Polymer Latexes. Preparation, Characterization, and Applications

469 Pages·1992·39.21 MB·English

by  Eric S. Daniels

ACS SYMPOSIUM SERIES 492
Polymer Latexes
Preparation, Characterization,
and Applications
Eric S. Daniels, EDITOR
Lehigh University
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6, 2102 Mohamed S. El-Aasser, EDITOR
ust 10. Lehigh University
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Atlanta, Georgia,
April 14-19, 1991
American Chemical Society, Washington, DC 1992
In Polymer Latexes; Daniels, E., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
library of Congress Cataloging-in-Publication Data
Polymer latexes: preparation, characterization, and applications / Eric S.
Daniels, editor, E. David Sudol, editor, Mohamed S. El-Aasser,
editor.
p. cm.—(ACS symposium series, 0097-6156; 492)
"Developed from a symposium sponsored by the Division of Polymeric
Materials: Science and Engineering and the Division of Colloid and
Surface Chemistry at the 201st National Meeting of the American
Chemical Society, Atlanta, Georgia, April 14-19, 1991."
g
or01 Includes bibliographical references and indexes.
cs.w0
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ust 10.
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PRINTED IN THE UNITED STATES OF AMERICA
In Polymer Latexes; Daniels, E., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
ACS Symposium Series
M. Joan Comstock, Series Editor
1992 ACS Books Advisory Board
V. Dean Adams Bonnie Lawlor
Tennessee Technological Institute for Scientific Information
University
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Mark Arnold Dow Chemical Company
University of Iowa
g Robert McGorrin
cs.orw001 David Baker Kraft General Foods
012 | http://pubs.a1/bk-1992-0492.f AUUnnleiivvxeeirrsssi iTttyy. ooBff eTClela nlinfoersnsieae— Berkeley JPulalUniut. SSs. cJDie. enMpcaerestn mInnesn tti tuotfe A, griculture
6, 2102 Arindam Bose Vincent Pecoraro
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y 89.163.3Date: June MNaatirognaarle Stc iAen. cCe aFvoaunnaduagtiohn AM.a cTarlausmtera Cno lSlecghew artz
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Hiroshi Ito
IBM Almaden Research Center Stephen A. Szabo
Conoco Inc.
Madeleine M. Joullie
University of Pennsylvania Robert A. Weiss
University of Connecticut
Mary A. Kaiser
E. I. du Pont de Nemours and Peter Willett
Company University of Sheffield (England)
Gretchen S. Kohl
Dow-Corning Corporation
In Polymer Latexes; Daniels, E., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
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 submit­
ted by the authors in camera-ready form. Papers are reviewed
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cs.w0 Advisory Board and are selected to maintain the integrity of the
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In Polymer Latexes; Daniels, E., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
Preface
THE FIELD OF EMULSION POLYMERS and latex technology continues to
develop at a rapid pace. The driving force for this development is both
commercial and environmental; latexes are water-based polymers in the
form of colloidal particles dispersed in an aqueous medium. Millions of
pounds of latexes are manufactured today for use as commodity and
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bs.92. fabrics, high-impact thermoplastic composites, latex foam, carpet backing,
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31
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d bon of emulsion polymerization and latex technology: the mechanisms of par­
wnloadeublicati tsiicolne npuoclylemateiorinza (ttihone )m aonstd impaprotrictalen tg arnodw tmh;o smt iccornotsrtrouvcetrusriael satnedp ipna retmicluel ­
Do P morphology; and recent advances in applications such as immunodiagnos-
tics, encapsulation of pigments, and catalysis.
Two leading scientists in the field were invited to review the state of
the art of the mechanisms of particle nucleation and growth. Finn K.
Hansen (University of Oslo, Norway) contributed a personal view of
where the theories of nucleation in emulsion polymerization currently
stand and where further advances are required In the next chapter,
Robert G. Gilbert (University of Sydney, Australia) and his colleagues
first examine data that have been used to prove or disprove micellar
nucleation; they then provide further information and arguments for a
combined nucleation mechanism.
Of the following chapters, six contributions relate to recent progress
in the area of particle formation and growth. Advances in the study and
characterization of polymer microstructure and particle morphology are
ix
In Polymer Latexes; Daniels, E., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
discussed in 11 chapters. Seven chapters deal with diverse applications of
and extensions from polymer latexes in such areas as catalysis and immu-
nodiagnostics.
