Comb copolymers of polystyrene-poly(tert-butyl (meth)acrylate) prepared by combination of nitroxide mediated polymerization and photoinduced iniferter technique

Comb copolymers consisting of polystyrene backbone and poly(tert-butyl (meth)acrylate) side chains were synthesized by combination of nitroxide (TEMPO)-mediated polymerization (NMP) and photoinduced grafting from macro-iniferters. First, poly(chloromethylstyrene), PCMS, with the degree of polymerization and two random poly(styrene-co-chloromethylstyrene) copolymers, P(S-co-CMS), with similar but different content (8 and 14 mol%) of CMS units, were synthesized by NMP. In the second step the CMS units both in the homopolymer and the copolymers were converted to N,N-diethyldithiocarbamyl groups (DC) yielding photosensitive multifunctional macro-iniferters. Finally, tert-butyl methacrylate tBuMA was grafted from the synthesized polymer backbones by iniferter technique under UV-irradiation yielding copolymers polystyrene-graft-poly(tert-butyl methacrylate) PS-g-P(tBuMA). Grafting initiated by the macro-iniferters containing ∼6-11 DC initiating sites per macromolecule proceeded by pseudo-living polymerization mechanism, i.e., the number-average molecular weight increased with conversion and the SEC traces were unimodal. In contrast, photo-polymerization initiated by highly functionalized polystyrene backbone was poorly controlled. Hydrolysis of loosely grafted copolymers PS-g-P(tBuMA) afforded amphiphilic copolymers polystyrene-graft-poly(methacrylic acid). Molecular parameters of the synthesized graft copolymers in dilute THF solutions were determined by scattering (DLS, SLS, SAXS) and viscometric measurements.     

Partial molar volumes and heat capacities of the N-acetyl amide derivatives of the amino acids asparagine, glutamine, tyrosine, and lysine monohydrochloride in aqueous solution at temperatures from T = 288.15 K to T = 328.15 K

The partial molar volumes, , and partial molar heat capacities, , at infinite dilution have been determined for the compounds N-acetylasparaginamide, N-acetylglutaminamide, N-acetyltyrosinamide, and N-acetyllysinamide monohydrochloride in aqueous solution at T = (288.15, 298.15, 313.15, and 328.15) K. These results, along with the literature data for the compound N-acetylglycinamide, have been used to calculate the amino acid side-chain contributions to the thermodynamic properties. These side-chain contributions are compared with those obtained using small peptides as side-chain model compounds.     

Effect of initial monomer concentration on the equilibrium swelling and elasticity of hydrogels

The linear swelling ratio α and the effective network chain length N of a series of poly(N,N-dimethylacrylamide) (PDMAAm) hydrogels were investigated as a function of the gel preparation concentration . PDMAAm hydrogels were prepared at a fixed cross-linker ratio but at various initial monomer concentrations. It was found that α is not a monotonic function of . As is increased, α first decreases up to about and remains constant in a narrow range of , but then it increases continuously. The -dependence of α is due to the variation of the network chain length N depending on the gel preparation concentration. In the range of below 0.1, N follows the scaling relationship , while at higher concentrations, N varies only slightly with . The increase of α with N obeys the relation , as predicted by the Flory-Rehner theory.     

Graft copolymers of natural rubber and poly(dimethyl(acryloyloxymethyl)phosphonate) (NR-g-PDMAMP) or poly(dimethyl(methacryloyloxyethyl)phosphonate) (NR-g-PDMMEP) from photopolymerization in latex medium

Graft copolymers of natural rubber and poly(dimethyl(acryloyloxymethyl)phosphonate) (NR-g-PDMAMP), and natural rubber and poly(dimethyl(methacryloyloxyethyl)phosphonate) (NR-g-PDMMEP), were prepared in latex medium via a “grafting from” methodology based on the photopolymerization of dimethyl(acryloyloxymethyl)phosphonate (DMAMP) and dimethyl(methacryloyloxyethyl) phosphonate (DMMEP), respectively, used as phosphorus-containing monomers. The grafting polymerization was initiated from N,N-diethyldithiocarbamate groups previously bound in side position of the rubber chains. The effects of monomer concentration on monomer conversion and grafting rate were investigated, showing that conversion and grafting rate increased with increasing monomer concentration and reaction time. Highest conversions and grafting rates were obtained with a molar ratio [DMAMP]/[initiating units] = 7 for a reaction time of 180 min. Calculation of the graft average length () from ¹H NMR spectra of the synthesized graft copolymers showed values were in the range of 9-73. Visualizations of NR-g-PDMAMP and NR-g-PDMMEP latices by Transmission Electron Microscopy (TEM) showed that they exhibit core-shell morphologies. Degradation of NR-g-PDMAMP and NR-g-PDMMEP occurred in two steps: decomposition of dimethylphosphonate-functionalized grafts took place prior to the second step corresponding to the decomposition of NR backbone, but the degradation temperature of this last step was higher than that of pure NR.     

