Branching Regulation in Olefin Polymerization via Lewis Acid Triggered Isomerization of Monomers

Article abstract of DOI:10.1002/anie.201914742

We present a new strategy to regulate branching in chain-walking olefin polymerization by triggering a rapid isomerization of 1-alkene monomers into internal olefins by adding a Lewis acid. Polymerization of internal alkenes proceeds via chain-walking to give polymers with much higher branching than 1-alkene analogues. The utility of this approach is exemplified by synthesis of well-defined block copolymers with distinct branching characteristics per block by addition of Lewis acid midway through a reaction. We propose a novel mechanism whereby Lewis acid undergoes a counterion swap with the complex which favors isomerization as well as forming adducts with ancillary ligands, freeing coordination sites for internal alkene coordination polymerization.

Full text of DOI:10.1002/anie.201914742

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: Branching Regulation in Olefin Polymerization via Lewis Acid
Triggered Isomerization of Monomers
Authors: Hatice E. Basbug Alhan, Glen R. Jones, and Eva Harth
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201914742
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10.1002/anie.201914742
Angewandte Chemie International Edition
RESEARCH ARTICLE
Branching Regulation in Olefin Polymerization via Lewis Acid
Triggered Isomerization of Monomers
Hatice E. Basbug Alhan,[a] Glen R. Jones,*[a] Eva Harth,*[a]
Abstract: We present a new strategy to regulate branching in chain-
walking olefin polymerization by triggering a rapid isomerization of 1-
alkene monomers into internal olefins by adding a Lewis acid.
Polymerization of internal alkenes proceeds via chain-walking to give
polymers with much higher branching than 1-alkene analogues. The
utility of this approach is exemplified by synthesis of well-defined block
copolymers with distinct branching characteristics per block by
addition of Lewis acid midway through a reaction. We propose a novel
mechanism whereby Lewis acid undergoes a counterion swap with
the complex which favors isomerization as well as forming adducts
with ancillary ligands, freeing coordination sites for internal alkene
coordination polymerization.
Scheme 1: Example enchainments from chain-walking of A) 1-hexene, and B)
Introduction
2-hexene.
linearity. Tuning electronics of the catalyst through ligand design
Polyolefins are the most important class of polymers in
terms of volume of material produced and ubiquity in everyday life.
Comprised of alkenes with the general formula CnH2n, the wide-
ranging properties from different polyolefins arise from
parameters such as molecular weight, tacticity, and branching.
High branching, such as that found in low-density
polyethylene (LDPE), prevents chains from closely packing
making the material amorphous with high flexibility and low tensile
strength. Low branching allows polymer chains to closely pack
into a crystalline form, thus achieving a rigid, inflexible material
such as high-density polyethylene (HDPE). Block copolymers
which contain segments with both low and high branching are
highly valued due to thermoplastic elastomeric behavior[1] and
their ability to compatibilize immiscible polymer blends for
recycling applications.[2] These materials have typically been
prepared by living coordination-insertion polymerization with
sequential addition of different monomers, or variation of
temperature and pressure.[3] Other techniques[4] developed to
vary branching include chain-shuttling polymerization,[5] light
mediated approaches with iridium cocatalysts,[6] and redox active
catalysts.[7]
has been shown to alter the amount of chain-walking to give
polymers with different branching.[11] Differences in branching can
also arise from the position of the double bond in the monomer.
Scheme 1A shows examples of enchainments from chain-
walking; 1,2 vs. 2,1 insertion of a 1-alkene followed by chain-
walking can result in either a branched or linear unit. In
comparison, chain walking of internal olefins e.g. 2-alkenes are
unable to form highly linear sequences due to the internal position
of the double bond (scheme 1B). Chain-walking polymerization of
these monomers therefore results in highly branched polymers.
