Physicochemical characterization of poly(tert-butyl acrylate-b-methyl methacrylate) prepared with atom transfer radical polymerization by inverse gas chromatography

Poly(tert-butyl acrylate) (PtBuA) was synthesized by atom transfer radical polymerization (ATRP) using methyl-2-bromo propionate (MBP) as an initiator in bulk at 80 °C. The successive ATRP of methyl methacrylate in diphenyl ether at 80 °C using previously obtained PtBuA as a macroinitiator led to formation of poly(tert-butyl acrylate-b-methyl methacrylate) (poly(tBuA-b-MMA)). The synthesized macroinitiator and block copolymer have controlled molecular weight and low polydispersity (M_w/M_n<1.2). The block copolymer was characterized by gel permeation chromatography (GPC) and ¹H NMR. The retention diagrams of poly(tBuA-b-MMA) for some aliphatic esters and aromatic hydrocarbons were obtained using inverse gas chromatography (IGC) technique. The glass transition temperatures, T_gs of poly(tBuA-b-MMA) were determined by both differential scanning calorimeter (DSC) and IGC. It was observed that the block copolymer represents three T_gs at 50, 75 and 100 °C by IGC although it represents only one T_g at 71 °C by DSC. After the column was quenched from 180 to 0 °C, the T_g at 100 °C shifted to 105 °C however others did not change. Specific retention volumes, and the thermodynamical polymer-solvent interaction parameters such as Flory-Huggins, , equation-of-state, and effective exchange energy, X_eff were found for all studied solvents. Partial molar heat of sorption, , partial molar heat of mixing, and molar heat of vaporization, ΔH_v, were determined. In addition, the solubility parameter of the corresponding block copolymer, δ₂ was determined as 11.0 (cal/cm³)^1/2 at 25 °C.     

Synthesis, characterization and thermodynamic properties of poly(3-mesityl-2-hydroxypropyl methacrylate-co-N-vinyl-2-pyrrolidone)

Poly(3-mesityl-2-hydroxypropyl methacrylate-co-N-vinyl-2-pyrrolidone) P(MHPMA-co-VP) was synthesized in 1, 4-dioxane solution using benzoyl peroxide (BPO) as initiator at 60 °C. The copolymer was characterized by ¹H ¹³C NMR, FT-IR, DSC, TGA, size exclusion chromatography analysis (SEC) and elemental analysis techniques. According to SEC, the number-average molecular weight (M_n), weight-average molecular weight (M_w) and polydispersity index (PDI) values of PMHPMA-co-VP were found to be 58,000, 481,000 g/mol and 8.26, respectively. According to TGA, carbonaceous residue value of PMHPMA-co-VP was found to be 6% at 500 °C. Also, some thermodynamic properties of PMHPMA-co-VP such as the adsorption enthalpy, ΔH_a, molar evaporation enthalpy, ΔH_v, the sorption enthalpy, , sorption free energy, , sorption entropy, , the partial molar free energy, , the partial molar heat of mixing, , at infinite dilution was determined for the interactions of PMHPMA-co-VP with selected alcohols and alkanes by inverse gas chromatography (IGC) method in the temperature range of 323-463 K. According to the specific retention volumes, , the weight fraction activity coefficients of solute probes at infinite dilution, , and Flory-Huggins interaction parameters, between PMHPMA-co-VP-solvents were determined in 413-453 K. According to and , selected alcohols and alkanes were found to be non-solvent for PMHPMA-co-VP at 413-453 K. The glass transition temperature, T_g, of the PMHPMA-co-VP found to be 370 and 363 K, respectively, by IGC and DSC techniques, respectively.     

Melting parameters of poly(glycolic acid)

Equilibrium melting temperature T_m⁰, heat of fusion ΔH_f, and entropy of fusion ΔS_f of poly(glycolic acid) (PGA) was determined by using Clapeyron-Clausius equation. Equilibrium melting temperature T_m⁰ was 504.6 K which was determined by Hoffman-Weeks plots. The pressure dependence of T_m⁰ was determined by high pressure DTA up to 150 MPa. Volume change ΔV_f at melting was determined by using dilatometer. Heat of fusion in PGA was 183.2 (J g⁻¹), which is very close to the value reported by Chujo et al. who determined it by using T_m depression in copolymer with poly(lactic acid). ΔS_f of PGA was 0.363 (J g⁻¹ K⁻¹), which is about twice that of PLA, and the reason was discussed on the basis of the elastic modulus below T_m.     

