Photoinduced Reversible Solid-to-Liquid Transitions and Directional Photofluidization of Azobenzene-containing Polymers

Photoinduced reversible liquefaction and solidification of polymers enable processing and healing of polymers with light. Some azobenzene-containing polymers(azopolymers) exhibit two types of photoinduced liquefaction properties: photoinduced reversible solid-toliquid transition and directional photofluidization. For the first type, light switches the glass transition temperature(Tg) values of azopolymers and induces reversible solid-to-liquid transitions. For the second type, polarized light gu...     

Photochemical Hole Burning: A Spectroscopic Study of Relaxation Processes in Polymers and Glasses

Photochemical hole burning is a special type of saturation spectroscopy in the optical domain having many analogies with NMR methods. The holes, which are burnt with laser irradiation, appear as small indentations in the absorption spectra of dye molecules which are doped into a polymer or glass in minute concentrations. Based on their narrow line width, photochemical holes can be regarded as highly sensitive spectroscopic probes. They can be used to detect small perturbations of the system by external parameters, giving rise to line-shifts and broadenings. Besides the many well documented, spectroscopic applications of hole burning, it may offer interesting future developments for the spectroscopy of biomolecules and for high-density data storage.     

Polymers in medicine

The problems encountered in the use of artificial materials in the body are discussed, using as example the artificial heart. In the quest for suitable materials, numerous investigations have been carried out, including, inter alia, studies on the adsorption of proteins on polymer surfaces and on the passivation of such surfaces by coating with proteins or by the growth of cell cultures. The development of passive artificial substances is also discussed.     

液晶高分子材料的新功能:微管执行器及其光控微量液体运动

微量液体的精确操控在生物医药、液体传输等领域具有广泛的应用价值.目前,基于光诱导的毛细作用力操控液体的方法引起了人们极大的兴趣,因为这类方法在操控过程中无需特殊的光学装置和复杂的微组装过程.但是目前报道的方法只适用于少数特定的液体,并且驱动距离短、运动速度慢、局限于直线运动.最近,俞燕蕾等设计了一种新型结构的侧链液晶高分子材料,以此制备了液晶高分子微管执行器,可以通过不对称光致形变诱导毛细作用力,实现了光控各种类型液体按照设计的速度和方向运动,有望在可控微流体传输、微反应系统、微机械系统、芯片实验室等领域展现出巨大的应用价值.     

Polymers as Reagents in Organic Synthesis

Polymeric reagents offer a range of unique advantages. Intramolecular reactions, such as the cyclization of peptides or Dieckmann cyclizations, can be brought about by attaching the reactive molecules at remote points along a polymer chain. In contrast, if the reactive molecules are anchored in close proximity on a polymeric support then intermolecular reactions occur, as demonstrated for a ketone synthesis. Apart from such proximity effects, cooperative effects can also be exploited, e.g. in the formation of a 2:1 complex of a crown ether and an alkali metal ion. The hydrolysis of an ester with polyvinylimidazole provides a detailed illustration of hydrophobic interactions. The simple separation of polymer-bound and low-molecular compounds by filtration is another significant advantage.     

光致形变液晶高分子

交联液晶高分子兼具液晶的各向异性和高分子网络的弹性,并且具有优异的分子协同作用.在交联液晶高分子中引入光响应基团,例如偶氮苯后,即可赋予其光致形变性能,利用分子协同作用可以将光化学反应引起的分子结构变化放大为宏观形变,从而将光能直接转化成机械能.通过合理的分子结构和取向设计可以使液晶高分子产生诸如伸缩、弯曲、扭曲、振动等多种形式的光致形变,并用于各类光控柔性执行器件的构筑,在人工肌肉、微型机器人、微量液体操控等领域呈现出独特的优势和广阔的应用前景.本文总结和评述了光致形变液晶高分子的研究,包括材料结构对光致形变性能的影响、新型可加工光致形变材料的研究、利用可见光和近红外光触发形变的策略,以及光致形变液晶高分子微执行器在微量液体操控中的应用,最后展望了该领域的发展方向.     

