Cationic Polymerization. Fundamentals and Applications

226 Pages·1997·17.03 MB·English

by  Rudolf Faust and Timothy D. Shaffer (Eds.)

Cationic Polymerization
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In Cationic Polymerization; Faust, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
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In Cationic Polymerization; Faust, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
665
ACS SYMPOSIUM SERIES
Cationic Polymerization
Fundamentals and Applications
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k-1 Rudolf Faust, EDITOR
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21/ University of Massachusetts Lowell
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s.org 7 | doi: Timothy D. Shaffer, EDITOR
s.ac199 Exxon Chemical Company
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August 20, 20 Publication

Developed from a symposium sponsored
by the Division of Polymer Chemistry, Inc.
American Chemical Society, Washington, DC
In Cationic Polymerization; Faust, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
Library of Congress Cataloging-in-Publication Data
Cationic polymerization: fundamentals and applications / Rudolf Faust, editor,
Timothy D. Shaffer, editor.
p. cm.—(ACS symposium series, ISSN 0097-6156; 665)
"Developed from a symposium sponsored by the Division of Polymer
Chemistry, Inc., at the 211th National Meeting of the American Chemical
Society, New Orleans, Louisiana, March 24-28, 1996."
Includes bibliographical references and indexes.
1
0
0
w ISBN 0-8412-3507-4
5.f
6
06 1. Addition polymerization—Congresses.
7-
9
9 I. Faust, Rudolf, 1951- . II. Shaffer, Timothy D. (Timothy Daniel),
1
k- 1960- . III. American Chemical Society. Division of Polymer Chemistry.
b
1/ IV. American Chemical Society. Meeting (211th: 1996: New Orleans, La.)
2
10 V. Series.
0.
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s.org 7 | doi: 5Q4D72'.2818.—P6Cd3c28613 1997 97-6C9I1P2
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p://pMay This book is printed on acid-free, recycled paper.
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In Cationic Polymerization; Faust, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
Advisory Board
ACS Symposium Series
Mary E. Castellion Omkaram Nalamasu
ChemEdit Company AT&T Bell Laboratories
Arthur B. Ellis Kinam Park
University of Wisconsin at Madison Prudue University
1
00 Jeffrey S. Gaffney Katherine R. Porter
w
5.f Argonne National Laboratory Duke University
6
6
0 Gunda I. Georg
7- Douglas A. Smith
9 University of Kansas
19 The DAS Group, Inc.
k-
b Lawrence P. Klemann
1/ Martin R. Tant
02 Nabisco Foods Group
1 Eastman Chemical Co.
0.
s.org 7 | doi: 1 RUnicivherasritdy Nof. M Lisoseouprpi ky MParikceh-aDealv iDs P. hTaarmyaloceru tical
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s.a19 Cynthia A. Maryanoff Research
p://pubMay 1, R. WRe.s Jeoahrcnhso Inn sPtihtuatrem aceutical Leroy Β. Townsend
August 20, 2012 | htt Publication Date: RUnoaigvte eUrrs ritAbya .no afM -IClilhinnaeomiaspr aign UWDuniPivlolenirast imtCy o Comf.p MaWnicyah ligkaenr

In Cationic Polymerization; Faust, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
Foreword
T HE ACS SYMPOSIUM SERIES was first published in 1974 to provide
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5.f proposed table of contents is reviewed for appropriateness to the topic
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10. editor(s) of the book. The authors then revise their papers according to
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August 20, 20 Publication ACS BOOKS DEPARTMENT

