Photo-initiated post-polymerization in micellar system of amphiphilic poly(ethylene oxide) macromonomers

Aqueous micellar polymerization of amphiphilic poly(ethylene oxide) macromonomers carrying p-vinylphenylheptyl end-group has been found to persist to proceed after turning-off of the UV-irradiation. Simulation of the kinetics revealed a high propagation rate constant coupled with a low termination constant, supporting a living-like polymerization at the initial stage. Micellar copolymerization with equimolar styrene also proceeded after UV-irradiation. Polymer molecular weights in MALLS-SEC were also found to evolve with time after irradiation.     

Effective size and fractal dimension of polyelectrolytes determined by diffusion NMR

Polyelectrolytes are macromolecules containing dissociable or charged groups on the main chain or in side groups. These charges are the basis of the water solubility of polyelectrolytes. The solution properties namely the conformation is determined by an interplay of thermodynamic and electric interactions. The electrostatic interaction is influenced by the ionic strength of the solution. As a measure of the effective size of the macromolecules the hydrodynamic radius is determined from the self-diffusion coefficient measured via pulsed- field gradient nuclear magnetic resonance. From variation of the hydrodynamic radius with molecular weight for each ionic strength, the fractal dimension has been determined for the example of poly(styrenesulfonate). With increasing ionic strength the fractal dimension, which describes the use of space for the fictitious growth of the molecule when increasing the molecular weight, increases. This implies a denser packing of the molecules in higher ionic strength.     

Studies on the thermal ageing of organic coatings

The ageing of organic protective coatings depends on environmental impacts and is associated with a variety of ichemical and physical processes. The results of former thermal ageing studies indicate that evaporation and polymer degradation are the decisive processes for changes in coating properties. For the verification of these assumptions the impact of - the thermal exposure temperature T_L and - the length of the exposure time t_L on properties of clear lacquer coatings was determined by further studies. The gradation of T_L was aimed at creating conditions where on the one hand only evaporation processes occur, while on the other hand evaporation and polymer degradation reactions occur in parallel. The objective was to find the time t_L and the temperature T_L at which degradation starts to prevail.     

Lanthanoid Antimonides Ln2Sb5 (Ln = Sm,Gd, Tb,Dy) and Rationalization of Chemical Bonding within the Antimony Polyanion by Combining the Zintl‐Klemm Concept with Bond‐Length Bond‐Strength Relationships

The title compounds are formed by peritectic reactions. Single crystals could be isolated from samples with high antimony content. Their structure was determined for Dy₂Sb₅ from four‐circle X‐ray diffractometer data: P2₁/m, a = 1306.6(1) pm, b = 416.27(4) pm, c = 1458.4(1) pm, β = 102.213(8)°, Z = 4, R = 0.061 for 2980 structure factors and 86 variable parameters. All dysprosium atoms have nine antimony neighbors forming tricapped trigonal prisms with Dy–Sb distances varying between 308 and 338 pm. The antimony atoms occupy ten different sites with greatly varying coordination. One extreme case is an antimony atom surrounded only by dysprosium atoms in trigonal prismatic arrangement, the other one is an antimony atom in distorted octahedral antimony coordination. The various antimony‐antimony interactions (with Sb–Sb distances varying between 284 and 338 pm) are rationalized by combining the Zintl‐Klemm concept with bond‐length bond‐strength considerations.     

Gd3Pt4In12 and Tb3Pt4In12 — New Ternary Indides with Condensed Distorted [PtIn6] Trigonal Prisms

The ternary indium compounds Gd₃Pt₄In₁₂ and Tb₃Pt₄In₁₂ were synthesized from an indium flux. Arc‐melted precursor alloys with the starting compositions ∼GdPtIn₄ and ∼TbPtIn₄ were annealed with a slight excess of indium at 1200 K followed by slow cooling (5 K/h) to 870 K. Both compounds were investigated by X‐ray powder diffraction: a = 990.5(1), c = 1529.5(3) pm for Gd₃Pt₄In₁₂ and a = 988.65(9), c = 1524.0(1) pm for Tb₃Pt₄In₁₂. The structure of the gadolinium compound was solved and refined from single crystal X‐ray data: P3¯m1, wR2 = 0.0470, 1469 F² values and 62 variable parameters. Both crystallographically different platinum sites have a slightly distorted trigonal prismatic indium coordination. These [PtIn₆] prisms are condensed via common edges and corners forming a complex three‐dimensional [Pt₁₂In₃₂] network. The gadolinium, In1 and In7 atoms fill cavities within this polyanion. Tb₃Pt₄In₁₂ is isotypic with the gadolinium compound.     

Intramolecular Substitution Reaction of Alkylidene‐Lithium Carbenoids: Regioselective Synthesis of Indenes

Intramolecular substitution reaction of geminal dibromo alkenes proceeds to afford indenes, dihydronaphthalenes, dihydrofurans, and dihydropyran via in situ generated lithium alkylidene carbenoids, which have a carbon or oxygen nucleophilic moiety. This reaction provides a regioselective method for the preparation of polysubstituted indenes.