with different NaCl and MgCl2 solutions. Results show that resistance values are strongly dependent on concentration, but membrane capacitance is almost constant for the whole range of concentrations studied (10(-3) < C(N) < 5 x 10(2)). The ionic permeabilities in the membrane were determined from membrane potential and resistance results. The presence of polar side substituents causes lower resistivity in modified polyamides compared with the unsubstituted parent, and the higher the polarity of the substitutent, the lower the resistivity. This trend is valid for both NaCl and MgCl2 solutions.
Abstract: The mechanical and dielectric relaxation of a set of aromatic-aliphatic polyamides containing ether linkages have been examined as a function of temperature (-140 to 190 degrees C) and frequency (3 to 10(6) Hz). The polymers differ in the orientation (meta and para) of the aromatic rings, in the length of the aliphatic chain, and in the number of ether Linkages per repeating unit. Dynamic mechanical experiments showed three main relaxation peaks related to the glass transition temperature of the polymers (alpha relaxation), the subglass relaxations associated to the absorbed water molecules (beta) and to the motion of the aliphatic moieties (gamma). Dielectric experiments showed two subglass relaxation processes (beta and gamma) that correlates with the mechanical beta and gamma relaxations, and a conduction process (sigma) above 50 degrees C that masks the relaxation associated to the glass transition. A molecular interpretation is attempted to explain the position and intensity of the relaxation, studying the influence of the proportion of para- or meta-oriented phenylene rings, the presence of ether Linkages and the length of the aliphatic chain. (C) 1997 John Wiley & Sons, Inc.
Abstract: Four aromatic diamines containing aliphatic spacers and meta and para oriented oxyphenylene rings, and their corresponding hydrochlorides, were combined with isophthaloyl chloride (IPC) and terephthaloyl chloride (TPC) to give high molecular weight polyamides by interfacial and low-temperature solution methods. The synthesis and characterization of monomers and polymers are reported, and the differences observed in polycondensation yields, molecular weights and molecular weight distributions, as a function of the method of synthesis, are discussed. Values of number-average molecular weight ((M) over bar(n)) up to 8 x 10(4) g/mol and weight-average molecular weight ((M) over bar w) up to 1 x 10(5) g/mol could be measured by gel permeation chromatography using aromatic polyamide standards, and values of (M) over bar(n), up to 2 x 10(5) g/mol and (M) over bar(w) up to 3.6 x 10(5) g/mol by using polystyrene standards.
Abstract: Two sets of aromatic polyamides were prepared from m-phenylenediamine (MPD) and 4,4'-diaminodiphenyl sulfone (DDS) in combination with a set of new halogenated diacyl chlorides, namely, 5-fluoroisophthaloyl chloride, 5-chloroisophthaloyl chloride, 5-bromoisophthaloyl chloride and 5-iodoisophthaloyl chloride. The polymers were synthesized in high yields and in high molecular weight (as determined by gel permeation chromatography) by means of the low temperature condensation method. Noticeable changes in the spectral characteristics of the halogen-modified polyisophthalamides were observed compared to those of the corresponding unmodified polyisophthalamides. Slight improvements were observed for the glass transition temperatures, which increased 5-30 degrees C relative to those of the conventional polyisophthalamides. Moreover, a correlation was found between the size of the halogen substituents and the increase in T-g values. Thermogravimetric analysis showed that the new polymers are almost as thermally resistant as the unmodified ones, while solubility in organic solvents was somewhat poorer.
Abstract: The effect of the chemical structure in the electrical response (membrane potential, Delta phi, salt diffusion, D-s, resistance, R(m), and capacitance, C-m) of two new aliphatic-aromatic polyamide membranes is considered. They are poly(ether-amide)s with an oxygen atom difference. Measurements were carried out with NaCl and MgCl2 solutions at different concentrations. Equivalent circuits were determined by impedance spectroscopy and a parallel R(m)C(m) association was obtained for both membranes and electrolytes. Under identical external conditions, significant differences for the membrane resistance values were found as a function of the membrane chemical nature, but the capacitance hardly depends on both membrane and electrolyte. From Delta phi and R(m) values some membrane characteristic parameters such as transport numbers and ionic diffusion coefficients were determined. Concentration dependence of all these parameters was also studied.
