Efficient synthesis of long-chain highly branched polymers via one-pot tandem ring-opening metathesis polymerization and acyclic diene metathesis polymerization

Article abstract of DOI:10.1021/ma1020903

A facile one-pot synthesis of long-chain highly branched polymers (LCHBPs) was accomplished by a tandem ring-opening metathesis polymerization (ROMP) and acyclic diene metathesis (ADMET) polymerization procedure. A telechelic polymer with two terminal allyloxy groups and many pendent acrylates was first prepared through the first generation Grubbs catalyst-mediated chain transfer ROMP of 7-oxanorborn-5-ene-exo,exo-2,3-dicarboxylic acid bis(2-(acryloyloxy)ethyl) ester in the presence of a symmetrical multifunctional olefin 1,4-diallyloxy-cis-2- butene as chain transfer agent (CTA), and then utilized as an A ₂B_2n-type macromonomer in subsequent ADMET polymerization between allyloxy and acrylate triggered by the most activated second generation Grubbs catalyst, yielding LCHBPs as the reacton time prolonged. The CTA, monomer, macromonomer, and the resulting LCHBPs were characterized by mass spectroscopy, elemental analysis, gel permeation chromatography with multiangle laser light scattering, NMR and matrix-assisted laser desorption ionization time-of-flight mass measurements. The LCHBPs have comparatively high molecular weights and relatively moderate polydispersity indices.

Full text of DOI:10.1021/ma1020903

10336 Macromolecules 2010, 43, 10336–10342
DOI: 10.1021/ma1020903
Efficient Synthesis of Long-Chain Highly Branched Polymers via One-Pot
Tandem Ring-Opening Metathesis Polymerization and Acyclic Diene
Metathesis Polymerization
Liang Ding, Meiran Xie,* Dan Yang, and Chunmei Song
Department of Chemistry, East China Normal University, Shanghai 200062, China
Received September 9, 2010; Revised Manuscript Received November 18, 2010
ABSTRACT: A facile one-pot synthesis of long-chain highly branched polymers (LCHBPs) was accom-
plished by a tandem ring-opening metathesis polymerization (ROMP) and acyclic diene metathesis
(ADMET) polymerization procedure. A telechelic polymer with two terminal allyloxy groups and many
pendent acrylates was first prepared through the first generation Grubbs catalyst-mediated chain transfer
ROMP of 7-oxanorborn-5-ene-exo,exo-2,3-dicarboxylic acid bis(2-(acryloyloxy)ethyl) ester in the presence
of a symmetrical multifunctional olefin 1,4-diallyloxy-cis-2-butene as chain transfer agent (CTA), and then
utilized as an A2B2n-type macromonomer in subsequent ADMET polymerization between allyloxy and
acrylate triggered by the most activated second generation Grubbs catalyst, yielding LCHBPs as the reacton
time prolonged. The CTA, monomer, macromonomer, and the resulting LCHBPs were characterized by
mass spectroscopy, elemental analysis, gel permeation chromatography with multiangle laser light scattering,
NMR and matrix-assisted laser desorption ionization time-of-flight mass measurements. The LCHBPs have
comparatively high molecular weights and relatively moderate polydispersity indices.
Introduction
with functionality is the ruthenium-catalyzed chain transfer ring-
opening metathesis polymerization (ROMP or ROMP-CT) of
Long-chain branched polymers (LCBPs), as one type of hyper-
branched polymers,1 have attracted increasing attention due
to their unique architectures and properties including higher
solubility, lower solution or melt viscosity, stronger melt elasticity
and storage modulus, and special strain hardening in elongational
flow relative to their linear analogues.2-5 Generally, LCBPs can be
obtained from the polymerization of AB2-type macromonomers in
either chain-growth fashion or step-growth fashion. The former
strategy has been extensively utilized in the synthesis of graft-
copolymers6 and the LCBPs with different branch densities by the
chain-extending reaction of linear multifunctional prepolymers.7
The latter strategy, founded on the conversion of R,ω-functional
AB2 macromonomers into LCBPs, is primarily actualized through
Williamson coupling reaction,8-14 esterification,15-17 and hydro-
silylation reaction.18,19 Using the same concept, the LCBPs based
on ABn-type macromonomers are constructed by the esterification
reaction.20 The common drawbacks for these conventional poly-
condensation processes, however, are that the resulting polymers
have broad molecular weight distribution and low branched degree
of polymerization, and only a few systems allow the control over
molecular weight and molecular weight distribution of the LCBPs.
