Synthesis,characterization and recent developments of liquid crystalline polymers

Recent developments of polymer liquid crystals (PLCs) are reviewed. The virial expansion method of Onsager and the lattice model used by Flory to appreciate the most relevant parameters in establishing mesomorphic behavior in polymeric systems are presented. These and other theoretical predictions are confirmed by numerous experiments. Both lyotropic (polymer solutions) and thermotropic (polymer melts) types of PLCs are considered with emphasis placed on the latter. The general properties of mesophases formed by such polymers are surveyed and some chemical structures capable of producing mesophases are classified in relation to their ability to form lyotropic and thermotropic systems. The synthetic routes, the effects of polymer structure on physical properties, and applications of two major classes of lyotropic systems (polypeptides, polyamides) and of a range of potentially important thermotropic polymers are discussed.     

Some recent developments in pressure tuning spectroscopy

Pressure tuning spectroscopy has proved to be a powerful tool for studying a wide variety of electronic phenomena. In this review we present two recent examples of the application of high pressure luminescence: (1) a test of the validity of a kinetic model for the emission characteristics of molecules that emit from excited states with different degrees of charge transfer and different geometries (molecules with twisted intramolecular charge transfer (TICT)); (2) an elucidation of the mechanism for the large difference observed between the luminescence efficiencies of [Ru(bpy)₃]²⁺ and [Ru(bpy)₂(py)₂]²⁺ in solid media.In 1994, Prof. H. G. Drickamer was awarded theHonoris causa degree by the Russian Academy of Sciences.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1195–1202, July, 1995.     

Some recent developments in the historiography of alchemy

The number of researchers and publications devoted to the history of alchemy has seen exponential growth and diversification in recent decades, to such an extent that some scholars speak of a "New Historiography of Alchemy". On the occasion of the seventy-fifth anniversary of the Society for the History of Alchemy and Chemistry, this paper outlines some highlights of the literature since 1990, with a view to identify current trends but also challenges for the future. Some of the most important changes identified are a marked awareness of the risks of presentism, a shift from ambitious histories to contextualised microhistories, a heightened recognition of the internal diversity of historical alchemy, and a greater emphasis on its practical dimensions and its role in the Scientific Revolution. Among the challenges, the paper underscores the potential risks of an excessive historiographical fragmentation, the need for further interdisciplinary training and cooperation, and the responsibilities of alchemy historians towards students and the general public alike.     

Some recent developments on cost-effective flow-based analysis

This paper reviews some recent developments on cost-effective flow-based analysis. They include the newly developed Lab-at-Valve (LAV), concepts in using the stopped-flow injection approach, on-line sample pretreatment systems, including bead injection–flow injection and flow injection–ion-chromatography, systems for size-based speciation, and cost-effective reagents. Applications and advantages of such techniques are discussed.     

An overview on the recent developments in reactive plasticizers in polymers

This review is about the reactive plasticizer. Plasticizers are small molecules with low molecular weight. These compounds typically have an esteric structure. The plasticizers reduce the glass transition temperature, and the viscosity of the polymer also enhances the flexibility and processability of polymer materials. The main problem of these additives is that, over time, they migrate from the polymeric matrix and exude to the surface of polymeric matrix. As a result, the physical and mechanical properties of the polymer are affected. Various strategies, such as increasing molecular weight of plasticizer, selection of oligomeric structure for plasticizer, and adding nanoparticles of minerals, have been investigated to reduce and eliminate migration. An approach that has recently been of great interest to researchers is the use of reactive plasticizers. In this approach, plasticizers covalently bond to the polymeric chains and prevent migration.     

Some recent developments in the chemical synthesis of inorganic nanotubes

Inorganic nanotubes have been a subject of intensive research in the past decade. We recently developed a number of synthetic strategies for generating nanotubes from inorganic materials that do not have a layered structure. It is the intention of this contribution to provide a brief account of these research activities.     

Molecularly imprinted polymers in capillary electrochromatography: recent developments and future trends

The developments in molecularly imprinted polymer (MIP)-based capillary electrochromatography (CEC) achieved during the past years are reviewed in this article. The MIP is prepared using a templated polymerization reaction and results in a material with a high selectivity towards a predetermined target. The selectivity of the MIP is comparable to that of the biological antibodies, however, the MIP is much more stable and is thus able to withstand extremely harsh conditions in terms of pH, temperature, and organic solvents. The high selectivity and stability of the MIP made it an interesting candidate for application as stationary phase sorbent in chromatography. However, due to slow kinetics the efficiency of the early MIP columns, which were predominantly applied in high-performance liquid chromatography (HPLC), were limited. The use of CEC was thought to improve the efficiency of the MIP-based separation system. The small dimensions of the capillary format employed in CEC have put demands on the polymer systems which have resulted in the development of many different polymer formats. Thus, this need for novel MIP formats for applications in CEC has contributed a lot to the general development of MIP formats as well as to the knowledge in MIP synthesis and characteristics.     

