On the use of infrared spectroscopy in the study of carbon dioxide decomposition on copper containing methanol synthesis catalysts

A novel and convenient procedure for the catalytic acylation of a series of aromatic compounds such as benzene, toluene, xylenes (o-, m-, p-), mesitylene, isopropylbenzene and N,N-dimethylaniline to the corresponding ketones using medium- and large-pore zeolites as catalyst and acetic acid or acetyl chloride as acylating agent at different reaction temperatures in a tubular reactor is demonstrated for the first time. The H-ZSM5 and H-beta zeolite catalysts exhibited the higher turnover rates (TOF× 10^-3 s^-1 mol^-1 Al) for the acetic acid or acetyl chloride conversion to the products. In some cases, nearly total conversion of acylating agent with very high selectivity to the para product is achieved. It is found that the reactivity of the aromatic compounds increases with the increase of -CH₃ groups in the benzene ring. Mechanistically, it is assumed that an active species (CH₃CO⁺) is generated catalytically from the acylating agent by an acidic zeolite which attacks the aromatic ring and produces corresponding aromatic ketones.     

Thermo- and CO2-triggered swelling polymer microgels for reducing water-cut during CO2 flooding

CO₂ has been widely used in the process of enhanced oil recovery (EOR) over decades. However, the heterogeneity of oil reservoirs renders CO₂ to flow preferentially into highly permeable zones, leaving tight areas unswept with oil unrecovered in these areas. While conventional water-swelling gels were used for blocking the “channeling” path, most of them experience the risks of shrinkage under high temperature and CO₂-induced acidic environment. Here, we developed double swelling smart polymer microgels (SPMs) triggered by both heat and CO₂. Such SPMs were prepared by copolymerization of acrylamide (AAm) in combination with N,N-2-(dimethylamino)ethyl methacrylate (DMAEMA) and [2-(methacryloyloxy) ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA), and with N,N′-methylene bisacrylamide (MBA) as the crosslinker. These SPMs swell when temperature is higher than 65 °C or in the presence of CO₂, with an ameliorative salinity tolerance ability. Artificial sand pack flooding carried by SMPs at 65 °C showed an elevated plugging efficiency at around 97% under a simulated pressurization at 5 MPa, proposing a valid candidate for future EOR applications during CO₂ flooding. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48305.     

Influences of van der waals volume of substitute groups on CO2 permselectivity of polyimide‐A molecular simulation study

Polyimide (PI) as a typical glassy polymer material was investigated by molecular simulation to reveal the relationship between polymer molecular structure and its gas separation properties. The influences of van der waals volume (V_w) on CO₂ permselectivity of PI polymers (with four kinds of backbone substitute groups and a series of side substitute groups from small to large volume) and V_w was proposed as an intermediate to establish the relationship between the substitute group and permselectivity. The results show that the CO₂ permeability (P) simply increases and CO₂/N₂ selectivity (S) decreases with the increasing V_w of side substitute groups. The linear fitline of P‐V_w is much suitable to describe and predict the effect of the increasing V_w of side substitute group on improving permeability by analyzing the experimental and calculated CO₂ permeability. The increasing V_w of backbone substitute group can slow down the increasing of CO₂ permeability, but result in the decreasing first and then recovering to the original level. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41082.     

Self‐healing imidazolium‐based ionene‐polyamide membranes: an experimental study on physical and gas transport properties

