自由基引发马来酸二丁酯熔融接枝低密度聚乙烯的研究

用马来酸二丁酯(DBM)为接枝单体,过氧化二枯基(DCPO)为引发剂,对低密度聚乙烯(LDPE)进行了熔融接枝功能化。样品的红外光谱表明接枝反应确已发生。通过对样品中酯基的皂化水解测定产物的接枝率,对产物进行萃取,用凝胶量间接表征产物的交联程度;用溶液的特性粘度从侧面显示样品的支化或降解情况。实验结果表明,产物的接枝率和凝胶量可以通过选择反应条件(温度、时间及反应混合物的组成)来控制;过量的DCPO是引起交联产生凝胶的主要原因;向体系中添加DMF可阻止交联反应的发生,但产物的接枝率也有所下降,以自由基机理对上述结果进行了讨论。     

Effects of sugar inhibition on cellulases and β-glucosidase during enzymatic hydrolysis of softwood substrates

A quantitative approach was taken to determine the inhibition effects of glucose and other sugar monomers during cellulase and β-Glucosidase hydrolysis of two types of cellulosic material: Avicel and acetic acid-pretreated softwood. The increased glucose content in the hydrolysate resulted in a dramatic increase in the degrees of inhibition on both β-Glucosidase and cellulase activities. Supplementation of mannose, xylose, and galactose during cellobiose hydrolysis did not show any inhibitory effects on β-Glucosidase activity. However, these sugars were shown to have significant inhibitory effects on cellulase activity during cellulose hydrolysis. Our study suggests that high-substrate consistency hydrolysis with supplementation of hemicellulose is likely to be a practical solution to minimizing end-product inhibition effects while producing hydrolysate with high glucose concentration.     

PEG-PLA嵌段共聚物的合成及~(13)C NMR对平均链段长度的测定

本文报道聚乙二醇(PEG)在辛酸亚锡存在下与丙交酯(LA)反应合成PEG-PLA嵌段共聚物,用~(13)C NMR测定了共聚物的结构,估算了平均链段长度.实验结果表明,L_(PEG)在反应过程中保持不变,而L_(PLA)随反应时间和LA在原料配比中含量的增加而增加,呈逐步聚合反应特点.对聚合反应机理作了推测.     

数均聚合度计算的教学方法

总结毛者提出的线型缩聚中当量系数的新定义及引入缩聚体系单体平均官能度的新方法，本文总结出了一套讲授数均聚合度计算问题的简单方法。     

A competitive (dual) simplex method for the assignment problem

Where there is abundance of mystery and confusion in every direction, the truth seldom remains hidden for long. It's a matter of having plenty of angles to go at it from. Only the utterly simple crimes - the simplex crimes, you may say - have the trick of remaining baffling. - Sir John (from Michael Innes,The Open House (A Sir John Appleby Mystery), Penguin Books, 1974).A dual simplex method for the assignment problem leaves open to choice the activity (i,j) of rowi and columnj that is to be dropped in pivoting so long asx _ij < 0. A choice (i,j) over columnsj having at least 3 basic activities that minimizesx _ij is shown to converge in at most ( ₂ ^n-1 ) pivots, and at most O(n ³) time, and it is argued that on average the number of pivots is at mostn logn. Dedicated with affection to George B. Dantzig on the occasion of his seventieth birthday.     

An average fock operator technique of approximate open-shell LCAO-MO-SCF calculation

The exchange part of the usual Hartree-Fock potential in the unrestricted Hartree-Fock (UHF) theory is suitablyaveraged to construct an, average one-electron model Hamiltonian which generates a set of spin-restricted one-electron orbitals in a self-consistent manner. These orbitals are then used to calculate the electronic energy of the open-shell system by using the proper functional form for the energy which handles the exchange terms correctly. The eigenvalues ofF ^av can be used for calculating either the spin-polarised or spin-averaged ionisation potentials of different orbitals at theKoopmans’ theorem level of approximation. Comparison ofE ^ac with the UHF-energy shows thatE _UHF<E ^ac in each case revealing some kind of an upper bound nature ofE ^ac. An approximate variational argument is given. Relationship of our model with the hyper-Hartree-Fock theory of slater is explored and the general problem of eliminating ‘self-interaction’ terms in average Fock-operator based theories is discussed.     

