Effect of the polyethylene confinement and topology on its crystallisation within semicrystalline ABC triblock copolymers

The isothermal crystallisation behaviour of the polyethylene block within polystyrene-b-polyethylene-b-poly(ε-caprolactone), SEC, triblock copolymers was studied by differential scanning calorimetry. The morphology was observed by transmission electron microscopy. Melting scans after isothermal crystallisation performed at different times were employed to determine the crystallisation kinetics one step at a time (“isothermal step crystallisation”). Double melting endotherms were observed after isothermal crystallisation and they were interpreted as a result of the melting of two lamellar populations. These arise from the intrinsic short chain branching distribution within the hydrogenated polybutadiene chains that conform the PE blocks and from their location within the copolymer microdomains. The Hoffman-Weeks procedure failed to yield reasonable values for the equilibrium melting point of the PE blocks as a result of the distribution of linear sequences present in these blocks. The results indicate that as the degree of PE confinement increases the Avrami index decreases to values that are even lower than 1, a result that can be explained by the nature of the homogeneous nucleation process that is in between sporadic and instantaneous.     

Configuration assignment for 3-bromo-2-butenoic acids

Conclusions ¹H and¹³C NMR spectroscopy was used for the reliable determination of the configurations of the E- and Z-isomers of 3-bromo-2-butenoic acids and their esters.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1409–1412, June, 1989.     

Ab initia MO calculation in terms of localized orbitals of the 14N electric field gradient in nitriles

The contributions of each localized orbital of the CN group and of the molecular remainder to the N electric field gradient (EFG) were calculated for nitriles with R=H, F, CH₃, OH, NH₂, CCH, COH, NO, CN and the E and Z forms of iminoacetonitrile. The changes in the EFG introduced by substituents resulted mainly from the polarization and conjugation of the C-N bonds, with a small contribution from the N lone pair. The total EFG has a large and rather constant contribution from the N lone pair, which is modified by the contributions from the three C-N bonds and the molecular remainder. The resulting EFG is determined by the signs and magnitudes of the C-N bonds' contributions for each substituent and to a lesser degree by the molecular remainders. The asymmetry parameter of the EFG is mainly determined by the inequivalence of the C-N bonds with a very small contribution from the molecular remainder. The molecular remainder and the crystal field in solids contribute more to the largest component of the EFG than to the asymmetry parameter. All these results have allowed us to discuss the validity of the assumptions made in the Townes and Dailey theory when it is applied to nitriles.     

Theoretical study in gas phase of linear and nonlinear optical properties of the ortho-, meta- and para-nitrophenol isomers

The linear (α), and nonlinear (β, γ) optical NLO properties of ortho-, meta- and para-nitrophenol (ONP, MNP and PNP) isomers have been calculated in gas phase by using ab initio (HF, MP2 and MP4) and density functional theory (DFT) (B3LYP, CAM-B3LYP) methods, with the 6-31+G(d,p) and 6-311+G(3d,3p) standard and the Sadlej specialized basis sets. These properties were evaluated both at static and at dynamic regime within the finite field FF numerical techniques and the time-dependent-Hartree–Fock approach at 1,910 nm, respectively. Additional calculations were performed for the β static hyperpolarizability of these isomers in presence of p-dioxane solvent with the Onsager Model and the SCRF-PCM approach, using B3LYP/6-31+G(d,p) and MP2/6-31+G(d,p) levels of theory. Additionally, CCSD/6-31+G(d,p) calculations were performed for the α, β and γ properties of PNP isomer. The B3LYP and MP2 α _ave results of the nitrophenol isomers are comparable to the experimental α _ave reports; while the tendency for the β _v calculated values (β _v PNP > β _v MNP > β _v ONP), that can be explained in terms of the O _x atomic charge of the –NO₂ group, does not follow exactly the experimental ones. The B3LYP γ _ave results are in correspondence to the experimental measurements, the correlation of which is r ² = 0.99. The use of FF methodology in conjunction with the B3LYP and MP2 methods and the 6-31+G(d,p) basis set show to be appropriate approaches to predict qualitative optical properties of Push–Pull like organic molecules, provided are considered the solvent effects or frequency dependence. However, to have a clear picture of the NLO properties of an isolated molecule, higher order correlation effects combined with specialized basis sets, frequency and solvent effects should be employed. We have demonstrated that MP4/Sadlej level of theory is able to reproduce NLO properties that can be considered equivalent to those from more sophisticated approaches, such as CCSD together with extended basis sets.     

Synthesis of long-chain methyl-branched 1-alkynes from alkylmagnesium halides and methoxyallene

Conclusions The reaction of methoxyaliene with aliphatic Grignard reagents gave methyl-branched terminal acetylenes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2384–2385, October, 1987.     

Fluorescence quantum yield of rhodamine 101 in the presence of absorption saturation

Using the photothermal method we measure the fluorescence quantum yield of a rhodamine 101 solution in ethanol for different values of the pump-field fluence. Our experiments reveal a depletion of the fluorescence quantum yield as the pump fluence increases. To explain the observed fluorescence quenching, a dependence of the nonradiative relaxation rates on the field fluence is proposed. Predictions of the model are in good agreement with the experiments. Received: 16 November 1999 / Revised version: 5 July 2000 / Published online: 13 September 2000     

Heavy metal (Cd2+, Ni2+, Pb2+ and Ni2+) adsorption in aqueous solutions by oxidized starches

Superabsorbent materials based on natural products have been synthesized by free radical oxidation of corn starch using a redox system consisting of potassium permanganate and sodium bisulfite. The resulting oxidized starches were characterized by analyzing the variation of carbonyl and carboxyl contents. The swelling ability of these samples has been determined by gravimetric method in water and in saline solutions. The effect of oxidant concentration and bleaching procedure on the water absorption capacity has been studied. The ability to remove heavy metals in water solution has been tested against Cd²⁺, Ni²⁺, Pb²⁺ and Zn²⁺ ions, showing higher percentage of remotion for the unbleached oxidized starches, in particular against nickel ions. Copyright © 2014 John Wiley & Sons, Ltd.     

Hydroformylation of alkenes with paraformaldehyde catalyzed by rhodium-phosphine complexes

The hydroformylation of medium-chain C6 olefins and of allyl alcohol was achieved with paraformaldehyde in dioxane solution using rhodium catalysts with mono-, bi-, and tri-dentate phosphine ligands. The highest activities with n/i ratios around 2, were obtained for a system derived from [Rh(dppe)₂]⁺, prepared in situ by reaction of Rh(acac)(CO)₂ with 2 eq of dppe.