Glass transition temperatures in binary polymer blends

Knowledge of the glass transition temperatures (T_gs) as function of composition reflects miscibility (or lack of it) and is decisive for virtually all properties of polymer‐based materials. In this article, we analyze single blend‐average and effective T_gs of miscible polymer blends in full concentration ranges. Shortcomings of the extant equations are discussed to support the need for an alternative. Focusing on the deviation from a linear relationship, defined as ΔT_g = T_g ? φ₁T_g,1 ? φ₂T_g,2 (where φ_i and T_g,i are, respectively, the weight fraction and the T_g of the i‐th component), a recently proposed equation for the blend T_g as a function of composition is tested extensively. This equation is simple; a quadratic polynomial centered around 2φ₁ ? 1 = 0 is defined to represent deviations from linearity, and up to three parameters are used. The number of parameters needed to describe the experimental data, along with their magnitude and sign, provide a measure of the system complexity. For most binary polymer systems tested, the results obtained with the new equation are better than those attained from existing T_g equations. The key parameter of the equation a₀ is related to parameters commonly used to represent intersegmental interactions and miscibility in binary polymer blends. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 80–95, 2008     

Electron Paramagnetic Resonance Study on Supported Molybdenum Catalysts. Part 1: Interaction of Molybdenum Oxide with Silica and Signal Anlsotropy

The effects of reduction, evacuation and adsorbate adsorption on Mo/SiO₂ catalysts prepared by impregnation were studied by means of the electron paramagnetic resonance (EPR) technique. Pentavalent molybdenum species in the overlayer (Mo₀⁵⁺, g? = 1.941, g| = 1.895) and at the interface (Mo_i⁵⁺, g? = 1.952, g| = 1.866) between MoO₃ and SiO₂ were distinguished in the EPR spectra; they were observed from samples reduced at T < 573 K and T > 573 K respectively. The difference in their nature reflected the extent of their interaction with the support. Mo₀⁵⁺ existed in the MoO3 overlayer of the catalyst and interacted only weakly with the support. Mo_i⁵⁺ from the Mo ions connected directly to SiO₂ was affected strongly by the support. The anisotropic factor of the measured Mo_i⁵⁺ signals increased with the extent of support interaction. Superoxide ions (O₂, g₁ = 2.016, g₂ = 2.011, g₃ = 2.006) were found upon oxygen adsorption on samples evacuated at temperatures above 573 K. The observed O₂ may exist at the interface between MoO₃ and the support.     

Magnetic properties and optical spectra of bis (Cinchoninium tetrachlorocopper (II) trihydrate single crystal

Distorted tetrahedral symmetry (D_2d) of two crystallographically nonequivalent copper tetrahedrons is postulated on the basis of reflectance spectrum, magnetic susceptibility measurements and EPR single crystal spectra. Molecular g-values are g_∥ = 2.292(4) and g_⊥ = 2.051(4). Exchange coupling determined by computer simulation is equal to | J | = 0.0030(5) cm⁻¹.     

[iPr2P]2P?SiMe3 und [iPr2P]2PLi – Synthese und Reaktionen Struktur des [iPr2P]2P?P[PiPr2]2

[iPr₂P]₂P? SiMe₃ and [iPr₂P]₂PLi – Synthesis and Reactions Structure of [iPr₂P]₂P? P[PiPr₂]₂ [iPr₂P]₂P? SiMe₃ 1 and [iPr₂P]₂PLi 2 were prepared to investigate the influence of the bulky alkyl groups on formation and properties of the ylides R₂P? P?P(X)R₂ (R = iPr, tBu; X = Br, Me) in reactions of 1 with CBr₄ and of 2 with 1,2-dibromoethane or MeCl, resp. Compared to the iPr groups the tBu groups favour the formation of ylides. With CBr₄ 1 forms iPr₂P? P?P(Br)iPr₂ 5 just as a minor product which decomposes already below ?30°C. With 1,2-dibromoethane 2 yields only traces of 5 but [iPr₂P]P? P[P(iPr)₂]₂ 7 as main product. With MeCl 2 gives iPrP? P?P(Me)iPr₂ 9 and [iPr₂P]₂PMe 10 in a molar ratio of 1:1. 9 is considerably more stable than 5. 7 crystallizes triclinic in the space group P1 (No. 2) with a = 10.813 Å, b = 11.967 Å, c = 15.362 Å, α = 67.90°, β = 71.36°, γ = 64.11° and two formula units in the unit cell.     