The best excuse for organizing a symposium and the best way of
ensuring its success in terms of participation is to honor a colleague.
This symposium was organized to honor Robert M. Fitch and his contri­
butions to the field of emulsion polymerization. His fame in this fieldi s
due to, among other contributions, the quantification of the homogene­
ous mechanism for particle formation in emulsion polymerization. The
symposium, which succeeded in attracting numerous scientists from
academia and industry, resulted in lively discussions about the current
status and outstanding issues in the field. This volume should prove use­
g ful to engineers and scientists who are actively involved in the fields of
s.or001 emulsion polymerization and latex technology.
acpr
s.2. We thank all of the authors for their prompt responses to our
b9
pu04 requests. In addition, we thank the many reviewers, whose names will
p://92- remain anonymous, for putting up with our intrusion on their time and
htt19
012 | 1/bk- for making valuable suggestions to the authors.
22
6, 10 ERIC S. DANIELS
August doi: 10. EM. ODHAAVMIDE DS USD. OELL -AASSER
6 on 992 | Lehigh University
34.13e 3, 1 Bethlehem, PA 18015
y 89.163.Date: Jun January 24, 1992
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In Polymer Latexes; Daniels, E., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
Chapter 1
Overview of Emulsion Polymerization
Stepping Toward Prediction
E. David Sudol1, Eric S. Daniels1, and Mohamed S. El-Aasser1,2
1Emulsion Polymers Institute and 2Department of Chemical Engineering,
Lehigh University, Bethlehem, PA 18015
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22
6, 10 be the ultimate goal.
August doi: 10. oofft ethne csoTemh pepr lueedsxeic ptoirvfo emc emuslsoti dpvelalesr i.ma Atoionnn ousmn, dgerreser,as ttailnnytdr coiondmguc poelidfc a thttheers od uthegvehe dl oeapv nmeuloempnmbte earnn otd f
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34.1e 3, mercial need and application of polymer particles possessing narrowly
9.163.e: Jun dtheefisnee dpa prrtiocpleesrt iceosn. tAinduvea ntoce esv oinlv oeu. r abilities to prepare and characterize
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Do P pendulum which when set in motion rapidly reaches a state in which its exact move­
ments are no longer predictable (i.e., its motion deviates from predictions). In some
ways, emulsion polymerization can be viewed as chaotic. The fate of a single species,
such as a monomer molecule, is not predictable. At best, some estimate of its probabili­
ty of reacting and becoming a part of a polymer particle can be made. But which parti­
cle, where in the particle, at what position in a polymer chain, these cannot be predict­
ed.
Although chaos is not used to describe emulsion polymerization, it has fre­
quently been referred to as an art. And those who practice the art, recognize the diffi­
culty in consistently reproducing a batch of latex in terms of desired properties such as
stability, particle size and distribution, mechanical properties in application, etc. The
origins of irreproducibilities most often derive from a lack of a complete understanding
of a process and the variables which affect this process. In emulsion polymerization, the
process of creating latex particles is by far considered the greatest source of irreproduc­
ibilities observed. Typically, nucleation is described as being chiefly dependent on the
0097-6156/92/0492-0001$06.00A)
© 1992 American Chemical Society
In Polymer Latexes; Daniels, E., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
2 POLYMER LATEXES
emulsifier (its concentration and properties) and the initiator (its concentration or the
rate of radical generation). The monomer (type(s) and concentration(s)), added electro­
lyte (type and concentration), and reaction temperature are also key variables in the
nucleation process. Quantification of the time evolution of the number of latex particles
as a function of these variables has been advanced by many authors striving to trans­
form the art into a science, and perhaps in a sense, to impose order on chaos. These
efforts have been generally successful in modeling the behavior of specific systems
under specific conditions but not without some adjustment of mechanistic parameters
which are at best uncertain. This uncertainty has led others to invest effort in the clarifi­
cation of important rate parameters governing the kinetics of emulsion polymerization
(2,3). These include the initiator decomposition rate constant (k), the monomer propa­
d
gation rate constant (k), the first- (p) and second-order (k^) rate coefficients for radical
p
entry into latex particles, the desorption rate coefficient from the polymer particles (k),
and the termination rate constants in the particle (k) and aqueous phases (k^). Activity
t
in this area continues as an essential element to improved mechanistic model develop­
ment. However, true predictability has yet to be achieved.
g
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cs.h0 introduce a preformed seed. Although this may circumvent the more complex nuclea­
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22
6, 10 principally propagation and termination in the aqueous phase or in the polymer parti­
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36 on 1992 | dwioamrke (t4er).. Unlike the other mechanisms, it claims no dependence of entry on the particle
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tures, these representing the morphologicanimits of these latex particles. In practice,
particles with morphologies ranging between these extremes are often found and even
multiple morphologies can be found in a single latex.