In Situ Photoisomerization of an Azobenzene-Based Triple Helicate with a Prolonged Thermal Relaxation Time

The phosphate-coordination triple helicates A₂L₃ (A=anion) with azobenzene-spaced bis-bis(urea) ligands (L) have proven to undergo a rare in situ photoisomerization (without disassembly of the structure) rather than the typically known, stepwise “disassembly-isomerization-reassembly” process. This is enabled by the structural self-adaptability of the “aniono” assembly arising from multiple relatively weak and flexible hydrogen bonds between the phosphate anion and bis(urea) units. Notably, the Z→E thermal relaxation rate of the isomerized azobenzene unit is significantly decreased (up to 20-fold) for the triple helicates compared to the free ligands. Moreover, the binding of chiral guest cations inside the cavity of the Z-isomerized triple helicate can induce optically pure diastereomers, thus demonstrating a new strategy for making light-activated chiroptical materials.     

偶氮苯光致异构化对紫精-曙洪络合的调控

报导了α，ω－偶氮苯，紫精双发色团化合物的合成与性质研究，结果表明偶氮苯的光致顺反异构化以可调控与之相连的紫精与曙红络合行为，其作用程度的强弱与连接两者的亚甲基链的长度有关，借助ＨＮＭＲ通过对构象进行分析解释了上述的研究结果。     

Photodielectric Polymers for Holographic Use

The use of polymeric materials as “thick” recording media for holographic applications is discussed. These materials offer some interesting applications owing to their high diffraction efficiency, high storage density, excellent angular and spectral discrimination, as well as in situ real-time recording. The present state of art is outlined, as are prospects for the future.     

The Photoisomerization of cis-Stilbene Does Not Follow the Minimum Energy Path

Thermal activation is not required for barrier crossing reactions in the photoisomerization of cis-stilbene, as demonstrated by computer simulations. The activation is achieved by using the excess energy from the photoexcitation. Moreover, the reaction proceeds with large energy transfers but small conformational changes. The reaction pathway is influenced by these effects and also by the solvent.     

Liquid Crystalline Polymers

The liquid crystalline behavior of low molecular weight compounds has been known for more than a century; synthetic polymers have been manufactured on a large scale for several decades, but just recently it was found possible to produce polymers using the structural principles of liquid crystalline compounds. The resulting materials have, as expected, unusual properties. Numerous applications, not only in opto-electronics, are already anticipated for such materials.     

含偶氮苯主-客体复合物的光致异构化反应对结合能与几何构象的影响

在分子尺度上构建光驱动的人工分子机器是超分子化学研究的一个热点。偶氮苯是一类具有双稳态的光致开关分子,能够完成高效、可逆的反式(E)$\to $顺式(Z)的光致异构化过程,因而可以作为人工分子机器的功能单元。本文采用密度泛函理论(DFT)和反应分子动力学(RMD)模拟,研究了含偶氮苯封端基团的互锁型超分子体系中冠醚主体与二烷基铵客体间结合强度,模拟了偶氮苯Z$\to $E异构化反应的动态过程,讨论了异构化反应对主客体分子构象的影响。在偶氮苯封端基团通过发生Z$\to $E异构化实现体系单向可控运动时,较强的主-客体间结合能力是保证互锁型超分子体系稳定的必要前提。顺式客体与主体大环氢键相互作用比反式客体更强,因此顺式复合异构体具有比反式异构体更大的结合强度。偶氮苯基团发生E$\to $Z光致异构化引入位阻效应,使得顺式复合物只能从环戊基准封端处进行脱环。主客体复合过程对偶氮苯基团的几何结构没有明显影响。偶氮苯光致异构化发生的速度快于客体脱环的速度是实现单向运动的动力学上的必要条件。在异构化反应后的500 ps内,大环会经历一个明显的结构驰豫过程。冠醚大环主体的柔性构象有助于实现在偶氮苯光致异构化发生过程中主客体间持续稳定的结合。各种超分子体系中,尽管客体组成各不相同,但是包含相似的主客体识别位点的超分子体系具有相似的结合能,显示了机械互锁型复合体系中各种功能性构建单元间主客体相互作用具有正交性。引入双稳态的偶氮苯功能基团对客体其他部分的几何结构影响很小。理论计算结果有助于理性设计更复杂的刺激响应性人工分子机器。     