A new series of six imidazolium‐based ionenes containing aromatic amide linkages has been developed. These ionene‐polyamides are all constitutional isomers varying in the regiochemistry of the amide linkages (para, meta) and xylyl linkages (ortho, meta, para) along the polymer backbone. The physical properties as well as the gas separation behaviors of the corresponding membranes have been extensively studied. These ionene‐polyamide membranes show excellent thermal and mechanical stabilities, together with self‐healing and shape memory characteristics. Most importantly, [TC‐API(p)‐Xy][Tf₂N] and [IC‐API(m)‐Xy][Tf₂N] membranes (TC, terephthaloyl chloride; API, 1‐(3‐aminopropyl)imidazole; Xy, xylyl; Tf₂N, bis(trifluoromethylsulfonyl) imide; IC, isophthaloyl chloride), where the amide and xylyl linkages are attached at para and meta positions, exhibit superior selectivity for CO₂/CH₄ and CO₂/N₂ gas pairs. We also demonstrate the transport properties and diverse applicability of our newly developed ionene‐polyamides, particularly [TC‐API(p)‐Xy][Tf₂N], for various industrial applications. © 2019 Society of Chemical Industry     

Mechanism of NO reduction by CO over Pt/SBA-15

The mechanism of the CO + NO reaction catalyzed by Pt/SBA-15 was studied via independent investigations of CO oxidation and NO disproportionation. Below 400 °C, both CO + O₂ and CO + NO reactions approach 100 % conversion, while the catalyst shows negligible activity for NO disproportionation. These results suggest that CO oxidation by atomic oxygen arising from NO dissociation is not a major route for CO₂ formation in the CO + NO reaction. In situ IR spectra reveal the formation of isocyanates (NCO⁻) adsorbed on silica. Their surface concentration changes with the extent of the CO + NO reaction. A mechanism is proposed in which isocyanates are reaction intermediates.     

Evaluation of CO2 adsorption capacity of electrospun carbon fibers with thermal and chemical activation

The use of urea was investigated as an alternative to the poisonous and expensive NH₃ gas, commonly used for amination of adsorbents. First, we fabricated activated carbon nanofibers (AnFs) by electrospinning of urea‐doped polyacrylonitrile solution (N‐AnF). By increasing the activation temperature, the average specific surface area (S_BET) and micropore volume (V_micro) of pristine nFs improved from 27.3 to 300 m²/g and 0.004 to 0.13 cm³/g, respectively. Upon urea doping, both properties were further enhanced to 542 m²/g and 0.22 cm³/g, respectively. However, with chemical investigation via X‐ray photoelectron spectroscopy, we observed that the urea‐doping incorporated more of less desired quaternary‐N, along with other more basic and desirable N‐functionalities (i.e., nitrile, pyridinic, pyrrolic N) tethered. Based on the eventual CO₂ adsorption results, we realized that average pore diameter (d_avg) is a limiting factor with regard to CO₂ adsorption by AnFs; the lower the d_avg, the better the adsorption. Further examination via adsorption isotherm model fitting showed that CO₂ molecules were homogenously collected in a monolayer pattern. However, three‐parameter model Redlich–Peterson model best fits the experimental data, suggesting that the adsorption is concentration‐driven and that it tends toward Langmuir rather than Freundlich at elevated concentration of CO₂. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45534.     

Solubility and diffusion behavior of compressed CO2 in polyurethane oligomer

In CO₂-assisted polyurethane (PU) foaming, the solubility and diffusion coefficient of CO₂ is vitally important to the cell nucleation and growth. This work is aimed at the effect of molecular weights (M _n) and crosslinking densities (V _e) on the solubility and diffusion coefficient of CO₂ in PU oligomers. A series of PU oligomers with different M _n and V _e were synthesized. The solubility and diffusivity of CO₂ in PU oligomers were measured experimentally in the temperature from 80 to 140 °C and with pressures up to 15 MPa. It was shown that the solubility and diffusion coefficients of CO₂ was decreased 20.5 and 21.0%, respectively, with the M _n increasing from 5864 to 153,754 g mol⁻¹ at 80 °C, 15 MPa. The solubility and the diffusion coefficient also decreased 11.1 and 38.0% as the V _e was increased from 64 to 1493 mol m⁻³. Furthermore, the diffusion mechanism of CO₂ in PU oligomers was explored via molecular dynamics simulations. The results indicated that the calculated diffusivity of CO₂ showed the same changing trend as the experimental values, and the smaller M _n or crosslinking degree contributed to an increase in fractional free volume and stronger polymer–CO₂ interactions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47100.     