Supramolecular Architectures in Three Metal(II) Coordination Polymers with 2,5-Dichloroterephthalate and Flexible Bis(Benzimidazole) Ligands

Three supramolecular coordination polymers, namely [Ni(L1)(DCTP)(H₂O)] _n (1), [Cu(L2)(DCTP)] _n (2), [Co(L3)(DCTP)] _n (3) (L1?=?1,5-bis(5,6-dimethylbenzimidazole)pentane, L2?=?1,4-bis(5,6-dimethylbenzimidazole)butane, L3?=?1,4-bis(benzimidazole)-2-butylene) have been hydrothermally synthesized and characterized by single crystal X-ray structure determination, FT-IR, elemental analysis, X-ray powder diffraction (XPD), and thermogravimetric analysis (TGA). CP 1 exhibits 2D 6³ honeycombed network structure, which is further extended into a 3D Moganite (mog) supramolecular framework by classical O–H?O hydrogen-bonding interaction. CPs 2 –3 present 2D (4,4) layers, and 3D supramolecular frameworks that are formed by π–π stacking interactions. Furthermore, the catalytic activities of CPs 1–3 for the degradation of methyl orange in a Fenton-like process has been investigated, and CPs 1–3 show strong photoluminescence properties at room temperature in solid state.     

Mixed Micellar Properties and Related Interaction Parameters of Butanediyl-1,4-bis(dodecyl dimethyl ammonium bromide) Gemini Surfactant with Nonionic Amphiphiles

Mixed micellization of cationic gemini surfactant butanediyl-1,4-bis(dimethyldodecylammonium bromide) with nonionic surfactants (sorbitan esters, alcohols and phenol ethoxylates) and triblock copolymers has been studied tensiometrically. Various physicochemical parameters of the studied systems including ideal CMC values, experimental and ideal micellar compositions, interaction parameters, activity coefficients of the components, etc. have been evaluated by considering theoretical models of Clint, Rubingh, Rosen and Maeda. The experimental critical micelle concentration (CMC) values of the mixed micelles were lower than the CMC values of the individual components and showed a negative deviation from ideal CMC (CMC*) values. The analysis reveals that the mole fractions of gemini are lower compared to the nonionic surfactants/triblock polymers and the values of ΔG _m ^° , ΔG _ad ^° , G _min and ΔG _ex ^m show that the spontaneity of the studied mixed micelles relatively decreases as the content of the gemini in the bulk phase increases.     

Copolymerization of ethene with norbornene using palladium(II) α-diimine catalysts: Influence of feed composition, polymerization temperature, and ligand structure on copolymer properties and microstructure

Four cationic palladium(II) α-diimine complexes, [{ArNC(R)-C(R)NAr}Pd(Me)(CH₃CN)] (1, R=H, Ar=2,6-Me₂C₆H₃, =B[3,5-C₆H₃(CF₃)₂]₄; 2, R=CH₃, Ar=2,6-iPr₂C₆H₃; 3, R=CH₃, Ar=2-tBuC₆H₄; 4, R,R=An, Ar=2,6-iPr₂C₆H₃) were used for the copolymerization of ethene with norbornene. The copolymerization behavior of the catalysts and the influence of the polymerization temperature were investigated. The copolymers were characterized using ¹³C NMR spectroscopy, differential scanning calorimetry, and gel permeation chromatography techniques. Sterically demanding ortho -N-aryl substituents and rigid bulky bridge units increase the copolymer molar masses, while the incorporation level of norbornene is decreased. Microstructures with isolated norbornene units and alternating sequences are predominant. Less bulky substituted catalysts yield copolymers with higher norbornene contents and lower molar masses. Norbornene diblock sequences are dominant which are exclusively racemic connected, indicating that the insertion proceeds under chain end control. Optimal polymerization results are achieved at temperatures between 10 and 30 °C, while temperatures below 0 °C result in lower polymerization rates and molar masses. Above 30 °C, activities, molar masses, and norbornene incorporation decreases due to catalyst decomposition.     

