Quantitative Structure/Property Subject

These models require accurate data on physico-chemical properties of organic substances, which is the subject of Dr. Mackay s other interest, namely their measurement and correlation. This includes the compilation and critical review of these properties and their quantitative structure property relationships. He is co-author of the five-volume Illustrated Handbook of Physical Chemical Properties and Environmental Fate of Organic Chemicals, which documents data reported in the literature, and is also available in CD-ROM format from CRC Press. Dr. Mackay s hope is that a combination of the information reported in these handbooks, and the estimated data as described in the present volume, can provide a sound basis for assessment of the large and growing number of chemical substances of environmental concern. 

The structure of a chemical is responsible for the presence and magnitude of its properties. The properties can be energy levels and their derivatives, as well as physicochemical, or biological, properties. To avoid discrimination between the different properties (which are the subject of detailed consideration in Chapters 3, 4, and 6) in the context of quantitative relationships between structural descriptors (i.e., topological indices [TIs]) and various properties, we will use the broader abbreviation QSPR (Quantitative Structure-Property Relationship). 

The second appendix, by Dr. Donald B. Boyd, is an updated compendium of software for molecular modeling, computational chemistry, de novo molecular design, quantitative structure-property relationships, synthesis planning, and other facets of computers helping molecular science. This is one of the most current and most complete compilations anywhere. Appendix 2 provides addresses, telephone numbers, and electronic mailing addresses of suppliers of software. Combined with the subject index of this volume, it is possible to... 

The search for quantitative structure-property relationships for the control and prediction of the mechanical behaviour of polymers has occupied a central role in the development of polymer science and engineering. Mechanical performance factors such as creep resistance, fatigue life, toughness and the stability of properties with time, stress and temperature have become subjects of major activity. Within this context microhardness emerges as a property which is sensitive to structural changes. 

The main contribution to the ability to predict the mechanical properties of polymers, by the work presented in this book, is then the new set of quantitative structure-property relationships, not subject to the limitations traditionally imposed by the need for group contributions, for the many input parameters entering the correlations developed for the mechanical properties. This development has allowed the prediction of the mechanical properties of many novel polymers whose mechanical properties could not be estimated previously. 

There are a number of considerations that must be addressed when formulating quantitative 13c NMR procedures - these include solvent effects, spectral overlap, line widths, dynamic and nuclear Overhauser effects and detailed assignments. The steps required to develop sound quantitative methods will be the subject of this chapter. It is imperative that excellent quantitative methods be established so that NMR can be utilized in studies of polymer structure-property relationships. Polymer molecular structure needs to be related to the incipient solid state structure and ultimately to observed solid state physical properties such as density, flexural moduli, environmental stress cracking behavior, to name a few. 

When we progress from the foregoing qualitative discussion of structure-property relationships to the quantitative specification of mechanical properties, we enter a jungle that has been only partially explored. The most convenient point of departure into this large and complex subject is provided by the topic of "linear viscoelasticity." Linear viscoelasticity represents a relatively simple extension of classical (small-strain) theory of elasticity. In situations where linear viscoelasticity applies, the mechanical properties can be determined from a few experiments and can be specified in any of several equivalent formulations (11). 

In this review recent theoretical developments which enable quantitative measures of molecular orientation in polymers to be obtained from infra-red and Raman spectroscopy and nuclear magnetic resonance have been discussed in some detail. Although this is clearly a subject of some complexity, it has been possible to show that the systematic application of these techniques to polyethylene terephthalate and polytetramethylene terephthalate can provide unique information of considerable value. This information can be used on the one hand to gain an understanding of the mechanisms of deformation, and on the other to provide a structural understanding of physical properties, especially mechanical properties. 

Exponents of molecular-orbital theory treat the subject in two fairly well defined ways. One is to apply the theory in a qualitative or even semi-quantitative manner to aid understanding of chemical processes and the other is concerned more with ab initio calculations of molecular properties. Present ill-defined knowledge of ion structures and reaction mechanisms suggest that the latter approach is unlikely to be rewarding. 

There is a series of materials with very interesting properties showing large qualitative and quantitative changes in their electronic structure arising from small composition, temperature or pressure changes. Among them the rare earth and actinide mixed valence compounds are currently the subject of extense experimental and theoretical studies (2 ). Boppart and... 

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