Kinetics of isocyanate amine reactions

Development of polyurea-urethane and polyurea reaction injection molding (RIM) systems has created a need for kinetics of polyurea formation. Adiabatic batch reactions in solution were used to determine heats of reaction and relative reactivity of several aromatic amines and n-butanol with phenyl isocyanate (PI). In addition to comparing times required to reach 25, 50 and 75% conversion for both catalyzed and uncatalyzed reactions, n-th order models with Arrhenius rate constants were used to fit some of the exotherms. The reaction of 3,5-diethyl toluene (2,4 and 2,6)-diamine and PI could not be modeled due to unequal reactivity of the two amine groups. This unequal reactivity was studied using high performance liquid chromatography (HPLC) separation of the reaction products. The reactions of primary aliphatic amines and aromatic isocyanates were too rapid to be monitored in the batch apparatus. With a flow apparatus the reaction half time was estimated to be ～ 0.002 s.     

A Rapid Synthesis of Fatty Acyl Urea Derivatives

Fat-based aliphatic amides react with aromatic isocyanates in refluxing xylene generally within 1 hr to form crystalline acylaryl urea compounds in 50-80% yields. The reaction appears to be general with either component being aliphatic or aromatic. Although the reaction occurs in various solvents, xylene is the preferred solvent in which the reactions were completed within 4 hr for the chosen amides and isocyanates. The progress of the reaction was conveniently monitored by infrared through the disappearance of the intense isocyanate band at 2258 cm⁻¹. Agricultural Research Service, USDA.     

Nature of Surface Deposits on Sulfated Zirconia Used as Catalyst in the Benzoylation of Anisole

The effects of CO₂, CO and H₂ co-reactants on CH₄ pyrolysis reactions catalyzed by Mo/H-ZSM-5 were investigated as a function of reaction temperatures and co-reactant and CH₄ concentrations. Total CH₄ conversion rates were not affected by CO₂ co-reactants, except at high CO₂ pressures, which led to the oxidation of the active MoC _x species, but CH _x intermediates formed in rate-determining C–H bond activation steps increasingly formed CO instead of hydrocarbons as CO₂ concentrations increased. CO formation rates increased with increasing CO₂ partial pressure; all entering CO₂ molecules reacted with CH₄ within the catalyst bed to form two CO molecules at 950-1033 K. In contrast, hydrocarbon formation rates decreased linearly with increasing CO₂ partial pressure and reached undetectable levels at CO₂/CH₄ ratios above 0.075 at 950 K. CO formation continued for a short period of time at these CO₂/CH₄ molar ratios, but then all catalytic activity ceased, apparently as a result of the conversion of active carbide structures to MoO _x . The removal of CO₂ from the CH₄ stream led to gradual catalyst reactivation via reduction-carburization processes similar to those observed during the initial activation of MoO _x /H-ZSM-5 precursors in CH₄. The CO₂/CH₄ molar ratios required to inhibit hydrocarbon synthesis were independent of CH₄ pressure because of the first-order kinetic dependencies of both CH₄ and CO₂ activation steps. These ratios increased from 0.075 to 0.143 as reaction temperatures increased from 950 to 1033 K. This temperature dependence reflects higher activation energies for reductant (CH₄) than for oxidant (CO₂) activation, leading to catalyst oxidation at higher relative oxidant concentrations as temperature increases. The scavenging of CH _x intermediates by CO₂-derived species leads also to lower chain growth probabilities and to a significant inhibition of catalyst deactivation via oligomerization pathways responsible for the formation of highly unsaturated unreactive deposits. CO co-reactants did not influence the rate or selectivity of CH₄ pyrolysis reactions on Mo/H-ZSM-5; therefore, CO formed during reactions of CO₂/CH₄ mixtures are not responsible for the observed effects of CO₂ on reaction rates and selectivities, or in catalyst deactivation rates during CH₄ reactions. H₂ addition studies showed that H₂ formed during CH₄/CO₂ reactions near the bed inlet led to inhibited catalyst deactivation in downstream catalyst regions, even after CO₂ co-reactants were depleted.     

