Fortschritte der Hochpolymeren-Forschung

194 Pages·1972·3.739 MB·English-German

by  J. P. Kennedy, J. K. Gillham (auth.)

Advances in Polymer Science
Fortschritte der Hochpolymeren-Forschung
Volume IO
Edited by
H.-J. CANTOW, Freiburg i. Br. . G. DALL’ASTA, Milan0
J. D. FERRY, Madison . H. FUJITA, Osaka. W. KERN, Mainz
G. NATTA, Milan0 . S. OKAMLJRA, Kyoto . C. G. OVERBERGER, Ann Arbor
W. PRINS, Syracuse . G. V. SCHULZ, Mainz . W. P. SLICHTER, Murray Hill
A. J. STAVERMAN, Leiden . J. K. STILLE, Iowa City . H. A. STUART, Mainz
With 50 Figures
Springer-Verlag Berlin. Heidelberg. New York 1972
Editors
Prof. Dr. H.-J. CANTOW, Institut fur Makromolekulare Chemie der Universitat, 7800 Frei-
burg i. Br., Stefan-Meier-Str. 31, BRD
Dr. G. DALL’ASTA, Istituto di Chimica Industriale de1 Politecnico, Milano, Italia
Prof. Dr. J. D. FERRY, Department of Chemistry, The University of Wisconsin, Madison 6,
Wisconsin 53706, USA
Prof. Dr. H. FUJITA, Osaka University, Department of Polymer Science, Toyonaka, Osaka,
Japan
Prof. Dr. W. KERN, Institut fiir Organische Chemie der Universitlt, 6500 Mainz, BRD
Prof. Dr. G. NATTA, Istituto di Chimica Industriale de1 Politecnico, Milano, Italia
Prof. Dr. S. OKAMURA, Department of Polymer Chemistry, Kyoto University, Kyoto, Japan
Prof. Dr. C. G. OVERBERGERT, he University of Michigan, Department of Chemistry, Ann.
Arbor, Michigan 48104, USA
Prof. Dr. W. PRINS, Department of Chemistry, Syracuse University, Syracuse, N.Y. 13210,
USA
Prof. Dr. G. V. SCHULZ, Institut fur Physikalische Chemie der Universitat, 6500 Mainz,
BRD
Dr. WILLIAM P. SLICHTER, Bell Telephone Laboratories Incorporated, Chemical Physics
Research Department Murray Hill, New Jersey 07971, USA
Prof. Dr. A. J. STAVERMAN, Chem. Laboratoria der Rijks-Universiteit, afd. Fysische
Chemie 1, Wassenaarseweg, Postbus 75, Leiden, Nederland
Prof. Dr. J. K. STILLE, University of Iowa, Department of Chemistry, Iowa City, USA
Prof. Dr. H. A. STUART, Institut fiir Physikalische Chemie der Universitat, 6500 Mainz,
BRD
ISBN 3-540-05838-9 Springer-Verlag Berlin . Heidelberg . New York
ISBN o-387-05838-9 Springer-Verlag New York Heidelberg Berlin
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Contents
Cationic Polymerization of 01efins with Alkylaluminium Initiators
J. P. YDENNEK and J. K. MAHLLIG . . . . . . . . . . . . . 1
Polymere aus Nitrilen. D. ELRHOW 53
. . . . . . . . . . . . . .
Zur Thermodynamik der enthalpisch und der entropisch bedingten
Entmischung von Polymerl6sungen. B. A. FLOW ....... 901
The Chemical Synthesis and Properties of Polysaccharides of Bio-
medical Interest. C. HCREUHCS 371
. . . . . . . . . . . . . .
