Processing, Structure and Properties of Block Copolymers

218 Pages·1985·5.17 MB·English

by  S. L. Aggarwal (auth.)

PROCESSING, STRUCTURE AND PROPERTIES
OF BLOCK COPOLYMERS
PROCESSING, STRUCTURE
AND PROPERTIES OF
BLOCK COPOLYMERS
Edited by
M. 1. FOLKES
Department of Materials Technology,
Brunei University, UK
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British Library Cataloguing in Publication Data
Processing, structure and properties of block
copolymers.
1. Block copolymers
I. Folkes, M. J.
547.8'4 QD382.B5
ISBN-13: 978-94-010-8687-5 e-ISBN-13: 978-94-009-4936-2
DOl: 10.1007/978-94-009-4936-2
WITH II TABLES AND 85 ILLUSTRATIONS
© ELSEVIER APPLIED SCIENCE PUBLISHERS LTD 1985
Softcover reprint of the hardcover 1st edition 1985
First edition 1985
Reprinted 1986
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Preface
Block copolymers represent an important class of multi-phase material,
which have received very widespread attention, particularly since their
successful commercial development in the mid-1960s. Much of the
interest in these polymers has arisen because of their rather remarkable
micro phase morphology and, hence, they have been the subject of
extensive microstructural examination. In many respects, the quest for a
comprehensive interpretation of their structure, both theoretically and
experimentally, has not been generally matched by a corresponding
enthusiasm for developing structure/property relationships in the context
of their commercial application. Indeed, it has been left largely to the
industrial companies involved in the development and utilization of these
materials to fulfil this latter role. While it is generally disappointing that
a much greater synergism does not exist between science and technology,
it is especially sad in the case of block copolymers. Thus these materials
offer an almost unique opportunity for the application of fundamental
structural and property data to the interpretation of the properties of
generally processed artefacts.
Accordingly, in this book, the editor has drawn together an eminent
group of research workers, with the specific intention of highlighting
some of those aspects of the science and technology of block copolymers
that are potentially important if further advances are to be made either
in material formulation or utilization. For example, special consideration
is given to the relationship between the flow properties of block copo
lymers and their microstructure. This relates closely to the development
of mechanical anisotropy during processing, which is discussed in the
context of both block copolymers and their blends with homopolymers.
Considerable possibilities exist for the practical application of this anis-
v
VI PREFACE
otropy in the design of advanced rubber systems having specified proper
ties. The link between the mechanical properties of idealized test speci
mens and practical moulded artefacts is achieved through the use of
comparatively elementary fibre reinforcement theory. This treatment
serves as a salutary reminder in showing how studies of model com
posites can be used to interpret the mechanical properties of more
generally processed components. This is complemented by an extensive
discussion of the segmented copolymers, with special emphasis on seg
mented polyurethanes, which clearly shows the important modifications
to the properties of these block copolymers that can result from changes
in their molecular architecture.
Above all, it is hoped that this book will prompt further thought and
activities in this important area of polymer science and engineering and
assist in the gradual evolution of a rational design basis for block
copolymer systems.
M. 1. FOLKES
Contents
Preface v
List of Contributors. IX
1. Introduction and Overview 1
S. L. AGGARWAL
2. The Interrelation between Microstructure and Properties of
Block Copolymers 29
A. KELLER and J. A. ODELL
3. Melt Flow Properties of Block Copolymers 75
J. LYNGAAE-J0RGENSEN
4. Block Copolymers and Blends as Composite Materials . 125
R. G. C. ARRIDGE and M. J. FOLKES
5. Segmented Copolymers with Emphasis on Segmented
Polyurethanes 165
S. ABOUZAHR and G. L. WILKES
Index . 209
vii
List of Contributors
S. ABOUZAHR
Polymer Materials and Interfaces Laboratory, Department of
Chemical Engineering, Virginia Polytechnic Institute and State
University, Blacksburg, Virginia 24061, USA.
S. L. AGGARWAL
The General Tire & Rubber Company, Research Division, Akron,
Ohio 44329, USA.
R. G. C. ARRIDGE
H. H. Wills Physics Laboratory, University of Bristol, Royal Fort,
Tyndall Avenue, Bristol BS8 1 T L, UK.
M. J. FOLKES
Department of Materials Technology, Brunei University, Kingston