For instance, the well-defined long-chain hyperbranched polysty-
renes with high degree of polymerization and narrow molecular
weight distribution21 have recently been prepared by click reaction
of AB2 macromonomer.
cyclic monomers in the presence of functional chain transfer
agents (CTAs).25 When the symmetrical CTAs of R,ω-allylic ether
or ester deduced from cis-1,4-butenediol are employed, the
telechelic polymers can be obtained and the number-average
degree of chain-end group functionality (Fn) values approaching
two are typically achieved. Usually, ROMP-CT of high or even
low ring strained cycloolefins is readily accomplished by adopting
the first generation Grubbs catalyst (Ru-I),26 while it is necessary
for using the highly active and more functional group tolerance of
the second generation Grubbs catalyst (Ru-II) to initiate the
lower ring strained cyclooctene with large pendant substituents27
and/or CTAs capped with either bulky dendrons or Lewis basic
functionalities.25,28 However, as far as we are concerned there are
few literature examples to date describing the synthesis of long-
chain highly branched polymers (LCHBPs) and not so many
examples regarding the synthesis of LCBPs via olefin metathesis
techniques including ROMP and acyclic diene metathesis
(ADMET) polymerization. Grubbs et al.29 synthesized a series
of hyperbranched polymers by means of ADMET polymerization
of ABn monomers with one terminal olefin and two or more
acrylates using the metathesis catalyst Ru-II. Subsequently,
Meier and co-workers30 investigated acyclic triene metathesis of
a triglyceride using different amounts of methyl acrylate as a chain
stopper to prevent full cross-linking and obtain branched poly-
mers in a straightforward one step one-pot polymerization.
Mathers et al.31 provided a different ROMP-based approach
for the preparation of functional hyperbranched polymers using
the one-pot polymerization of dicyclopentadiene. Moreover, a
simple route through ADMET polymerization of AB2 monomer
containing an azo-moiety to generate a functional hyperbranched
polymer has been exhibited in our previous work.32
Olefin metathesis polymerization, as one of the most conve-
nient synthetic tool for the synthesis of polyolefins, had an
enormous impact on polymer chemistry,22 especially on the field
of the living polymerization23 to prepare highly functional
polymers.24 A well-known method for controlling molecular
weight, tailoring polymeric architecture, and enduing the polymer
Despite having developed some strategies for the preparation
of branched polymers, constant efforts are needed to devote to
*Corresponding author. Fax: (þ86) 21 62232414. E-mail: mrxie@
chem.ecnu.edu.cn.
pubs.acs.org/Macromolecules
Published on Web 12/02/2010
r 2010 American Chemical Society

Article
Macromolecules, Vol. 43, No. 24, 2010 10337
Scheme 1. One-Pot Synthesis of Long-Chain Highly Branched Poly-
mers via the Combination of ROMP and ADMET Polymerization
information). The functional monomer, 7-oxanorborn-5-
ene-exo,exo-2,3-dicarboxylic acid bis(2-(acryloyloxy)ethyl)
ester (2) bearing a cyclic norbornenyl group and two acyclic
acrylates, was synthesized through a similar procedure as the
1
previous reports.37 Elemental analysis, and H NMR and
13C NMR spectroscopy (Figure S2, Supporting Information)
affirmed the successful preparation of monomer 2 with the
expected chemical structure.
Functional Telechelic Polymer by ROMP-CT. It has been
shown that in a ruthenium-catalized metathesis/chain trans-
fer system, ROMP is favorably realized in a chain growth
fashion and subsequently chain transfer events.25 That is to
say a chain transfer cross metathesis reaction happened
between the ruthenium alkylidene species at the end of a
living ROMP polymer chain and CTA, which shorten the
polymer chains, and over time the amount of CTA on
polymer chain end steadily increased.28,38 In this case, taking
advantage of ROMP-CT for synthesis of the functional
telechelic polymer 3 with the terminal allyloxy and the
pendent acrylate, three crucial aspects are the most con-
cerned with monomer, CTA, and catalyst: (i) monomer 2
provides an apparently reactive norbornenyl functionality
for ROMP-CT and two essentially latent acrylate function-
alities, which is a potentially useful precursor and will
become the reactive functionality for subsequent ADMET
polymerization; (ii) differing from the commonly CTA of
R,ω-allylic cis-olefin, CTA 1 is such a symmetrical multi-
allylic ether of cis-1,4-butenediol containing one internal cis-
olefin and two R,ω-diallyl end olefins, although it is of
seldom use as CTA in ROMP, that guarantees the telechelic
polymer chain end-capped with two allyloxy groups by
means of this special CTA being whether cleaved the internal
cis-olefin into two symmetrical fragments or metathesized
any one of the two end allylic olefins via ruthenium carbene
since it exhibits the high rate of reactivity toward terminal
olefins;38,39 (iii) catalyst Ru-I is of an optimal candidate for
ROMP-CT, based on the comprehensive considerations of its
moderate functional group tolerance, proper metathesis activ-
ity, and good control over the polymer structure and molecular
weight in the metathesis-mediated polymerizations, to pre-
cisely tailor the telechelic polymer architecture and depress
possibly secondry metathesis reactions (such as back-biting) or
even ADMET polymerization of allyloxy groups.
