E. V. Chubarova

Coordination of Phenylsulfinate PhSO2— to Mo3MS44+ Clusters (M = Ni, Pd)

Reaction of heterometal cuboidal clusters [Mo3(MCl)S4(H2O)9]3+ (M = Ni, Pd) with PhSO2Na in aqueous HCl leads to the substitution at Ni or Pd to give the [Mo3(M(PhSO2))(H2O)9—xClx](3—x)+species, isolated as supramolecular adducts with cucurbituril (Cuc) [Mo3(Ni(PhSO2))S4Cl1.17(H2O)7.83][Mo3(Ni(PhSO2))S4Cl2.22(H2O)6.78]Cl2.61 · Cuc · 15H2O (1) and [Mo3(Pd(PhSO2))S4Cl1.12(H2O)7.88][Mo3(Pd(PhSO2))S4Cl2.29(H2O)6.71]Cl2.59 · Cuc · 11H2O (2), respectively. Crystal structure of 1 and 2 was determined, revealing that the PhSO2 is coordinated via its sulfur atom (Ni — S 2.182 A, Pd — S 2.305 A). The structure of these isostructural compounds is built from triple aggregates {(cluster)(Cuc)(cluster)} united into zigzag chains via hydrogen bonds between coordinated PhSO2 and H2O ligands. Die Koordination von Phenylsulfinat PhSO2— an Mo3MS44+ Cluster (M = Ni, Pd). Die Reaktion von kubanartigen Clustern [Mo3(MCl)S4(H2O)9]3+ (M = Ni, Pd) mit PhSO2Na in Salzsaure fuhrt zum Ligandenaustausch an Ni oder Pd. Dabei entstehen die Komplexe [Mo3(M(PhSO2))(H2O)9—xClx](3—x)+, die sich als Supramolekularaddukte mit Kukurbituril (Cuc), [Mo3S4Ni(PhSO2)Cl1.17(H2O)7.83][Mo3S4Ni(PhSO2)Cl2.22(H2O)6.78]Cl2.61 · Cuc · 15H2O (1), [Mo3(Pd(PhSO2))S4Cl1.12(H2O)7.88][Mo3(Pd(PhSO2))Cl2.29(H2O)6.71]Cl2.59 · Cuc · 11H2O (2) isolieren lassen. Die Kristallstrukturen der isostrukturellen Komplexe 1 und 2 wurden bestimmt. Der Ligand PhSO2— ist durch das Schwefelatom koordiniert (Ni — S 2.175 A, Pd — S 2.305 A). Die Struktur zeigt, dass zwei Cluster- und ein Kukurbirurilmolekul Addukte vom Typ {(Cluster)(Kukurbituril)(Cluster)} bilden, die sich weiter durch Wasserstoffbrucken zwischen PhSO2 und koordiniertem H2O zu Zickzackketten verknupfen.

Degradation of Macromolecular Chains in Fullerene C60–Polystyrene Composites

Fullerene C60–polystyrene composites prepared by mixing benzene solutions of polystyrene and of C60 with subsequent lyophilization have been studied by hydrodynamic and optical methods. The distributions of effective hydrodynamic radii of polystyrene samples within a wide range of molecular weights have been compared to those of composites with fullerene by size exclusion chromatography in tetrahydrofurane. Simultaneously, under real conditions in a porous system of chromatographic columns with the medium (tetrahydrofurane), in which fullerene is virtually insoluble, the possibility of fullerene transport by polymer molecules because of the formation of the C60‐polystyrene molecular complex was investigated. Comparative analysis of spectra of composites, mixtures of polystyrene and fullerene as well as spectra of fullerene‐containing star‐shaped polystyrenes, in which the fullerene core is covalently bound to polystyrene arms, was carried out by UV spectroscopy. The experimental data suggests that during the preparing of composites and their subsequent dissolution the degradation of polystyrene chains occurs with the formation of a covalent bond between chain fragments and fullerene. A qualitative mechanism of polystyrene macromolecules degradation has been proposed.

Analysis of Interactions in Fullerene‐solvent‐polymer System by UV‐spectroscopy

It has been shown that UV‐spectroscopy of fullerene C60 solutions in different solvents as well as of mixed solutions (PS+C60) allows us to reveal particularities of interactions in fullerene‐solvent‐polymer systems. The absorption band with maximum at wave‐length λ∼330 nm is the good proof of such interactions. The possibility of identification of polymer‐fullerene covalent bond by using UV‐spectroscopy has been shown for star‐shaped fullerene‐containing polystyrenes.