Effect of monomer molecular flow on electrode surface on the structure of poly(α-tetrathiophene) obtained by anodic polymerization

Different structures have been found for poly(α-tetrathiophene) [poly(α-4TF)] electrosynthesized on Pt by anodic oxidation of 1.0 mM monomer solutions in media such as 45:35:20 (v/v/v) acetonitrile/THF/DMF, 45:35:20 (v/v/v) acetonitrile/ethanol/DMF and 72:28 (v/v) acetonitrile/DMF containing 0.1 M LiClO₄; as well as 72:28 (v/v) acetonitrile/DMF with 0.1 M NaClO₃, under dynamic and static conditions at 25 °C. In all cases the polymer was generated by chronoamperometry at 1.000 V vs. Ag∣AgCl, corresponding to the first oxidation peak detected by cyclic voltammetry. Uniform, adherent, insoluble and black polymer films were obtained under these conditions. The resulting structures have been elucidated by combining the information of their IR spectrum, n_ox-value and doping level of the counterion. The degree of crosslinking of every polymer has been quantified and related to the molecular flow of monomer on the Pt electrode. A monomer concentration flow between 4 × 10⁻⁶ and 5 × 10⁻⁶ mmol cm⁻² s⁻¹ was determined as the limiting value below which the polymer grows with crosslinking. This value corresponds to the electropolymerization rate of α-4TF by Pt area unit at 25 °C.     

硅氧聚合度对细胞毒性的影响

本文采用家兔肺泡巨噬细胞(AM)存活率和细胞过氧化脂质(LPO)值为测定指标,研究了硅氧的聚合度对其细胞毒性的影响。结果表明:各种聚合度的硅氧都有一定的细胞毒性,聚合度愈大,细胞毒性也愈大。胶体SiO_2的粒径增大,其细胞毒性降低。十硅酸盐及粒径小于5nm的硅溶胶的细胞毒性大于α-石英。聚合度小于6的低聚硅酸及其盐、粒径18nm以上的硅溶胶以及硅胶H的毒性皆小于α-石英。本实验细胞存活率降低和过氧化脂质值升高的趋势基本一致,这表明硅氧可能主要与细胞表面膜作用,膜上磷脂等表面活性物质被氧化和变性,从而导致细胞损伤。     

Nitrate ion association with Nd3+

The overall stability constantsK ₁ andK ₂ of NdNO ₃ ²⁺ and Nd(NO₃) ₂ ⁺ complexes were determined (K ₁=1.77;K ₂=1.28) using an extraction method with tri-n-butyl phosphate as the extractant. The ratio ₁/₂ of the stepwise stability constants is discussed. It was established that the Nd(NO₃) ₂ ⁺ complex was an outer-sphere ion pair.

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Die Assoziation von Nitrat-Ion mit Nd³⁺

Zusammenfassung Mittels einer Extraktionsmethode wurden die StabilitätskonstantenK ₁ undK ₂ von NdNO ₃ ²⁺ - und Nd(NO₃)⁺-Komplexen bestimmt (K ₁=1.77;K ₂=1.28; Tri-n-butylphosphat als Extraktionsmittel). Das Verhältnis ₁/₂ der stufenweisen Stabilitätskonstanten wird diskutiert. Es stellte sich heraus, daß der Nd(NO₃)⁺-Komplex als ein Outer-Shere-Ionenpaar vorliegt.

     

四氢呋喃-水-乙醇三元溶液体系制备高合金化Pt-Ru/CMK-3催化剂

提出了在四氢呋喃(THF)、H2O和乙醇三元体系中用一般的化学还原法在室温下制备高合金化Pt-Ru/CMK-3催化剂的新方法. 与在纯水中制得的商品化ETEK催化剂相比, 其Pt-Ru粒子的合金化程度高、平均粒径较小且相对结晶度低, 因此, 该催化剂对甲醇氧化的电催化活性远高于在纯水中制得的Pt-Ru催化剂. 高合金化程度的原因是H2PtCl6和RuCl3在THF、H2O和乙醇三元溶液体系中的起始还原电位相近. 此外, CMK-3以其规整的二维有序孔道结构, 为直接甲醇燃烧电池(DMFC)中电子和物质的传输提供了方便的路径, 其巨大的比表面积也为Pt-Ru 纳米粒子的均匀分散提供了良好的载体.