The great advantage of ROMP-CT for the preparation of
telechelic polymers is the ability to conveniently control the
molecular weight through regulating the molar ratio of mono-
mer to CTA.26 In order to get the telechelic polymer 3 with
relatively low molecular weight, the polymerization of mono-
mer 2 in the presence of CTA 1 is initiated by catalyst Ru-I
using the monomer to CTA and catalyst ratios of 1000/200/1,
i.e., a low monomer to CTA ratio of 5/1 and a high CTA to
catalyst ratio of 200/1 are employed according to that of
previous studies where a CTA/catalyst ratio of 200 or more
is necessary to ensure the prepared telechelic polymers with
difunctionality.25,40 After the metathesis polymerization/chain
transfer reaction being conducted for 24 h, the end-capping of
a ROMP polymer chain with a CTA has reached completion.
In other words, at thermodynamic equilibrium, every CTA
molecule has been incorporated into the polymer chain,33,41
affording a functionalized telechelic polymer with high Fn and
in a high yield. A monomodal peak in the GPC chromatogram
(Figure 1) is observed for this as-obtained telechelic polymer 3
with a relatively low polydispersed index (PDI) of 1.45, and the
molecular weight (Mn,GPC) is found to be 3.8 kDa as envi-
sioned low (Table 1).
seek more efficient and versatile methods for the synthesis of
LCBPs through olefin metathesis polymerization. It is known
that ROMP of norbornene and its derivatives is extremely fast
because of the release of large amounts of ring strain, with rate
constants several orders of magnitude faster than cross metath-
esis reactions. Similarly, cross metathesis is several orders of
magnitude faster than secondary metathesis (back-biting) of
substituted polynorbornenes. On the basis of the great differences
in reactivity between ROMP, cross metathesis, and secondary
metathesis,33,34 we expected that a combination of various
metathesis polymerizations would be possible to synthesize
functional polymers in one-pot. To achieve the attractive goal,
herein, we originate a tandem ROMP and ADMET polymeri-
zation method to prepare LCHBPs using different ruthenium
metathesis catalysts in one-pot procedure under certain condi-
tions (Scheme 1). First, a deliberately designed telechelic polymer
bearing electron-rich olefins;two terminal allyloxy groups at the
polymer chain ends;and electron-poor olefins;many pendent
acrylates along the polymer chain;was synthesized by ROMP-
CT25 of oxanorbornenyl derivative in the presence of a CTA
using Ru-I as the initiator; and then cross metathesis could be
utterly transformed into ADMET polymerization between ally-
loxy and acrylate of the functional telechelic polymer (acted as an
A2B2n-type macromonomer, and the A and B functionalities
readily react with each other, but neither one reacts with itself or
do so very slowly29,34-36) when treating it with catalyst Ru-II,
yielding finally the LCHBPs.
Results and Discussion
Monomer and CTA. Novel versatile CTA and monomer
were designed tactfully and prepared readily by the conven-
tional methods (Scheme 1). Multiallylic CTA, 1,4-diallyloxy-
cis-2-butene (1), was obtained by the Williamson coupling
reaction of cis-2-butene-1,4-diol with an inexpensive allyl
bromide in a high yield. The structure and purity of CTA
were fully tested by GC-MS, elemental analysis, and 1H
NMR and 13C NMR spectroscopy (Figure S1, Supporting
To make more accurate exploration, the absolute molec-
ular weight characterization method of gel permeation

10338 Macromolecules, Vol. 43, No. 24, 2010
Ding et al.
chromatography (GPC) with multiangle laser light scatter-
ing (MALLS) is employed, and the MALLS chromatogram
of telechelic polymer is shown in Figure 2. The MALLS-
derived molecular weight (Mn,MALLS) of telechelic polymer 3
follows: DP = k = Ip/Idþe = (Sp/2)/(Sdþe/8) = 4Sp/Sdþe. The
value of k is found to be eight and then used to determine the
number-average molecular weight of telechelic polymer 3, Mn,
NMR = k ꢀ M(monomer 2) þ M(CTA 1) = 3.2 kDa. It is delighted
to note that such a good agreement between the absolute
molecular weight (Mn,MALLS) obtained from GPC utilizing a
is 3.1 kDa, which is slightly lower than that of Mn,GPC
.
The 1H NMR spectrum and the corresponding peak
assignments of telechelic polymer 3 are shown in Figure 3a.
