Multiphase Polymers: Blends and Ionomers

514 Pages·1989·8.877 MB·English

by  L. A. Utracki and R. A. Weiss (Eds.)

ACS SYMPOSIUM S E R I E S 395
Multiphase Polymers:
Blends and Ionomers
L. A. Utracki, EDITOR
National Research Council of Canada
R
University of Connecticut
Developed from a symposium sponsored
by the Division of Polymeric Materials: Science
and Engineering of the American Chemical Society
and by the Division of Macromolecular Science
and Engineering of the Chemical Institute of Canada
at the Third Chemical Congress of North America
(195th National Meeting of the American Chemical Society),
Toronto, Ontario, Canada,
June 5-11, 1988
American Chemical Society, Washington, DC 1989
In Multiphase Polymers: Blends and Ionomers; Utracki, L., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Library of Congress Cataloging-in-Publication Data
Multiphase polymers: blends and ionomers/ L. A. Utracki, editor;
R. A. Weiss, editor.
p. cm.—(ACS Symposium Series, ISSN 0097-6156; 395).
"Developed from a symposium sponsored by the
Division of Polymeric Materials: Science and Engineering
of the American Chemical Society and by the Division of
Macromolecular Science and Engineering of the Chemical
Institute of Canada at the Third Chemical Congress of
North America (195th Meeting of the American Chemical
Society), Toronto, Ontario, Canada, June 5—11, 1988."
Bibliography: p.
Includes indexes.
ISBN 0-8412-1629-0
1. Polymers—Congresses. 2. Ionomers—Congresses.
I. Utracki, L. Α., 1931- . II. Weiss, R. Α., 1950- .
III. American Chemical Society. Division of Polymeric
Materials: Science and Engineering. IV. Chemical Institute
of Canada. Macromolecuiar Science Division.
V. American Chemical Society. Meeting (195th: 1988:
Toronto, Ont.). VI. Chemical Congress of North America
(3rd: 1988: Toronto, Ont.). VII. Series.
QD380.M85 1989
547.7—dc20 89-6987
CIP
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In Multiphase Polymers: Blends and Ionomers; Utracki, L., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
ACS Symposium Series
M. Joan Comstock, Series Editor
1989 ACS Books Advisory Board
Paul S. Anderson Mary A. Kaiser
Merck Sharp & Dohme Research E. I. du Pont de Nemours and
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In Multiphase Polymers: Blends and Ionomers; Utracki, L., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Foreword
The ACS SYMPOSIUM SERIES was founded in 1974 to provide a
medium for publishing symposia quickly in book form. The
format of the Series parallels that of the continuing ADVANCES
IN CHEMISTRY SERIES except that, in order to save time, the
papers are not typeset but are reproduced as they are submitted
by the authors in camera-ready form. Papers are reviewed under
the supervision of th
Advisory Board and
symposia; however, verbatim reproductions of previously pub
lished papers are not accepted. Both reviews and reports of
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types of presentation.
In Multiphase Polymers: Blends and Ionomers; Utracki, L., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Preface
APPEARANCE OF MANY NEW PRODUCTS AND APPLICATIONS based
on multiphase polymer systems has spawned considerable research
activity in recent years on this class of materials in both academic and
industrial laboratories. The properties of multiphase polymers, such as
their phase behavior, morphology d mechanical behavior
complicated by the problem
highly viscous media. These problems are exacerbated by the poorly
understood relationships between thermal and stress histories and the
attainment of multiphase morphologies in transient stress, non-
isothermal processing operations. The solution of these problems
involves a multidisciplinary effort involving chemistry, physics, and
engineering. The development of the underlying science remains in its
infancy, despite major advances in theory, materials, and experimental
instrumentation over the last decade. Yet, the development and
commercialization of multiphase polymers has proceeded at a rapid
pace.
The field of multiphase polymers is too broad for any single volume.
