Relationships between structure and properties

This chapter sets the stage for all of the others by reminding us that the relationship between structure and properties is what chemistry is all about It begins with a review of Lewis structures moves to a discussion of the Arrhenius Brpnsted-Lowry and Lewis pictures of acids and bases and the effects of structure on acidity and basicity... 

The relationship between structure and properties of polyethylene is largely in accord with the principles enunciated in Chapters 4, 5 and 6. The polymer is essentially a long chain aliphatic hydrocarbon of the type... 

The relationships between structures and properties are well documented, and tlte different approaches to get processable polyimides have been discussed in Section 5.2.2. 

There are difficulties in analysing conductive polymers, and information on the relationship between structure and properties somewhat difficult to obtain. These materials have already found a variety of uses, including flat panel displays, antistatic packaging and rechargeable batteries, and other applications are likely to emerge in the future. 

Computers have greatly enhanced the speed and accuracy of the predictive nature of QSAR, however they are only tools to aid investigation and elucidation of the relationship between structure and properties. A clear understanding of the system and the fundamental questions that need to be answered are still a requirement for future research. 

The relationships between structures and properties can be classified as intrinsic and extrinsic owing to the molecular arrangement and morphology, respectively. The term intrinsic refers to the 3D packing of molecules, which depends on the geometry and chemical nature of the molecules, and thus on intermolecular interactions. Extrinsic structure-property relationships are related to the formation of interfaces, e.g., grain boundaries, and the presence of defects. In both cases the role of external variables such as T, P, B as well as of internal variables such as the type of guest molecules is essential. 

Polytetrafluoroethylene (PTFE) is an attractive model substance for understanding the relationships between structure and properties among crystalline polymers. The crystallinity of PTFE (based on X-ray data) can be controlled by solidification and heat treatments. The crystals are large and one is relieved of the complexity of a spherulitic superstructure because, with rare exceptions, spherulites are absent from PTFE. What is present are lamellar crystals (XL) and a noncrystalline phase (NXL) both of which have important effects on mechanical behavior. 

Another frequently used method to derive empirical relationships between structure and property is to divide the structure into chemically logic parts such as groups of atoms (functional groups) and to assign each group a contribution to the property of the whole molecule. This approach is termed the group contribution model (GCM). Since groups cannot be measured individually, it is necessary to derive... 

These examples illustrate how to obtain results about crystallinity and disorder for a better understanding of the relationships between structure and properties. The reader is, however, cautioned that crystallinity and disorder parameters determined by x-ray diffractometry are average values and that they should be carefully compared with local order measured by electron diffraction on ultra-thin cross sections of textile fibers (9) with differing crystallite sizes (10,11). 

With the advent of advanced characterization techniques such as multiple detector liquid exclusion chromatography and - C Fourier transform nuclear magnetic resonance spectroscopy, the study of structure/property relationships in polymers has become technically feasible (l -(5). Understanding the relationship between structure and properties alone does not always allow for the solution of problems encountered in commercial polymer synthesis. Certain processes, of which emulsion polymerization is one, are controlled by variables which exert a large influence on polymer infrastructure (sequence distribution, tacticity, branching, enchainment) and hence properties. In addition, because the emulsion polymerization takes place in an heterophase system and because the product is an aqueous dispersion, it is important to understand which performance characteristics are influended by the colloidal state, (i.e., particle size and size distribution) and which by the polymer infrastructure. 

In fact, a lot remains to be done for getting a clear knowledge of the relationships between structure and properties of sugar-grafted polysiloxanes. Both the set up of easier syntheses and a better knowledge of their properties would help their development. 

Figure 12.9 Relationship between structure and properties of HIPS [8]...

The solution of the basic problem of the science of construction materials, namely the establishment of the relationship between structure and properties acquires special complexity for gas-filled polymers. Six levels of structural organization can be distinguished in these materials ... 

Fig. 4 Relationship between structure and properties of hydrogels. The selection of monomers and cross-linking agent determines hydrogel properties. On the other hand, a hydrogel with specific properties must be synthesized using specific monomers and cross-linking agent.

Quantitative relationship of chemical structure to physical properties in network polymers has received considerably less attention and study than in the case of thermoplastics. However, in recent years, progress has been made towards elucidation of the quantitative relationships between structure and properties. We have chosen to illustrate the quantitative effect of structural factors on physical properties in four representative areas glass transition temperature, modulus of elasticity, mechanical damping, solvent resistance. 

Silicon exhibits a diverse range of electrochemical phenomena, such as current oscillation, anisotropic etching, formation of porous silicon, etc. Each of these phenomena has extremely rich details that are governed by complex relationships between structures and properties of silicon electrodes on the one hand and between properties and experimental conditions on the other. The silicon/electrolyte interface is a complex system in which a great many variables are interacting with each other in a great many ways." ... 

Styrene-butadiene rubber could be produced by using emulsion and solution process, thus it can be divided into emulsion-polymerized styrene-butadiene rubber (E-SBR) and solution-polymerized styrene-butadiene rubber (S-SBR). In this entry, we will describe their development and introduce their synthesis process, relationship between structure and property, processing property, blends, and applications. 

Basic science in the general field of macromolecules includes the principles of their synthesis the investigation of the size and structure of individual molecules in solution, and the relationship between structure and properties in the bulk phase. Approximately 450 scientists in 90 laboratories all over the world devote the major portion of their time to basic science in the subject field. The results of their work are published in about 150 technical journals which include literature on plastics. Reviewing the literature at present is difficult. The author suggests services which include a weekly news letter, monthly journal for papers, semiannual journal for review articles, and formula and data sheets in addition to regularly appearing monographs, textbooks, and handbooks. 

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