Reactions of pyridyl donors with halogens and interhalogens: an X-ray diffraction and FT-Raman investigation

Three different N-donors L, namely N-ethyl-N′-3-pyridyl-imidazolidine-4,5-dione-2-thione (1), N,N′-bis(3-pyridylmethyl)-imidazolidine-4,5-dione-2-thione (2), and tetra-2-pyridyl-pyrazine (3), bearing one, two and four pyridyl substituents, respectively, have been reacted with halogens X₂ (X = Br, I) or interhalogens XY (X = I; Y = Cl, Br). CT σ-adducts L · nXY, bearing linear N?XY moieties (L = 3; X = I; Y = Br, I; n = 2), and salts containing the protonated cationic donors H_nLⁿ⁺ (L = 1 − 3; n = 1, 2, 4), counterbalanced by Cl⁻, Br⁻, , , , , I₂Br⁻, , or anions, have been isolated. Among the reactions products, (H1⁺)Cl⁻, (H1⁺)Br⁻, , , and 3 · 2IBr have been characterised by single-crystal X-ray diffraction. The nature of the products has been elucidated based on elemental analysis and FT-Raman spectroscopy supported by MP2 and DFT calculations.     

Synthesis of poly(ethylene adipate) and poly(ethylene adipate-co-terephthalate) via ring-opening polymerization

Syntheses of poly(ethylene adipate) (ROP-PEA) and poly(ethylene adipate-co-terephthalate) (ROP-PEA-co-PET) were achieved via ring-opening polymerization of corresponding cyclic oligoesters. In case of ROP-PEA, cyclic oligo(ethylene adipate) (C-OEA) was equilibrated in the presence of di-n-butyltin oxide as a catalyst under high-concentration conditions at 180 and 200 °C for 1-24 h. The polymer products were obtained in yields up to 100% with the and in the ranges of 3000-23 000 g/mol and 5000-60 000 g/mol, respectively. The ROP-PEA-co-PET was prepared by equilibrating an equimolar amount of C-OEA and cyclic oligo(ethylene terephthalate) (C-OET) using di-n-butyltin oxide catalyst under high-concentration conditions at 250 °C for 24 h. The copolyester produced was obtained in yield of 97% with the and of 18 000 and 46 000 g/mol, respectively. ¹H NMR spectrum of ROP-PEA-co-PET showed two new proton signals of ethylene unit representing the existence of heterolinkage with different chemical environment in the copolymer. This indicated the random transesterification of C-OEA and C-OET resulting in random structure in copolyester. In addition, the result of ROP-PEA-co-PET from DSC showed the glass transition temperature in the values of −8 °C with no melting temperature indicating thermoplastic elastomeric behavior.     

Radial basis network analysis of color parameters to estimate lycopene content on tomato fruits

With the purpose of estimating the lycopene concentration in tomato food samples, in an non-destructive way, several types of linear models of color parameters have been tested using individual values of L*, a* and b* values, (a*/b*), (a * ²/b * ²) and chroma parameters from tomato juice and fresh tomato fruits obtained with two different apparatus (Minolta CR-200b triestimulus colorimeter and HunterLab LabScan XE). Lycopene concentrations of fresh tomato and tomato juice (used as an input) were analyzed by UV-Vis spectroscopy. For all linear methods applied, the best one to estimate the lycopene concentration in tomato was the L*, a* and b* values of tomato juice measured with Hunter colorimeters (adjusted correlation coefficient, and mean prediction error, MPE < 6.59%). Four different RBEF models were designed firstly using three color parameters (L*, a* and b*) designated as “Lab case”, and secondly individually by the (a*/b*), (a * ²/b * ²) and chroma parameters. The lycopene concentration estimations were carried out with the lowest MPE and highest values possible. In order to test the reliability of the non-linear models, external validation process was also performed. From the testing of the all non-linear models applied, the RBEF Lab case model was the best to estimate lycopene content from color parameters (L*, a* and b*) using Minolta or Hunter equipments (MPE lower than 0.009 and higher than 0.997). This was a simple non-destructive method for predicting lycopene concentration in tomato fruits and tomato juice, which was reproducible and accurate enough to substitute chemical extraction determinations, and may be a useful tool for tomato industry.     