Some recent developments in reference methodology within the United Kingdom

 The UK Valid Analytical Measurement Programme has pump-primed developments in chemical metrology, through a major project on reference methodology and reference materials. This paper provides an overview of developments during 1994–1997 and covers work on primary methods for trace inorganic and trace organic analysis, including the use of isotope dilution mass spectrometry; studies of sample pre-treatment, including digestion, extraction, and separation aimed at improving this weak link in the traceability chain; prioritisation, production and marketing of both pure substance and matrix reference materials; and international collaboration concerned with interlaboratory comparisons and the development of concepts, terminology and systems to underpin the international chemical measurement system. References are given to a number of papers covering specific parts of the programme. Received: 5 August 1998 · Accepted: 12 September 1998     

Monte Carlo simulation in polymer physics: Some recent developments

The computer simulation of macromolecular materials has to deal with phenomena on length scales from 1Å to 100Å, as well as with time scales ranging over many orders of magnitude, and thus still presents a challenge. With suitably coarse-grained models which disregard detailed information on chemical structure nevertheless collective phenomena can be described, such as unmixing of polymer blends, mesophase ordering of block-copolymer melts, “blob formation” in semidilute solutions, etc. Simulations of such models provide a sensitive test of approximate theories and give valuable hints for experiments.     

Some recent developments in the surface-analytical application of X-ray fluorescence spectrometry

Summary Standard depth profiles of an analyte deposited into (diffusion or ion implantation) or on (thin-film deposition) a plane surface can be analyzed for profile type and centroid depth or film thickness by means of a standardless method in which the matrix-attenuated signals of the fiuorescing analyte measured at two different take-off angles are related to the mathematical distribution moments of the profile. For a binary thin film the element ratio can also be established. Results obtained on phosphorus profiles in silicon and on zinc sulphide optical coatings are referred to.The quantity or concentration level can be determined by use of a reference standard which may contain the analyte in an entirely different distribution. This simplifies the calibration of secondary reference standards.A good lateral resolution in the sub-millimeter range can be achieved with synchrotron radiation. A further improvement of lateral resolution is possible by direct excitation with electron microbeams, though at significantly inferior detection limits.

---

Neuere Entwicklungen bei der oberflächen-analytischen Anwendung der Röntgenfluorescenz-Spektrometrie

     

New functional polymers for liquid crystal displays review of some recent developments

Polymeric materials play an important role in the construction and performance of liquid crystal displays. New functional polymers are developed to improve the displays on brightness, power efficiency and viewing angle performance. Polymer films with a controlled molecular structure and architecture provide new polarization optics to convert non‐polarized light into polarized light with higher efficiency than the traditional polarizers based on stretched iodine doped poly(vinyl alcohol). Other films provide a polarization compensation function to maintain an angular invariant net optical retardation of the display device and therewith a better contrast to wider viewing angles. Color generation by non‐absorbing methods is believed to improve on the display brightness. Special control of the liquid crystal alignment by photo‐sensitive orientation layers, polymer protrusions or photo‐formed polymer walls provide multiple director patterns within a single pixel to average out angular LC effects.     

Sugar amino acids and related molecules: Some recent developments

To meet the growing demands for the development of new molecular entities for discovering new drugs and materials, organic chemists have started working on many new concepts that can help to assimilate knowledge-based structural diversities more efficiently than ever before. Emulating the basic principles followed by Nature to build its vast repertoire of biomolecules, organic chemists are developing many novel multifunctional building blocks and using them to create ‘nature-like’ and yet unnatural organic molecules. Sugar amino acids constitute an important class of such polyfunctional scaffolds where the carboxyl, amino and hydroxyl termini provide an excellent opportunity to organic chemists to create structural diversities akin to Nature’s molecular arsenal. In recent years, sugar amino acids have been used extensively in the area of peptidomimetic studies. Advances made in the area of combinatorial chemistry can provide the necessary technological support for rapid compilations of sugar amino acidbased libraries exploiting the diversities of their carbohydrate frameworks and well-developed solid-phase peptide synthesis methods. This perspective article chronicles some of the recent applications of various sugar amino acids, furan amino acids, pyrrole amino acids etc. and many other related building blocks in wide-ranging peptidomimetic studies     

Some recent developments in the field of catalysis by metals at the IFP

This paper presents some of IFP's results in the field of catalysis by metals. Selective hydrogenation of unsatured C₄ hydrocarbons and hydrogenation or dehydrogenation of different C₄ oxygenated molecules are presented. New preparations and the help of new characterization technics have allowed the development of new industrial catalysts.     

Liquid crystalline polymers

The suitabilities of thermo-optometry and differential scanning calorimetry for the characterization of certain copolyethers were compared. Under certain conditions, such polymers do not exhibit the endotherm signal corresponding to the solid/liquid crystalline transition in the DSC curves. Thermo-optometry provides evidence of these phase transitions into the liquid crystalline state, and is a very useful additional method.     

New developments in photochromic polymers

New developments on photochromic polymers have been obtained with systems containing spirobenzopyran derivatives. The importance of the chemical incorporation of the photochrome within the polymer backbone is stressed, and the influence of matrix orientation on the rate of fading is shown. Well known fatigue phenomena are illustrated on the basis of the changes of photostationary optical density on repeating the irradiation–dark recovery cycle. The photomechanical properties and characteristics of rubbery polyethylacrylates crosslinked with the photochrome bismethacrylate are considered in detail. Another principle of photochromism based on photodissociation phenomena is also discussed in the case of the photodissociation and photorecombination of anthracene derivatives and benzacridizinium tosylate, as well as in the case of the photodissociation and thermal recombination of benzpinacol groups incorporated in the polymer main chain. In these experiments in the solid state, it can be shown that the recombination involves always two successive steps: a rapid step corresponding to cage recombination and a second slow step related to diffusion and segment mobility (T_g) of the polymer.