Preparation of composites and nanocomposites based on bentonite and poly(sodium acrylate). Effect of amount of bentonite on the swelling behaviour

A series of composite and nanocomposite hydrogels were synthesized by copolymerization reaction of partially neutralized acrylic acid (SA) on bentonite micropowder (BT) using N,N′-methylenebisacrylamide (MBA) as a crosslinker and potassium persulfate (I) as an initiator in aqueous solution. The influences of Na⁺-BT, organoBT (O-BT), and the content of the BT in the copolymeric gels on the swelling behaviour in deionized water and saline solution (0.2 wt.% NaCl_(aq)) were investigated. Results showed that the equilibrium swelling (W_∞) was decreased by adding a small amount of the BT, however, at higher BT contents, the W_∞ increased with the increase of the amount of clay. It was found that a concentration of 14 wt.% Na⁺-BT gave the best results absorption (955 g/g). Moreover, the amount of swelling for these absorbents in saline solution was smaller than that in deionized water. These hydrogels were characterized by X-ray diffraction and scanning electron microscopy. Finally, the thermogravimetric analysis indicated that introduction of clay to the polymer network resulted in an increase in thermal stability.     

Synthesis and water sorption studies of pH sensitive poly(acrylamide-co-itaconic acid) hydrogels

Superabsorbent copolymers of acrylamide (Am) and itaconic acid (ItA) were prepared by free radical solution polymerization using sodium persulfate and N,N,N′,N′-tetramethylenediamine (TMEDA) as initiating system at 35 °C. Two series were prepared. The first series (SA series) used varied amount of itaconic acid and fixed amount of N,N′-methylenebisacrylamide (MBAm), while in the second series (SB series) the amount of (MBAM) changed and the amount of itaconic acid was fixed. The swelling behavior was studied at room temperature and the swelling percentage, swelling kinetics parameters such as initial swelling rate, swelling rate constant, and diffusion parameters were determined. The effect of pH and saline sensitivity on swelling behavior was also studied.     

Effects of synthesis-solvent on swelling and elastic properties of poly(N-isopropylacrylamide) hydrogels

Thermosensitive N-isopropylacrylamide (NIPA) hydrogels were synthesized by a free radical copolymerization with N,N′-methylenebisacrylamide (MBAA) in four solvents: water, ethanol, acetone and N,N-dimethylformamide. The swelling and elastic properties of the hydrogels were affected by the synthesis-solvents; the hydrogels (e.g. NIPA/MBAA = 1000/50 mol/m³-pre-gel solution) synthesized in water have smaller swelling volume and larger shear modulus at 10 °C than those synthesized in amphiphilic solvents. The network structure of hydrogels was estimated in terms of the conversion and two sorts of effective crosslinking density based on the Flory theory and the concentration of crosslinker. The hydrogels synthesized in water can have the microscopic inhomogeneous network arising from the entanglement of polymer chains, while the hydrogels synthesized in amphiphilic solvents can have the homogeneous network arising from the polymer concentration lower than the pre-gel solution and can be similar in network structure to the lightly crosslinked hydrogel synthesized in water.     

Fluorometric determination of fluoride ion by reagent tablets containing 3-hydroxy-2'-sulfoflavone and zirconium(IV) ethylenediamine tetraacetate

A reagent tablet for determination of fluoride ion has been prepared using ethylenediamine-N,N,N′,N′-tetraacetate complex of zirconium (Zr-EDTA), 3-hydroxy-2′-flavone (FS) and an appropriate pH buffer. Dissolving of the tablet into water exhibits an intense blue fluorescence (λ_max = 460 nm) upon excitation at 377 nm and the fluorescence intensity decreases with the presence of fluoride ion. Hence, a simple fluorescent detection procedure for fluoride ion in aqueous media was successfully constructed with this tablet. The principle of this detection system is the ligand exchange reaction of FS bound to Zr-EDTA with fluoride ion. The present system provides an easy, rapid and selective determination method of fluoride ion ranging from 5 × 10⁻⁶ to 1 × 10⁻³ mol dm⁻³. The measurement of real samples with this tablet showed the similar results as those by the common method with the Alfusone reagent.     