Thermodynamic studies on the interactions of diglycine with magnesium chloride in aqueous medium at different temperatures

Apparent molar heat capacities (C_P2,?), apparent molar volumes (V_2,?), and viscosities (η) of diglycine in water and in aqueous magnesium chloride (MgCl₂) solutions of molality m_S ≈ (0.05 to 0.70) mol · kg⁻¹ over the temperature range T = (288.15 to 328.15) K have been determined using high sensitivity micro-differential scanning calorimeter, vibrating-tube digital density meter, and automatic viscosity measuring unit (AVS 350), respectively. The data have been used to calculate the partial molar heat capacities and partial molar volumes at infinite dilution. The viscosity B-coefficients have also been obtained from viscosity data using Jones-Dole equation. The and values of diglycine in aqueous MgCl₂ solutions are higher than those in water and thus exhibit positive transfer functions ( and ), which are indicative of strong interactions between diglycine and MgCl₂. Corresponding viscosity B-coefficients of transfer are also generally positive. The transfer functions decrease with increase in temperature and increase with the concentration of MgCl₂. The free energies, enthalpies and entropies of activation for viscous flow of diglycine in aqueous MgCl₂ solutions have been obtained by using the Feakins transition-state theory. Partial molar expansibilities and at infinite dilution along with their temperature dependence, the interaction coefficients from the volume, heat capacity, and viscosity B-coefficients have been used to divulge the various kinds of plausible interactions between solute (diglycine) and cosolute (MgCl₂) in solutions.     

Synthesis characterizations and properties of a new fluoro-maleimide polymer

Novel 4-(4-trifluoromethyl)phenoxy N-phenyl-maleimide (FPMI) was synthesized. The free radical-initiated polymerization of FPMI was carried out in 1,4-dioxane solution using azobisisobutyronitrile as initiator. The monomer was investigated by FTIR, ¹H NMR, ¹³C NMR and elemental analysis, while the polymer was investigated by FTIR, ¹H NMR and ¹³C NMR. The effect of the monomer concentration, initiator concentration and temperature on the rate of polymerization (R_p) was studied. The activation energy of the polymerization was calculated (ΔE = 48.94 kJ/mol). The molecular weight of PFPMI and polydispersity index of the polymer were determined by gel permeation chromatography and were equal to 73,500, 16,700 and 2.27, respectively. The properties of PFPMI, including thermal behavior, thermal stability, the glass transition temperature (T_g = 236 °C), photo-stability, solubility and solution viscosity were studied.     

Geometry and chemical bonding in polyhedral boranes, metallaboranes, and dimetallaboranes: From closo to isocloso to oblatocloso polyhedra

The geometry and chemical bonding in the closo metal-free boranes and the isoelectronic carboranes and C₂B_n−2H_n with 2n + 2 skeletal electrons are based on the most spherical deltahedra with a preference for degree 5 vertices, particularly for the boron atoms. Such deltahedral boranes can be considered to be three-dimensional aromatic systems, as indicated by strongly diatropic nucleus independent chemical shift values for (n = 6, 8, 9, 12). Metallaborane structures, particularly those with 9-11 vertices and only 2n rather than 2n + 2 apparent skeletal electrons, are often based on isocloso deltahedra with the metal atom at a degree 6 vertex. Dimetallaborane structures, particularly the rhenium derivatives Cp₂Re₂B_n−2H_n−2 (8 ? n ? 12), are based on highly non-spherical and very oblate deltahedra with the metal atoms typically at degree 6 or 7 vertices, which are the lowest curvature sites of the deltahedra. A viable model for the skeletal bonding in such dimetallaboranes can be developed if each of the two metal vertices is assumed to contribute five internal orbitals to the skeletal bonding. This leads to 2n + 4 skeletal electrons, which are partitioned into n surface bonds and a formal metal-metal double bond inside the oblate deltahedron.     