Lane, Uxbridge, Middlesex UB83PH, UK.
A. KELLER
H. H. Wills Physics Laboratory, University of Bristol, Royal Fort,
Tyndall Avenue, Bristol BS8 1TL, UK.
J. LYNGAAE-J0RGENSEN
Instituttet for Kemiindustri, The Technical University of Denmark,
Building 227, DK-2800 Lyngby, Denmark.
IX
x LIST OF CONTRIBUTORS
J. A. ODELL
H. H. Wills Physics Laboratory, University of Bristol, Royal Fort,
Tyndall Avenue, Bristol BS8 ITL, UK.
G. L. WILKES
Polymer Materials and Interfaces Laboratory, Department of
Chemical Engineering, Virginia Polytechnic Institute and State
University,Blacksburg, Virginia 24061, USA.
CHAPTER 1
Introduction and Overview
S. L. AGGARWAL
The General Tire & Rubber Company, Akron, Ohio, USA
1. INTRODUCTION
The intent of this chapter is to provide a broad perspective of the
chemistry and technology of block copolymers and their characteristic
properties. It should serve as an overview of the structural features of
block copolymers, and as an introduction to the subsequent chapters
which treat in depth various topics concerning processing, structure and
properties of block copolymers.
2. HISTORICAL
The rapid development of block copolymers from the early basic studies
on organometallic compounds as polymerization catalysts, to the present
level of commercial production, is astounding indeed. Extensive work
from academic and industrial laboratories from all over the world has
contributed to this development, and references to the technical literature
are well documented in several reviews and recent books.1-14 Readers of
this chapter are urged to study particularly the reviews9-14 in order to
obtain a broad perspective of the chemistry and of the early studies on
the structure of block copolymers.
The conceptual hypothesis of block copolymer structure may be traced
to Alfrey et al. In their book on copolymerization15 they pointed out
that the presence of long sequences of a particular monomer in a
copolymer may result in incompatability at a SUbmicroscopic level. They
predicted that such materials may show properties quite different from
either a random copolymer or a macroscopic blend of the corresponding
two homopolymers. The path of discoveries and developments from such
2 s. L. AGGARWAL
a hypothetical prediction to the present state of the development of block
copolymers as important materials, of both scientific and commercial
interest, is a fascinating one. It has been highlighted in one of the recent
publications.16 Four milestones along this path of discoveries and de
velopments stand out and are described below.
2.1. 'Living Polymers'
In 1956, Professor M. Szwarc and co-workers reported that certain
anionic polymerization systems with sodium naphthalene resulted in
'living polymers' with anionically reactive ends to which a second
monomer may be added without termination so that block copolymers
may be prepared.17-19 In the polymers that contain butadiene, the
sodium naphthalene di-initiators, that were used by these workers in
their studies, resulted in the 1:2 or 3:4 addition structures, which had
some properties that were undesirable in commercial application. Thus,
these studies did not attract sufficient interest in industrial laboratories.
2.2. Domain Structure
Bateman20 and Merret21 in 1957 observed that graft polymers of methyl
methacrylate (MMA) on natural rubber (NR) may have two distinctly
different physical forms, depending upon the solvent from which these
polymers were precipitated. If precipitated from a solvent which was a
'good' solvent for poly(methyl methacrylate) and thus resulted in exten
ded chains, but was a 'poor' solvent for NR resulting in collapsed NR
chains, then the material was hard and non-tacky. However, if on the
other hand the solvent was such that the reverse was true, i.e. extended
NR segments but collapsed PMMA segments, the material was soft and
flabby. Both physical forms were stable even under heavy milling. The
vulcanizates prepared from these two forms had different properties, and
they were different from those of the mixtures of the corresponding
homopolymers.2o Merret explained these differences by the postulate
that the dry polymer consists of domains of the collapsed polymer chains
as a distinct phase in a continuous matrix of the polymer that had
existed in the extended chain form in the solution from which it was
precipitated. At the time, it was an imaginative postulate for the two
phase structure of the graft polymers in the solid state. It turned out to
be a characteristic feature of the graft and block copolymers.
2.3. Alkyl Lithium Catalysts
The polymerization of isoprene with lithium metal as catalyst to prepare