Polyamide-imides

A novel preparation of polyamide-imides from diphenylmethane diisocyanate and trimellitic anhydride in N-methylpyrrolidone is described. Partial substitution of trimellitic anhydride with either maleopimaric acid, terephthalic acid, or by various di-anhydrides permitted a correlation of structure with solution stability and thermal properties. Heat resistance improved with increasing imide content of the polyamide-imide. Almost all solutions advanced in viscosity on storage at room temperature. The least stable solutions were those that deviated the most from 50–50 amide-imide. However, the viscosity changes depended somewhat on the type of modifying ingredient. For example, polyamide-imides modified by substitution of 10% PMDA (pyromellitic anhydride) or BPDA (benzophenone tetracarboxylic acid dianhydride) were less stable than those modified with 10% (cyclopentanetetracarboxylic acid dianhydride) CPDA or THFDA (tetrahydrofuran-2,3,4,5-tetracarboxylic acid dianhydride). The use of excess reagent and of monofunctional chain stopper was investigated as a means of controlling solution stability.     

On the Products of Cholesterol Autoxidation in Phospholipid Bilayers and the Formation of Secosterols Derived Therefrom

In homogenous solution, cholesterol autoxidation leads to a mixture of epimers of 5 primary products, whose concentrations vary in the presence/absence of antioxidants, such as vitamin E. Two of the products (5α‐OOH and 6β‐OOH) undergo Hock fragmentation to yield electrophilic secosterols implicated in disease. Herein, we show that the product distribution is similar in phospholipid bilayers, in that the 7‐OOHs are the major products, but the presence/absence of vitamin E has no effect on the distribution. Cholesterol 7α‐OOH, but not 7β‐OOH, undergoes Hock fragmentation to yield a mixture of unprecedented A‐ring cleavage products and 6,7‐epoxides. When subjected to typical derivatization conditions, 7α‐OOH yields products with essentially indistinguishable chromatographic and spectroscopic features from the previously identified secosterols, casting further doubt on their controversial origin from endogenous O₃.     

Spin coupling and resonance

The resonating block localize wave function (RBLW) method is introduced, a resonating modification of the block localized wave functions introduced by Mo et al. [Mo, Y.; Peyerimhoff, S. D. J. Chem. Phys. 1998, 109, 1687].This approach allows the evaluation of resonance energies following Pauling's recipe. The method is tested on two model molecules, hexagonal H(6) and benzene. Calculations have been done with (local) and without local restrictions (delocal). Resonance energies for both molecules have been obtained for each type of calculation, in agreement with Pauling's concept. From a comparison of the resonance energies obtained from RBLW and standard valence bond calculations, the resonating block localize wave functions prove to yield resonance energies close to standard valence bond delocal calculations.     

非平衡态/不可逆过程的热力学理论(Ⅱ)

<正> 7 解的唯一性 如果不考虑非平衡态和不可逆性,则等能密度理论中的基本命题与经典弹性理论中的在形式上完全相同。无论整个系统的动能是大还是小,图6中(sumform)_o上的面力T_i和在(sumform)_c和在的位移u_i将始终在空间坐标系x_i和时刻i下给出。与一般力学中相同,必须知道有关位移u_i及其时间导数的初始条件。它们的影响则可通过(38)和(39)向等能面转化,从而得到     

Substituent Effects on the Bands Near 1600 cm−1 in The Ir Spectra of Azobenzene and Some Substituted Azobenzenes

Abstract

The mean positions and apparent extinction coefficients of the ring stretching bands near 1600 cm^?1 in the IR spectra of trans azobenzene and some substituted trans azobenzenes are reported. These results are discussed in relation to values reported for substituted benzenes.     

Substituent Effects On The Carbonyl Stretching Vibration In The Ir Spectra Of Some Substituted Benzophenones

The band frequencies and integrated intensities of the carbonyl stretching absorptions in a series of substituted benzophenones were examined as a function of the inductive and mesomeric effects of the substituents.     

The mechanism and stability of thermal transitions in hair keratin

Differential Scanning Calorimetry (DSC) has been applied to study the interactions between components of human hair keratin. Keratin is a biopolymeric composite made of several proteins forming basically two phases: amorphous matrix and crystalline microfibrillar phase. Water, the content of which depends on atmospheric humidity, is also an integral part of keratin structure. The following processes are apparent from the DSC: removal of loosely bound water (ca. 70°C), a transition in the amorphous phase (155°C) and melting/denaturation of the -crystalline phase (233°C). The process occurring in keratin at ca. 155°C has an opposite character to a glass transition; we refer to this process as the toughening transition. The area of the -keratin peak increases significantly upon annealing at temperatures from 80°C to 150°C and decreases for higher annealing temperatures. Water affects both the crystalline and amorphous phases of keratin. The process similar in nature to annealing — induced recrystallization in synthetic polymers is strictly correlated with removal of strongly bound fraction of water in keratin.     

Temperature-programmed desorption of carbon monoxide from 3% Ir?Fe/Al2O3 catalysts

An increase in percentage of iron in 3% Ir–Fe/Al₂O₃ brings about a considerable decrease in desorptive effects of CO and small qualitative changes in TPD spectra, suggesting the predominant role of iridium, slightly modified by the presence of iron.

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3%- Ir–Fe/Al₂O₃ CO . , , .