Two of the more important topics within the field from the perspectives
of both applications and scientific challenges are polymer blends and
ionomers. The high level of interest in these areas is evidenced by the
explosive growth of the literature and patents devoted to these subjects.
With this in mind, we felt that a book devoted to recent advances in
these fields was justified.
The chapters in this volume represent the current trends in the fields
of polymer blends and ionomers, including materials development,
characterization, theory, and processing. They are grouped into six
sections: the first three are concerned with polymer blends and
interpenetrating networks and the latter three with ionomers.
Although immiscible polymer blends and ionomers share a common
feature in that both exhibit more than a single phase, a major difference
between the two systems involves the dispersed phase size. For blends,
this is generally of the order of micrometers and may be detected
optically. Ionomers, however, are microphase-separated with domain
sizes of the order of nanometers. Thus, blends and ionomers represent
two extremes of the subject of multiphase polymers. In this book, the
reader will observe similarities as well as differences in the problems
be
In Multiphase Polymers: Blends and Ionomers; Utracki, L., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
associated with these materials and the approaches used to study them.
In addition, we expect that the reader will find many parallels with
multiphase systems that are not discussed here, such as block copolymers
and liquid crystalline polymers.
Although this book provides only a small sampling of the kinds of
materials and the activities in the field of multiphase polymers, the range
of topics covered here clearly reflects the breadth of the field. For
example, the subjects discussed include synthetic chemistry, theory,
solution behavior, morphological characterization, and rheology. We
expect that this material will be stimulating to academic and industrial
scientists alike, whether their primary interests are in fundamental
science or the development of the next generation of commercial
polymer systems.
Finally, the editors
cooperation in ensuring timely publication of this volume. We especially
thank Younghee Chudy for her invaluable assistance to the editors in
the preparation of this book.
L. A. UTRACKI
Industrial Materials Research Institute
National Research Council of Canada
Boucherville, Quebec J4B 6Y4, Canada
R. A. WEISS
Polymer Science Program and
Department of Chemical Engineering
University of Connecticut
Storrs, CT 06260-3136
March 8, 1989
x
In Multiphase Polymers: Blends and Ionomers; Utracki, L., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Chapter 1
Polymer Alloys, Blends, and Ionomers
An Overview
L. A. Utracki1, D. J. Walsh2, and R. A. Weiss3
1Industrial Materials Research Institute, National Research Council
of Canada, Boucherville, Québec J4B 6Y4, Canada
2E. I. du Pont de Nemours and Company, Experimental Station,
Wilmington, DE 19898
3Polymer Science Program and Department of Chemical Engineering,
University of Connecticut Storrs CT 06269-3136
This chapter provides a broad overview of the
subjects of polymer blends and ionomers. Specific
topics concerning polymer blends include the
thermodynamics of mixing of polymer-polymer pairs,
polymer interfaces, rheology, and mechanical
properties. For ionomers, the chemistry, structure,
rheology and solution properties are discussed.
Multiphase polymer systems are becoming an increasingly important
technical area of polymer science. By definition, a multiphase
polymer is one that has two or more distinct phases. The phases
may differ in chemical composition and/or texture. Thus, in its
broadest sense, the term includes not only multi-component systems,
such as immiscible polymer blends and filled-polymers, but also
semi-crystalline polymers, block copolymers, segmented polymers,
and ionomers. The latter four systems are characterized by a
microphase-separated morphology wherein a single polymer chain
participates i n more than one phase. In addition, even
homopolymers that have experienced complex thermal and mechanical
histories, such as encountered in most common polymer processing
operations, may possess morphologies containing more than one
crystalline texture. These may also be considered multiphase
materials.
Because of the great diversity of multiphase polymers,
coverage of the entire field in a single volume is neither possible
nor practical. Instead, this book concentrates on two specific
subjects: polymer blends, including interpenetrating polymer
networks, and ionomers. Even with this specialization, a
comprehensive treatise on both subjects is not possible, and this
book focusses on selected contemporary topics from the two fields.