Solution of the Hartree–Fock problem by expansion onto nested bases

A method for solving the Hartree–Fock problem in a finite basis set is derived, which permits each orbital to be expanded in a different basis. If the basis set for each orbital ?_i contains the basis functions for the preceding orbitals, ?_i?1, ?_i?2,… ?₁, then the ?_i form an orthonormal set. One advantage over the standard Hartree–Fock method is that a different long range behavior for each orbital, as for example is required in the Hartree–Fock-Slater method, can be forced. A calculation on the ground state of beryllium is performed using the nested procedure. Very little energy is lost because of nesting, and the node in the 1s orbital disappears.     

Small Figure-Eight Luminophores: Double-Twisted Tethered Cyclic Binaphthyls Boost Circularly Polarized Luminescence

Double-twisted cyclic binaphthyls, in which two naphthalenes are tethered by -O(CH₂)_nO- linkage (n=1–3), have been synthesized. X-ray analyses and DFT calculations revealed a tightly constrained stereogenic figure-eight geometry. Tethering of two naphthalenes by short linkage forces a small dihedral angle, and the cyclic binaphthyls with short tether (n=1, 2) exhibit remarkable boosting of the g_lum value (1.0–1.6×10⁻²) in circularly polarized luminescence (CPL) and unusual g_lum/g_abs ratios (0.93–1.3). These experimental high |g_lum| values are in accord with the results of excited state TD-DFT calculations, which show transannular interactions and that consequent extensive delocalization occurs throughout the figure-eight π-core. As a result, the present figure-eight luminophore promote the elongation of the magnetic transition dipole moment that results in significant increases in g_lum values.     

复杂无机离子晶体晶格能的估算

A novel connectivity index ~mG based on adjacency matrix of molecular graphs was proposed as follows:~mG=∑(g_i·g_j·g_k…)~(0.5).The element g_i of adjacency matrix was defined as g_i=(1 Z_i~(1.4))/(1 r_i~(1.4)),where Z_i and r_i are thecharge number and the thermochemical radius of ion i respectively,and the radii r_i for metal ions are taken to be theGoldschmidt radius.The regression analysis by the connectivity index ~1G can provide a high-quality QSPR modelfor the lattice energies of 245 complex inorganic ionic crystal samples.The results imply that the lattice energiesmay be expressed as a linear model of the connectivity index ~1G.For the linear model the correlation coefficient rand the standard error s are 0.9998 and 228.72 kJ/mol,respectively.The cross-validation by the leave-one-outmethod demonstrates that the model is highly reliable from the point of view of statistics.     

Enhancing Circularly Polarized Phosphorescence via Integrated Top-Down and Bottom-Up Approach

In the dynamic domain of chiroptical technologies, it is imperative to engineer emitters endowed with circularly polarized luminescence (CPL) properties. This research demonstrates an advancement by employing a combined top-down and bottom-up strategy for the simultaneous amplification of photoluminescence quantum yield (Φ) and the luminescence dissymmetry factor (g_lum). Square-planar Pt(II) complexes form helical assemblies, driven by torsional strain induced by bis(nonyl) chains. Integration of chiral anions leads these assemblies to prefer distinct helical sense. This arrangement activates the metal-metal-to-ligand charge transfer (MMLCT) transition that is CPL-active, with Φ and |g_lum| observing an upswing contingent on the charge number and aryl substituents in chiral anions. Utilizing the soft-lithographic micromolding in capillaries technique, we could fabricate exquisitely-ordered, one-dimensional co-assemblies to achieve the metrics to Φ of 0.32 and |g_lum| of 0.13. Finally, our spectroscopic research elucidates the underlying mechanism for the dual amplification, making a significant stride in the advancement of CPL-active emitters.     

