聚碳酸酯聚氨酯弹性体的模拟生物老化性能的研究

研究了聚碳酸酯聚氨酯的水解剂，氧化，钙化等生物老化性能，并与聚醚聚氨酯样品做了比较，结果表明，胺扩链样品具有较好的耐水解性能，聚碳酸酯氨酯的抗氧化性能优于聚醚聚氨酯，同了聚醚氨酯一样，聚碳酸酯聚氨酯同样受钙的影响，含水氯化钙对聚碳酸酯聚氨酯的相结构产生影响，并对弹性具有增强作用。     

On the Ramsey numbers R(3, 8) and R(3, 9)

Using methods developed by Graver and Yackel, and various computer algorithms, we show that 28 ≤ R(3, 8) ≤ 29, and R(3, 9) = 36, where R(k, l) is the classical Ramsey number for 2-coloring the edges of a complete graph.     

The analysis of solutions containing mixtures of linear sodium phosphates

A new method for analysis of sodium ortho-, pyro-, and triphosphate is reported. This procedure consists of the measurement of three values which permit a simultaneous solution of three independent equations, yielding the relative amounts of linear phosphates present in the mixture. The measured quantities were: 1) pyrophosphate, gravimetrically determined as zinc pyrophosphate, reprecipitated at 19° and at a pH of 4.0 – 4.5, 2) silver phosphate, determined by a conductance titration at 12°, of standardized silver nitrate solution, and 3) total phosphate, determined after complete hydrolysis to orthophosphate in hot acid solution.     

Allinger's gauche hydrogen hypothesis as tested by an alternative force field model

Allinger's hypothesis that gauche hydrogen, rather than gauche methyl interactions are mainly responsible for conformational equilibria was tested by molecular mechanics calculations using the Engler force field model. For the gauche-anti conformational energy of n-butane, effective cancellation among non-bonded in teractions involving the methyl groups results in the gauche hydrogen interactions across the central C-C bond as the single largest contribution to the energy difference. However, the contribution of this interaction is only one third of the 0.9 kcal difference. For 2,3-dimethylbutane, strain analysis of the gauche-anti conformational energy contributions reveals that geminal and gauche CH₃/CH₃ interactions dominate over the gauche hydrogen interaction Similar analyses for several monosubstituted cyclohexanes confirm that “across-the-ring” interactions. between axial substituents and syn -axial hydrogen atoms are still largely responsible for the instability of the axial relative to the equatorial conformer. In disagreement with Allinger's proposal, the “equatorial hydrogen effect” is found to contribute only a minor amount to the conformational energy difference. Allinger's hypothesis is concluded to be force field dependent, and not to have general validity.     

Mechanism of electrochemical reduction of oxamide analytical applications

Oxamide is electrochemically reduced at mercury electrodes between pH 5.6 and 11.6. The overall mechanism proceeds by an initial 2e reduction of the 1,2-carbonyl groups of oxamide to give a dianion. This then protonates, rearranges, and loses ammonia to glyoxylamide, which is reduced in a further 2e/2H⁺ reaction giving glycolamide as the ultimate product. The reaction thus proceeds by a typical e.c.e. mechanism. The overall homogeneous rate contant for the chemical reaction(s) interposed between the two charge-transfer steps was measured by peak voltammetric, potentiostatic and d.c. polarographic methods. The d.c. polarographic wave of oxamide between pH 5.6 and 11 provides the basis for a very simple analytical method for the determination of oxamide.