Compared to that of monomer 2, it is clearly detected that a
clean chemical shift of alkene protons g on oxanorbornene
ring initially at 6.41 ppm in Figure S2 (Supporting In-
formation) to higher field approximately at 5.88-5.59 ppm
in Figure 3a for the protons of alkene on polymer chain after
ring-opened. Moreover, the resonance signals of protons
a (5.86 ppm), c (5.27 ppm), and d and e (3.99-3.96 ppm),
corresponding to the chemical structure of CTA 1, are also
observed. These characteristic proton resonances indicate
that ROMP is performed under good control and the CTA
has been successfully incorporated into the polymer chain.
Furthermore, other types of end-groups, specifically ter-
minal phenyl and ruthenium carbene species, are not observed
light scattering detector and the molecular weight (Mn,NMR
)
determined by 1H NMR end group analysis indicates that the
polymer is telechelic,27 and also can serve as an additional
evidence for the end group difunctionality42 of telechelic
polymer 3.
1
in their expected regions of the H NMR spectrum (7.2-
7.4 ppm for phenyl and 19.5-20 ppm for ruthenium carbenes).
Hence, the result of terminal-group analysis by H NMR
1
spectroscopy has demonstrated that the polymer obtained
under the situations of Ru-I as catalyst and CTA/catalyst
ratio of 200 is really a functionalized telechelic polymer with
a high degree of allyloxy end group functionality (Fn ≈ 2).
Additionally, the average degree of polymerization (DP) and
the molecular weight are calculated from the end-group
Figure 2. Representative multiangle laser light scattering-gel permea-
tion chromatography chromatograms for A2B2n-type macromonomer
3 and long-chain highly branched polymers 4.
1
analysis of the H NMR spectrum. DP is estimated by the
integral intensity ratio of olefinic protons on each monomer
unit at 6.17-6.11 ppm (Hp, 2 protons for each unit) [Ip = Sp/2]
to that of methylene protons on polymer chain at 3.99-3.96
ppm (Hdþe, 8 protons for end groups) [Idþe = Sdþe/8] as
Figure 1. Gel permeation chromatography (GPC) traces of telechelic
polymer (A2B2n-type macromonomer) 3 and highly branched polymers
4.
Figure 3. 1H NMR spectra for (a) A2B2n-type macromonomer 3, and
(b) highly branched polymer 4b.
Table 1. Characteristics of Telechelic Polymer by ROMPa and Long-Chain Highly Branched Polymers via ADMET Polymerizationb
t (h)
GPC analysisd MALLS analysise
ADMET
polymer
ROMP
24
conversionc (%)
Mn (kDa)
PDI
Mn (kDa)
Mw (kDa)
PDI
Mn,NMR (kDa)
DP
3
91
87
89
3.8
13.9
49.6
1.45
1.98
1.89
3.1
36.7
89.3
4.3
79.3
180.4
1.42
2.16
2.02
3.2f
nd
ndg
18h
42h
4a
4b
24
72
92.8i
a Reaction conditions for preparation of 3: polymerization temperature = 50 °C, polymerization time = 24 h, [M]0 = 0.4 mol/L, [Ru-I] = 4 ꢀ 10-4
mol/L, [M]/[CTA] = 5/1. b Reaction conditions: polymerization temperature = 50 °C, [Ru-II] = 1.6 ꢀ 10-3 mol/L for preparation of 4. c Obtained
gravimetrically from the dried polymer. d Number-average molecular weight (Mn) and polydispersed index (PDI) were determined by gel permeation
chromatography in THF relative to monodispersed polystyrene standards. e Obtained from MALLS analysis. f Mn,NMR = (4Sp/Sdþe) ꢀ M(monomer 2)
þ
M(CTA 1) was calculated by 1H NMR spectroscopy assuming Fn = 2.0, where M(monomer) = 380.3 and M(CTA) = 168.2 are the molar masses of monomer
2 and CTA 1, respectively. g Not determined. h DPw,MALLS = Mw(4)/Mw(3), where Mw(4) and Mw(3) were determined by MALLS. i Mn,NMR = m ꢀ Mn(3)
,
where m is calculated from the formula: 8(m þ 1)/m = Sdþe/St, and Mn(3) is the molar mass of macromonomer obtained by 1H NMR spectroscopy.

Article
Macromolecules, Vol. 43, No. 24, 2010 10339
Figure 5. MALDI-TOF MS spectrum of A2B2n-type macromonomer 3.
peaks among the group, suggesting that all of the polymer
chains are capped at both ends.26a,44 These data provide
evidence for the formation of a telechelic polymer with the
CTA functionality successfully being placed onto both ends
of each polymer chain.