Electro‐optic properties of CO2 fixed‐polymer/nematic LC composite films

Bis(cyclic carbonate) was obtained from the epoxide and CO₂ reaction with a quaternary ammonium halide salt catalyst. Cyclic carbonate derivatives were then reacted with amine to obtain quantitatively poly(hydroxy)urethanes that were reacted with isophorone diisocyanate (IPDI) and end capped with acrylate to form prepolymers. These prepolymers were mixed with reactive diluents and nematic LCs, and subjected to UV cure to form polymer/LC composite films in a transparent cell. Three types of diglycidyl ether [poly(propyleneglycol), cyclohexane, bisphenol A], three types of end‐capping acrylates [2‐hydroxyethyl acrylate (HEA), 2‐hydroxypropyl acrylate (HPA), and 2‐hydroxyethyl methacrylate (HEMA)], three types of multyfunctional diluents [tripropylene glycol diacrylate (TPGDA), trimethylolpropane triacrylate (TMPTA), dipentaerythritol hydroxy penta/hexa acrylate (DPHPA)], and three types of photoinitiators (Irgacure‐651, Irgacure‐184, Darocure‐1173) were incorporated to control the morphology, and hence, the electro‐optic properties of the polymer/nematic LC composite films. Poly(propylene glycol) diglycidyl ether segment of polyurethane acrylate (PUA) showed lower viscosity and gave larger domain size resulting in lower threshold (V₁₀) and driving (V₉₀) voltages, together with larger nematic–isotropic transition temperature depression. HEA end‐capped PUA gave larger polymer–LC phase separation and smaller V₁₀ as well as V₉₀. TPGDA‐based PUA showed the lowest V₁₀ and V₉₀ and the shortest response time. Among the three types of photoinitiators used Irgacure‐651 showed the larger LC domain, and smaller V₁₀ and V₉₀. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2744–2753, 2001     

Indane‐based bismaleimide and cloisite 15a nanoclay blends: Kinetics of thermal curing and degradation of particulate nanocomposites

Bismaleimide, 5(6)‐maleimide‐1(4′‐maleimidophenyl)‐1,3,3′‐trimethyl indane (BMII) was prepared, different weight ratios (1, 3, 5, 7, and 9%) of cloisite 15a were blended with BMII ultrasonically and thermally polymerized at 230°C for 6 h. The Fourier transform infrared spectrophotometry (FTIR) studies of the polymerized materials reveal that the clay particles affect only the indane nucleus present in the bismaleimide. Differential scanning calorimetry results reveal that the nanoclay particles affect the enthalpy of curing and the extent of this effect depends on the degree of clay loading. In the case of particulate nanocomposites, irrespective of the amount of clay loading, the endset degradation temperatures of the nanocomposites were found to increase (35–60°C). The change noted in the apparent activation energies (E_a) for curing and degradation with respect to the extent of the reaction (α) is much dependent on the amount of cloisite 15a present in BMII. The TG‐FTIR studies showed the compounds such as CO, CO₂, aromatic amine, and aromatic isocyanates are the major degradation products from polyBMII. Possible degradation mechanism of polyBMII is presented and discussed. The scanning electron microscopy results show that the aggregation of clay particles are noted for higher level loadings (5 and 7%) of cloisite 15a nanoclay particles in BMII. POLYM. COMPOS. 34:1279–1297, 2013. © 2013 Society of Plastics Engineers     

Influence of Nature of Spacer and Hydrocarbon Chain Length on Micellar Encapsulation of Polynuclear Aromatic Hydrocarbons by Carbohydrate Derived Non-Ionic Gemini Surfactants in Aqueous Ethanol Medium