Crystal growth, characterization and physical properties of PrNiSb3, NdNiSb3 and SmNiSb3

The crystal structures of three new intermetallic ternary compounds in the LnNiSb₃ (Ln=Pr, Nd and Sm) family have been characterized by single crystal X-ray diffraction. PrNiSb₃, NdNiSb₃ and SmNiSb₃ all crystallize in an orthorhombic space group, Pbcm (No. 57), Z=12, with , , , and ; , , , and ; and , , , and , for Ln=Pr, Nd and Sm, respectively. These compounds consist of rare-earth atoms located above and below layers of nearly square, buckled Sb nets, along with layers of highly distorted edge- and face-sharing NiSb₆ octahedra. Resistivity data indicate metallic behavior for all three compounds. Magnetization measurements show antiferromagnetic behavior with (PrNiSb₃), 4.6 K (NdNiSb₃), and 2.9 K (SmNiSb₃). Effective moments of 3.62 μ_B, 3.90 μ_B and 0.80 μ_B are found for PrNiSb₃, NdNiSb₃ and SmNiSb₃, respectively, and are consistent with Pr³⁺ (f ²), Nd³⁺ (f ³), and Sm³⁺ (f ⁴).     

PbI4Cu2(PPh3)4: A heterometallic iodide with unusual cis-divacant octahedral coordination sphere for lead: Synthesis, structure, red-infrared fluorescence and theoretical studies

A new heterometallic iodide, PbI₄Cu₂(PPh₃)₄, was synthesized by reactions of PbI₂, CuI and triphenylphosphine (PPh₃) in DMF solution. The single-crystal X-ray diffraction analyses show that Pb(II) center adopts an unusual cis-divacant octahedral geometry. Crystal data: triclinic, space group , , , , α=106.623(4)°, β=103.478(6)°, γ=93.574(5)°, and Z=2. Density function theory (DFT) calculations and fragment orbital interaction analyses reveal the presence of a three-center four-electron (3c-4e) hypervalent bonding about lead; and the formation of the unusual cis-divacant [PbI₄]²⁻ octahedron is energetically favorable. The title yellow compound has an optical bandgap of 2.69 eV and shows remarkable red-infrared fluorescence emission at 732 nm with lifetime of 24 μs which is assigned as an iodine 5p-lead 6s to PPh₃-lead 6p charge transfer (XM-LM-CT).     

Impregnation synthesis of a novel macroporous silica-based TODGA polymeric composite and its application in the adsorption of rare earths in nitric acid solution containing diethylenetriaminepentaacetic acid

A macroporous silica-based N,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) polymeric composite (TODGA/SiO₂-P) was synthesized. It was done through impregnation and immobilization of TODGA molecule into the pores of the SiO₂-P particles utilizing a vacuum sucking technique. The macroporous SiO₂-P particles were the silica-based organic/inorganic composite synthesized by immobilizing styrene-divinylbenzene copolymer inside SiO₂ through the complicated polymerization reaction. The adsorption of rare earth (RE(III)) elements onto TODGA/SiO₂-P was investigated in HNO₃ solution containing diethylenetriaminepentaacetic acid (DTPA), an acidic multi-dentate chelating agent. It was found that in the presence of 0.05 M DTPA, and H⁺ had significant effect on the TODGA/SiO₂-P adsorption due to the competition reactions of RE(III) with different species, H₄DTPA⁻ and H₂DTPA³⁻. With an increase in the concentration of from 0.115 M to 3.015 M, the adsorption of RE(III) onto TODGA/SiO₂-P increased noticeably. On the other hand, RE(III) showed strong adsorption at 0.1 M H⁺, weak adsorption at around pH 2, and no adsorption in excess of pH 2.3. In a 0.1 M H⁺-0.115 M -0.05 M DTPA solution, a change of the distribution coefficient of RE(III) onto TODGA/SiO₂-P with an increase in atomic number of RE(III) from La(III) to Lu(III) was investigated. The silica-based TODGA/SiO₂-P polymeric composite showed strong adsorption for heavy RE(III) over the light one. In a 0.01 M H⁺-1.0 M -0.05 M DTPA solution, the effect of the ratio of solid phase to liquid one on the relationship of the distribution coefficient of RE(III) with the change in atomic number of RE(III) was also studied. Based on the complicated disassociation equilibrium of DTPA, the influence of the concentrations of and H⁺ on the adsorption of TODGA/SiO₂-P for RE(III) was demonstrated. This makes the partitioning of RE(III) and MA(III) together from high level liquid waste (HLLW) by the polymeric composite TODGA/SiO₂-P promising.     