Mechanical Fabrication of Thermoplastic Polymers

One of the most important features influencing the mechanical behavior of a fabricated thermoplastic item is the spatial arrangement of the polymer molecules. Inter alia processes developed for controlling the pattern of orientation of the polymer molecules are discussed.     

聚合物薄膜交流电致发光器件

We have demonstrated an electroluminescent (EL) device having the structure of ITO/PPV/Alq3:PVK/Al. This device could be driven by either forward bias or backward bias, and its EL originated from PPV layer.     

8—羟基喹啉的高分子化及其应用展望

综述了８－羟基喹啉的各种高分子化方法,介绍了其在分析,环境,材料等领域中的应用情况,并展望了其在有机电致发光领域和导电聚合物等领域中的应用前景,提出了一些与之相关的值得深入研究的问题。     

Swelling-induced Mechanochromism in Multinetwork Polymers

We report a novel and versatile approach to achieving swelling-induced mechanochemistry using a multinetwork (MN) strategy that enables polymer networks to repeatedly swell with monomers and solvents. The isotropic expansion of the first network (FN) provides sufficient force to drive the mechanochemical scission of a radical-based mechanophore, difluorenylsuccinonitrile (DFSN). Although prompt recombination generally occurs in such highly mobile environments, the resulting pink radicals are kinetically stabilized in the gels, probably due to limited diffusion in the extended polymer chains. Moreover, the DFSN embedded in the isotropically strained chain exhibits increased thermal reactivity, which can be reasonably explained by an entropic contribution of the FN to the dissociation. The utility of the MN polymers is demonstrated not only in terms of swelling-force-induced network modification, but also in the context of tunable reactivity of the dissociative unit through proper design of the hierarchical network architecture.     

Perspectives in the Development of High-Temperature Polymers

Research on high-temperature organic polymers was initiated in the late 1950s primarily to meet the needs of the aerospace and electronics industry. Since then, many different heat-resistant polymer systems have been reported, of which several are now commercially available. These polymers are used in many diverse applications such as circuitry in microelectronic components, coatings on cookware, binders in brake systems, sealants for fuel tanks in high-speed aircraft, gears in copying machines, structural components in high-speed aircraft, and space vehicles, films and wire coatings for electrical insulation. Worldwide use for high-temperature polymers in 1988 was estimated at 90 million kilograms with a value of $ 2.3 billion. This market is expected to double by the end of this decade. The major polymer classes discussed in the present paper are polyimides and poly(aryl ethers).     

透明－白浊热可逆型高聚物及其应用前景

本文在简述了目前国内外各种透明－白浊热可逆型高分子材料的基础上，着重介绍新近提出的（甲基）丙烯酰胺类高聚物的热敏特性、合成方法、应用及发展前景。     

Scale-Hopping in Computer Simulations of Polymers

Polymer simulations can be performed at many different length scales by using techniques ranging from quantum chemistry to finite element via a hierarchy of coarser and coarser particle or field-based methods. Recent years have seen many efforts to connect simulations at different levels to 1) indirectly predict large-scale properties starting from fundamental models and 2) to accelerate the equilibration at more fundamental levels via the detour of coarse-grained levels. It is the purpose of the present synopsis to review some of the recent methodological advances concerning the systematic and, where available, automatic bridging between different levels of polymer simulation.     

医用可生物降解高分子材料

对目前医用可生物降解高分子材料的研究及应用状况分化学合成，天然和生物技术合成三类作了综述。对材料的生物相容性、可生物降解性及物理机械性能进行了分析和比较。并就医用生物降解高分子材料的发展趋势作了预测。