Synthesis and characterization of polyamides containing pendant pentadecyl chains

A new aromatic diacid monomer viz., 4-(4′-carboxyphenoxy)-2-pentadecylbenzoic acid was synthesized starting from cardanol and was characterized by FTIR, ¹H- and ¹³C NMR spectroscopy. A series of new aromatic polyamides containing ether linkages and pendant pentadecyl chains was prepared by phosphorylation polycondensation of 4-(4′-carboxyphenoxy)-2-pentadecylbenzoic acid with five commercially available aromatic diamines viz., 1,4-phenylenediamine, 4,4′-oxydianiline, 4,4′-methylenedianiline, 1,3-phenylenediamine, and 4,4′-(hexafluoroisopropylidene)dianiline. Inherent viscosities of the polyamides were in the range 0.45-0.66 dL/g in N,N-dimethylacetamide at 30 ± 0.1 °C. The introduction of ether linkages and pendant pentadecyl chains into polyamides led to an enhanced solubility in N,N-dimethylacetamide and 1-methyl-2-pyrrolidinone at room temperature or upon heating. The polyamides could be solution-cast into tough, flexible and transparent films from their N,N-dimethylacetamide solution. Wide angle X-ray diffraction patterns exhibited broad halo indicating that the polymers were essentially amorphous in nature. X-Ray diffractograms also displayed a diffuse to sharp reflection in the small-angle region (2θ = ∼2-5°) for the polyamides characteristics of formation of loosely to well-developed layered structure arising from packing of flexible pentadecyl chains. The glass transition temperature observed for the polyamides was in range 139-189 °C. The temperature at 10% weight loss (T₁₀), determined by TGA in nitrogen atmosphere, of the polyamides was in the range 425-453 °C indicating their good thermal stability.     

rac-Lactide polymerization using aluminum complexes bearing tetradentate phenoxy-amine ligands

A family of aluminum-methyl complexes supported by tetradentate phenoxy-amine ligands has been prepared and employed in the ring-opening polymerization of rac-lactide; the ligands include N,N-bis(3,5-dimethyl-2-hydroxybenyl)-N′,N′-dimethyl-1,2-diaminoethane (L¹), N,N-bis(3,5-diisopropyl-2-hydroxybenyl)-N′,N′-dimethyl-1,2-diaminoethane (L²) and N,N-bis(3,5-dichloro-2-hydroxybenyl)-N′,N′-dimethyl-1,2-diaminoethane (L³). Polymerizations of rac-lactide were carried out by treatment of the aluminum-methyl complexes with PhCH₂OH and rac-lactide at 70 °C, affording well-controlled formation of polylactide (PLA) and a moderate isotactic bias for initiators bearing L¹ and L²; the chloro-substituted ligand L³ afforded largely atactic PLA.     

Synthesis, characterization and thermal properties of new aromatic quaternary ammonium bromides: precursors for ionic liquids and complexation studies

Series of new aromatic R₂R′₂N⁺Br⁻ (R=benzyl, 4-methylbenzyl, 2-phenylethyl, 3-phenylpropyl; R′=ethyl, methyl, isopropyl) or RR′₂NH⁺Br⁻-type (R=benzyl, R′=isopropyl) quaternary ammonium bromides were prepared by using novel synthetic route in which a formamide (N,N-diethylformamide, N,N-dimethylformamide, N,N-diisopropylformamide) is treated with aralkyl halide in presence of a weak base. The compounds were characterized by ¹H-NMR and ¹³C-NMR spectroscopy and mass spectrometry. Structures of the crystalline compounds were determined by X-ray single crystal diffraction, and in addition the powder diffraction method was used to study the structural similarities between the single crystal and microcrystalline bulk material. Three of the compounds crystallized in monoclinic, two in orthorhombic and one in triclinic crystal system, showing ion pairs, which are interconnected by weak hydrogen bonds and weak π-π interactions between the phenyl rings. Three of the compounds appeared as viscous oil or waxes. Finally, TG/DTA and DSC methods were used to analyze thermal properties of the prepared compounds. The lowest melting points were obtained for diethyldi-(2-phenylethyl)ammonium bromide (122.2 °C) and for diethyldi-(3-phenylpropyl)-ammonium bromide (109.1 °C). In general, decomposition of the compounds started at 170-190 °C without identifiable cleavages, thus liquid ranges of 30-70 °C were observed for some of the compounds.     