Chain-walking of internal alkenes is of interest because it
allows for highly branched polymers. However, polymerization of
these monomers is more challenging than 1-alkenes, which has
been suggested to be due to steric and electronic barriers to
insertion in the Cossee-Arlman mechanism.[12] Early work by
Brookhart showed that palladium catalysts polymerized trans-2-
hexene at a very slow rate, reporting only 0.8% yield of polymer
in a typical reaction time frame (scheme 2).[13] Low rates were also
observed for cyclopentene with a similar palladium complex, with
reactions taking 6 days.[14] Nickel catalysis has been shown to be
more successful at polymerizing internal alkenes due to their
higher activity, although initial work from Brookhart indicated a
strong preference for trans isomer; no polymerization of cis-2-
butene was reported.[15] In 2017 Shiono and coworkers reported
successful homopolymerization of a range of 2-alkenes from a
nickel diimine catalyst.[12, 16] Nickel catalysts have shown further
potential in the polymerization of internal olefins,[17] although block
copolymers with 1-alkenes have never been reported. Another
downside is the higher cost of internal alkenes compared to 1-
alkene counterparts.
In 1995 Brookhart and coworkers first reported the use of
palladium and nickel diimine catalysts for the polymerization of
olefins.[8] These catalysts are known to be able to incorporate
small amounts of polar functionality into a polymer chain[9] and
operate with a so-called chain-walking mechanism whereby a
series of β-hydride eliminations and insertions can allow the metal
to effectively ‘walk’ along the chain.[10]
The nature of chain-walking enables the synthesis
polyethylene with branches as well as poly(1-alkenes) with high
We envisioned that a potential way to overcome the
limitations and downsides of internal alkene polymerization and to
form block copolymers with different branching structures would
be to utilize an isomerization reaction in order to transform readily
available 1-alkenes into internal alkenes which could then go on
to polymerize via a chain walking mechanism to give highly
branched polymers. Pioneering work by Otsu and coworkers in
the 1960’s and 70’s explored the polymerization of 2-alkenes such
[a]
H. E. Basbug Alhan, Dr G. R. Jones, Prof. E. Harth
Department of Chemistry, Center of Excellence in Polymer
Chemistry
University of Houston
3585 Cullen Blvd., Houston, Texas, USA, 77204
E-mail: gjones7@uh.edu, harth@uh.edu
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/anie.201914742
Angewandte Chemie International Edition
RESEARCH ARTICLE
Block copolymers of 1-alkenes and internal alkenes can be
prepared using triggered isomerization by adding Lewis acid
midway through a normal 1-alkene polymerization. This new
concept in polyolefin block copolymer synthesis is a one pot
process that only requires one starting monomer and an
inexpensive additive.
Results and Discussion
Scheme 3: Polymerization of 1-hexene with palladium catalyst 1 in the
presence of AlCl3 showing full isomerization at 5 minutes. Branched polymer
structure due to chain-walking is represented by n and R.
Our initial observation of enchanced alkene isomerization in the
presence of Lewis acid was noted during a study of reactivity
ratios of alkenes and polar monomers in palladium-diimine
catalyzed polymerizations. Attempts to alter polar monomer
reactivty with Lewis acids showed low rates of polymerization.
However, a control reaction in which a Lewis acid, AlCl3, was
added to a polymerization of 1-hexene with palladium catalyst, 1,
scheme 3, yielded a polymer with a dramatically different structure
in 1H NMR (fig. 1A). Poly(hexene) synthesized without Lewis acid
was calculated to have 105 branches per 1000 carbon atoms,
whereas addition of Lewis acid (4 eq.) yielded a polymer with 152
branches per 1000 carbon atoms.
Regular sampling and kinetic analysis of the polymerization
revealed that in the presence of AlCl3 1-hexene is rapidly
isomerized to 2-hexene and 3-hexene within the first five minutes,
as evidenced by the disappearance of 1-alkene protons (5.82
ppm and 4.96 ppm, t=0, fig. 2) and the appearance of internal
olefin protons (5.42 ppm, t=5, fig. 2). Polymerization of these
internal olefins then proceeds with living characteristics including
a linear increase in molecular weight with conversion, ESI section
5.3, (85% conversion in 3 hours, Mn = 46.1 kDa (SECTHF)) and low
dispersity (Đ = 1.10, fig. 1C). Insignificant amounts of oligomeric
species are formed in the initial stages of the reaction, which is
attributed to cationic polymerization initiated from the Lewis acid.
The concentration of these oligomers does not increase after 5
minutes and they are easily removed by precipitation of the final
polymer (ESI section 5.3). Optimization of the amount of AlCl3
added to the polymerization (fig. 1C, ESI Section 5.4) shows that
~20% of 1-hexene is isomerized within 5 minutes in the absence
of Lewis acid, consistent with previous literature.[13] 1 or 2 eq. with
respect to the palladium catalyst yielded ~80% isomerization.
