Properties of Polymers (eBook)

D.W. van Krevelen (Autor)

eBook Download: PDF | EPUB

2012 | 3. Auflage
898 Seiten
Elsevier Science (Verlag)
978-0-444-59612-3 (ISBN)

Infos

Properties of Polymers: Their Correlation with Chemical Structure; Their Numerical Estimation and Prediction from Additive Group Contributions summarizes the latest developments regarding polymers, their properties in relation to chemical structure, and methods for estimating and predicting numerical properties from chemical structure. In particular, it examines polymer electrical properties, magnetic properties, and mechanical properties, as well as their crystallization and environmental behavior and failure. The rheological properties of polymer melts and polymer solutions are also considered. Organized into seven parts encompassing 27 chapters, this book begins with an overview of polymer science and engineering, including the typology of polymers and their properties. It then turns to a discussion of thermophysical properties, from transition temperatures to volumetric and calorimetric properties, along with the cohesive aspects and conformation statistics. It also introduces the reader to the behavior of polymers in electromagnetic and mechanical fields of force. The book covers the quantities that influence the transport of heat, momentum, and matter, particularly heat conductivity, viscosity, and diffusivity; properties that control the chemical stability and breakdown of polymers; and polymer properties as an integral concept, with emphasis on processing and product properties. Readers will find tables that give valuable (numerical) data on polymers and include a survey of the group contributions (increments) of almost every additive function considered. This book is a valuable resource for anyone working on practical problems in the field of polymers, including organic chemists, chemical engineers, polymer processers, polymer technologists, and both graduate and PhD students.

Textauszug

CHAPTER 1

POLYMER PROPERTIES

Publisher Summary

The design of manufacturing and processing equipment of polymeric substances requires a considerable knowledge of the processed materials and related compounds. The continuous development of the modern process industries has made it increasingly important to have information about the properties of materials, including many new chemical substances whose physical properties have never been measured experimentally. There are thousands of chemical compounds of interest in science and practice; however, the number of structural and functional groups that constitute all these compounds is very much smaller. The assumption that a physical property of a compound, e.g., a polymer, is in some way determined by a sum of contributions made by the structural and functional groups in the molecule or in the repeating unit of the polymer forms the basis of a method for estimating and correlating the properties of a very large number of compounds or polymers.

APPROACH AND OBJECTIVE

The continuous development of the modern process industries has made it increasingly important to have information about the properties of materials, including many new chemical substances whose physical properties have never been measured experimentally. This is especially true of polymeric substances. The design of manufacturing and processing equipment requires considerable knowledge of the processed materials and related compounds. Also for the application and final use of these materials this knowledge is essential.

In some handbooks, for instance the “Polymer Handbook” (Brandrup and Immergut, 1966, 1975, 1989), “Physical Constants of Linear Homopolymers” (Lewis, 1968), the “International Plastics Handbook for the Technologist, Engineer and User” (Saechtling, 1988), and similar compilations, one finds part of the data required, but in many cases the property needed cannot be obtained from such sources.

The aim of the present book is twofold:

1. to correlate the properties of known polymers with their chemical structure, in other words: to establish structure-properties relationships.

2. to provide methods for the estimation and/or prediction of the more important properties of polymers, in the solid, liquid and dissolved states, in cases where experimental values are not to be found.

Thus, this book is concerned with predictions. These are usually based on correlations of known information, with interpolation or extrapolation, as required. Reid and Sherwood (1958) distinguished correlations of three different types:

– Purely empirical; on extrapolation these correlations are often unreliable, or even dangerous to use.

– Purely theoretical; these are seldom adequately developed or directly usable.

– Partly empirical, but based on theoretical models or concepts; these “semi-empirical” correlations are the most useful and reliable for practical purposes.

Among scientists there is often a tendency to look down upon semi-empirical approaches for the estimation of properties. This is completely unjustified. There are almost no purely theoretical expressions for the properties in which practice is interested.

One of the great triumphs of theoretical physics is the modern kinetic theory of gases. On the basis of an interaction-potential function, e.g. the Lennard-Jones force function, it is possible to develop theoretical expressions for all the important properties of gases, such as the p-v-T relationships, viscosity, molecular diffusivity, thermal conductivity and thermal-diffusion coefficient. The predicted variations of these properties with temperature are in excellent agreement with experimental data. But it should be realized that this extremely successful theoretical development has a purely empirical basis, viz. the force function. Except for the most simple cases, there is no sufficiently developed theory for a quantitative description of the forces between molecules. Whereas the theory of gases is relatively advanced, that of solids is less well understood, and the theory of liquids is still less developed.