Pattern formation of polyimide by using photosensitive polybenzoxazole as a top layer

A versatile method for positive-type patterning of polyimide (PI) based on a two-layer photosensitive poly(benzoxazole) (PSPBO) and poly(amic acid) (PAA) film has been developed to provide a promising material in the field of microelectronics. This patterning system consisted of a pristine PAA thick bottom-layer and a poly(o-hydroxy amide) (PHA) thin top layer with 9,9-bis[4-(tert-butoxycarbonyl-methyloxy)phenyl]fluorene (TBMPF) as a dissolution inhibitor, and (5-propylsulfonyloxyimino-5H-thiophene-2-ylidene)-(2-methylphenyl)-acetonitrile (PTMA) as a photoacid generator (PAG). The PHA and PAA were prepared from 4,4′-(hexafluoroisopropylidene)-bis(o-aminophenol) and 4,4′-oxybis(benzoic acid) derivatives, and 3,3′,4,4′-biphenyltetracarboxylic dianhydride and 4,4′-oxydianiline, respectively, in N,N-dimethylacetamide. This two-layer system based on PHA (150-nm thickness) and PAA (1.5-μm thickness) showed high sensitivity of 35 mJ/cm² and high contrast of 10.3 when exposed to a 365 nm line (i-line), post-baked at 100 °C for 2 min, and developed in a 2.38 wt.% tetramethylammonium hydroxide aqueous solution/5 wt.% iso-propanol at 25 °C. A clear positive image of a 4-μm line-and-space pattern was printed on a film which was exposed to 100 mJ/cm² of i-line by a contact-printing mode and fully converted to the corresponding PBO/PI pattern upon heating at 350 °C, confirmed by FT-IR spectroscopy. This two-layer system could be applied to the patterning of various PAAs.     

Observations on the swelling characteristics of the zwitterionic hydrogel of poly(1-3-sulfopropyl)-2-vinyl-pyridinium-betaine hydrogel

Samples of poly[1-(3-sulfopropyl)-2-vinyl-pyridinium-betaine] (PSPV) have been synthesized to high conversion by free radical polymerization in aqueous solution of the zwitterionic monomer SPV with several concentrations of the crosslinker N,N′-methylene-bis-acrylamide (MBA). The densities of the resultant xerogels increased regularly with the content of MBA. Hydrogels obtained by swelling them in water and aqueous KSCN solution were examined by gravimetric and dimensional analysis. The water contents increased with decreasing content of MBA, the value of 92.7 wt% at the lowest MBA content being higher than that for other zwitterionic hydrogels. Enhanced swelling occurred in 1 M aq. KSCN at each MBA content, the total swelling being 98.1 wt% at the lowest crosslinker content. Swelling increased with increasing temperature. An approximate procedure to formulating swelling equilibrium in term of the volume fraction of water in hydrogel, in conjunction with the van’t Hoff equation, yields a small positive value for the enthalpy of swelling. This is compared with values derived similarly for other hydrogels.     

Novel thermally stable and chiral poly(amide-imide)s bearing from N,N′-(4,4′-diphthaloyl)-bis-l-isoleucine diacid: Synthesis and characterization

Novel optically active aromatic poly(amide-imide)s (PAIs) were prepared from newly synthesized N,N′-(4,4′-diphthaloyl)-bis-l-isoleucine diacid (3) via polycondensation with various diamines. The diacid was synthesized by the condensation reaction of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (1) with l-isoleucine (2) in a mixture of acetic acid and pyridine (3:2 v/v). All the polymers were obtained in quantitative yields with inherent viscosities of 0.20-0.43 dL g⁻¹. All the polymers were highly organosoluble in solvents like N-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran, γ-butyrolactone, cyclohexanone and chloroform at room temperature or upon heating. These poly(amide-imide)s had glass transition temperatures between 198 and 231 °C, and their 10% weight-loss temperatures were ranging from 368 to 398 °C and 353 to 375 °C under nitrogen and air, respectively. The polyimide films had tensile strengths in the range of 63-88 MPa and tensile moduli in the range of 0.8-1.4 GPa. These poly(amide-imide)s possessed chiral properties and the specific rotations were in the range of −3.10° to −72.92°.     