Abstract: The synthesis and characterization of aromatic polyamides containing oxyethylene units is reported, and the differences observed in polycondensation yields, molecular weights, and molecular weight distributions, as a function of the method of synthesis, are discussed. Four diamines containing oxyethylene units and aromatic rings, meta and para oriented, and their corresponding hydrochlorides were prepared as condensation monomers to be combined with isophthaloyl chloride (IPC) and terephthaloyl chloride (TPC). High molecular weight polyamides were obtained by interfacial and low-temperature solution methods. Values of (M) over bar(n) up to 6 X 10(4) g/mol and (M) over bar(w) up to 2 X 10(5) g/mol could be measured by gel permeation chromatography using aromatic polyamide standards, and values of (M) over bar(n) up to 2 X 10(5) g/mol and (M) over bar(w) up to 5 X 10(5) g/mol by using polystyrene standards. (C) 1996 John Wiley & Sons, Inc.
Abstract: The kinetics of different reactions between acid chlorides and poly- and amino-alcohols are experimentally and theoretically analysed and kinetic equations obtained that permit calculation of the molar fractions of the different compounds which can be synthesized.
Abstract: Experimental values at different temperatures of the mean-square dipole moment, (mu(2)),of 2,2'-bisphthalimido diethyl ether (PTDE) and 1,8-bisphthalimido-3,6-dioxaoctane (PTDO), model compounds of imide-ether molecular chains, are reported. The values obtained for this quantity in dioxane are 8.28-8.31 D-2 and 11.04-11.22 D-2 for PTDE and PTDO, respectively, in the temperature range 20-50 degrees C. These results indicate that imide-ether chains exhibit much lower polarity than their benzamide-ether counterparts. The interpretation of the H-1 NMR spectrum of PTDE suggests that an increase in the polarity of the solvent raises the gauche population about NCH2-CH2O bonds. Both the NMR results and the conformational energy calculations by semiempirical methods suggest that these bonds are nearly freely rotating. However, the evaluation of the mean-square dipole moments as a function of the energy of gauche states about NCH2-CH2O bonds indicates that good agreement between theory and experiments is obtained for values of this energy 0.4 +/- 0.2 K cal mol(-1) above that of the alternative trans states.
Abstract: The synthesis of 1,5-dibenzamido-3-oxapentane (DEBA) and 1,8-dibenzamido- 3,6-dioxaoctane (TEBA), model compounds of polyamides with repeating units [-HNCOC6H4CONH(CH2)2O(CH2)2-] and [-HNCOC6H4-CONH(CH2)20(CH2)2O(CH2)2-1, respectively, is reported. The mean-square dipole moment, [mu2], of both compounds was measured in dioxane solutions in the interval of temperatures 30-60-degrees-C. The values of this quantity lie in the ranges 24.6-24.5 D2 and 25.4-26.0 D2, for DEBA and TEBA, respectively. The analysis of the spectral patterns of the model compounds indicates that the energy E(sigma') of gauche states about the CH2-CH2 bonds adjacent to the amide groups is 0.44 +/- 0.08 kcal mol-1 below that of the alternative trans states. Moreover, semiempirical calculations show that gauche states about NH-CH2 bonds are also preferred over the alternative trans, in contrast with CH2-O bonds in polyesters, where the opposite occurs. The critical interpretation of the dipole moments of both DEBA and TEBA by the rotational isomeric state (RIS) model suggests that their polarities are very sensitive to the modulus of the dipole moments associated with the amide groups, but they are nearly insensitive to their orientation. Calculations of the dipolar distribution and the corresponding average energies carried out for DEBA and TEBA suggest that the conformers of higher polarity also have the highest energy.
