Organic Polymer Chemistry: An Introduction to the Organic Chemistry of Adhesives, Fibres, Paints, Plastics, and Rubbers

479 Pages·1973·10.21 MB·English

Organic Polymer Chemistry
Organic
Polymer Chemistry
An Introduction to the Organic Chemistry of
Adhesives, Fibres, Paints, Plastics, and Rubbers
K.J.SAUNDERS
Department of Chemical and Metallurgical Technology
Ryerson Polytechnical Institute, Toronto
Springer-Science+ Business Media, B.V.
© 1973 Springer Science+Business Media Dordrecht
Origina11y published by Chapman and Han Ltd in 1973
Softcover reprint of the hardcover 1s t edition 1973
Set by
Santype Limited (Coldtype Division)
Salisbury, Wiltshire
ISBN 978-94-017-2506-4 ISBN 978-94-017-2504-0 (eBook)
DOI 10.1007/978-94-017-2504-0
AH rights reserved. No part of this book may be reprinted, or
reproduced or utilized in any form or by any electronic,
mechanical or other means, now known or hereafter invented,
including photocopying and recording, or in any
information storage and retrieval system,
without permission in writing from the Publisher.
This book is dedicated with gratitude to
my parents, Leonard and Marjorie Saunders,
for their sacrifices in earlier years and to
my wife, Jeannette, for her steadfast encouragement
in recent times.
Preface
This book deals with the organic chemistry of polymers which find technological
use as adhesives, fibres, paints, plastics and rubbers. For the most part, only
polymers which are of commercial significance are considered and the primary
aim of the book is to relate theoretical aspects to industrial practice. The book is
mainly intended for use by students in technical institutions and universities
who are specializing in polymer science and by graduates who require an
introduction to this field. Several excellent books have recently appeared dealing
with the physical chemistry of polymers but the organic chemistry of polymers
has not received so much attention. In recognition of this situation and because
the two aspects of polymer chemistry are often taught separately, this book
deals specifically with organic chemistry and topics of physical chemistry have
been omitted. Also, in this way the book has been kept to a reasonable size. This
is not to say that integration of the two areas of polymer science is undesirable;
on the contrary, it is of the utmost importance that the inter-relationship should
b~ appreciated.
I wish to record my thanks to my colleagues with whom I have had many
helpful discussions, particularly Mrs S. L. Radchenko. I also thank Miss E.
Friesen for obtaining many books and articles on my behalf and Mr H. Harms
for encouragement and assistance. I am also grateful to Mrs M. Stevens who
skilfully prepared the manuscript.
Department of Chemical and Metallurgical Technology,
Ryerson Polytechnical Institute, K.J.S.
Toronto, Ontario, Canada.
July, 1971.
vii
Contents
Preface page vii
1. Basic concepts 1
2. Polyolefins 45
3. Polystyrene and styrene copolymers 71
4. Poly(vinyl chloride) and related polymers 84
5. Poly(vinyl acetate) and related polymers 104
6. Acrylic polymers 116
7. Fluoropolymers 137
8. Polyethers 152
9. Polyamides and related polymers 175
10. Polyesters 203
11. Cellulose and related polymers 245
12. Phenol-formaldehyde polymers 272
13. Aminopolymers 301
14. Polyurethanes 318
15. Silicones 347
16. Epoxies 370
17. Sulphur-containing polymers 394
18. Polydienes 406
19. Miscellaneous polymers 448
Appendix I. Trade names and
manufacturers 456
Appendix II. International system of
units 462
Index 463
ix
1
Basic Concepts
1.1. Definitions
A polymer may be defined as a large molecule comprised of repeating structural
units joined by covalent bonds. (The word is derived from the Greek:
poly - many, meros - part.) In this context, a large molecule is commonly
arbitrarily regarded either as one having a molecular weight of at least 1000 or as
one containing 100 structural units or more. By a structural unit is meant a
relatively simple group of atoms joined by covalent bonds in a specific spatial
arrangement. Since covalent bonds also connect the structural units to one
another, polymers are distinguished from those solids and liquids wherein
repeating units (ions, atoms or molecules) are held together by ionic bonds,
metallic bonds, h~rdrogen bonds, dipole interactions or van der Waals forces.