The H2O-D2O solvent isotope effects on the molar volumes of alkali-chloride solutions at T = (288.15, 298.15, and 308.15) K

Densities of LiCl, NaCl, KCl, and CsCl in normal and heavy water solutions have been measured using a vibrating-tube densitometer with (1-2) · 10⁻⁶ precision at T = (288.15, 298.15, and 308.15) K over a wide concentration range from (0.1 to 5) molal, m. Solvent isotope effects (IE) on apparent molar volumes, as well as both on solute- and solvent-partial molar volumes were evaluated to establish their trend with cationic size in a systematic way. With the exception of the LiCl, both the “normal” standard IEs, , and the “inverse” excess IEs of the solutes, , increase linearly with the electrostriction effect of the cations (1/r_ion), while with increasing temperature and/or concentration, the excess effects become almost the same.In contrast to the solute excess IEs, which show linear m^1/2-dependence over the whole concentration range, except for LiCl, the “inverse” excess IEs of the solvent, , hardly change over the lower concentration range (, m ? 1). However, with further increase of the concentration, these IEs significantly decrease. Individual ionic standard and excess volume contributions are derived and the results are discussed in terms of structural concepts of ionic hydration.     

Detection of microphase separation in poly(tert-butyl acrylate-b-methyl methacrylate) synthesized via atom transfer radical polymerization by inverse gas chromatography

A trace amount of solvents such as n-octane, n-nonane, n-decane, ethyl acetate, n-propyl acetate, isoamyl acetate, toluene, ethyl benzene, n-propyl benzene, isopropyl benzene and chloro benzene was passed through the column of a gas chromatograph of which the stationary phase is poly(tert-butyl acrylate-b-methyl methacrylate), poly(tBA-b-MMA), block copolymer with low polydispersity, prepared via ATRP of tBA and MMA, respectively. The retention diagrams to determine the thermal transition of the polymer were obtained by plotting the logarithm of the specific retention volumes of isoamyl acetate and toluene against reciprocal values of absolute column temperatures between 40 and 170 °C by inverse gas chromatography (IGC) technique. Three glass transition temperatures, T_gs of poly(tBA-b-MMA) were determined at 50, 70 and 105 °C by IGC indicating the phase separation of the polymeric blocks in the copolymer. The thermodynamical interaction parameters such as weight fraction activity coefficient of solvent at infinite dilution, , Flory-Huggins polymer-solvent interaction parameter, , equation-of-state polymer solvent interaction parameter, , effective exchange energy parameter, X_eff, and solubility parameter of the copolymer, δ₂ were calculated at studied temperatures. The closeness of parameters of the poly(tBA-b-MMA) to those of the PMMA indicated that the continuous phase is MMA block in the microphase separated block copolymer. It seems that IGC is a reliable technique to study a phase separated block copolymer which contains nanosized domains.     

Solvent effect in cis-1,4 polymerization of 1,3-butadiene by a catalyst based on neodymium

In this work a laboratory polymerization scale process was studied for the production of polybutadiene with high content of cis-1,4 repeating units. A Ziegler-Natta catalytic system based on neodymium versatate (catalyst), diisobutylaluminium hydride (cocatalyst) and tert-butyl chloride (chlorinating agent) was used. The influence of solvent nature (pure grade) and possible contaminants (electron donors) in a recovered solvent from a butadiene-styrene anionic polymerization industrial plant on the stereoselectivity and catalytic activity, molecular weight and molecular weight distribution of the resultant polybutadienes was studied. The polymers were characterized by infrared spectroscopy and size exclusion chromatography. Polybutadienes with cis-1,4 units content in the range of 99-98% were produced. The polymers weight-average molecular weight, , varied from 2.23 × 10⁵ to 4.47 × 10⁵ and the molecular weight distribution, MWD, from 3.1 to 5.1.