Structural, spectral and thermal studies of substituted N-(2-pyridyl)-N′-phenylthioureas

N-2-(3-picolyl)-N′-phenylthiourea, 3PicTuPh, monoclinic, P2₁/n, a=7.617(2) b=7.197(5), c=22.889(5) Å, β=94.63(4)°, V=1250.7(1) Å³ and Z=4; N-2-(4-picolyl)-N′-phenylthiourea, 4PicTuPh, triclinic, P-1, a=7.3960(5), b=7.9660(12), c=21.600(3) Å, α=86.401(4), β=84.899(8), γ=77.769(8)°, V=1237.5(3) Å³ and Z=4; N-2-(5-picolyl)-N′-phenylthiourea, 5PicTuPh, monoclinic, P2₁/c, a=14.201(1), b=4.905(3), c=17.689(3) Å, β=91.38(1)°, V=1231.8(7) Å³ and Z=4; N-2-(6-picolyl)-N′-phenylthiourea, 6PicTuPh, monoclinic, C2/c2, a=14.713(1), b=9.367(1), c=18.227(1) Å, β=92.88(1)°, V=2515.5(1) Å³ and Z=8 and N-2-(4,6-lutidyl)-N′-phenylthiourea, 4,6LutTuPh, monoclinic, C2/c, a=11.107(2), b=11.793(2), c=20.084(4) Å, β=96.10(3)°, V=2616(1) Å³ and Z=8. Intramolecular hydrogen bonding between N′H and the pyridyl nitrogen and intermolecular hydrogen bonding involving the thione sulfur are affected by substitution of the pyridine ring, as is the planarity of the molecule. ¹H NMR studies in CDCl₃ show the NH′ hydrogen resonance considerably downfield from other resonances in the spectrum for each thiourea.     

Synthesis and properties of poly(aryl ether benzimidazole) copolymers for high-temperature fuel cell membranes

A series of poly(aryl ether benzimidazole) copolymers bearing different aryl ether linkage contents were synthesized by condensation polymerization in polyphosphoric acid (PPA) by varying the feed ratio of 4,4′-dicarboxydiphenyl ether (DCPE) to terephthalic acid (TA). As the ether unit content in the copolymer increased, the solubility of the copolymer in PPA and N,N′-dimethylacetamide/LiCl improved. For example 3–7 wt.% DMAc solution containing 2 wt.% of LiCl could be prepared from the copolymers. XRD studies revealed that the incorporation of flexible aryl ether linkages increased the chain d-spacings of the polymer backbones and decreased the crystallinity of the copolymers. Still, these copolymers having ether linkages showed reasonably good thermal/mechanical stability and high proton conductivity. For example, the copolymer with 30 mol% ether linkage had a tensile strength of 43 MPa (at 26 °C and 40% relative humidity) at an acid doping level of 7.5 mol H₃PO₄ and a proton conductivity of 0.098 S cm⁻¹ (at 180 °C and 0% relative humidity) at an acid doping level of 6.6 mol H₃PO₄.     