Long-Chain Highly Branched Polymers by ADMET Po-
lymerization. The allyloxy functionality on the telechelic
polymer chain ends has been proved to be “unreactive” to
both ADMET polymerization with itself (maybe stemming
from the lack of strong enough metathesis reactivity or very
low concentration of allyloxy in the closed reaction system)
and cross metathesis with acrylate within a limited time scale,
allowing for ROMP-CT developed adequately. On the other
hand, as the time prolonged, allyloxy will take eventually
part in ADMET polymerization with acrylate in an equilib-
rium step propagation condensation fashion,45 either on the
basis of some extent electron-rich feature of the allyloxy
functionality itself, which matched the requirement of the
cross metathesis after all, or stimulated by a more active
ruthenium catalyst than Ru-I. Therefore, the telechelic
polymer 3 bearing allyloxy and potential activated acrylate
can be used as an A2B2n-type macromonomer for ADMET
polymerization, where electron-poor acrylate olefins do not
homopolymerize or even homodimerize but do participate in
a cross metathesis reaction with more reactive electron-rich
allyloxy olefins.
Followed by addition of highly active catalyst Ru-II to
the rest of above-mentioned ROMP mixture in an opened
reaction system, as expected, ADMET polymerization of
macromonomer 3 is actually promoted and gradually
formed the LCHBPs 4. To provide a better understanding
of the polymerization systems described above, the GPC
method is used to trace the polymerization of macromono-
mer 3, and the results are listed in Table 1. GPC curves of the
LCHBPs displayed multiple peaks including unreacted
macromonomer. For the LCHBP 4a formed at the early
polymerization stage for 24 h after adding Ru-II, it had a
remarkably increase in molecular weight (Mn,GPC = 13.9
kDa) and a broad molecular weight distribution (PDI =
1.98) as shown in Figure 1 compared to its macromonomer.
Considering the length of the catalyst’s lifetime in the reac-
tion solution,29 a fresh batch of 0.5 mol equivalent of Ru-II
was then added to the reaction vessel at about 36 to 48 h
intervals to ensure the effectiveness of prolonging the po-
lymerization time past 36 h. With evolution of ADMET
polymerization, the peaks at low molecular weight positions
decreased, and after polymerization for 72 h, the LCHBP 4b
showed almost unimodal GPC trace with little unreacted
Figure 4. 13C NMR spectra for (a) A2B2n-type macromonomer 3, and
(b) highly branched polymer 4b.
1
Beyond our expectations, however, the H NMR spec-
trum of telechelic polymer 3 shows no (or as low as un-
detectable) resonances at around 6.99 ppm in Figure 3a,
which is deemed as the evidence for none of the newly formed
internal acrylates and the branched structures. The macro-
monomer 3 is also characterized using 13C NMR spectros-
copy as shown in Figure 4a. The strong resonances of
methylene, methine, and acrylate carbons from monomer 2
are observed at about 172.5, 166.3, 131.3, 127.9, 82.6, 62.4,
and 39.9 ppm. Simultaneously, the resonance signals of
carbons A (117.8 ppm), B (132.4 ppm), C (71.8 ppm), and
D (74.3 ppm), corresponding to the chemical structure of
CTA 1, are still presented. Additionally, the 13C NMR
spectrum of 3 shows none of the newly formed internal
acrylate peaks in Figure 4a, indicating the absence of cross-
linked or branched structures. These observations confirmed
that the telechelic polymer has a linear architecture, and also
excluded the possible occurrence of cross-metathesis be-
tween pendent acrylate and terminal allyloxy or chain back-
bone olefin under given conditions, making ADMET
polymerization be temporarily “frozen” on the early stage
of reaction because of the stability of the ruthenium carbene
species toward the acrylate groups42,43 despite the absence of
a free-radical inhibitor.
Figure 5 shows the MALDI-TOF spectrum for macro-
monomer 3. The peaks are separated by 380 mass units,
which corresponds to the molecular weight of each monomer
unit (380.34). Mn of 3 calculated from the MALDI-TOF
spectrum is 3196, which is in good agreement with the value
determined by MALLS-GPC (3100) and calculated by 1H
NMR (3200). Furthermore, the enlarged region of MAL-
DI-TOF MS spectrum of macromonomer 3 in Figure 5
reveals a difference of 71 mass units corresponding to a
terminal group (CH2OCH2CHdCH2) between two adjacent

10340 Macromolecules, Vol. 43, No. 24, 2010
Ding et al.
macromonomer, and the elution curve of branched polymer
was gradually shifted to much higher molecular weight
region (Mn,GPC = 49.6 kDa) and molecular weight distribu-
tion also became narrow (PDI = 1.89), indicating longer
polymerization time resulted in higher molecular weight and
lower molecular weight distribution. Although GPC is well-
known to determine the molecular weight and molecular
weight distribution for linear polymers by using calibration
with linear polystyrene, for branched polymer, its size is
smaller than that of linear ones with same molecular weight
because of the difference in hydrodynamic volume.46 There-
fore, an absolute molecular weight characterization method of
MALLS was employed to further characterize the branched
polymers. The typical MALLS chromatograms of the LCHBPs
obtained from different polymerization time are shown in
Figure 2. Indeed, the molecular weights Mn,MALLS of LCHBPs
are significantly higher than their GPC values based on poly-
styrene calibration, which is consistent with the general trends
for branched polymers. The LCHBPs 4a and 4b have the
moderate to high molecular weights ranging from 36.7 kDa to
89.3 kDa with PDIs within 2.16 to 2.02.