Cationic Polymerization of Olefins with
Alkylaluminum Initiators
J. P. KENNEDY
Institute of Polymer Science, The University of Akron
Akron, OH 44325/USA
J. K. GILLHAM
Polymer Materials Program
Department of Chemical Engineering, Princeton University
Princeton, NJ 08540/USA
Table of Contents
.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
.2 Initiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
a) Historical Background . . . . . . . . . . . . . . . . . . . . . 3
b) Coinitiator Efficiency . . . . . . . . . . . . . . . . . . . . . . 5
c) Effect of Solvent . . . . . . . . . . . . . . . . . . . . . . . . 41
d) Grafting with Alkylaluminum Compounds ............ 81
3. Propagation and Transfer . . . . . . . . . . . . . . . . . . . . . 20
a) Effect of Counter-Ion . . . . . . . . . . . . . . . . . . . . . . 20
b) Effect of Solvent . . . . . . . . . . . . . . . . . . . . . . . . 23
c) Effect of Coinitiator . . . . . . . . . . . . . . . . . . . . . . 25
4. Termination . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
.5 Model Experiments to Simulate Olefin Polymerization ........ 30
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
.1 noitcudortnI
The discovery and use of alkylaluminum compounds in Ziegler-
Natta catalysis in the middle fifties led to their availability at modest cost
and to extensive experimentation with them as initiators in polymeriza-
tion. Olefins can be polymerized cationically using compounds such as
AI(C/Hs)C12 and A1CI 3 without requiring the explicit addition of
coinitiator, the presence of which is invoked to provide the true initiator.
On the other hand, some of the dialkylaluminum halides (e.g. AI(CH 2)3 C1)
and aluminum trialkyls (e.g. AI(CH3)3) exhibit certain theoretically
important and also useful features which set them apart from conven-
tional Lewis acids (e.g. BF 3, A1C13, TiCI4) and justify their separate
2 J.P. Kennedy and J, K. Gillham:
consideration. These initiators require the purposeful addition of
coinitiator for polymerization of olefins. This has led in recent years to
considerable research being directed toward the elucidation of the
fundamentals of cationic polymerization of mono- and di-olefins, with
dialkylaluminum halides and aluminum trialkyls as initiators and with
alkyt halides, aryl halides and protonic acids as coinitiators. This report
presents a review of this field of polymer chemistry. In addition to a
review of the pertinent scientific literature, significant and as yet un-
reported advances that have been made recently will be discussed.
The need for a coinitiator has led to mechanistic studies of models for
cationic polymerization, to the formation of higher molecular weight
polyolefins at more modest temperatures and at more controllable
rates than is obtained with aluminum trichloride, and to novel grafting
reactions.
Systems in which alkylaluminum compounds are used in conjunction
with transition metal halides (Ziegler-Natta catalysis), or systems in
which alkylaluminum compounds are used to polymerize monomers
other than olefins, fall outside the scope of the review. However, the
stereospecific polymerization of isobutyl vinyl ether to crystalline,
isotactic high polymer using AI(C2Hs)2C11 by Natta et al.(l), and of
propylene oxide using Al(CH3) 3 with small amounts of water to give
crystalline polymer by Colclough et al. (3) are to be noted.
At the outset some of the physical characteristics of alkylaluminum
compounds are noted which, together with the need for finite quantities
of coinitiator, make these systems better suited toc ontrolled experimenta-
tion than those employing AIC13. At(C2Hs)2C1, AI(C2Hs) 3 and related
compounds are readily available and inexpensive liquids which are easy
to purify and are readily soluble in common hydrocarbon solvents,
chlorinated hydrocarbons and carbon disulfide. Soluble polymerization
initiators are preferred over insoluble initiators because controlled
concentrations are easily prepared, and the solutions are easy to transfer.