Gemini surfactants with rigid aromatic spacer -CH₂-Ar-CH₂-: 6,6′-(N,N′-di(alkyl)-1,4-phenylenedimethylamino)bis(6-deoxy-1,2-O-isopropylidene-α-D-glucofuranose) and Gemini surfactants with flexible aliphatic spacer -(CH₂)₆-: 6,6′-(N,N′-di(2-hydroxyalkyl)-1,6-hexanediamino)bis(6-deoxy-1,2-O-isopropylidene-α-D-glucofuranose) have been synthesized, and their micellar properties for encapsulation of polynuclear aromatic hydrocarbons (PAH) viz. fluorene, anthracene, triptycene, and pyrene in aqueous ethanol medium have been studied by means of electronic spectroscopy. The micellar study reveals that nature of spacer and length of hydrocarbon chain of the surfactant has profound effect on micellar encapsulation of PAH. The surfactants with rigid aromatic spacer show greater encapsulation as compared to surfactants with flexible aliphatic spacer. Moreover, the more hydrophobic surfactant, i.e. the surfactant with a longer hydrocarbon chain, shows greater encapsulation toward PAH which are encapsulated in the order of their smaller size.     

Eine neue,breit anwendbare Synthese für aromatische Aldehyde

Diformamide ( 1 ) reacts with activated aromatic compounds like toluene, anisole, m‐xylene, 1,2‐dimethoxybenzene in the presence of AlCl₃ to give N‐(diarylmethyl)‐formamides 2a—d , the corresponding aromatic aldehydes 3—6 are formed as by‐products in low yields. From N,N‐dimethylaniline and 1 /AlCl₃ the triphenylmethane derivative 7 can be obtained. The reaction of anisole with N‐methyl‐diformamide ( 9 ) affords the formamide 10 . The mixture of formamide, P₄O₁₀ and AlCl₃ reveals to be a reagent which is capable to formylate toluene and anisole, resp. Triformamide ( 14 )/AlCl₃ is an effective formylating system which allows the preparation of aromatic aldehydes (e.g. 3,4,17—32 ) from the corresponding aromatic hydrocarbons. Aluminiumchloride can be replaced by borontrichloride. The yields of the formylation reactions depend strongly from the reaction conditions (molar ratio: aromatic hydrocarbon/AlCl₃/ 14 ; solvent, reaction temperature). The scope of the reaction covers nearly complete those of the Gattermann‐Koch‐, Gattermann‐ and Vilsmeier—Haack‐reaction.     

Synthesis,characterization, and gas permeability of aromatic polyimides containing pendant phenoxy group

A diamine containing a pendant phenoxy group, 1-phenoxy-2,4-diaminobenzene, was synthesized and condensed with different aromatic dianhydrides [4,4′-oxydiphthalic dianhydride, 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, 3,3′,4,4′-biphenyltetracorboxylic dianhydride, and pyromellitic dianhydride] by one-step synthesis at a high temperature in m-cresol to obtain polyimides in high yields. Most of the polyimides exhibited good solvent solubility and could be readily dissolved in chloroform, sym-tetrachloroethane, N,N-dimethylformamide, N,N-dimethylacetamide, and nitrobenzene. Their inherent viscosities were in the range of 0.33–1.16 dL/g. Wide-angle X-ray spectra revealed that these polymers were amorphous in nature. All these polyimides were thermally stable, having initial decomposition temperatures above 500°C and glass-transition temperatures in the range of 248–281°C. The gas permeability of 4,4′-oxydiphthalic dianhydride and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride based polyimides was investigated with pure gases: He, H₂, O₂, Ar, N₂, CH₄, and CO₂. A polyimide containing a  C(CF₃)₂ linkage showed a good combination of permeability and selectivity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Single‐Pot Ethane Carboxylation Catalyzed by New Oxorhenium(V) Complexes with N,O Ligands