The purpose of this overview chapter is to provide a cursory
0097-6156/89/0395-O001$09.75A)
o 1989 American Chemical Society
In Multiphase Polymers: Blends and Ionomers; Utracki, L., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
2 MULTIPHASE POLYMERS: BLENDS AND IONOMERS
introduction to these subjects and to outline the organization of
the book. Those requiring a more detailed review of polymer blends
and ionomers are directed to other monographs and review articles
(1-22).
POLYMER BLENDS
There i s some confusion i n the literature regarding polymer blend
nomenclature. Here the following definitions are assigned to the
commonly used terms:
POLYMER BLEND (PB) - the all-encompassing term for any mixture
of homopolymers or copolymers;
HOMOLOGOUS POLYMER BLENDS - a sub-class of PB limited to
mixtures of chemically identical polymers differing in molar
mass;
POLYMER ALLOYS - a
tures with stabilized morphologies;
MISCIBLE POLYMER BLENDS - a sub-class of PB encompassing those
blends which exhibit single phase behavior;
IMMISCIBLE POLYMER BLENDS - A sub-class of PB referring to
those blends that exhibit two or more phases at a l l
compositions and temperatures;
PARTIALLY MISCIBLE POLYMER BLENDS - a sub-class of PB
including those blends that exhibit a "window" of miscibility,
i.e., are miscible only at some concentrations and
temperatures;
COMPATIBLE POLYMER BLENDS - a utilitarian term, indicating
commercially useful materials, a mixture of polymers without
strong repulsive forces that is homogeneous to the eye;
INTERPENETRATING POLYMER NETWORK (IPN) - a sub-class of PB
reserved for mixtures of two polymers where both components
form continuous phases and at least one i s synthesized or
crosslinked in the presence of the other.
From the standpoint of commercial applications and
developments, polymer blending represents one of the fastest
growing segments of polymer technology. Both the open and the
patent literature have become voluminous. In principle, blending
two materials together in order to achieve a balance of properties
not obtainable with a single one i s an obvious and well-founded
practice, one that has been successfully exploited in metallurgical
science. With polymers, however, the thermodynamics of mixing do
not usually favor mutual solubility and most binary polymer
mixtures form two distinct phases. This i s a direct consequence of
their high molecular mass. Still, many immiscible systems form
useful products and are commercial. Key examples include rubber-
In Multiphase Polymers: Blends and Ionomers; Utracki, L., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
1. UTRACKI ETAL. Polymer Alloys, Blends, and Ionomers 3
toughened plastics such as high impact polystyrene (HIPS) and ABS
resins and blends of synthetic rubber with natural rubber.
The problems and challenges inherent to developing useful
materials with optimal morphologies and properties from an
immiscible or partially miscible polymer blend are not trivial and
have spawned considerable industrial and academic research. Work
on polymer miscibility, compatibilizing agents, reactive systems,
and the influence of flow on the structure and properties of blends
is described in later chapters.
The major technological problem in the use of polymer blends
concerns determining correlations between composition, processing,
structure and properties. Each variable has inherent
characterization problems, e.g., of the preparation process, of the
chemistry and morphology, and of what are meaningful properties.
None of these correlations or characterizations are easy to make or
particularly well understood.
Because polymer science is by nature interdisciplinary the
solution of the above proble
fields, including chemistry
discussion that follows will highlight a number of areas where
progress has recently been made i n understanding the subject.
Considerably more detail will be found in the subsequent chapters
of this book.
Mechanical Mixing of Polymer Blends
Most commercial polymer alloys and blends are prepared by
mechanical mixing, largely because of its simplicity and low cost.
The preferred industrial method of mechanical mixing is to use a
screw compounder or extruder that can be run continuously and
generate a product i n a convenient form for further processing.