By diluting with ethyl chloride or pentane, their freezing point can be
conveniently lowered, in some cases to below -130°C. In contrast to
the alkylaluminum compounds, commercial solid A1CI 3 contains
various quantities of ill-defined hydrolysis products (AIC12OH, A1OC1,
etc.) and absorbed HCI. These impurities are difficult to remove and
Nattaetal.coined(t)theterm"modifiedFriedet-Craftscatalysts'todesignate
1
halides of multi-valent metals in their highest valence state in which the halogen
atoms are partly substituted by organic groups. This terminology does not serve a
useful purpose and it helps to confuse further a rather confused area of chemical
terminology. sA it si very difficult to define what a "Friedel-Crafts catalyst" is or
si not [see for example, the Preface to "Friedel-Crafts and Related Reactions'(2)],
the modification of such an definition elusive becomes meaningless. Unfortunately
the terminology been has adopted by researchers. well-meaning some
Cationic Polymerization of snifelO 3
undoubtedly affect the polymerization mechanism, but the exact mode
of these influences is largely a matter of conjecture. 31CIA is only sparingly
soluble in methyl or ethyl chloride and is essentially insoluble in hydro-
carbons, carbon disulfide and carbon tetrachloride. Subtle problems
might arise during polymerization with the sparingly soluble 31C1A
initiator. Furthermore, since 31C1A is insoluble in hydrocarbon-rich
methyl chloride (a preferred polymerization medium), immediately
after introduction of a methyl chloride solution of this salt (a common
polymerization catalyst solution) into a monomer-charge containing
a large amount of olefin, 1C1A a precipitation is likely to occur. This
precipitation cannot always be observed because the polymerization of,
for example, isobutylene or styrene, ensues instantaneously and solid
polymer precipitates as a slurry. However, precipitation of 31C1A
is noticeable when a methyl chloride solution of this salt is introduced
into a mixture in which the isobutylene monomer is replaced by isobutane.
2. Initiation
a) Historical dnuorgkcaB
The highly effective polymerization of isobutylene, and copolymeri-
zation of isobutylene with diolefins, using dialkylaluminum halides
) AI(C~Hs)2CI (e.g. in conjunction with suitable coinitiators HC1, (e.g. HF)
in polar (e.g. CH3C1 ) and nonpolar solvents (e.g. n-CsH12 ) was dis-
covered in 1961 )4( by Kennedy. The coinitiator (e.g. HC1) was found
to be inactive in the absence of the dialkylaluminum chloride. Prior
to that time he had investigated the catalytic properties of the well-
known 31C1A and z AI(C2Hs)C1 initiators in polymerizing olefins and
diolefins; during these studies AI(CzHs)2C1 and AI(C2Hs) 3 were found
to be totally inactive under essentially identical conditions. According
to the theory of polymerization initiation with Friedel-Crafts halides,
a coinitiator is required for successful initiation. Adventitious traces
of protogenic impurities (e.g. H20, HC1) in the system are usually
sufficient to meet this requirement. In a number of systems (isobutylene-
TiCt4, isobutylene-BF ,3 styrene-A1C13, etc.) it has been repeatedly
demonstrated that polymerization cannot be initiated unless a protogenic
or carbocation-generating 2 agent is introduced. A summary of this
area has been provided by Pepper (2). The concentration of thec oinitiator
required for initiation with the various Friedet-Crafts halides has not
2 ehT term earbocations si used to in atoms carbon electrophilic denote .lareneg
Trivalent carbocations are termed carbenium ions. The term carbonium noi si
reserved to denote tetra- or terminology This penta-coordinated carbocations. sah
been proposed recently by G. .A Olah .J( Soc. Chem. Amer ,49 808 .))2791(
4 J.P. Kennedy dna .J .K Gillham:
yet been elucidated in detail. Kennedy considered that the inactivity of
1C2)sH2C(IA and 3 AI(CaHs) as initiators was due to the fact that for
sormeea son these materials require larger amounts of suitable coinitiators
than the related but more acidic 31CtA and AI(CzHs)C12. To test this
theory, small but measurable amounts of HCI were added to quiescent
and essentially open (not under high vacuum) isobutylene-At(C2Hs)2C1
and styrene-At(CzHs)2C1 systems at tow temperatures (5). Immediate
and sometimes even explosive polymerization occurred. The high
molecular weight of the products gave impetus for the subsequent
systematic exploration of these observations.
The scientific and patent literature contains some interesting pertinent
information. Kraus )6( as early as 1938 recognized that a mixture of
1C)3HC(IA a and AI(CH3)2C1 polymerizes isobutylene at -78°C to a
solid polymer. Even 1C2)3HC(tA alone seemed to have initiating activity.