Increasing the aluminum chloride to 3 eq. increased the
isomerization to >90%. 4 eq. yielded a monomer composition of
80 mol% 2-hexene and 20 mol% 3-hexene with less than 0.5%
remaining 1-hexene. The 2-hexene formed in the isomerization is
~75% trans (ESI Section 5.4) and the ratio between cis and trans
species remains constant throughout polymerization.
Scheme 2: (Top) Examples of previous work involving the polymerization of
internal alkene monomers using cationic palladium and nickel diimine catalysts.
(Bottom) The triggered isomerization approach described in this work.
as 2-heptene and 2-octene with Ziegler-Natta catalysts in a
process known as monomer-isomerization polymerization.[18] The
polymers formed were found to be structurally identical to those
of the corresponding 1-alkene. Mechanistically the reaction was
found to occur via isomerization of charged 2-alkenes to 1-
alkenes which are then consumed in polymerization, driving the
isomerization equilibrium to form more 1-alkene. Our approach
differs from Otsu’s work as we are able to trigger isomerization at
a time of our choosing by adding a Lewis acid cocatalyst, our
isomerization is very fast compared to polymerization, the MWDs
are narrow in our polymerization, and the starting material is the
more readily available 1-alkene. More recently, Takeuchi has
reported chain-walking catalysts for the polymerization of
alkenylcyclohexanes which was dubbed “precise isomerization
polymerization”.[19] This work is perhaps better described as
catalysis with full chain-walking, otherwise known as ‘chain-
straightening’,[20] yielding only ω-1 enchainment.
Herein we describe the use of a Lewis acid cocatalyst with
palladium diimine complexes which facilitates an isomerization of
1-alkenes to yield free internal alkene monomers in just 5 minutes.
Surprisingly, the polymerization of these isomers occurs to high
conversions in just 3 hours to yield polymers with narrow
molecular weight distributions (MWDs) and much higher
branching than traditional Pd-mediated polymerizations of 1-
alkenes. Preliminary mechanistic investigations implicate
a
counterion switch in the fast isomerization reaction, and the
formation of adducts between Lewis acid and ancillary ligands
which would otherwise inhibit internal alkene polymerization.
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10.1002/anie.201914742
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RESEARCH ARTICLE
Figure 1: (A) 1H NMR of purified polymers. Blue Trace: poly(hexene). Red trace: poly(hexene) synthesized in the presence of AlCl3. Branches per 1000C =
(CH3/3)/[(CH+CH2+CH3)/2]*1000. (B) SEC traces for polyhexene synthesized with 0 eq. AlCl3 (blue) and 4 eq. (red). (C) monomer composition at t = 5 minutes for
1-hexene polymerization with increasing amounts of AlCl3 (eq. relative to palladium).
Table 1: Branch distributions for polymerizations aDenotes monomer that was added to the reaction. bMol. eq. relative to Pd cat. cBranches per 1000 C =
(CH3/3)/[(CH+CH2+CH3)/2]*1000 by 1H NMR. dAll Branching numbers are given per 1000 carbon atoms and rounded to the nearest whole number. Individual
branching numbers were calculated by setting integral of a quantitative 13C NMR to 1000 and then further integrating the CH3 peak from each contributing branch.
eDetermined by differential scanning calorimetry (DSC). fTg could not be measured due to broad Tm.