Studies with inorganic precipitate membranes—XII: Consideration of membrane field strength and energetics of permeation

Electrolytic transfort processes occuring across parchment supported membranes have been described by Nernst Planck flux equation taking into account the membrane resistance R_m, membrane potential E_metc.E_m values for various electrolytes display very interesting phenomena. In the case of 1:1 electrolyte the E_m values are all positive, while in the case of (2:1) and (3:1) electrolytes surface charge reversal takes place. The diffusion rate sequence and selectivity of the membrane for different uni- bi- and trivalent cations was found to be primarily dependent on the difference in the hydration energies of counter ions in the external solution. On the basis of Eisenman-Sherry theory the diffusion rate sequence of alkali metal cations point towards the weak field strength of the fixed charge groups. Various thermodynamic parameters, ΔH^≠, ΔF^≠ and ΔS^≠ were evaluated by applying the theory of absolute reactions rates to the diffusion process through parchment supported membranes. The values of ΔS^≠ were found to be negative, indicating that diffusion takes place with partial immobilization in the membrane phase. The relative partial immobility was found to increase with increase in the valence of the ions constituting the electrolyte. A formal relation between ΔH_hydration, ΔF_hydration and ΔS_hydration of cations with the corresponding values of ΔH^≠, ΔF^≠ and ΔS^≠ for diffusion, was also found to exist for these membranes.     

Inverse gas chromatography of poly(vinylisobutyl ethers) and polymer-solute thermodynamic interactions

Gas chromatography (GC) retention behavior of atactic and isotactic poly(vinylisobutyl ether) stationary phases has been studied in the temperature range 30–90°C using 16 solutes which include various alkanes, alkylbenzenes, and chlorinated aliphatic hydrocarbons. The bulk sorption equilibrium retention data have been employed to derive various thermodynamic quantities at infinite dilution of solutes in the polymers, viz., χ, χ^*, χ_H, χ_S, X₁₂, δH_S, h . Their dependence on temperature, polymer structure, and chemical nature of solutes has been discussed.     

A fluorene-containing water-soluble poly(p-phenyleneethynylene) derivative: Highly fluorescent and sensitive conjugated polymer with minor aggregation in aqueous solution

A novel cationic fluorene-containing water-soluble poly(p-phenyleneethynylene) (PPE) derivative, poly[(9,9-bis{6′-[(N,N-diethyl)-N-methylammonium]hexyl}-2,7-fluorenyleneethynylene)-alt-co-(2,5-bis{3′-[(N,N-diethyl)-N-methylammonium]-1′-oxapropyl}-1,4-phenylene)] tetraiodide (P1′), was synthesized through Sonogashira reaction and a post-polymerization treatment. P1′ emits bright blue fluorescence in H₂O with a high photoluminescence quantum yield (Φ_pl=26%). Studies on the optical properties and quenching experiments with in H₂O and MeOH show that P1′ presents minor aggregation and high Stern-Volmer constant (K_sv=2.4×10⁸ M⁻¹) in aqueous solution. The remarkably reduced tendency towards aggregation, relative to previously reported water-soluble PPEs, made the optical properties of P1′ almost insensitive to the disturbance from the common ions (non-quencher) in the solution.     

On the determination of surface areas in activated carbons

The paper examines the validity of two approaches frequently used to determine surface areas in activated carbons, namely the BET method and the use of immersion calorimetry. The study is based on 21 well characterized carbons, whose external and microporous surface areas, S_e and S_mi, have been determined by a variety of independent techniques. It appears clearly that S_BET and the real surface area S_mi + S_e are in agreement only for carbons with average pore widths L_o around 0.8-1.1 nm. Beyond, S_BET increases rapidly and S_BET − S_e is practically the monolayer equivalent of the micropore volume W_o. This confirms that a characterization of surface properties based on S_BET is, a priori, not reliable. The study of the enthalpy of immersion of the carbons into benzene at 293 K, based on Dubinin’s theory, shows that Δ_iH consists of three contributions, namely from the interactions with the micropore walls (−0.136 J m⁻²), the external surface (−0.114 J m⁻²), and from the volume of liquid found between the surface layers in the micropores (−141 J cm⁻³). It appears that for carbons where L_o > 1 nm, the real surface area cannot be determined in a reliable way from the enthalpy of immersion and a specific heat of wetting alone.     