In Cationic Polymerization; Faust, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
Preface
THE FIELD OF CARBOCATIONIC POLYMERIZATION has undergone
rapid growth in recent years. In just over a decade, this field has expanded from
1 the first examples of living polymerization to numerous monomers that undergo
0
0
pr living polymerization by a variety of initiator-coinitiator pairs. These newly
5.
6 discovered living systems have permitted the synthesis of advanced materials
6
0
7- such as block copolymers and end-functional polymers. Preparation of these
9
19 materials was either not possible or extremely difficult using conventional
k-
b techniques.
1/
2
0 This volume was developed from an international symposium titled
1
10. "Carbocationic Polymerization and Related Ionic Processes", which was held at
cs.org 97 | doi: tLhoeu 2is1i1antha ,N Matairocnha l2 M4-e2e8t,i n1g9 o9f6 .t hTeh Ae msyemripcoansi Cumhe mmaicrkael dS occoinettyin iuni nNge pwr oOgrrelesas nisn,
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2 | httDate: and documented in this book, deal with the use of living cationic polymerization
01n for the synthesis of advanced materials. In the early years after the original
2o
20, cati discoveries, research focused mainly on the expansion of the scope of living
August Publi cfoacrbuosecda tioonn icim pporolyvminegr iozuart iounn.d eDrsutrainndgi ntgh e ofl atsht e fievlee myeenatarsr,y tmhee cehmanpihstaisci s stehpass
and using the technique for the synthesis of advanced materials. Its great value
as a premier technique for material synthesis validates the role of living
carbocationic polymerization as a synthetic tool despite ongoing debate
regarding the appropriate name (controlled, living, quasi-living, etc.), the role of
additives (nucleophiles), and some other aspects of these polymerizations. The
field has matured to a point where some of these processes may advance into
commercialization (witness the increased patent activity).
Although scientists engaged in ionic (cationic and anionic) polymerizations
frequently exchange ideas at specialized meetings, and are thus aware of these
developments, these meetings are not easily accessible to a general audience.
Researchers not directly associated with this field may be genuinely surprised by
the powerful capabilities now made available by cationic polymerization.
ix
In Cationic Polymerization; Faust, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
With the organization of this symposium, and the publication of this book, we
hope to present the favorable features of cationic polymerizations to a general
audience.
RUDOLF FAUST
Polymer Science Program
Department of Chemistry
University of Massachusetts Lowell
One University Avenue
Lowell, MA 01854
TIMOTHY D. SHAFFER
Βaytown Polymers Center
Exxon Chemical Company
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5. Baytown, TX 77522-5200
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In Cationic Polymerization; Faust, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
Chapter 1
Carbocationic Polymerization: A Rejuvenation
Timothy D. Shaffer
Baytown Polymers Center, Exxon Chemical Company, 5200 Bayway Drive,
Baytown, TX 77522-5200
1
0
0
h
c
5.
6 The discovery of living carbocationic polymerization has rejuvenated the
6
7-0 field of carbocationic polymerization by creating new opportunities for
9 alkene polymer synthesis. This review discusses the key mechanistic
9
k-1 elements of living carbocationic polymerization emphasizing control of
1/b the propagation equilibria and the initiation step. This review further
2 shows how living processes have enabled the synthesis of new alkene
0
0.1 based polymers that exhibit remarkable properties.
1
s.org 7 | doi:
ac99 Why has interest in this field increased in the past ten years? The discovery of living
ubs.1, 1 vinyl/alkene polymerization is the main reason. This breakthrough has impacted the
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previously observed, but poorly explained phenomena. This activity may have the
largest future impetus in this field. Previous studies have often generated contradictory
findings from seemingly identical experiments. Such confusion has hurt efforts to
understand the fundamentals of carbocationic polymerization. The extreme dependence
on, and susceptibility of carbocations to, impurities in the solvents and monomers
triggers what look like inconsistent results. This fact alone contributed significantly to
the time lag between discovery of the living technique in anionic and cationic
polymerization.
In the current period of heightened interest, many books have been published on
carbocationic polymerization (1-4). Several reviews have also appeared (5-11). As
these materials provide a sufficiently up to date and comprehensive review of this
subject, one will not be provided here. Instead, the key elements of living vinyl/alkene
polymerization will be generally presented here, followed by a discussion of how living
carbocationic polymerization is used in new material synthesis.
1
© 1997 American Chemical Society
In Cationic Polymerization; Faust, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
2 CATIONIC POLYMERIZATION
The Key Elements of Living Polymerization
Living polymerization of alkenes became possible when two important concepts
were clearly understood: the dynamics of the propagation equilibria and the control of
the number and type of initiating species. The growing chain end may be represented
by a Winstein equilibrium. A simplified representation is shown below.
*A~RX • vwR+X" (1)
D C+
This simplification is justified by the independence of the carbenium ion's reactivity
regardless of the degree of dissociation (12,13). Both the dormant (D) and active (C+)
chain ends are interchangeable through this equilibrium. The exchange rate around the
equilibrium is influenced by the mode of initiation, the temperature, the solvents, the
1 presence of nucleophilic additives in the system and the nature of the monomer.
0
h0 Molecular control is only possible when the exchange rate between D and C+ is faster
c
5. than propagation. In essence, the lifetime of the ion is relatively small, producing a low
6
6 instantaneous concentration of active growing chain ends. This low level of
0
7- carbocations results in a low overall polymerization rate. Because of the rapid turnover,
9
9 only a few monomer units are added to the chain before collapse to the dormant state.
1
k- The length of all the polymer chains becomes more homogeneous as the polymerization
b
1/ proceeds.
2
0
1 To understand this, let us consider a living polymerization system at low
0.
1 conversion. The oligomers formed have an average length of ten, but vary from this
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ac99 before collapse to dormancy. This addition or propagation probability is not broad
ubs.1, 1 because of the rapid exchange rate between D and C+. At this point, however,
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Living cationic polymerization systems are not exempt from transfer or
termination (11). They are usually carried out in molecular weight regimes where the
influence of chain transfer or termination is not observable. The ratio of propagation to
transfer rates (kn/kr,M) then becomes the limit of molecular control. Since transfer to
t
monomer (k^M) is the most important chain breaking event for most cationic systems,
its rate is used in this determination. Matyjaszewski suggests the expression DP < 0.1
n
kp/ktr,M be used as a guide in choosing the polymerization conditions (9). DP is the
n
number average degree of polymerization for the desired polymer molecular weight.
There are a set of k, k^M, etc. values for each type of monomer. By knowing these
p
values and using the DP rule of thumb above, we may choose conditions under which
n
polymerization of the chosen monomer can easily reach the desired DP and maintain
n
control of the molecular weight, chain end structure, etc. For a given monomer, the
temperature dependence of k is not the same as k M due to different activation
p tr>
energies for each (14). Since the activation energy fof chain transfer is higher than
propagation, lower temperatures afford higher molecular weight polymer because
kp/ktr,M is larger. Obviously, a broader range of temperatures may be used to make
low molecular weight polymers. In addition, because k, k M, etc. values are
p tr
In Cationic Polymerization; Faust, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1997.