Gel formation with multiple interunit junctions. I—Molecules carrying different functional groups

Number‐ and weight‐average molecular weight of condensation polymers formed by primary molecules carrying different species of functional groups {A_i} (i = 1, 2, …, s) are derived by cascade theory. These functional groups are allowed to form multiple junctions of variable multiplicity k. The gel point condition is found to be given by ∑ w_i/|μ_w,i + 1/∑ f_i ? 1 = 0, where f_i is the number of A_i groups specified by the index i on a primary molecule, w_i ≡ f_i/∑ f_i the number fraction of the species i it carries, and |μ_w,i the weight average multiplicity of the junctions formed by the groups A_i. The explicit form of the molecular weight distribution function is found for the simplest case of two components. Possible application to thermoreversible gelation is suggested. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2405–2412, 2003     

On the formulation of spin-free quantum chemistry

A set of spin-free functions ?_i(r),i = 1 …? f, is obtained which form the basis of spin-free quantum chemistry. The ?_i(r) show a one-to-one correspondence to antisymmetric space-spin functions Ψ_i(r, σ) with spin functions constructed according to Löwdin's projector operator method.     

Synthesis,Structure, and Chiroptical Properties of Indolo- and Pyridopyrrolo-Carbazole-Based C2-Symmetric Azahelicenes

Treatment of 11,12-bis(1,1’-biphenyl-3-yl or 6-phenylpyridin-2-yl)-substituted 11,12-dihydro-indolo[2,3-a]carbazole with an oxidizing system of Pd(II)/Ag(I) induced effective double dehydrogenative cyclization to afford the corresponding π-extended azahelicenes. The optical resolutions were readily achieved by a preparative chiral HPLC. It was found that the pyridopyrrolo-carbazole-based azahelicene that contains four nitrogen atoms exhibits ca. 6 times larger dissymmetry factors both in circularly dichroism (CD) and circularly polarized luminescence (CPL), |g_CD| and |g_CPL| values being 1.1×10⁻² and 4.4×10⁻³, respectively, as compared with the parent indolocarbazole-based azahelicene. Theoretical calculations at the RI-CC2 level were employed to rationalize the observed enhanced chiroptical responses. The (chir)optical properties of the former helicene was further tuned by a protonation leading to remarkable red-shift with a considerable enhancement of the |g_CPL| value.     

Electron impact mass spectra of polycyclic aromatic compounds with several types of pyridino- and benzobenzanthrone skeletons

Electron impact mass spectra were measured for five isomers of pyridinobenzanthrones and three isomers of benzobenzanthrones. The fragmentation pattern and intensity of M²⁺, [M – H]⁺, [M – CO]ⁱ⁺, [M – CO – H(or 2H)]ⁱ⁺ and [M – CO – HCN]ⁱ⁺ (i = 1, 2) ions indicated remarkable differences and very interesting features according to the isomers with or without nitrogen and condensation positions of a pyridino or benzo ring to the benzanthrone skeleton. Further, the competition of decompositions through [M – H]⁺, [M – CO]^+˙ or [M – HCN]^+˙ ions was confirmed by the observation of metastable ions and the appearance energies of fragment ions. Interesting observations from these results were expulsion of an H atom in close proximity to the area around an O?C group, a weak bonding interaction between sp² C? H and an O?C group, inducing specific hydrogen rearrangement, and characteristic charge localization on heteroatoms.     

Asymptotic behaviour of molecular bound state wavefunctions

Upper bounds are derived for |r^μ_i|, μ = 1,2, ·, where ? denotes an exact electronic bound state wavefunction of a molecular system in the Born-Oppenheimer approximation, and r_i is the distance of the ith electron from an appropriately chosen point, e.g., the molecular center. It is further shown that ? decays exponentially if r_i → ∞.     