Abstract: Aromatic polyamides, wholly aromatic polyamides, or aramids, are considered to be high-performance materials owing to their outstanding thermal and mechanical resistance. Their properties can be attributed to their fully aromatic structure and amide linkages, which give rise to stiff rod-like macromolecular chains that interact with each other via strong and highly directional hydrogen bonds. These physical links deeply favor the development of effective crystalline micro-regions or domains, resulting in a compact intermolecular packing and cohesive energy. The better-known commercial aramids, poly(p-phenylene terephthalamide) and poly(m-phenylene isophthalamide), are used in advanced technologies in every industrial field, and have been transformed into high-strength and flame resistant fibers and coatings with broad applications in advanced industrial products, such as heat and cut protective clothing, ballistic-protection products, sport fabrics, specialty paper products, transmission belts, friction products, industrial filters and membranes, and special pipes, among others. Owing to their above mentioned chemical and physical characteristics, they exhibit extremely high transition temperatures, which lie above their decomposition temperatures, are sparingly soluble in common organic solvents and, accordingly, can only be transformed upon solution from polar aprotic solvents or strong inorganic acids. Hence, the expansion of the applications of aramids involves, from one side, increasing their solubility, thereby improving their transformability, and, from other side, incorporating new chemical functionalities in the polyamide backbone or lateral structure in order to provide key characteristics for their application in cutting edge technological fields. These fields are related with new electrochromic, luminescent or optically active materials, gas separation and ion exchange membranes, macromolecules with sensing and supramolecular capabilities, biomaterials for medical applications, materials with even higher mechanical and thermal resistance, etc.
Abstract: The better-known commercial aramids are poly( p-phenylene terephthalamide) and poly( m-phenylene isophthalamide). Both of these polymers can be transformed into flame, cut-resistant and high-tensile strength synthetic fibers, with technological applications in the field of coatings and fillers in the aerospace and armaments industry, in asbestos substitutes, electrical insulation, bullet-proof body armor, industrial filters, and sport fabrics, among others.
Abstract: Poly(amide)s, usually known as polyamides, are polymers incorporating the amide group in their repeating unit. The synthetic aromatic polyamides differ from the aliphatic polyamides (nylons) on the highly aromatic nature of the polymer backbone. Both nylons and aromatic polyamides are considered engineering materials, but the aromatic structure of the main chain of the aramids endow this polymers with specialty characteristics making them less sensitive to oxidation, higher solvent resistant, and conferring the materials with superior thermal and mechanical resistance, thus being classified as high-performance materials.
The better-known commercial aramids are poly(p-phenylene terephthalamide) and poly(m-phenylene isophthalamide). Both of these polymers can be transformed into flame, cut-resistant and high-tensile strength synthetic fibers, with technological applications in the field of coatings and fillers in the aerospace and armaments industry, in asbestos substitutes, electrical insulation, bullet-proof body armor, industrial filters, and sport fabrics, among others.
Thus, owing to their chemical structure, there is currently a huge research effort directed toward exploiting the special high-performance characteristics of the polyamides to obtain electro- or photoluminescent materials, reverse osmosis, gas or ion-exchange membranes, optically active (OA) materials, nanocomposites, etc. with superior thermo-mechanical performances.
Abstract: Poly(amide)s, usually known as polyamides, are polymers incorporating the amide group in their repeating unit. The synthetic aromatic polyamides differ from the aliphatic polyamides (nylons) on the highly aromatic nature of the polymer backbone. Both nylons and aromatic polyamides are considered engineering materials, but the aromatic structure of the main chain of the aramids endow this polymers with specialty characteristics making them less sensitive to oxidation, higher solvent resistant, and conferring the materials with superior thermal and mechanical resistance, thus being classified as high-performance materials.
Abstract: La página web describe la preparación de colorantes azoicos realizada por un grupo de estudiantes de la Licenciatura en QuÃmica ( QuÃmica Orgánica, tercer curso) de la Facultad de Ciencias de la Universidad de Burgos, en el curso 2009-2010.
Abstract: La página web describe la preparación de una comuna de cromatografÃa para la separación de ferroceno y 4,6,8-trimetilazuleno. Se trata de una práctica de laboratorio realizada por un grupo de estudiantes de la Licenciatura en QuÃmica ( QuÃmica Orgánica, tercer curso) de la Facultad de Ciencias de la Universidad de Burgos, en el curso 2008-2009.
Abstract: Prácticas de determinación estructural para estudiantes de cuarto curso de la Licenciatura en QuÃmica de la Facultad de Ciencias de la Universidad de Burgos.