Reactivity of Mo3PdS4+4 Cluster: Evidence for New Ligands PhP(OH)2 and Ph2P(OH) and Structural Characterization of [Mo3(Pd(PPh3))S4(H2O)5Cl4]⋅0.5CH3OH⋅3H2O

Cuboidal cluster aqua complex [Mo3(PdCl)S4(H2O)9]3+ in 4M HCl causes isomerization of (HO)2P(O)(H), (HO)P(O)(H)2, PhP(O)(OH)(H), and Ph2P(O)(H) into hydroxo tautomers P(OH)3, HP(OH)2, PhP(OH)2, and Ph2P(OH) which are stabilized by P coordination to the Pd atom in the cluster. The reactions were followed by 31P NMR and UV/Vis spectroscopy. Hypophosphorous acid H2P(O)(OH) in the presence of the cluster is rapidly oxidized into phosphorous acid; the reaction can be made catalytic. Coordination of PPh3 also takes place, giving [Mo3(Pd(PPh3))S4(H2O)5Cl4]⋅0.5CH3OH⋅3H2O, whose crystal structure was determined.

Thermal field-flow fractionation of initially dilute polymer solutions as a shear degradation model. Scaling model of macromolecule degradation at concentrations exceeding the critical entanglement value

Experimental data are presented on thermal field-flow fractionation (TFFF) of anionic polystyrene (PS) samples in the range M = (4–12)·106. They show extensive degradation of macromolecular chains at relatively low rate gradients (G < 30 s−1). The possibility of the influence of relaxation effects on the shape of fractograms and the elution volumes of the samples was taken into account. Mean concentrations in accumulative zones were evaluated. It was shown that, in all cases when degradation was observed, the accumulative zones are the layers of entangled macromolecules. The use of the scaling approach made it possible to simulate layer extension toward the channel center under the influence of the rate gradient. It was shown that, during stretching, the layer is destroyed into blobs, the size of which is determined by experimental conditions. An expression for the critical gradient leading to layer degradation was derived. Quantitative evaluations of fragment sizes and critical gradients obtained from the model are in good agreement with experimental data. The model developed for specific experimental conditions confirms the proposed general mechanism of the so-called shear degradation of macromolecules. The physical picture of degradation in the TFFF channel was considered.

Chain Degradation during Dissolution of Polymer-Fullerene Nanocomposites as a Result of Interaction of Entangled Polymer Matrix with the Filler

Chain degradation of poly(α-methylstyrene) and polystyrene during dissolution of their nanocomposites with fullerene C60 in solvents of different quality with respect to fullerene was studied in detail by size exclusion chromatography and UV spectroscopy. Chain ruptures have been shown to arise during swelling of composites but only for samples with entangled polymer matrix. The data obtained confirm that the hindered mobility of chains because of interaction of the entangled matrix with fullerene is the only cause of degradation. Chain rupture leads to radical depolymerization accompanied by covalent binding of fullerene with the chain fragments, which results in changing of the polymer matrix structure. Chain degradation indicates deterioration of the mechanical properties of the polymers in the presence of C60. The possibility of chain degradation in polymer-filler nanocomposites under deformation with the simultaneous observation of an apparent reinforcement effect because of the addition of filler in the polymer matrix is discussed.

Chain Degradation under Low-Intensity Sonication of Polymer Solutions in the Presence of Filler: Mechanism of Ultrasonic Degradation of Flexible Chain Macromolecules

Routine dispersion of fillers in polymer solutions in a usual ultrasonic cleaning bath has been shown to lead to chain degradation. It is the filler presence, only, that has been demonstrated to provoke chain degradation under low-intensity sonication. A critical analysis of the literature concerned with the effects arising from propagation of acoustic waves in a liquid and an experimental study of ultrasonic degradation of polymers in solution were carried out. Based on these results, the mechanisms of chain degradation were discussed. Our previously proposed universal mechanism of chain degradation in inhomogeneous hydrodynamic fields has been shown to explain the basic facts repeatedly confirmed over the years of studying the ultrasonic degradation: (i) the existence of a limiting molecular weight such that macromolecules with lower molecular weights are not subject to degradation and (ii) the dependences of degradation rate on polymer molecular weight, polymer concentration, and temperature.