The term macromolecule simply means a large molecule (Greek: macros -
large) and is often used synonymously with 'polymer'. Strictly speaking, the
terms are not equivalent since macromolecules, in principle, need not be
composed of repeating structural units though, in practice, they generally are.
It may be noted that 'polymer' is often also used to refer to the massive state.
Then the term refers to a material whose molecules are polymers, i.e., a
polymeric material. Likewise, the term resin is sometimes used to refer to any
material whose molecules are polymers. Originally this term was restricted to
natural secretions, usually from coniferous trees, used mainly in surface coatings;
later, similar synthetic substances were included. Now the term is generally used
to indicate a precursor of a cross-linked polymeric material, e.g., epoxy resin and
novolak resin. (See later.)
1.2. Scope
A great variety of polymeric materials of many different types is to be found
throughout countless technological applications. For the purposes of this book it
is convenient to divide these materials according to whether they are inorganic
or organic and whether they are naturally occurring or synthetic. Using this
classification, the diverse nature and widespread application of polymeric
materials is illustrated by Fig. 1.1. This book is concerned solely with
2 ORGANIC POLYMER CHEMISTRY
POLYMERIC MATERIALS
INORGANIC ORGANIC
I I
I I I I
NATURAL SYNTHETIC NATURAL SYNTHETIC
I I I I
Clays Sands
,.......-11------1, I
I
Brick Cement Pottery Glass Fibres Adhesives Fibres Paints Plastics Rubbers
Polysaccharides Proteins Polyisrrene
I I
I I I I
Adhesives Fibres Adhesives Fibres Rubber
Fig. 1.1 Some applications of polymeric materials
technologically useful organic polymeric materials. These materials are commonly
classified as adhesives, fibres, paints, plastics and rubbers according to their use.
Although these are all polymeric materials, they clearly possess a great diversity of
properties about which few generalizations can be made. It is significant,
however, that no low molecular weight organic compounds are useful in the
above applications. The physical properties of an individual polymeric material
are largely determined by molecular weight, strength of intermolecular forces,
regularity of polymer structure and flexibility of the polymer molecule.
1.3. Rise of the concept of polymers
Nowadays the concept of polymers (or, simply, big molecules) is easy to accept
but this has not always been the case. The rise of the concept is of interest and a
brief historical review is given below.
By the 1850's the existence of atoms and molecules was accepted but mainly
in respect of simple inorganic compounds. The application of these ideas to
more complex organic materials was not understood so clearly. At least, by this
time the notion that organic compounds all contained a mysterious 'vital force'
derived from living things had been finally abandoned as more and more organic
compounds were synthesised in the laboratory.
In 1858 Kekule suggested that organic molecules were somewhat larger than
the simple 'inorganic molecules and consisted of atoms linked in chains by bonds.
This led to the realization that the order in which atoms are arranged in the
molecule is significant, i.e., the meaning of 'structure' was appreciated. These
ideas, aided by improving methods of elemental analysis, resulted in the
BASIC CONCEPTS 3
elucidation of the structure of many simple organic compounds such as acetic
acid and alcohol. However, virtually nothing was deduced about the structure of
more complex organic materials such as rubber, cellulose and silk. All that was
clear was that these materials had elemental analyses which were quite similar to
those of the simple compounds whose structures were known.
The first significant information came in 1861 when Graham found that
solutions of such natural materials as albumin, gelatin and glue diffused through
a parchment membrane at a very slow rate. Materials of this kind were called
colloids (Greek: kolla- glue). In constrast, solutions of materials like sugar and
salts diffused readily; these substances were called crystalloids since they were
generally crystalline. The reason for this difference was not clear, but it was
generally supposed that the colloid solute particles were rather large and
therefore their passage through the semi-permeable membrane was hindered.