Branches / 1000 C
b
Entry
Monomera
AlCl3
B (1H)c,d
B(13C)d
Tg (oC)e
Tm (oC)e
Med
Etd
Prd
Bud
≥Ped
1
2
3
4
5
6
7
1-Hexene
1-Hexene
2-Hexene
1-Octene
1-Octene
1-Decene
1-Decene
0
4
4
0
4
0
4
105
152
156
84
99
149
145
80
67
8
7
8
9
-49.4
-70.8
-69.8
-41.2
-71.6
-9.1
66
70
44
31
33
19
36
32
9
25
24
5
17
15
4
5
-
4
-
17.7
-
18
28
17
36
116
67
107
53
21
3
15
>1
9
12
>1
9
f
-
28.6
-
96
86
13
-72.0
Quantitative 13C NMR branching analysis of the precipitated
poly(hexene) samples (table 1, entries 1 & 2) shows good
agreement between the branches/1000 carbons as calculated by
1H and 13C NMR. Polymer synthesized in the absence of AlCl3
(table 1, entry 1) shows many methyl branches (67/1000) with
much smaller amounts of longer branches. The isomerization of
1-hexene to 2/3-hexene in the presence of AlCl3 significantly
increases the amount of longer branches in the polymer (table 1,
entry 2) while the methyl branch composition is like regular 1-
hexene polymerization, resulting in an overall increase in the
number of branches. We envision that the difference in branching
between entries 1 & 2 in table one are due to the different
enchainments that are possible from 2/3-alkene coordination
insertion and chain-walking versus 1-alkene. As described in the
introduction, 1-alkene can undergo 2,1-insertion followed by full
chain walking to yield linear segments, whereas internal alkenes
cannot form linear segments. Similar reactivity (3,2-insertion and
chain-walking) results in a methyl branch for 2-hexene. The
presence of butyl and pentyl branches in these polyhexene
samples is attributed to the palladium chain-walking ‘back’ along
the polymer chain. The physical differences between
polyhexenes prepared by regular polymerization and Lewis acid
triggered isomerization polymerization are highlighted by the
different thermal properties. Regular 1-hexene polymer has a
significant degree of linearity, hence chains can pack closely and
form crystalline domains, giving a Tm. In contrast, the triggered
isomerization to internal alkenes results in a polymerization where
a high degree of linearity is impossible. The polymer doesn’t
exhibit a Tm and the Tg is much lower than regular 1-hexene
polymerization, indicating a highly amorphous material.
An attempt was made to synthesize poly(2-hexene) starting
from the internal olefin monomer (trans-2-hexene) to compare
branching and corroborate the 1H NMR evidence in fig. 2 that the
polymerization system essentially allows us to obtain poly(2-
hexene) structure from 1-hexene monomer; however, only very
low conversion (<1%) was observed in a 3 hour reaction time, in
agreement with previously reported polymerization from similar
palladium diimine catalysts.[13] Repeating this reaction with 4 eq.
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RESEARCH ARTICLE
Scheme 4: Proposed mechanism is triggered isomerization polymerization showing: regular polymerization of 1-alkene from [BArF4]- complex 2 (blue pathway);
counterion swap in presence of AlCl3 promoting β-hydride elimation and reinsertion causing isomerization (gray pathway); chain-walking polymerization of internal
alkene (red pathway) from [BArF4]- complex or [AlCl4]- complex when ancillary ligand (ACN) is adducted with AlCl3.
of AlCl3 allowed a much more rapid polymerization to occur (ESI
Section 5.5), thus demonstrating the ability of the catalyst system
to directly polymerize internal olefins. This is further exemplified
by polymerization of 4-octene (ESI Section 5.5). Polymerization
of cis-2-hexene by catalyst 1 and AlCl3 was found to occur via
isomerization to the trans isomer. This is in stark contrast to other
diimine catalyst systems which have shown little polymerization
of cis isomers.[15] The versatility of isomerization-polymerization
with respect to regiochemistry and the position of the double bond
offers future potential in the polymerization of unconventional
alkenes from natural sources and industrial byproducts. Poly(2-
hexene) shows very similar branching to poly(hexene)
synthesized with AlCl3 (table 1, entry 3), indicating that
isomerization followed by polymerization occurs with 1- alkenes;
this is further supported by the very similar glass transition
temperatures of the two materials. Key benefits of our triggered
isomerization and polymerization approach over direct
polymerization of 2-hexene (with AlCl3) include a faster rate (85%
vs. 46% monomer conversion for a 3 hour reaction time),
improved control (Đ = 1.10 vs 1.17), and the higher availability
and lower cost of 1- alkene monomers. 1-Octene exhibited the
same isomerization behavior (ESI Section 5.6) when polymerized
with palladium-diimine catalyst, 1, and AlCl3, yielding polymeric
structures with a much higher degree of branching (116 branches
per 1000 carbons versus 84 branches, table 1 entries 4 and 5),
consistent with polymerization of the corresponding internal
olefins. Similar results were obtained with 1-decene (67 vs. 96
branches, table 1 entries 6 and 7, ESI section 5.7). 13C NMR
analysis reveals that poly(octene) and poly(decene) synthesized
in the presence of AlCl3 also contain larger amounts of longer
branches. The higher degree of linearity in regular 1-octene and
1-decene polymerizations is due to the lower theoretical
branching maximums for higher 1-alkenes (1 carbon per
monomer forming a branching point). This gives a greater
difference in physical properties between regular polymerization
and the highly amorphous polymers formed in triggered
isomerization-polymerization.
