Polymer structure-property characterization

The following discussion on polymers is not intended to be a comprehensive introduction but provides only basic information on the subject. Many important aspects of polymer structure, properties and characterization have been left out. Aspects discussed here are primarily those likely to assist the reader in understanding the content in subsequent chapters. The reader is, however, directed to excellent monographs on polymer science for more detailed and complete information (Coleman and Painter, 1998 Rudin and Choi, 2012 Young and Lovell, 2011). 

Electrochemical Polymer Electrolyte Membranes covers PEMs from fundamentals to applications, describing their structure, properties, characterization, synthesis, and use in electrochemical energy storage and solar energy conversion technologies. Featuring chapters authored by leading experts from academia and industry, this authoritative text ... 

Secondly, new techniques have been developed which allow a more detailed characterization of both polymer microstructures and the kinetics and mechanism of polymerizations. This has allowed mechanism-structure-property relationships to be more rigorously established. 

Besides synthesis, current basic research on conducting polymers is concentrated on structural analysis. Structural parameters — e.g. regularity and homogeneity of chain structures, but also chain length — play an important role in our understanding of the properties of such materials. Research on electropolymerized polymers has concentrated on polypyrrole and polythiophene in particular and, more recently, on polyaniline as well, while of the chemically produced materials polyacetylene stih attracts greatest interest. Spectroscopic methods have proved particularly suitable for characterizing structural properties These comprise surface techniques such as XPS, AES or ATR, on the one hand, and the usual methods of structural analysis, such as NMR, ESR and X-ray diffraction techniques, on the other hand. 

In this chapter we discussed the three basic types of solid state structure that we find in polymers and how they form from the molten state. We went on to describe the techniques that polymer scientists use to characterize polymer structures at scales ranging from less than one nanometer (1 X 10"9 m) up to a few millimeters (> 1 x 1CT3 m). The wide range of structures that we can generate from polymers contributes to their wide range of properties and corresponding breadth of finished items that we can create. 

Recent developments in polymer chemistry have allowed for the synthesis of a remarkable range of well-defined block copolymers with a high degree of molecular, compositional, and structural homogeneity. These developments are mainly due to the improvement of known polymerization techniques and their combination. Parallel advancements in characterization methods have been critical for the identification of optimum conditions for the synthesis of such materials. The availability of these well-defined block copolymers will facilitate studies in many fields of polymer physics and will provide the opportunity to better explore structure-property relationships which are of fundamental importance for hi-tech applications, such as high temperature separation membranes, drug delivery systems, photonics, multifunctional sensors, nanoreactors, nanopatterning, memory devices etc. 

Z. Chen, N.H.S. Lee, W. Huang, Y. Xu, and Y. Cao, New phenyl-substituted PPY derivatives for polymer light-emitting diodes — synthesis, characterization and structure-property relationship study, Macromolecules, 36 1009-1020, 2003. 

Finally, for practical reasons it is useful to classify polymeric materials according to where and how they are employed. A common subdivision is that into structural polymers and functional polymers. Structural polymers are characterized by - and are used because of - their good mechanical, thermal, and chemical properties. Hence, they are primarily used as construction materials in addition to or in place of metals, ceramics, or wood in applications like plastics, fibers, films, elastomers, foams, paints, and adhesives. Functional polymers, in contrast, have completely different property profiles, for example, special electrical, optical, or biological properties. They can assume specific chemical or physical functions in devices for microelectronic, biomedical applications, analytics, synthesis, cosmetics, or hygiene. 

W. Radke, Chromatography of polymers, in Macromolecular Engineering Structure-Property Correlation and Characterization Techniques, vol. 3, K. Matyjaszewski, Y. Gnanou, L. Leibler, eds., Wiley-VCH, Berlin, Germany, 2007 A.M. Striegel, J.J. Kirkland, W.W. Yau, D.D. Bly, Modem Size-Exclusion Liquid Chromatography, Wiley, Hoboken, New Jersey, 2009. 

In this section, we describe the mechanical properties of a class of materials that continues to grow in terms of use in structural applications. As issues related to energy consumption and global warming continue to increase demands for lightweight, recyclable materials, the development of new polymers and the characterization of recycled polymers will continue to dominate research and development efforts in this area. 

The need for well defined polymer species of low polydls-perelty and of known structure arises from the Increasing Interest In structure-properties relationship In dilute solution as well as In the bulk. A great variety of methods have been attempted, to synthesize so-called model macromolecules or tailor made polymers-over the past 20 years. The techniques based on anionic polymerization, when carried out In aprotic solvents, have proved best suited for such synthesis, because of the absence of spontaneous transfer and termination reactions that characterize such systems. The "living 1 polymers obtained are fitted at chain end with carbanionic sites, which can either Initiate further polymerization, or react with various electrophilic compounds, intentionally added to achieve functionalizations. Another advantage of anionic polymerizations is that di-functlonal Initiators are available, yielding linear polymers fitted at both chain ends with carbanionic sites. In this paper we shall review the various utility of anionic polymerization to the synthesis of tailor made well defined macromolecules of various types. 

The dynamic mechanical thermal analyzer (DMTA) is an important tool for studying the structure-property relationships in polymer nanocomposites. DMTA essentially probes the relaxations in polymers, thereby providing a method to understand the mechanical behavior and the molecular structure of these materials under various conditions of stress and temperature. The dynamics of polymer chain relaxation or molecular mobility of polymer main chains and side chains is one of the factors that determine the viscoelastic properties of polymeric macromolecules. The temperature dependence of molecular mobility is characterized by different transitions in which a certain mode of chain motion occurs. A reduction of the tan 8 peak height, a shift of the peak position to higher temperatures, an extra hump or peak in the tan 8 curve above the glass transition temperature (Tg), and a relatively high value of the storage modulus often are reported in support of the dispersion process of the layered silicate. 

Only a few non-linear viscoelastic properties have been studied with polymers of well-characterized structure. The most prominent of these is the shear-rate dependence of viscosity. Considerable data have now been accumulated for several polymers, extending over a wide range of molecular weights and concen-... 

Due to these different primary structures of the main chain, important modifications and a broad variety of systems is realizable. While linear polymers can be essentially characterized by the number of the monomer units, for branched and crosslinked systems e.g. the way of branching and their quantity is of significance for the polymer specific properties. In cases of crosslinked systems the molecular dimension is the macroscopic dimension of the sample. 

The fragments of macromolecules with ordered cholesterol group sequences, that are formed in bad solvents, may serve as nuclei of supermolecular order in films, obtained from these solvents. Structural and optical studies have shown that PChMA-11 films produced by solvent evaporation display different properties those obtained from chloroform and toluene solutions (small relaxation times, see Table 17) are optically isotropic, and those obtained from heptane solutions (large relaxation times, see Table 17) are optically anisotropic, what reflects the differences in conformational state of polymeric chains in these films. Contrary to the optically isotropic films, a high degree of side branch ordering characterizes optically anisotropic films, which is confirmed by X-ray studies. The observed difference of LC polymer structure in the bulk is thus the consequence of their different conformational state in solution this reveals some possibilities for the control of LC polymer structure at the initial steps of mesophase nucleation in solutions. 

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