In the relatively new field of macromolecular matter the semi-empirical approach is mostly necessary and sometimes even the only possible way.

Fundamental theory is generally too remote from the phenomena which have to be described. What is needed in practice is a formulation which is designed to deal directly with the phenomena and makes use of the language of observation. This is a pragmatic approach that is designed specifically for use; it is a completely non-speculative procedure.

In the low-molecular field Reid, Prausnitz and Sherwood (1977) have performed this task in a most admirable way, as far as gases and liquids are concerned. For molecular crystals and glasses Bondi (1968) gave a similar contribution which partly covers the polymeric field, too.

In the macromolecular field the amount of literature is already extremely large. Nevertheless the researcher is often confronted with the problem that neither directly measured properties, nor reliable methods to calculate them, can be found. This is the justification of the present book. The value of estimation and correlation methods largely depends, however, on their simplicity. Complicated methods have to be rejected. This has been one of our guiding principles.

The simplest and yet very successful method is based on the concept of additive group contributions.

The underlying idea in this concept is the following: There are thousands of chemical compounds of interest in science and practice; however, the number of structural and functional groups which constitute all these compounds is very much smaller. The assumption that a physical property of a compound, e.g. a polymer, is in some way determined by a sum of contributions made by the structural and functional groups in the molecule or in the repeating unit of the polymer, forms the basis of a method for estimating and correlating the properties of a very large number of compounds or polymers, in terms of a much smaller number of parameters which characterize the contributions of individual groups. These group contributions are often called increments.

Such a group contribution-, or increment-method is necessarily an approximation, since the contribution of a given group in one surroundings is not necessarily the same as that in another environment.

The fundamental assumption of the group-contribution technique is additivity. This assumption, however, is valid only when the influence of any one group in a molecule or in a structural unit of a polymer is not affected by the nature of the other groups. If there is mutual interaction, it is sometimes possible to find general rules for corrections to be made in such a case of interaction (e.g. conjugation of double bonds or aromatic rings). Every correction or distinction in the contribution of a group, however, means an increase in the number of parameters. As more and more distinctions are made, finely the ultimate group will be recovered, namely the molecule or the structural unit of the polymer itself. Then the advantage of the group-contribution method is completely lost.

So the number of distinct groups must remain reasonably small, but not so small as to neglect significant effects of molecular structure on physical properties. For practical utility always a compromise must be attained; it is this compromise that determines the potential accuracy of the method.

It is obvious that reliable experimental data are always to be preferred to values obtained by an estimation method. In this respect all the methods proposed in this book have a restricted value.

The first edition of the present book appeared 18 years ago. The approach then proposed found a growing number of applications.

That the approach is useful has been demonstrated in a variety of ways in the literature, including a Russian translation of the book and a book by Askadskii and Matvyeyev (1983, in Russian) which is also devoted to the group contribution method and its application in polymer science and engineering.

BIBLIOGRAPHY, CHAPTER 1

Askadskii, A.A., Matvyeyev, Yu. I.“Khimicheskoye stroyeniye i fizicheskiye svoislva polimerov” (Chemical structure and physical properties of polymers). Moskva: Nauka, 1983.

Bondi, A.“Physical Properties of Molecular Crystals, Liquids and Glasses”. New York: Wiley, 1968.

Brandrup J., Immergut E.H., eds. “Polymer Handbook”, 1st ed., New York: Wiley-Interscience, 1966. [2nd ed., 1975; 3rd ed., 1989].

Lewis, O. Griffin“Physical Constants of Linear Homopolymers”. Berlin, New York: Springer, 1968.

Reid, R.C., Sherwood, Th.K. “The Properties of Gases and Liquids”, 1st ed. New York: McGraw-Hill, 1958. [2nd ed., 1966].

Reid, R.C., Prausnitz, J.M., Sherwood, Th.K. “The Properties of Gases and Liquids”, 3rd Ed. New York: McGraw-Hill, 1977.

Saechtling,...

Produkt-Details

• Erscheint lt. Verlag: 2.12.2012
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Chemie ► Technische Chemie
• Themenwelt: Technik ► Maschinenbau
• Themenwelt: Wirtschaft ► Volkswirtschaftslehre ► Mikroökonomie
• ISBN-10: 0-444-59612-7 / 0444596127
• ISBN-13: 978-0-444-59612-3 / 9780444596123