The success of the polymerization with AI(CH3)2CI alone, was probably
due to the presence of large amounts of protogenic impurities in the
system and/or the particular experimental technique used (internal
cooling most probably with ice-laden dry-ice). Mavity )7( prepared
organoaluminum halides in situ by dissolving organoaluminum com-
pounds in hydrocarbon solvent and adding excess HCt. These mixtures
were active for alkylation and isomerization. Walsh and Schutze )8(
found that tert-butyl chloride and bromide have a powerful activating
effect on the catalytic action of Friedel-Crafts halides, such as A1Ct ,3
in the polymerization of olefins, notably, isobutylene. Ziegler et al. (9)
noted that AI(C2Hs)2C1 and 3 AI(C2Hs) are completely inactive toward
the polymerization of isobutylene. Young (lO) used mixtures of alkyl-
aluminum compounds and AICI3, for example A1Ct3, . 3 AI(CzHs) to
obtain soluble polymerization catalyst for olefins. Minckler etal.
(11,12) successfully used 3 AI(C2Hs) to activate such conventional
Friedel-Crafts catalysts as 41CnS which alone is inactive for isobutylene
polymerization and propylene oligomerization.
In the early sixties the area under review became defined. Kennedy's
early research has already received attention .)4( Gasparoni and Longiave
described in a patent (I3) a process for the polymerizatioofn isobutylene
in the presence of ,1C2)sH2C(IA which required using a solvent having a
dipole moment larger than one. This disclosure is misleading (see later).
In another patent (I4) the same authors with other coworkers reported
that dialkylaluminum halides can polymerize isobutylene in solvents
the dipole moment of which are less than one, provided a certain quantity
of water is added to the system. A significant paper appeared by Sinn
et al. (t5) who drew attention to the observation that the polymerization
of styrene with 3 AI(CzH~) commences only when traces of water or 1CH
are added. Significantly, they also found that traces of water are also
Cationic noitaziremyloP of snifelO 5
necessary for the polymerization of styrene, butadiene, isoprene and
vinyl ethers with Ziegler-Natta complex catalysts. Tinyakova et al. (16)
investigated the polymerization of isobutylene, styrene, butadiene and
isoprene in the presence of dialkylaluminum chloride (probably
AI(CzHs)zC1) and various coinitiators in benzene, hexane, toluene, and
ethyl chloride in the range of - 87 ° to C. ° + 20 The coinitiators of this
study were H20, CH3COOH and various hydrated salts LiC1. (e.g., xH20,
MgCI2.xH20, BaClz.xHzO, etc.). In nonpolar solvents dialkyl-
aluminum chloride initiated polymerization of these monomers in the
presence of coinitiators; however, aluminum trialkyl (probably
AI(C2Hs)3) either alone or together with the coinitiators was found
not to induce polymerization. Much higher activities of dialkylaluminum
chloride were obtained in ethyl chloride solvent, and the addition of the
above-mentioned coinitiators was unnecessary as the solvent itself (or
some contained impurity?) acted as the coinitiator. Under these condi-
tions at -78 C, ° a high molecular weight polyisobutylene was obtained.
The authors proposed a cationic initiation mechanism and suggested
the formation of an ion pair: + C2H5C1 5HzC~---1CzR1A ~. [A1R2Clz] ~
On the basis of independent evidence the present authors fully agree
with this formalism which shows that the initiator-coinitiator system si
not a true catalyst since part of the coinitiator is incorporated into the
polymer molecules .3 In the course of their elegant investigations on
vinyl and cyclic ether polymerization, Saegusa and his co-workers (l 7, 18)
also described experiments on the polymerization of styrene with
AI(CzHs)3/HzO and AI(CzHs)3/H20/CH3OCH2C1 initiator systems.