Although the papers included in this volume cover a broad range of research
activities related to polymer colloids, much of the activity is reflected in the proceeding
areas of nucleation and particle morphology. (A bibliography of books published on the
subject of Emulsion Polymerization over the past twenty years is given at the end of this
chapter.)
Nucleation
Harkins (5) and Smith & Ewart (6) began more than forty years ago what would
become a long series of incremental steps (some large & some small) towards the
understanding of the complex mechanisms of particle formation and growth in a proc­
ess simply referred to as emulsion polymerization. The research is ongoing and pub­
lished work reflects the difficulties (and successes) in advancing the science; both
In Polymer Latexes; Daniels, E., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1992.
1. SUDOL ET AL. Overview of Emulsion Polymerization 3
forward and backward steps have been taken, each contributing to the body of knowl­
edge arrayed at understanding the phenomena of this complex heterogeneous process.
And yet the original process has broadened considerably.
Much attention was initially focussed on the emulsion copolymerization of sty-
rene and butadiene through the U.S. Government Synthetic Rubber Program. Relatively
high emulsifier ("soap" SF Flakes) concentrations were employed in the "Mutual
Recipe" to produce large numbers of small latex particles. Emulsion polymerizations
were carried out with these relatively water insoluble monomers and at emulsifier
concentrations well above the critical micelle concentration (cmc). It seemed quite
logical to conclude that the micelles acted as loci for the formation of growing polymer
particles and convincing arguments were put forth by Smith and Ewart to support the
Harkins conceptualization.
Variations introduced to the process of emulsion polymerization brought new
information which could not be so readily described by early concepts. Polymerizations
producing colloidal polymer particles were being successfully carried out with emulsi­
fier concentrations well below their cmc and even without any added emulsifier. And
g
or01 the "emulsifiers" themselves have become more complex in the sense that combinations
cs.h0 of a bewildering variety of ionic, nonionic, and polymeric stabilizers are being em­
ac
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22
6, 10 (see Chapter 2, this volume, which reviews much of the history and developments
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36 on 1992 | escyael etsy poifc oabllsye rnvoattiicoens: ftehwe m(iafc arnoysc) orpemic,a mrkiacbrloes ccohpaincg, easn dd usuribnmg itchreo spcoolpyimc. eTrihzea tuinoani;d aend
34.1e 3, opaque, white emulsion produces an opaque, white latex (subtle changes are observable
9.163.e: Jun tgor athnde eerx cphearniegnecse da sp rthaec tibtrioonader d, ihsotrwibeuvteiro)n. Aonf mopotnicoaml meri cdrroospcloetpse, ccarena bteed u bseyd t htoe osbhseearrv oef
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Do P Much of the theory of this process has been based on indirect observation, evidence,
and speculation.
A mathematical description of nucleation in these loci is encompassed in what
has become known as HUFT theory, representing the contributions of Hansen & Ugel-
stad (7) and Fitch & Tsai (8). The relative contribution of each nucleation site in a par­
ticular system is governed by such factors as the solubility of the monomer in the con­
tinuous phase, the number of micelles, and the size and number of monomer droplets.
Although this theory is comprehensive, voids in our understanding persist. The dynam­
ics of aqueous phase radical growth and subsequent ad(b)sorption/desorption in mi­
celles, droplets, and particles are not yet resolved. Questions continue to be raised
regarding the nature of the radicals (particularly oligomeric) and their interaction with
these somewhat different species and additionally the free surfactant. These lie at the
heart of the complexities in further understanding nucleation in emulsion polymeriza­
tion. (Chapters 2, 3, and 4 of this volume address these issues and raise further ques­
tions.)
Nucleation in monomer droplets becomes important when their size is reduced
to within the same order of magnitude as the latex particles. (Chapters 6 and 7 of this
In Polymer Latexes; Daniels, E., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1992.