The oxorhenium(V) chelates [ReOCl(N,O‐L)(PPh₃)] [N,O‐L=(OCH₂CH₂)N(CH₂CH₂OH)(CH₂COO) ( 2 ), (OCH₂CH₂)N(CH₂COO)(CH₂COOCH₃) ( 3 )] and [ReOCl₂(N,O‐L)(PPh₃)] [N,O‐L=C₅H₄N(COO‐2) ( 4 ) C₅H₃N(COOCH₃‐2)(COO‐6) ( 5 )] have been prepared by reaction of [ReOCl₃(PPh₃)₂] ( 1 ), in refluxing methanol, with N,N‐bis(2‐hydroxyethyl)glycine [bicine; N(CH₂CH₂OH)₂(CH₂COOH)], N‐(2‐hydroxyethyl)iminodiacetic acid [N(CH₂CH₂OH)(CH₂COOH)₂], picolinic acid [NC₅H₄(COOH‐2)] or 2,6‐pyridinedicarboxylic acid [NC₅H₃(COOH‐2,6)₂], respectively, with ligand esterification in the cases of 3 and 5 . All these complexes have been characterized by IR and multinuclear NMR spectroscopy, FAB⁺‐MS, elemental and X‐ray diffraction structural analyses. They act as catalysts, in a single‐pot process, for the carboxylation of ethane by CO, in the presence of potassium peroxodisulfate K₂S₂O₈, in trifluoroacetic acid (TFA), to give propionic and acetic acids, in a remarkable yield (up to ca. 30%) and under relatively mild conditions, with some advantages over the industrial processes. The picolinate complex 4 provides the most active catalyst and the carboxylation also occurs, although much less efficiently, by the TFA solvent in the absence of CO. The selectivity can be controlled by the ethane and CO pressures, propionic acid being the dominant product for pressures about ca. 7 and 4 atm, respectively (catalyst 4 ), whereas lower pressures lead mainly to acetic acid in lower yields. These reactions constitute an unprecedented use of Re complexes as catalysts in alkane functionalization.     

Stable CO2/water foam stabilized by dilute surface-modified nanoparticles and cationic surfactant at high temperature and salinity

CO₂ enhanced oil recovery and storage could see widespread deployment as decarbonization efforts accelerate to meet climate goals. CO₂ is more efficiently distributed underground as a viscous foam than as pure CO₂; however, most reported CO₂ foams are unstable at harsh reservoir conditions (22 wt% brine, 2200 psi, and 80°C). We hypothesize that silica nanoparticles (NP) grafted with (3-trimethoxysilylpropyl)diethylenetriamine ligands (N3), to improve colloidal stability, and dimethoxydimethylsilane ligands (DM), to improve CO₂-phillicity, combined with the cationic surfactant N¹-alkyl-N³, N³-dimethylpropane-1,3-diamine (RCADA), will develop viscous, stable CO₂ foams at reservoir conditions. We grafted NP with N3 and DM ligands. We verified NP stability at reservoir conditions with measurements of zeta potential, amine titration curves, and NP diameter. We measured NP water contact angles (θ_w) at the water–air and water–liquid CO₂ interfaces. In a high-temperature, high-pressure flow apparatus, we calculated the viscosity of CO₂ foams across a beadpack and determined static foam stability with microscope observations. Modified NP were colloidally stable at reservoir conditions for 4 weeks, and had higher θ_w in liquid CO₂ than in air. Addition of at least 0.5 μmol/m² DM silane (0.5DM) greatly improved foam stability. RCADA-only foam coarsening rates (dD_SM³/dt) decreased 16–17× after adding 1 wt/vol% 8N3 + 1.5DM NP, and 5–10× with a 0.1–1 vol/vol% increase in RCADA concentration (with or without NP). 1 vol/vol% RCADA foam exhibited coarsening rates of 900 and 2400 μm³/min with 1 and 0.2 wt/vol% 8N3 + 1.5DM NP, respectively. These results demonstrate impressive foam stabilities at harsh reservoir conditions.     