Figure 6. Schematic illustration of the structural transformation from
A2B2n-macromonomer to long-chain highly branched polymer by cross
metathesis reaction.
Table 2. Various Characteristics of Branched Polymer Structure
number of cross number of newly number of number of methylene
metathesis
reaction
formed internal
acrylate
terminal beside the allylic ether
allyloxy
oxygen
1
Figure 3b shows the H NMR spectrum of polymer 4b
1
2
3
m
1
2
3
m
3
4
5
8 (=4 ꢀ 1 þ 4)
12 (=4 ꢀ 2 þ 4)
16 (=4 ꢀ 3 þ 4)
4m þ 4
with extending the polymerization time to 72 h. Notably, the
curve of branched polymer is similar to its macromonomer as
their structures mostly alike. Inspiringly, a new peak ap-
peared obviously at 6.99 ppm (t) due to the formation of
internal acrylates (cross-metathesized AB olefins). Figure 4b
shows the typical 13C NMR spectrum of LCHBP 4b, as
excepted, two new peaks appeared at about 139.7 (R) and
121.6 ppm (S). Moreover, there is another observation of a
chemical shift from 71.2 ppm (C) to the lower field at 73.8 ppm
(P) for part of the methylene carbons in allyloxy groups after
forming internal acrylates. All these points are the strongly
evidence for the branched structure of the resulting polymer,
indicating ADMET polymerization has occurred overwhelm-
ingly in the manner of the cross metathesis reaction between
pendent acrylate and terminal allyloxy, and the branched
structure of the resulting polymer has formed. Although an
example has been reported to describe ADMET-triggered
formation of cross-linked nanotubes between allylic ether
groups on the assembled amphiphile surface by catalyst Ru-I
under certain conditions,47 no sufficient data (such as DP)
were given to support the polymerization taken place effec-
tively, because the oligomerization of these assembled allyloxy
groups may also result in the same cross-linked nanostruc-
tures. Generally, in ADMET polymerization the polymeriza-
bility of a monomer is limited by the number of methylene
spacers between the olefin and the ether oxygen or the ester
from the oxygen side. To avoid suffering a negative neighbor-
ing group effect, the number of methylene spacers between
these functionalities is at least two for successful metathesis to
occur,48 despite in some classical catalyst systems, reactivity
has been observed in systems with only one methylene spacer
present.49 Consequently, the acrylate functionality and dial-
lylic ether as well as some symmetrical diallylic esters are
always failed to (homo)polymerize but the later two do
oligomerize or isomerize sometimes.29,34,36,50
m þ 2
methylene between two carbonyloxy groups from acrylate)
on both polymer chain and allyloxy end. For one more
reaction, there are an extra increase of one internal acrylate,
one allyloxy end, and four methylene groups beside the
allylic ether oxygen. That is, each cross metathesis would
form a new internal acrylate and simultaneously promote the
addition of one allyloxy end or four methylene groups beside
the allylic ether oxygen. If the number of newly formed
internal acrylate is m, the number of terminal allyloxy groups
is equal to (m þ 2), and the number of methylene groups
beside the allylic ether oxygen will reach to (4mþ 4) = 4(mþ 1).
Correspondingly, the number of protons on each type of
group is twice as the group(s) number, means that there are
2m of olefin protons on newly formed internal acrylate,
2(m þ 2) of olefin protons on allyloxy end, and 2 ꢀ 4(m þ 1)
of methylene protons beside the allylic ether oxygen on each
polymer chain, respectively. It should be pointed out that the
newly formed internal acrylate protons are in two categories
(Hs, Ht) with equal number according to different chemical
environments, thus there are m of olefin protons (Ht) and m
of olefin protons (Hs) on this internal acrylate. Because the
terminal alkene (allyloxy) protons (Ha, Hc) and the olefin
protons (Hs) on newly formed internal acrylate overlapped
with other olefin protons, we finally chose the integration
area ratio of methylene protons beside the allylic ether
oxygen at 3.99-3.96 ppm (Hdþe) to that of olefin protons
on newly formed internal acrylate at 6.99-6.90 ppm (Ht) to
calculate the value of m, namely the DP for the branching
reaction. It can be derived from the following formula: 2 ꢀ 4
(m þ 1)/m = Sdþe/St, and thus m = 8St/(Sdþe - 8St). For the
branched polymer 4b, m is found to be as high as 29, and the
value of m = 29 is used to determine the number-average
molecular weight: Mn,NMR = m ꢀ Mn(3) = 92.8 kDa, which
is in excellent accord with the value of Mn,MALLS. In conclu-
sion, all these results have demonstrated that upon comple-
tion of ROMP-CT of a strained cyclic olefin with a CTA,
addition of solely a more active catalyst can successfully
trigger ADMET polymerization and facilitate the formation
of LCHBPs in practically one-pot successive procedure.
