Structure and properties of clay nano‐biocomposites based on poly(lactic acid) plasticized with polyadipates

The use of nano‐biocomposites based on plasticized poly(lactic acid) (PLA) has been proposed as a way to improve the polymer ductility and to expand PLA applications window. Novative nano‐biocomposites were elaborated with PLA plasticized by polyadipates (15 wt%) with different molar masses (from 1500 to 2500 Da), with 2.1 wt% of an organo‐modified montmorillonite (O‐MMT). These materials showed enhanced ductility and barrier properties. The clay was swelled in liquid polyadipates prior to their blending with PLA to facilitate chains intercalation and nanofiller exfoliation during melt‐blending. In certain processing conditions, quite homogenous and exfoliated structures were obtained, as shown by X‐ray diffraction (XRD) and transmission electronic microscopy (TEM) results. Irrespective of the average molar mass of the polyadipate, the clay addition induced a reduction in around 25% in oxygen transmission rate (OTR) without an important detriment in tensile properties. Nano‐biocomposites prepared with higher molar masses polyadipates showed the highest thermal stability as well as the lowest OTR, resulting in very promising and novative materials for different applications such as soft packaging. Copyright © 2010 John Wiley & Sons, Ltd.     

First-principles studies of H2S adsorption and dissociation on metal surfaces

Density functional theory calculations were employed to investigate the molecular and dissociative adsorption of H₂S on the closed packed surfaces of a number of important noble metals (Ag(1 1 1), Au(1 1 1) and Cu(1 1 1)) and transition metals (Ir(1 1 1), Ni(1 1 1), Pd(1 1 1) and Pt(1 1 1)). Energy minima corresponding to adsorbed states were identified with H₂S binding preferentially at the top sites. The adsorption of other S moieties (SH and S) was also examined. SH and S were found to prefer bridge sites and hollow sites, respectively. The binding of H₂S and its S-containing dissociated species is stronger on the transition metals. The elementary reactions of abstraction of H from H₂S to form a surface SH intermediate and abstraction of H from SH to form a surface S intermediate as model pathways for the dissociation of H₂S were examined. Our results suggest that H₂S decomposition on the aforementioned transition metal surfaces is more facile, both thermodynamically and kinetically.     

N‐Chloro­acetyl‐β‐alanine

The β‐alanine residue of the title compound, C₅H₈ClNO₃, has a ggt folded conformation, which is mainly stabilized through intermolecular N—H⋯O=C (amide–acid) and O—H⋯O=C (acid–amide) hydrogen bonds. In addition, a cis conformation is found for the Cl—CH₂—C(=O)—NH torsion angle, which is associated with the presence of an intramolecular hydrogen bond.     

Coordination of ZnII,CdII, and HgII by 2‐Pyridineformamide‐3‐piperidyl‐thiosemicarbazone

Sodium in dry methanol reduces 2‐cyanopyridine in the presence of 3‐piperidylthiosemicarbazide and produces 2‐pyridine‐formamide‐3‐piperidylthiosemicarbazone, HAmpip. Complexes with zinc(II), cadmium(II), and mercury(II) have been prepared and characterized by elemental analyses and spectroscopic techniques. In addition, the crystal structures of [Zn(Ampip)₂], [Zn(Ampip)(Oac)]₂, [Cd(HAmpip)Cl₂]·(CH₃)₂SO, [Cd(HAm‐pip)Br₂] · (CH₃)₂SO, [Cd(HAmpip)I₂]·(CH₃)₂SO, [Cd(Ampip)₂] and [Hg(HAmpip)Br₂]·(CH₃)₂SO have been solved. Coordination of the anionic and neutral thiosemicarbazone ligand is via the pyridyl nitrogen, imine nitrogen and thiolato/thione sulfur atom, respectively. In [Zn(Ampip)(OAc)]₂ one of the bridging acetato ligands has monodentate coordination and the other bridges in a bidentate manner. ¹¹³Cd NMR studies were carried out on the [Cd(HAmpip)X₂](X = Cl, Br or I) and [Cd(Ampip)(OAc)]₂ complexes. The ¹¹³Cd chemical shifts are affected by the halogen and range from 411 to 301 ppm, and the spectrum of [Cd(Ampip)(OAc)]₂ shows two signals at 450 and 251 ppm. The ¹⁹⁹Hg NMR spectrum of [Hg(HAmpip)Cl₂] also is discussed.     

Dynamics of Aromatic Molecules Clathrated in Crystalline Syndiotactic Polystyrene: A Solid State 2H NMR Investigation of the Host/Guest Complexes

Syndiotactic polystyrene clathrates hosting benzene‐d₆ or toluene‐d₈ molecules in the cavities of the δ crystalline form have been prepared and investigated by means of solid state ²H NMR spectroscopy. Benzene‐d₆ molecules were found to be involved in a fast rotation about the C₆ symmetry axis whereas the toluene‐d₈ molecules exhibit a fast rotation of the methyl group about the symmetry axis passing through the C₁ and C₄ carbon atoms.     

Configurational-conformational entropy of 1,4-polydienes

A method based on matrix algebra and on the rotational isomeric state scheme to study the configurational- conformational entropy of 1,4-polydienes with geometrical isomerism has been developed. Bernoullian and first-and second-order Markovian statistics for the sequences of cis and trans units along the chains have been considered, and the explicit relation between entropy and mole fraction of cis units has been derived. Calculations performed by using available experimental data for the configurational parameters and the conformational partition functions of 1,4-polybutadiene and 1,4-polyisoprene show that entropy is a monotonic function of the geometrical isomer composition. While the entropy of polybutadiene increases with the content of cis units, the reverse is true for polyisoprene.