Swelling–shrinking behaviors of poly(N-isopropylacrylamide) and poly(N-n-propylacrylamide) gels prepared by chemical and radiation crosslinking methods

The swelling and shrinking kinetics of thermosensitive gels based on N-isopropylacrylamide (NiPAAm) and N-n-propylacrylamide (NnPAAm) were studied. Four gels cylindrical in shape were prepared by two different methods: γ-ray irradiation to aqueous solutions of poly(NiPAAm) (PNiPAAm) or poly(NnPAAm) (PNnPAAm) and redox polymerization of NiPAAm or NnPAAm monomer using N,N′-methylenebisacrylamide as a crosslinker. There were a few differences in the swelling kinetics among these gels. However, a marked difference was observed in the shrinking processes, the rate of which was faster in the order of radiation-crosslinked PNiPAAm gel > radiation-crosslinked PNnPAAm gel > chemically crosslinked PNnPAAm gel > chemically crosslinked PNiPAAm gel. This difference was discussed in terms of the microscopic structure of the gels, which was studied by light scattering techniques. It was found that the static inhomogeneities frozen in the chemically and radiation-crosslinked gels play a key role in their shrinking kinetics.     

Extractive spectrophotometric determination of palladium with N,N,N',N'-tetra(2-ethylhexyl)-thiodiglycolamide T(2EH)TDGA

A precise, sensitive and selective method for the spectrophotometric determination of palladium (II) using N,N,N′,N′-tetra(2-ethylhexyl) thiodiglycolamide T(2EH)TDGA as an extractant is described. Palladium (II) forms yellow colored complex with T(2EH)TDGA which exhibits an absorption maximum at ∼300 nm. The colored complex obeys Beer's law in the concentration range 1.0-15.0 μg ml⁻¹ of palladium with a molar absorptivity of 1.29 × 10⁵ M⁻¹ cm⁻¹. The effects of various experimental parameters have been studied to establish the optimum conditions for the extraction and determination of palladium. The precision of the method has been evaluated and the relative standard deviation has been found to be less than 0.5%. The method has been successfully applied to the determination of palladium in simulated high level liquid waste (SHLW) solution.     

Preparation of fast response superabsorbent hydrogels by radiation polymerization and crosslinking of N-isopropylacrylamide in solution

Macroporous temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels with high equilibrium swelling and fast response rates were obtained by a ⁶⁰Co γ- and electron beam (EB) irradiation of aqueous N-isopropylacrylamide (NIPAAm) monomer solutions. The effect of irradiation temperatures, the dose, the addition of a pore-forming agent on the swelling ratio, and the kinetics of swelling and shrinking of the PNIPAAm gels was studied. The gels synthesized above the LCST exhibited the highest equilibrium swelling (300–400) and fastest response rate measured by minutes. Scanning electron microscope (SEM) pictures revealed that the gels synthesized above the LCST have larger pores than those prepared at temperatures below the LCST. The gels showed a reversible response to cyclical changes in temperature and might be used in a pulsed drug delivery device. The gels synthesized above the LCST exhibited the highest testosterone propionate release.     

Synthesis of B-trisubstituted borazines via the rhodium-catalyzed hydroboration of alkenes with N,N′,N″-trimethyl or N,N′,N″-triethylborazine

Hydroboration of terminal and internal alkenes with N,N′,N″-trimethyl- and N,N′,N″-triethylborazine was carried out at 50 °C in the presence of a rhodium(I) catalyst. Addition of dppb or DPEphos (1 equiv.) to RhH(CO)(PPh₃)₃ gave the best catalyst for hydroboration of ethylene at 50 °C, resulting in a quantitative yield of B,B′,B″-triethyl-N,N′,N″-trimethylborazine. On the other hand, a complex prepared from (t-Bu)₃P (4 equiv.) and [Rh(coe)₂Cl]₂ gave the best yield for hydroboration of terminal or internal alkenes.     

Acyclic tertiary diamines and 1,4,7,10-tetraazacyclododecane with fluorine-containing β-diketones: Leading to low melting ionic adducts

N,N,N′,N′-Tetramethylmethanediamine (1a), N,N,N′,N′-tetramethylethanediamine (1b), N,N,N′,N′-tetramethyl-1,3-propanediamine (1c), and N,N,N′,N′-tetramethyl-1,6-hexanediamine (1d) were reacted at 25 °C with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (2a), 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione (2b), 2-thenoyltrifluoroacetone (2c), and 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione (2d) to form the ionic adducts 3-18. 1,4,7,10-Tetraazacyclododecane (1e) reacted at 25 °C with β-diketones (2a-d) and 1,1,1-trifluoro-2,4-pentanedione (2e) to give ionic solids 19-23 in good yields. Some of the products are liquid at 25 °C and are thermally stable over long liquid ranges as determined by thermal gravimetric analyses. Single-crystal X-ray structure determinations show that compounds 9 and 21 crystallize in the monoclinic space groups P2(1)/c and P2(1)/n, respectively. All the new compounds were characterized by ¹H, ¹⁹F and ¹³C NMR, electrospray MS and/or elemental analyses.     