Miscibility diagrams of random copolymer blend systems

The miscibility of copolymers A_xB_1?x and A_yB_1?y, derived from the same monomer pair (A, B) but differing in composition, was studied. The systems (A, B) were (S, MMA), (BMA, MMA), (S, BMA), and (CIS, BMA) (S: styrene, CIS: p-chlorostyrene, MMA: methylmethacrylate, BMA: n-butylmethacrylate). Miscibility diagrams were recorded, at low and high temperatures, using cast films and dry films. All blend systems feature hightemperature miscibility gaps. Unusual effects of the compositions x and y on miscibility in blends A_xB_1?x/A_yB_1?y were observed. The classical prediction that miscibility should depend only on the composition difference |x – y| usually is too simple. It appears necessary to consider dyad interactions.     

A variation principle for energy differences between states of two different Hamiltonians

A modification of a variation principle due to Delves, is derived which permits the direct calculation of energy differences between states of two different Hamiltonians: [Δ ??] = 〈X₀| ??_x – W_x|X₁〉 – 〈Y₀|??_y – W_y|y₁〉 + 〈X₀| Δ ??|Y₀〉 · 〈X₀| Y₀〉^?1. Δ ?? = ??_y – ??_x, |X₀〉 and |Y₀〉 are the wave functions for the X and Y states and |X₁〉 and |Y₁〉 are functions defined in the text. The principle is applied to a few simple examples.     

Theoretical Study of Pd11Si6 Nanosheet Compounds Including Seven‐Coordinated Si Species and Its Ge Analogues

Nanosheet compounds Pd₁₁(SiiPr)₂(SiiPr₂)₄(CNtBu)₁₀ ( 1 ) and Pd₁₁(SiiPr)₂(SiiPr₂)₄(CNMes)₁₀ ( 2 ), containing two Pd₇(SiiPr)(SiiPr₂)₂(CNR)₄ plates (R=tBu or Mes) connected with three common Pd atoms, were investigated with DFT method. All Pd atoms are somewhat positively charged and the electron density is accumulated between the Pd and Si atoms, indicating that a charge transfer (CT) occurs from the Pd to the Si atoms of the SiMe₂ and SiMe groups. Negative regions of the Laplacian of the electron density were found between the Pd and Si atoms. A model of a seven‐coordinated Si species, that is, Pd₅(Pd?SiMe), is predicted to be a stable pentagonal bipyramidal molecule. Five Pd atoms in the equatorial plane form bonding overlaps with two 3p orbitals of the Si atom. This is a new type of hypervalency. The Ge analogues have geometry and an electronic structure similar to those of the Si compounds. But their formation energies are smaller than those of the Si analogues. The use of the element Si is crucial to synthesize these nanoplate compounds.     

Synthesis of C(2)‐Substituted manno‐Configured Tetrahydroimidazopyridines and Their Evaluation as Inhibitors of Snail β‐Mannosidase

It was shown that retaining β‐glucosidases and galactosidases of families 1–3 feature a strong interaction between C(2)OH of the substrate and the catalytic nucleophile. An analogous interaction can hardly take place for retaining β‐mannosidases. A structure? activity comparison between the inhibition of the β‐glucosidase from Caldocellum saccharolyticum (family 1) and β‐glucosidase from sweet almonds by the gluco‐imidazoles 1 – 6 , and the inhibition of snail β‐mannosidase by the corresponding manno‐imidazoles 8 – 13 does not show any significant difference, suggesting that also the mechanisms of action of these glycosidases do not differ significantly. For this comparison, we synthesized and tested the manno‐imidazoles 9 – 13, 28, 29, 32, 35, 40, 41, 43, 46, 47 , and 50 . Among these, the alkene 29 is the strongest known inhibitor of snail β‐mannosidase (K_i=6 nM , non‐competitive); the aniline 35 is the strongest competitive inhibitor (K_i=8 nM ).     