A glutamic acid-based polymer keeping intact the integrity of all the three original functionalities of the amino acid

Dimethyl glutamate, on treatment with allyl bromide, afforded dimethyl N,N-diallylglutamate which upon alkaline ester hydrolysis followed by acidification with aqueous HCl gave N,N-diallylglutamic acid hydrochloride [(CH₂=CH–CH₂)₂NH⁺CH(CO₂H)(CH₂)₂CO₂H Cl^?] I. Using Butler’s cyclopolymerization protocol, new monomer I underwent ammonium persulfate-initiated polymerization to give pyrrolidine ring-embedded linear cyclopolymer II i.e. ?[?CH₂(C₄H₆)NH⁺{CH(CO₂H)(CH₂)₂CO₂H Cl^?}CH₂?]?_n retaining the integrity of all the three functionalities of glutamic acid. Under the influence of pH, the repeating units of triprotic acid (+) in II were equilibrated to those of water-insoluble diprotic polyzwitterionic acid (±) III, water-soluble monoprotic poly(zwitterion-anion) (±?) IV, and its conjugate base polydianion (=) V. The critical salt concentration required to promote water solubility of (±) III has been determined to be 0.548 M NaCl, 0.271 M NaBr, 0.133 M NaI. The basicity constants of the carboxyl groups and trivalent nitrogen in (=) V have been determined. A 5 ppm and 20 ppm concentrations of III are effective in inhibiting the precipitation of CaSO₄ from its supersaturated solution with a ≈100% scale inhibition efficiency at 40 °C for a duration of over 3 and 16 h, respectively.     

Soluble polyimides with propeller shape triphenyl core for membrane based gas separation

This article reports the synthesis and characterization of a series of new aromatic polyimides (PIs) having bulky tert butyl group containing propeller shaped triphenylamine unit in its structure. The PIs were prepared by the reaction of 4,4′‐diamino‐4″‐(2,4,6‐tri‐tert‐butylphenoxy) triphenylamine with different commercially available aromatic dianhydrides through the formation of corresponding poly(amic acid)s and subsequent thermal cycloimidization. The PIs showed high glass transition temperature (T_g up to 270 °C) and thermal stability (T_d10 up to 475 °C). The PI membranes showed good mechanical properties with tensile strength up to 70 MPa, excellent separation performance [P(CO₂) = 100.8, P(O₂) = 40.4 barrer], and good permselectivity [P(CO₂)/P(CH₄) = 50.9, P(O₂)/P(N₂) = 7.6]. The membranes exhibited extremely high solubility selectivity for the CO₂/CH₄ gas pair due to the strong affinity between CO₂ and nitrogen atoms of tertiary amine in triphenylamine. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46658.     

Photochromic polyacylsemicarbazides based on azobenzene containing dihydrazide

Polyacylsemicarbazides exhibiting photochromic behaviour were synthesised by solution polymerisation of azobenzene chromophore containing dihydrazide and various diisocyanates (aliphatic, cycloaliphatic and aromatic). A model compound was also prepared from o‐tolylene isocyanate and dihydrazide. The structures were confirmed by ¹H NMR and FTIR techniques. The polymers were found to exhibit λ_max values around 330 nm corresponding to the trans isomer which reduced with irradiation of the solutions of polymers in DMAc due to trans→cis isomerisation as observed by UV‐VIS spectrometry. The reverse reaction (cis→trans isomerisation) was found to take place photochemically when irradiated with visible light or when kept in the dark. The rates of isomerisation reactions were found to be independent of the chromophore concentration and the nature of the polymer backbone. The inherent viscosity of the solutions of polymers in DMAc reduced upon irradiation with UV light and was regained in the dark. Thermal studies showed that the polymer degradation started with the simultaneous cleavage of imino (N? N) and aromatic azo (? N?N? ) bond and that recrystallisation occurred on heating the samples. Copyright © 2004 Society of Chemical Industry