Figure 2. Selected NMR’s from the kinetic analysis of 1-hexene polymerization
in the presence of 4 eq. AlCl3. t=0 (blue) shows 1-hexene monomer, t=5 (gray)
shows shift in 1-hexene alkene protons to 2/3-hexene, t=30 (green) shows
appearance of characteristic broad polymer peaks ~1.00-1.35 ppm. Red trace
shows purified polymer, isolated after 3 hours.
From a mechanistic standpoint, Pd-diimine catalysts are
known to isomerize 1-alkenes to a certain extent, with β-hydrid
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Figure 3: (A) Synthesis of block copolymers of 1-hexene with different branching structures per block via addition of AlCl3 midway through the polymerization. (B)
Cartoon structure representing branching in a block copolymer. (C) SEC traces for branched hexene block copolymer. (D) 1H NMR showing branching in diblock
copolymer
elimination from agostic palladium alkyl complexes forming a
palladium hydride species which can then undergo 2,1-insertion
with 1-alkene followed by reinsertion of the hydride to yield the
isomeric 2-alkene.[21] The extent of isomerization seems to be
greatly enhanced by addition of AlCl3. Lewis acids have
previously been demonstrated to enhance nickel catalyzed olefin
isomerization through a Lewis adduct formed with the diimine
ligand, altering the electronic environment of the catalyst.[22]
However, the diimine ligand employed in this study did not contain
any likely binding motifs for Lewis adduct formation. AlCl3 in the
absence of Pd catalyst was found to promote an uncontrolled
polymerization (possibly cationic) with no evidence of
isomerization. We instead postulated that the Lewis acid was
faster than previously reported. We hypothesized that the ACN
ancillary ligand may be competing for binding sites with the 2-
alkene. Repeating the control experiment (chloride precursor,
AlCl3, 1-hexene) in the absence of ancillary ligand gave full
isomerization in 5 minutes and polymerization to high conversion
with high branching in 3 hours. A polymerization of trans-2-
hexene with a palladium diimine [BArF ]- complex also gave much
4
higher polymerization rates than an analoguous reaction in the
presence of ancillary ligand. Proton NMR shows a shift in the
protons of acetonitrile with addition of AlCl3, proposed to be
formation of a Lewis adduct, preventing competitive binding of
ACN to the catalyst. Reactions using other Lewis acids such as
FeCl3 and ZnCl2 also cause isomerization of 1-hexene followed
by polymerization of internal alkenes, although with varying rates
(ESI section 5.10).
forming a new counterion and displacing [BArF ]-. An experiment
4
in which 2 eq. of AlCl3 were added to the chloride precursor of 1
and an excess of acetonitrile (ACN) ancillary ligand yielded 1 with
an [AlCl4]- counterion, which was isolated and characterized by X-
ray crystallography (ESI section 5.10). Sen and coworkers have
With the experimental evidence of the counterion effects
detailed above, we propose a mechanism of Lewis acid triggered
isomerization and internal alkene polymerization in scheme 4.
previously investigated AlCl3 as an activator of diimine complexes, From the known intermediate 2, insertion and chain walking
proposing that the counterion formed is [Al2Cl7]-, however this was
not confirmed in a crystal structure.[23] Addition of 1-hexene to this
catalyst showed rapid isomerization to internal alkenes in 5
minutes, although no polymerization was observed in a typical 3
hour reaction time. Sen’s work only reported polymerization of
propylene, which cannot isomerize to give an internal olefin.[23]
Our result suggests that an aluminum counterion is responsible
for promoting β-hydride elimination and reinsertion to give
isomers, possibly due to an electron donating interaction from the
less bulky counterion with the palladium center.[24] Low rates of
polymerization of internal alkenes is in agreement with
Brookhart’s work on Pd-catalyzed polymerizations, attributed to
low binding rates of internal alkenes. However under our typical
polymerization conditions internal alkene polymerization is much
results in a regular 1-hexene polymerization (blue pathway).