The degree of branching (DB) is one of the important
molecular parameters to verify that the polymer does in fact
The specific resonances of the internal acrylate protons
can be used to calculate the molecular weight of LCHBPs.
Interestingly, a regular change is discovered from the inti-
mately insight into the concept structure of LCHBP in
Figure 6, and various characteristics are displayed in Table 2.
For once cross metathesis reaction between pendent acrylate
(red spherule) and terminal allyloxy (blue spherule), it forms
a new internal acrylate (green spherule), meanwhile, gives
three terminal allyloxy groups and eight methylene groups
adjacent to the allylic ether oxygen (not including any

Article
Macromolecules, Vol. 43, No. 24, 2010 10341
Table 3. Solubility and Intrinsic Viscosity Data for LCHBPs Synthesized from Macromonomer 3
solubilityc
b
polymers
[η]Ba (dL/g)
[η]La (dL/g)
g0
THF
CH2Cl2
CHCl3
acetone
DMF
DMSO
toluene
dioxane
4a
4b
0.202
0.279
0.399
0.716
0.55
0.39
þþ
þþ
þþ
þþ
þþ
þþ
-
-
þþ
þþ
þþ
þþ
-
-
þ-
þ-
a Measured by Ubbelohde viscometer. The B refers branched polymers, and the L refers linear polymers with the same molecular weights of branched
polymers. b g0 = [η]B/[η]L. c Key: þþ, soluble; þ-, partially soluble; -, insoluble.
have a branched architecture. However, DB of the LCHBPs
4 cannot obtain from the common technique using 1H NMR
spectra of polymer because of the characteristic protons
overlapped. Therefore, we got some idea of DB from the
branching factor g0, which was calculated by the ratio of the
intrinsic viscosity of the branched polymer [η]B to the
intrinsic viscosity of a linear polymer [η]L with the same
molecular weight,11,21,51 and the results are listed in Table 3.
The [η]Bs and the [η]Ls were measured by Ubbelohde vis-
cometer. Since the branched polymers have smaller hydrody-
namic volumes and more compact structures than linear poly-
mers of identical molecular weight, the [η]Bs therefore are much
lower than the [η]Ls (Table 3). The g0 values of the LCHBPs
decreased with the increase of DPw (Table 1). In a word, the
lower the g0 value is, the higher DP and DB values are.
Besides, the solubility of LCHBPs 4 were also investigated
simply. Despite their high molecular weight, they showed
excellent solubility in various organic solvents such as THF,
CH2Cl2, CHCl3, DMF, and DMSO (Table 3). Thus, we can
predict that the LCHBPs 4 are organosoluble polymers, and
do not form cross-linked structure.
Effect of Different Monomer or CTA on ROMP and
ADMET Polymerization. For comparison, we first designed
a comparative experiment to investigate the effect of differ-
ent monomer on polymerization. All polymerization condi-
tions are the same as those for macromonomer 3 and
LCHBPs 4, except for the monomer 2 with two acrylates
being replaced by ONBDM without acrylate (Scheme S1,
Supporting Information).
The polymers 5 and 6 obtained from ROMP-CT and AD-
MET reaction are characterized by GPC and NMR measure-
ments, and the results are listed in Table S1 (Supporting
Information). The monomodal GPC trace (Figure S3, Support-
ing Information) reveals that Mn,GPC of polymer 5 is 2.4 kDa
with a low PDI of 1.30, suggesting ROMP-CT is carried out
under good control, and further reaction between the growing
polymer chains and the CTA is severely suppressed. The
unimodal GPC curves of polymers 6 are also detected even
extending the reaction time to 72 h, which is different distinctly
from that of the LCHBPs 4. As compared to polymer 5, it is
clearly observed that a clean shifts of the elution peaks of
polymers 6 to the slightly higher molecular weight positions,
but no significant changes are seen in the values of Mn,GPC
(5.1-5.5 kDa) and PDI (1.31-1.33) for polymers 6 no matter
the reaction time shorter or longer. Viewing these points, we can
deduce that after adding a solution of Ru-II to the rest of
ROMP system, only a simple intermolecular metathesis cou-
pling reaction (not a really ADMET polymerization but an
oligomerization) of the chain end diene occurred to yield
polymers with low DP of 2-3, without other secondary me-
tathesis reaction between the terminal alkenes and the backbone
olefins (less reactive in ROMP and ADMET polymerization)
happened due to the steric hindrance of the adjacent centers on
substituted polyoxynorbornenes.38
polymer 5, and no resonances for unwanted branching
structure are detected, indicating polymers 5 and 6b have
the same linear structures. The Mn,NMR values of polymers 5,
1
6a and 6b calculated from H NMR spectra in Figure S4
(Supporting Information) are 1.8, 3.8, and 4.1 kDa (Table S1,
Supporting Information), respectively, which are relatively
low and in reasonable agreement with those of Mn,GPC. The
results of polymers 6 are much contrary to those of LCHBPs
4, suggesting that the pendent acrylates in macromonomer 3
play a role of key component to form the branched polymer
with high molecular weight.