Synthesis of 2,2,5,5‐Tetrasubstituted 1,4‐Dioxa‐2,5‐disilacyclohexanes via Organotin(IV)‐Catalyzed Transesterification of (Acetoxymethyl)alkoxysilanes

(Acetoxymethyl)silanes 2 , 7 a – c , and 10 a – c with at least one alkoxy group, of the general formula (AcOCH₂)Si(OR)_3?n(CH₃)_n (R: Me, Et, iPr; n=0, 1, 2), were synthesized from the corresponding (chloromethyl)silanes 1 , 6 a – c , and 9 a – c by treatment with potassium acetate under phase‐transfer‐catalysis conditions. These compounds were found to provide 2,2,5,5‐organo‐substituted 1,4‐dioxa‐2,5‐disilacyclohexanes 3 , 8 a – c , and 11 a – c if treated with organotin(IV) catalysts such as dioctyltin oxide. The reaction proceeds through transesterification of the acetoxy and alkoxy units followed by ring‐closure to form a dimeric six‐membered ring. The corresponding alkyl acetates are formed as the reaction by‐products. With these mild conditions, the method overcomes the drawbacks of previously reported synthetic routes to furnish 2,2,5,5‐tetramethyl‐1,4‐dioxa‐2,5‐disilacyclohexane ( 3 ) and even allows the synthesis of 1,4‐dioxa‐2,5‐disilacyclohexanes bearing hydrolytically labile alkoxy substituents at the silicon atom in good yields and high purity. These new materials were fully characterized by NMR spectroscopy, elemental analysis, mass spectrometry, and X‐ray analysis (trans‐ 8 a ).     

Synthesis and Characterization of Secondary Nitrosamines from Secondary Amines Using Sodium Nitrite and p‐Toluenesulfonic Acid

We synthesized nitrosamines (R₂N? NO) with R=iPr ( 1 ), nPr ( 2 ), nBu ( 3 ), and hydroxyethyl ( 4 ) from the amine using sodium nitrite/p‐toluenesulfonic acid in CH₂Cl₂. The rate of formation of 1 – 4 increases in the direction iPr<nPr<nBu2CH₂OH. Compounds 1 – 3 were obtained as colorless solids, whereas 4 is a bright yellow liquid. Compounds 1 – 4 were characterized by elemental analysis, MS, IR, and multinuclear NMR (¹H, ¹³C, and ¹⁵N) spectroscopies. Additionally, we measured the UV/Vis spectra of all compounds, which show maxima of absorption at approximately 221 nm and molar extinction coefficients between 3043 and 4859 L mol^?1 cm^?1. We calculated the optimized structures of 1 – 4 (B3LYP/6‐311+G(d,p)) and computed the NMR spectroscopic chemical shifts and infrared frequencies. Furthermore, we carried out a natural bond orbital (NBO) analysis of the nitrosamine moiety. Lastly, the compounds described in this work are valuable starting materials for the synthesis of 2‐tetrazenes with potential interest to replace highly toxic hydrazines in rocket propulsion.     

Residence times in kink sites and Markov chain model of alloy and intermetallic compound deposition

The concept of the residence time τ_ksp of an atom in a kink site has recently been suggested to understand the processes in electrochemical deposition of alloys and intermetallic compounds. Different kink sites with different residence times must be defined for alloys and intermetallic compounds. Based on this model, the finite Markov chain theory is applied to describe the selectivity of the growth process. An analytical relationship between the alloy composition and the metal ion concentrations in the electrolyte is derived. General model parameters are ratios g _i = K _ii/K _ij of equilibrium constants of the reaction of electrolyte ions with different kink sites on the surface (i, j representing different alloy components). These ratios are called selectivity constants. For simple conditions, the equation g _i ≈ τ_ii/τ_ij connects the g _i values with the residence times. The theory is tested in the deposition of alloys Co-Ni (anomalous co-deposition) and Ni-Mo (induced co-deposition). Additionally, Bi₂Te₃, an example of stoichiometric semiconductor deposition, is treated. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 10, pp. 1216–1223. The text was submitted by the authors in English.