咪唑封端聚氨酯予聚体改性环氧树脂E-51/双氰双胺固化体系性能研究

以聚丙二醇PPG10 0 0、甲苯二异氰酸酯 (TDI)、咪唑为原料 ,合成了咪唑封端的聚氨酯予聚体 ,简称扩链脲TIEU .利用DSC、粘弹谱仪、冲击试验机及扫描电镜 (SEM)等手段对TIEU改性的环氧树脂E 5 1/双氰双胺(dicy)固化体系的反应活性、动态力学行为、冲击性能、断裂面形态结构进行了系统研究 .实验结果表明 ,改性后的E 5 1 dicy体系反应活性明显提高 ,固化反应的表观活化能由未改性体系的 131kJ mol降至 75～ 80kJ mol.与咪唑促进体系比较结果显示 ,两种固化反应的促进机制具有一定的差异 .另外与未改性体系相比 ,经过改性的环氧树脂体系冲击强度提高 2～ 3倍 ,而玻璃化温度和模量基本不变 ,冲击断面呈韧性断裂     

刚性链侧链型液晶高分子（甲壳型液晶高分子）研究进展

普通的侧链型液晶高分子属柔性链高分子,而“甲壳型液晶高分子”虽从化学结构着属于侧链型液晶高分子,其性质却和典型的眩链型液晶高分子相似,具有很大的分子链刚性。本文介绍了“甲型液晶高分子”这一科学概念及其研究进展,并对尚待解决的问题进行了探讨。     

一类半马氏过程的常返性与正常返性

对于逗留时为正整数值的半马氏过程程｛ξ（ｔ）｝,本文研究了｛ξ（ｔ）｝、相应过程｛ξ（ｎ）｝、嵌入链｛ξ_ｎ｝的常返性和正常返性之间的关系．定理 ２．１证明了三过程的状态常返性是等价的．定理 ２．２证明了ξ（ｔ）、ξ（ｎ）的状态正常返性是等价的,ξ（ｔ）的状态正常返是嵌入链状态正常返的充分条件．定理２．３给出了ξ（ｎ）的状态正常返的充分条件．该条件在状态空间有限时也是必要条件．     

层间耦合与高温超导体链的能隙结构

根据高温超导体层状结构特点和层间耦合效应,在一个唯象的S-N双层高温超导模型(S表示超导层,N表示非超导层)下,求得了非超导层的格林函数,证实了YBCO中CuO链上大能隙的存在,与实验结果相一致。     

Rhenium(IV)–copper(II) heterobimetallic complexes: Synthesis,crystal structure and magnetic properties

Two Re(IV)–Cu(II) heterometallic complexes {(CuL_α)[ReCl₄(ox)]}_n (where L_α = N-meso-5,12-Me₂-7,14-Et₂-[14]-4,11-dieneN₄), 1, and (CuL_β)[ReCl₄(ox)] (L_β = N-rac-5,12-Me₂-7,14-Et₂-[14]-4,11-dieneN₄N-rac-5,12-Me₂-7,14-Et₂-[14]-4,11-dieneN₄), 2, were synthesized. The [CuL²⁺] macrocyclic cation is coordinated from above and below by [ReCl₄(ox)]²⁻ units through the chloro-ligands and creates a chloro-bridged heterometallic Re^IV–Cu^II one-dimensional zig-zag chain. Compound 2 can be viewed as a heterobimetallic dinuclear unit, in which the Re(IV)-Cu(II) centers are linked by an oxalato bridge. The magnetic behavior of 1 and 2 has been investigated over the temperature range 1.8–300 K. Compound 1 behaves like a ferrimagnetic {Re(IV)–Cu(II)} bimetallic, one-dimensional chain with intrachain antiferromagnetic coupling. Compound 2 shows a weak antiferromagnetic interaction within the [Re(IV)–Cu(II)] unit along with a strong single-ion anisotropy, D(Re) = −63 cm⁻¹.     

双端羟基预聚物扩链制备高分子量聚对二氧环己酮

以1,4-丁二醇(BD)为引发剂, 辛酸亚锡为催化剂, 引发对二氧环己酮(PDO)开环聚合, 得到双端羟基型聚对二氧环己酮预聚物, 再以六亚甲基二异氰酸酯(HDI)为扩链剂制备高分子量的聚对二氧环己酮. 采用核磁共振谱对预聚物和扩链产物的结构进行了确认, 并详细考察了各种因素对扩链反应的影响. 研究结果表明, 加入适量的HDI, 于150 ℃反应60 min, 扩链效率在预聚物基础上可提高52倍, 而扩链产物的粘均分子量可达到25.7×104 g/mol.     

连续时间马氏链中的两个计数过程

木文考虑连续时间齐次Markov链在(O,t]期间状态转移次数和从状态集A到B的转移次数.为计算平均转移次数,我们得到了某些在随机模型中极其有用的简便公式并引进了无限位相型(Phase Type)分布.     

Markov Chains in a Field of Traps

We consider a Markov chain on a countable state space, on which is placed a random field of traps, and ask whether the chain gets trapped almost surely. We show that the quenched problem (when the traps are fixed) is equivalent to the annealed problem (when the traps are updated each unit of time) and give a criterion for almost sure trapping versus positive probability of nontrapping. The hypotheses on the Markov chain are minimal, and in particular, our results encompass the results of den Hollander, Menshikov and Volkov (1995).     

Narcissistic aggregation of steroid compounds in diluted solution elucidated by CSI-MS, PFG NMR and X-ray analysis

Large-scale aggregated chain structures of progesterone, estrone, cortisone, hydrocortisone and cholic acid were observed in diluted solution by means of cold-spray ionization mass spectrometry (CSI-MS) and pulsed field gradient (PFG) NMR. The crystal structures were determined by X-ray crystallography, and the relationship between the crystal and solution structures is discussed. It is suggested that the intermolecular hydrogen bondings observed in the crystal might be partly retained in diluted solution.