We then adopted another comparative experiment to
explore the effect of different CTA on polymerization.
CTA 7 with saturated diester structure was given by esteri-
fication of cis-2-butene-1,4-diol with butyric acid (Scheme S2,
Supporting Information). The structure and purity of 7 were
1
tested by GC-MS, and H NMR (Figure S5a, Supporting
Information) spectroscopy.
The characteristic results of polymers 8 and 9 obtained
from ROMP-CT and ADMET reaction are listed in Table S2
(Supporting Information). The monomodal GPC trace
(Figure S6, Supporting Information) reveals that polymer
8 has a Mn,GPC of 4.4 kDa and a PDI of 1.42. For polymers
9a and 9b, there were no significant changes in the values of
M
n,GPC (4.7-4.9 kDa) and PDI (1.47-1.49) when compared
with polymer 8. In the light of these results, we can deduce
that after adding a solution of Ru-II to the rest of ROMP
system, no other metathesis reactions happened.
The 1H NMR spectrum of polymer 9b (Figure S5c,
Supporting Information) is wholly similar to that of polymer
8 (Figure S5b, Supporting Information), indicating polymers
8 and 9b have the same linear structures. The molecular
weight results (Table S2, Supporting Information) of poly-
mers 9a (Mn,NMR = 3.3 kDa) and 9b (Mn,NMR = 3.4 kDa)
are close to that of polymer 8 (Mn,NMR = 2.9 kDa) calcu-
lated from 1H NMR spectra in Figure S5 suggesting that the
pendent acrylates could not actualize cross-metathesis with
themselves or chain backbone olefins.
From the two comparative experiments, we concluded that
the terminal allyloxy groups could not form high molecular
weight polymers via ADMET, and the pendent acrylates are
also impossible to result in cross-linked or branched structures.
These conclusions further illuminated that LCHBPs 4 were
given just through cross metathesis between acrylate and ter-
minal alkene, rather than other secondary metathesis reaction.
Conclusions
Inthis work, a new strategy for the synthesis of polymers with a
long-chain highly branched architecture and many reactive
groups was developed through a simply tandem ROMP and
ADMET polymerization method under mild conditions. ROMP
of a functional oxanorbornene with two acrylates in the presence
of an extremely effective multiallylic cis-olefin CTA was per-
formed using catalyst Ru-I in the predetermined reaction time,
producing a linear functional telechelic polymer bearing two
terminal allyloxy groups and many pendent acrylates, which
can be used as an A2B2n-type macromonomer in subsequent
Furthermore, the obtained polymer chain structures are
confirmed by 1H NMR spectroscopy (Figure S4, Supporting
Information), and Mn,NMR of polymers is also estimated.
The 1H NMR spectrum of polymer 6b is the same as that of

10342 Macromolecules, Vol. 43, No. 24, 2010
Ding et al.
ADMET polymerization between allyloxy and acrylate triggered
substantially by adding a highly active metathesis catalyst Ru-II,
yielding the LCHBPs as the reacton time prolonged. The
MALLS analysis showed that the telechelic polymer has low
molecular weight of 3.1 kDa with a narrow PDI of 1.42, and the
LCHBPs have reasonably high molecular weights of 36.7-89.3
kDa with high branched DP of more than 20 and PDIs of
2.16-2.02. These results clearly demonstrated that it is possible
to prepare highly branched materials in a straightforward ap-
proach via merely olefin metathesis chemistry resorting to an
ingenious combination of monomer, CTA, and catalysts. This
would lead to the possibility of including new functionalities in
polymers directly in order to make the polyolefin materials
sensitive to other type of stimulus with a view to a future
modification to their properties and architectures. For instance,
the highly branched polymer structure inherently bearing a great
number of the peripheral reactive acrylates would be changed
into the permanent nanostructure through the intramolecular
cross-linking reaction induced by UV-irradiation.52 The exten-
sion of this work is further exploited.
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