Transfer equilibrium in the surface layer of a (PdH)-electrode with low hydrogen content

The constants of the equilibrium between H held in the surface layer and H dissolved in the bulk of Pd-H)-electrodes coated with different surface layers have been galvanostatically measured within 0 and 30°C, in 1 NH₂SO₄. The enthalpy change ΔH⁰ and entropy change ΔS⁰ have been estimated from van't Hoff plots. A physical effect in the linear correlation between ΔH⁰ and ΔS⁰ data has been detected. The dependence of ΔH⁰, ΔS⁰ and ΔG⁰₂₉₈ on the roughness factor (f_w = 2–60) explains the tendency of H to accumulate spontaneously in the surface layer. The schematic diagram of the potential energy of Pd/solution interface is compared with data on Pd/H₂ gas interface. The difference is ascribed to the specific adsorption of anions connected with the high density of defects in the surface layer.     

Oxidation kinetics of Iron(II) complexes of trans-1,2-diaminocyclohexanetetraacetate (cdta) with dissolved oxygen: Reaction mechanism, parameters of activation and kinetic salt effects

The present investigation takes concern about a spiny environmental problem afflicting the pulp mill industry exploiting the Kraft sulfate-pulp process where dilute total reduced sulfur contaminants are co-mixed with oxygen in large-volume gas effluents. A potential Redox process for removing the total reduced sulfurs consists in oxidizing them by means of iron(III) organometallic complexes while the co-mixed oxygen mediates the oxidative regeneration of iron(II) into iron(III) complexes. In this work, the oxidation kinetics of iron(II) trans-1,2,-diaminocyclohexanetetraacetate (cdta) complexes with molecular oxygen (O₂) as the source oxidant was investigated for a wide pH range (1.75<pH<12) in a 3.2 dm³ single-phase stirred cell reactor within the [281-323 K] temperature range. Simultaneous measurements of iron(II)-cdta (50-) and O₂ (0.5-) were used to clarify the reaction mechanism which has been interpreted differently in previous works. The observed kinetic data in alkaline solutions could be accounted for in terms of three forward [Fe²⁺cdta^4-+O₂ (rate-limiting, k_1,app), , 2Fe²⁺cdta^4-+H₂O₂] and one reverse [ (k_-1,app,n=0 or 1)] elementary steps. Assessment of the rate-limiting apparent rate constant led to the following results ( at and , , ). Fe³⁺OH^-cdta^4-, being the dominating iron(III) product at pH>10, was found to be less reactive than Fe³⁺cdta^4- with the superoxide intermediate , thus reducing the effect of the reverse step at higher pH. A study on the effect of electrolytes on the reaction rate led to the conclusion that salts increase the rate constant k_1,app. Finally, kinetic results in acidic conditions leading to the formation of other iron(II)-cdta complexes (i.e., Fe²⁺cdta^4-H⁺) and another superoxide intermediates are reported and discussed.     

A Comprehensive Study on the Synthesis and Micellization of Disymmetric Gemini Imidazolium Surfactants

Two groups of disymmetric Gemini imidazolium surfactants, [C₁₄C₄C _m im]Br₂ (m = 10, 12, 14) and [C _m C₄C _n im]Br₂ (m + n = 24, m = 12, 14, 16, 18) surfactants, were synthesized and their structures were confirmed by ¹H NMR and ESI–MS spectroscopy. Their adsorption at the air/water interface, thermodynamic parameters and aggregation behavior were explored by means of surface tension, electrical conductivity and steady-state fluorescence. A series of surface activity parameters, including cmc, γ _cmc, π _cmc, pC ₂₀, cmc/C ₂₀, Γ _max and A _min, were obtained from surface tension measurements. The results revealed that the overall hydrophobic chain length (N _c) for [C₁₄C₄C _m im]Br₂ and the disymmetry (m/n) for [C _m C₄C _n im]Br₂ had a significant effect on the surface activity. The cmc values decreased with an increase of N _c or m/n. The thermodynamic parameters of micellization (ΔG _m ^θ , ΔH _m ^θ , ΔS _m ^θ ) derived from the electrical conductivity indicated that the micellization process of [C₁₄C₄C _m im]Br₂ and [C _m C₄C _n im]Br₂ was entropy-driven at different temperatures, but the contribution of ΔH _m ^θ to ΔG _m ^θ was enhanced by increasing N _c or m/n. The micropolarity and micellar aggregation number (N _agg) were estimated by steady-state fluorescence measurements. The results showed that the surfactant with higher N _c or m/n can form larger micelles, due to a tighter micellar structure.     

