Single-Phase Polymer Alloys of Polyvinyl Chloride and New Polymers

Polymer alloying is acquiring ever increasing significance for the modification of polymeric materials. Polymer alloys are defined by their phase character, which in turn is determined by the mutual compatibility or incompatibility of the components. Suitable techniques for the analysis of the phase character include, inter alia, dynamic-mechanical methods, according to which a polymer alloy may be considered in a simplified manner as single-phase when only one glass transition is observed, even if it extends over a broader temperature range than in the case of the pure components. Aliphatic (polyester)-polycarbonates and tetramethylbisphenol-A polycarbonate are new, PVC-compatible, polymer modifiers. The (polyester)-polycarbonates (from adipic acid, hexane-1,6-diol, neopentanediol, and diphenyl carbonate) yield with PVC single-phase alloys that at temperatures above the glass transitions of the mixture display the characteristics of soft PVC and that are tough far below this temperature. The special high-temperature properties of the resin-like tetramethylbisphenol-A polycarbonate permits the preparation of alloys with increased dimensional stability under heat (higher deflection temperatures under load).     

Factors controlling the addition of carbon-centered radicals to alkenes

The addition rate constants of radicals to alkenes are strongly substituent dependent because of enthalpic, polar and steric effects. Recent absolute experimental and high level ab initio data for many prototype additions of small radicals are analyzed with the aid of the state correlation diagram. This leads to a unifying rationalization of the various effects and allows the prediction of rate constants to one order of magnitude or better. Propagation rate coefficients of homo- and copolymerizations and penultimate effects are also discussed.     

Durability prediction of p-urethane clearcoats using infrared p(hoto) a(coustic) s(pectroscopy)

The durability of topcoats is dependent on a large number of factors as polymer composition, stabilization package and the conditions during the weathering process. For obvious reasons prediction of the long-term (5-10 year) durability of coatings is very important. The rate-determining factor for the degradation of PUR coatings is photo-oxidation. The photo-oxidation rate is controlled by the polymer structure but also stabilizers as HALS has a large influence. The prediction of the durability of clearcoats is based on tracing of the photo-oxidation rate and of the HALS longevity during exposure. The photo-oxidation rate is measured using FTIR-PAS. The results show that degradation can be detected much earlier compared with classical methods as gloss loss. Moreover detection of differences between systems after short exposure times as well as prediction of the long-term durability are possible.     

Triethylphosphanimin-Komplexe der Acetate von Kupfer(II) und Zink. Kristallstrukturen von [Zn(O2C–CH3)2(HNPEt3)], [Cu5(O2C–CH3)10(HNPEt3)2] und [Cu(O2C–CH3)2(HNPEt3)2]

Triethylphosphanimine Complexes of the Acetates of Copper(II) and Zinc. Crystal Structures of [Zn(O₂C–CH₃)₂(HNPEt₃)], [Cu₅(O₂C–CH₃)₁₀(HNPEt₃)₂], and [Cu(O₂C–CH₃)₂(HNPEt₃)₂] The title compounds originate from the anhydrous acetates of zinc and copper(II) with trimethylsilyl-triethylphosphanimine, Me₃SiNPEt₃, in the presence of water in dichloromethane. They form colourless ( 1 ), bluish-green ( 2 ), and blue ( 3 ), respectively, single crystals, which were characterized by IR spectroscopy and by crystal structure analyses. [Zn(O₂C–CH₃)₂(HNPEt₃)] ( 1 ): Space group P 4 2₁c, Z = 8, lattice dimensions at –83 °C: a = b = 1709.6(2), c = 982.4(1) pm, R = 0.0551. 1 has a polymeric chain structure in which the zinc atoms are μ₂-bridged via the oxygen atoms of one of the two acetato groups, while the second acetato group and the phosphanimine are bonded terminally. [Cu₅(O₂C–CH₃)₁₀(HNPEt₃)₂]( 2 · 4 CH₂Cl₂): Space group P2₁/c, Z = 8, lattice dimensions at –80 °C: a = 1761.18(13), b = 4074.5(2), c = 1733.34(15) pm, β = 91.383(10)°, R = 0.0413. 2 consists of the two structural units [Cu₂(O₂C–CH₃)₄] and [Cu₃(O₂C–CH₃)₆(HNPEt₃)₂], which are connected via two of the acetato groups of the Cu₃-unit along the crystallographic a-axis to form three crystallographically independent polymeric strands. [Cu(O₂C–CH₃)₂(HNPEt₃)₂] ( 3 ): Space group P2₁/n, Z = 2, lattice dimensions at 20 °C: a = 695.49(8), b = 1217.85(10), c = 1380.05(7) pm, β = 96.451(7)°, R = 0.0291. 3 forms monomeric, centrosymmetric molecules with a square planar environment at the Cu atoms.     

Planar-Tetracoordinate Carbon in a Neutral Saturated Hydrocarbon: Theoretical Design and Characterization

Exact planarity at the central carbon atom is achieved, according to molecular orbital calculations, in the strained polycyclic cage hydrocarbon dimethanospiro[2.2]octaplane (see structure). There are no glaringly long C−C bonds, which might have reflected inherent instability in this molecule that is yet to be synthesized.     

Long-range electronic interactions in androstanediones

The results of MNDO SCF MO calculations on 5α-androstane (1), androstan-3-one (2), androstan-16-one (3), androstan-17-one (4), androstane-3,16-dione (5), and androstane-3,17-dione (6) and the experimental ¹³C-NMR chemical shifts observed in various solvents (C₆D₁₂, CDCl₃, CD₃CO₂D, CD₂Cl₂, CD₃COCD₃, CD₃OD, CD₃CN) were used to assess the nature of long-range interactions between 3,16- and 3,17-carbonyl groups in androstanediones. The ¹³C-NMR results appear to confirm the proposition that the interactions in androstane-3,16-dione are stronger. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 797–803, 1997     

MBO(N)D: A multibody method for long‐time molecular dynamics simulations

A modeling approach that can significantly speed up the dynamics simulation of large molecular systems is presented herein. A multigranular modeling approach, whereby different parts of the molecule are modeled at different levels of detail, is enabled by substructuring. Substructuring the molecular system is accomplished by collecting groups of atoms into rigid or flexible bodies. Body flexibility is modeled by a truncated set of body‐based modes. This approach allows for the elimination of the high‐frequency harmonic motion while capturing the low‐frequency anharmonic motion of interest. This results in the use of larger integration step sizes, substantially reducing the computational time required for a given dynamic simulation. The method also includes the use of a multiple time scale (MTS) integration scheme. Speed increases of 5‐ to 30‐fold over atomistic simulations have been realized in various applications of the method. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 159–184, 2000