Not surprisingly, much effort has gone into trying to understand
the flow of polymer blends.
Mixing from Ternary Systems and by Reaction
Other methods for forming blends such as by evaporation of a
solvent or by polymerization of a monomer i n the presence of a
polymer involve at least three components i n the preparation
process. Mixing in a common solvent followed by its removal i s a
convenient way of making blends on a laboratory scale, but has
obvious commercial disadvantages due to the cost and difficulty of
solvent recovery as well as the potential environmental hazards
associated with handling large volumes of often toxic chemicals.
In specific applications, however, such as membrane formation or
paints and coatings where thin films are required, the use of
solvents is unavoidable.
The third component of such a blend, i.e., the solvent, and
the kinetics of its removal can influence the resulting morphology.
For example, i f two miscible polymers are cast from a common
solvent, one does not necessarily obtain a homogeneous mixture. A
two-phase region can exist in the ternary phase diagram as shown in
Fig. la, and as the solvent evaporates the composition may enter
the two- phase region as shown by progressing from point A to point
In Multiphase Polymers: Blends and Ionomers; Utracki, L., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
4 MULTIPHASE POLYMERS: BLENDS AND IONOMERS
B. As the evaporation of solvent continues, the composition may
leave the two-phase region, but at that point the viscosity may be
too high and the phase sizes may be too large for homogenization to
occur.
The more common situation, illustrated in Fig. lb, is where
the two polymers are immiscible but form a homogenous solution in a
common solvent. In this case, film casting along the line C to D
generates a variety of structures depending on the selected solvent
(and its interaction parameters X-jo an<* X-j^)» the chemical nature
of the two polymers (X23) as well as on the kinetics of the
process. Three phase-separated types of morphologies can result:
co-continuous, dispersed, and layered.
The co-continuous morphology with the polymers forming
interpenetrating networks is the most interesting. This structure,
which is known to exist even at concentrations as low as 10 to 15
vol%, can be created by judiciously selecting the casting
conditions to assure dominance of the spinodal decomposition (SD)
mechanism of phase separation
generated structures var
a micron (23, 24). This morphology allows for coexistence of the
best characteristics of each polymer in the blend (25). For
example, the combination of good mechanical properties with
permeability, accomplished with a blend composition above the
percolation threshold, has yielded a highly successful membrane
technology (26).
The phase-separated droplet/matrix morphology is an outcome of
the nucleation and growth mechanism (NG) of phase separation. The
phase dimensions are similar to those observed for SD, but in this
case the properties are dominated by the matrix polymer with the
dispersed phase playing the role of a compatibilized filler. A
similar dispersed morphology, but with large drops, can be obtained
by allowing the SD or NG system to ripen. The coarsening usually
leads to a non-uniformity of properties.
The layered structure of a cast film is controlled by the
surface properties during evaporation. Significant compositional
gradients can be generated by making use of the natural tendencies
of one polymer to migrate toward the air-polymer interface and the
other toward the substrate. Hydrophobicity/hydrophilicity of
macromolecules is often cited as the driving force (27, 28).
Reactive mixing finds application in many commercial blends
such as HIPS and rubber modified thermosets. Many IPN's can also
be included here. In the case of the polymerization of monomer in
the presence of a polymer, the monomer-l/polymer-1/polymer-2
ternary phase diagram also plays a role in determining the final
morphology. Where the two polymers are immiscible, such as
polystyrene and polybutadiene, a two-phase mixture will result.
However, in cases where the polymers are miscible, single phase
morphologies are not always achieved. For example, in the
polymerization of vinyl chloride in the presence of poly(butyl
acrylate) a two-phase region is present in the phase diagram, Fig.
2. Polymerization pathways that pass through this region, such as
line A-B in Fig. 2, may yield a two-phase system for the same
reasons as described above for solvent evaporation from a blend.
In Multiphase Polymers: Blends and Ionomers; Utracki, L., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1989.