Study on physical and electrostatic interactions of counterions in poly(perfluorosulfonic) acid matrix: Characterization of diffusion properties of membrane using radiotracers

The self-diffusion coefficients of water and ions were used to study the physical (tortuosity) and electrostatic interactions of counterions in poly(perfluorosulfonic) acid membrane (Nafion-117) matrix. The self-diffusion coefficients of water were measured in the water swollen Nafion-117 membrane with Zn²⁺, Ca²⁺, Sr²⁺, and Fe²⁺ counterions by analyzing the experimental exchange rates between tritium tagged water (HTO) in membrane and equilibrating water. In order to study the effects of equilibrating solution, the HTO-desorption rate profiles between the membrane samples in H⁺ or Cs⁺ forms and equilibrating solution containing CsCl or HCl (0.25 mol/L) were measured. It was observed that the HTO-exchange rate profile was slower in case of membrane sample in Cs⁺-from equilibrated with salt/acid solution than that equilibrated with deionized water in same ionic form. However, HTO-exchange rate profile did not alter in case of H⁺-form of membrane on equilibration with salt or acid solution. The variation of ln  with polymer volume function V_p/(1 − V_p), where V_p is polymer volume fraction, indicated that: (i) in the membrane with multivalent counterions was lower than that reported for membrane with monovalent counterions at same V_p, and (ii) the linear trends observed in variation of ln  with V_p/(1 − V_p) for multivalent and monovalent counterions were significantly different. The values of in membrane normalized with at V_p = 0 were taken as an estimate of the tortuosity factor for self-diffusion of ions in the membrane matrix. The self-diffusion coefficients of ions reported in the literature along with tortuosity factor obtained from in the corresponding ionic forms of the membrane were analyzed to obtain the charge (Z_i) independent electrostatic interaction parameter g(φ) of monovalent and divalent ions in the membrane. This analysis indicated that g(φ) also vary exponentially as a function of V_p/(1 − V_p) irrespective of charge on counterions. In order to study the influence of V_p on diffusional transport rates of Na⁺ and Cs⁺ ions in membrane, a permeation experiment was carried out using H⁺-form of membrane having high water volume fraction. The diffusional transport rates of Cs⁺ and Na⁺ in H⁺-form of membrane were found to be similar indicating that the water volume fraction in membrane has strong influence on the parameters that govern the diffusion across the Nafion-117 membrane.     

The effects of fullerene (C60) crystal structure on its electrochemical capacitance

The electrochemical properties of different types of fullerene crystals (x-C₆₀), having hollow-long cylindrical (C-C₆₀), hollow-long square (S-C₆₀), and thick solid-short hexagonal (H-C₆₀) shapes were investigated. The prepared x-C₆₀ samples had specific dimensions with respect to aspect ratio (12.0, 6.7, and 1.5) and lattice spacing distance (1.12, 1.04, and 1.00 nm). Interestingly, it was possible to control the aspect ratio and lattice spacing distance by adjusting the molecular ratio of C₆₀ to the aromatic solvent (m-xylene) used in the preparation. In addition, the number of m-xylene molecule in the x-C₆₀ crystal structure increased with decreasing ratio of x-C₆₀ to m-xylene in the solution, corresponding to ca. C₆₀·0.83m-xylene (for C-C₆₀), C₆₀·0.39m-xylene (for S-C₆₀), and C₆₀·0.36m-xylene (for H-C₆₀). A more ordered arrangement of m-xylene molecules resulted in an improved electrochemical capacitance of x-C₆₀. Importantly, in the case of the regular structure (C-, S-, H-C₆₀), when m-xylene was assembled in the x-C₆₀ structure, the large lattice spacing distance increased. This explains why the C-C₆₀ sample had the largest electrochemical capacitance, compared to the S- and H-C₆₀ samples. Such a configuration would allow for a high charge accumulation and the formation of a donor-acceptor complex, which would permit an easier charge transfer.     

Solutions of benzoic acid in formamide—II. thermodynamic properties from electromotive force measurements

The emf of the cell Pt, H₂, HBz(m), Hg₂Bz₂, Hg in formamide has been measured at 5°C intervals over the temperature range 5–45°C. The values of the standard potentials of the mercury—mercurous benzoate electrode can be fitted in the form of equation, obtained by using the least squares method:

The standard thermodynamic quantities (ΔG°, ΔH°, and ΔS°) for the cell reaction have been evaluated for different temperatures.