There were a few tentative suggestions that the colloids had high molecular
weights so that a solute particle was large simply because it comprised one large
molecule. However, this view was not at all acceptable to most scientists of the
day. At this time the current practices of organic chemistry demanded the
preparation of crystalline compounds of great purity with exact elemental
analyses and sharp melting points. It was generally felt that if the colloids were
'cleaned up' they would crystallize and reveal themselves as 'normal' low
molecular weight compounds. This view was apparently reinforced by the fact
that many inorganic materials of low molecular weight can be prepared so that
they behave as colloids, e.g., colloidal arsenious sulphide, gold and silver
chloride. It was held, quite rightly, that in these cases the colloidal particles are
aggregates of small molecules held together by secondary valency forces of some
kind. (Incidentally, the physically associated groups were frequently called
'polymers' in the literature.) This view was very much in keeping with the great
emphasis which was being placed on van der Waals forces in the 1890's and early
1900's. By analogy, the organic colloids were assumed to be molecular
aggregates or micelles, a concept still to be found in the literature of the
1940's.
The first worker to take a clearly opposite view was Staudinger in Germany in
a paper of 1920. He maintained that the colloidal properties of organic materials
are due simply to the large size of the individual molecules and that such
macromolecules contain only primary valency bonds. Staudinger's initial
evidence was mainly negative. Firstly, he demonstrated that the organic
materials retain their colloidal properties in all solvents in which they dissolve.
This is in contrast to the inorganic association colloids which often lose their
colloidal characteristics on change of solvent. Secondly, he showed that,
contrary to then current expectations, chemical modification does not destroy
the colloidal properties of the organic materials. At that time it was commonly
held that natural rubber was a cyclic material composed of isoprene residues
4 ORGANIC POLYMER CHEMISTRY
linked in rings of various sizes as, for example, in the following structure:
CH
3
I
C-CH
I \2
CH CH
2
I I
CH C-CH
H;c2 -& 3
Such molecules were then supposed to aggregate by virtue of secondary valency
forces arising from the presence of double bonds. (Incidentally, the cyclic
structure was held to account for the fact that no end-groups could be detected.)
However, Staudinger showed that the hydrogenation of natural rubber produces
a saturated material which still exhibits colloidal properties. Thus he
demonstrated that secondary forces originating from the unsaturation of natural
rubber are unlikely to be responsible for colloidal behaviour. Staudinger
proposed the long chain structures, which are accepted today, for several
polymers. Additional support for the existence of macromolecules came with
the development of methods of molecular weight determination. Until this time,
only cryoscopic methods were available and these were inadequate for the very
high molecular weights involved; also, it was commonly held that the laws which
hold for ordinary solutions were not applicable to colloidal solutions.
Thus by about 1930 the concept of polymers was firmly established even if
not universally accepted. The macromolecular viewpoint was finally secured
largely by the work of Carothers in the United States. This work was begun in
1929 and had as its objectives, clearly stated at the outset, the preparation of
polymers of defmite structure through the use of established reactions of organic
chemistry and the elucidation of the relationship between structure and
properties of polymers. These researches were brilliantly successful and fmally
dispelled the mysticism surrounding this field of chemistry.
One outstanding result of Carothers' work was the commercial development
of nylon. Nylon stocking came on the market in 1940, when polymers, in terms
of popular acceptance, might be said to have arrived. The theoretical, practical
and economic foundations had been laid and since this date progress has been
phenomenal.
1.4. General methods of preparation of polymers
There are three general methods by which polymers may be prepared from
relatively simple starting materials (monomers). Each of these methods is briefly
described in this section; more detailed considerations are to be found
throughout later chapters.