Among the less common hydrocarbon monomers, 2-methyl-l,3 penta-
diene (I9) and 1-isopropylidene-3a, ,4 ,7 7a-tetrahydroindene (20) have
been polymerized by AI(C2Hs)2C1/H20 and AI(C2Hs)zC1/t-C4H9CI
initiator systems respectively.
b) Coinitiator Efficiency
It seems that in agreement with the theory of coinitiation in cationic
polymerizations, proton donors (Bronsted acids) in general can act as
coinitiators in conjunction with alkylaluminum compounds. Charges
consisting of olefins with or without diolefins in bulk or in solution
can be stirred in the presence of AI(C2Hs)2C1 in the temperature range
of +30 ° to -100°C without polymerization occurring. However,
reaction takes place instantaneously upon introducing strong mineral
acid coinitiators which must be carefully diluted before introduction
3 For this "cocatalyst" and "catalyst" terms the reason eht rof munimulalykla
organohalide and compound era and "initiator" place their in and avoided -inioc"
tiator" era entity initiating actual the though even used sesira from eht .rotaitinioc
6 J.P. and Kennedy .J .K :mahlliG
into the quiescent systems; otherwise uncontrollably rapid poly-
merization will occur (4, 21). Weaker acids result in slower polymerization
and lower yields even in polar solvents (21). The rates obtained with the
less active coinitiators cannot be accelerated by employing higher
concentrations, since ill-defined side reactions compete effectively.
Polymerization si often readily noticeable by a haziness developing
suddenly upon coinitiator addition: for example, polyisobutylene and
isobutylene-isoprene copolymer are insoluble in the methyl chloride-
rich medium and precipitate as they are formed. This haziness is a
sensitive indicator for polymerization and is clearly noticeable even at
about one percent conversion.
The findings of experiments carried out by introducing various
Bronsted acids into isobutylene/isoprene/Al(C2Hs)2C1 in methyl chloride
and determining the yield of the polymer formed, suggest the following
series of coinitiator (in efficiencies terms of yield) fort he polymerization:
HCt > H20 > CH3OH > CH3COCH .3 This follows series approximately
the acidity function of the materials. Acetone probably acts as a proton
donor through its enolic form.
Implicit in the incomplete conversion of monomer with the weaker
coinitiators si that the systems are deactivated after some reaction. On
the other hand, implicit in the complete conversions of monomer with
the stronger coinitiators is that the efficiency of these systems is such as
to minimize the influence of the competitive deactivating reactions.
The dipole moment of the solvent has little influence on the success
or tailure of the polymerization of isobutylene with .1C2)sH2C(IA The
reaction can readily be induced in hydrocarbons (n-pentane) or carbon
disulfide, provided a suitable coinitiator is introduced. This statement
is forcefully corroborated by the fact that excellent products can be
obtained in undiluted isobutylene/isoprene charges. Experiments were
conducted with charges consisting of 97/3, 95/5 and 92/8 vol./vol.
isobutylene/isoprene in the absence of solvent, that ,si using the unreacted
monomers as diluent (2I). The AI(CzHs)2Ct initiator was added to the
monomers and polymerization was initiated by gradually introducing an
HC1/monomers mixture to the Al(C2Hs)2C1/monomers charge at
-98 C. ° Smooth, controlled polymerizations resulted, and high mole-
cular weight copolymers (butyl rubber) were obtained which could be
vulcanized to high quality elastomers. Table 1 shows some data.
The mechanism of polymerization-initiation with diatkylaluminum
halides in conjunction with Bronsted acids may be visualized as follows:
First the Bronsted acid and the A1R2X interact to provide the true
initiating species, e : HeA1R2X2
2RIA + X HX~-HeAIR2X~ 3 (or He//AIR2X2 e) )1(
E" o © N"
%
Unsatn. mol- 1.9 3.21 5.42
Gel. % 9.2 4.7 70
wt. -3)
10
Mol. (× 211
used.
(21)
a
323 13.5
in bulk % mixture
20.0
Yield
Yield g 28.0 18.0
monomer
mol
last.
copolymerizations mol 544 particular
A1Et2C1, HC1, 12.0 143 143 added the
in
9.0
b solution gas
HC1 3)
soln. 10
Isobutylene-isoprene mol (× 0.14 0.14 dry HCI
1. 4760 coinitiator
Table Coinitiator ml 0.0042 100 100 ° C; absorbing
-98 by
3 at
A1EtzCI mol
0.02 preparely
0.02 0.02
ml experiments
all solution
5
charge,
3 8
Monomer Isobutylene Isoprene 97 95 92 Conditions: b Coinitiator