Addition of AlCl3 is proposed to disproportionate and displace the
[BArF ]- counterion to give an [AlCl4]- counterion, 3, as evidenced
4
by x-ray crystallography. We envision that only a small fraction of
palladium centers would have to undergo this counterion swap
(minor pathway), as a control reaction utilizing much lower
concentrations of Pd catalyst still showed quantitative
isomerization in
5 minutes (ESI section 5.10). β-Hydride
elimination from 4 followed by 2,1-insertion and a further β-
hydride elimination (5 to 6) gives the complexed internal alkene,
7. This alkene is displaced by much stronger binding 1-alkene to
regenerate complex 5 and give free internal alkene. This
isomerization pathway (grey) is supported by previous literature
examples of diimine mediated isomerzation[21-22] and
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10.1002/anie.201914742
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RESEARCH ARTICLE
experimental evidence of enhanced isomerization from [AlCl4]-
counterioned complexes. Finally, polymerization of the internal
alkene (red pathway) occurs when there is no 1-alkene left to
compete for the coordination site, occuring via a chain-walking
mechanism to give highly branched polymer. The polymerization
can either occur from complex 7 or 2‘, as ancillary ligand from the
starting complex is most likely in adduct form with the excess
aluminum chloride added to the reaction, further promoting the
polymerization.
branching characteristics per block. Future work will explore the
synthesis of block copolymers with drastic differences in
crystallinity, polymerization of internal alkenes from natural
sources and waste streams, and further probing the effects of the
[AlCl4]- counterion on of the isomerization-polymerization process.
Acknowledgements
Due to the change in properties associated with higher
degrees of branching, the possibility of synthesizing block
copolymers using isomerization-polymerization was explored by
The authors thank the Robert A. Welch Foundation for generous
support of this research (#H-E-0041) through the Center of
Excellence in Polymer Chemistry.
adding AlCl3 mid-way through
a reaction. 1-Hexene was
polymerized with Pd-diimine catalyst, 1, and a sample was taken
after 1 hour (44% conv., Mn = 24.0 kDa, Đ = 1.03, 95/1000C
branches) after which 4 eq. of AlCl3 was added to the reaction.
Total isomerization was observed after 5 minutes. Sampling after
an hour yielded a polymer with a narrow, monomodal MWD (67%
conv., Mn = 32.5 kDa, Đ = 1.05, 116/1000C branches). The narrow
MWD and the full shift in the SEC trace indicates the formation of
a well-defined block copolymer. Knowing the branching from the
total block copolymer and the branching from the first block we
were able to calculate the degree of branching in the second block
by taking monomer conversion into account (ESI section 5.11).
the second block is calculated to have ~155 branches/1000C; this
is in perfect agreement with the branching observed in
homopolymerizations of 1-hexene and triggered isomerization-
polymerizaton (table 1 entries 1-3). The triggered isomerization
approach yields poly(1-hexene) as a first block followed by a
triggered isomerization of the remaining monomer upon addition
of Lewis acid to form a second block of poly(n-hexene) with higher
branching (fig. 3). According to our proposed mechanism
(scheme 4), addition of Lewis acid midway through the reaction
must result in some palladium centers eliminating the first block,
in order to be able to isomerize the remaining monomer. The
fraction of palladium centers which swap counterions to [AlCl4]- is
presumed to be small as the clear shift in the SEC trace and low
dispersity indicate high fidelity blocks. Triggering isomerization as
opposed to performing sequential monomer additions to yield
blocks has the advantage of avoiding the typical deviation from
first order kinetics seen at high conversions of 1-alkene in typical
polymerizations. This new approach to polyolefin block copolymer
synthesis is a one pot process in which the composition of the
blocks can be tuned by altering the point of addition of the Lewis
acid
Keywords: Isomerization • Olefins • Branching • Block
Copolymers • Chain-walking
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10.1002/anie.201914742
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RESEARCH ARTICLE
RESEARCH ARTICLE
Hatice Basbug Alhan, Glen R. Jones,*
Eva Harth*
Page No. – Page No.
Branching Regulation in Olefin
Polymerization via Lewis Acid
Triggered Isomerization of Monomers
Addition of AlCl3 to a Pd-mediated chain-walking polymerization results in rapid
isomerization of 1-alkenes to internal alkenes which polymerize with high
branching. Block copolymers can be prepared by adding AlCl3 midway through the
reaction.
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