Preparation and properties of new ortho-linked polyamide-imides bearing ether, sulfur, and trifluoromethyl linkages

A CF₃-containing diamine, 2,2′-thiobis-[4-methyl(2-trifluoromethyl)4-aminophenoxy) phenyl ether] (DA), was successfully synthesized from 2-2′-sulfide-bis-(4-methyl phenol) and 2-chloro-5-nitrobenzotrifluoride. The sulfur containing diimide-diacid (DIDA) was prepared by condensation reaction of diamine DA and trimellitic anhydride. A series of novel organic-soluble polyamide-imides (PAIs) bearing flexible ether and sulfide links, electron-withdrawing trifluoromethyl groups and ortho-phenylene units were synthesized from DIDA, by direct polycondensation with various aromatic diamines in N-methyl-2-pyrrolidone using triphenyl phosphite and pyridine as a condensing agent in the presence of dehydrating agent (LiCl). The polyamide-imides were obtained in high yields and possessed inherent viscosities in the range of 0.42-0.95 dL g⁻¹. All of the polymers were amorphous in nature, showed outstanding solubility and could be easily dissolved in amide-type polar aprotic solvents (e.g., N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide) and even dissolved in less polar solvents (e.g., pyridine and tetrahydrofuran). They showed good thermal stability with glass transition temperatures between 195-245 °C, 10% weight loss temperatures in excess of 485 °C, and char yields more than 50% at 700 °C in nitrogen atmosphere. Moreover, these PAIs possessed low refractive indexes (n = 1.57-1.59) and low birefringence (Δ ≈ 0.02) due to the trifluoromethyl pendent groups and thioether bridged ortho-catenated aromatic rings that interrupt chain packing and increase free volume.     

Timolol maleate release from pH-sensible poly(2-hydroxyethyl methacrylate-co-methacrylic acid) hydrogels

Multifunctional polymeric materials were obtained from poly(methacrylic acid-co-2-hydroxyethyl methacrylate), to be used as a raw material in the manufacture of contact lens and as drug delivery systems. Poly(methacrylic acid-co-2-hydroxyethyl methacrylate) was prepared by free-radical polymerization in aqueous solution at 60 °C using potassium persulfate (KPS) as initiator and N,N^′-methylenebisacrylamide (BIS) as cross-linker agent. The dynamic and equilibrium swelling properties of dry glassy poly(methacrylic acid-co-2-hydroxyethyl methacrylate) polymeric networks were studied as a function of pH and methacrylic acid (MAA) content. The water content increase as MAA content and pH increase. Timolol maleate delivery from poly(MAA) and poly(2-hydroxyethyl methacrylate) (HEMA) homopolymers was studied and the results show a Fickian diffusion behavior.     

On the dehydrogenation of N,N′-substituted p-phenylenediamine antioxidants. I. N-Phenyl-N′-isopropyl-p-phenylenediamine (IPPD)

Using B3LYP/6-31G^∗ treatment, the optimal geometries, electronic structures and IR spectra of N-phenyl-N′-isopropyl-p-phenylenediamine antioxidant (IPPD) and its doubly dehydrogenated oxidation products have been obtained. Experimental IR spectra of IPPD sample heated in air at 140 °C correspond to the doubly dehydrogenated IPPD structure with the Phenyl-NC double bond and not to its N,N′-dehydrogenated quinonediimine-type counterpart as supposed in the literature. This finding supports the idea of preferential dehydrogenation at N-bonded tertiary carbon atom in comparison with the amine nitrogen bonded to two phenyl rings.