Cleavable multiblock copolymer synthesized by ring-opening metathesis copolymerization of cyclooctene and macrocyclic olefin and its hydrolysis to give carboxyl-telechelic polymer

Article abstract of DOI:10.1002/pola.23795

A novel cleavable multiblock copolymer was synthesized by ring-opening metathesis polymerization (ROMP) of cyclooctene (COE) and a flexible 27-membered macrocyclic olefin (MCO), which is acted as the spacer to collect the polymer structure block by block. MCO 2 was prepared via ring-closing metathesis of the long chain alkyldiene, and then 2 was wellconducted ROMP with COE to provide the multiblock copolymer [Poly(COE)-2]_m consisting of homo-Poly(COE) blocks and ringopened 2 segments with different molecular weights (M_n = 30.0 - 249.6 × 10³) and polydispersity index (PDI) within 1.45- .67 as variation of the feed ratio of COE to 2. The multiblock copolymer chain containing weak ester linkage can be cleaved under alkali condition to afford the carboxyl-telechelic Poly(COE) blocks with much lower molecular weights (M_n,_h 1/4 3.6-35.7 10³) and slight higher PDIs (1.65-1.88). The average block number on multiblock copolymer chain was obtained from the ratio of M_n toM_n,_h and was reached up to the value of 7-16.

Full text of DOI:10.1002/pola.23795

Cleavable Multiblock Copolymer Synthesized by Ring-Opening
Metathesis Copolymerization of Cyclooctene and Macrocyclic
Olefin and Its Hydrolysis to Give Carboxyl-Telechelic Polymer
MEIRAN XIE,1 WEIZHEN WANG,1 LIANG DING,1 JINGWEI LIU,1 DAN YANG,1 LING WEI,2 YIQUN ZHANG1
1Department of Chemistry, East China Normal University, Shanghai 200062, People’s Republic of China
2Department of Physics, East China Normal University, Shanghai 200062, People’s Republic of China
Received 29 July 2009; accepted 20 October 2009
DOI: 10.1002/pola.23795
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A novel cleavable multiblock copolymer was synthe-
sized by ring-opening metathesis polymerization (ROMP) of
cyclooctene (COE) and a flexible 27-membered macrocyclic ole-
fin (MCO), which is acted as the spacer to collect the polymer
structure block by block. MCO 2 was prepared via ring-closing
metathesis of the long chain alkyldiene, and then 2 was well-
conducted ROMP with COE to provide the multiblock copolymer
[Poly(COE)-2]m consisting of homo-Poly(COE) blocks and ring-
opened 2 segments with different molecular weights (Mn ¼ 30.0
– 249.6 ꢀ 103) and polydispersity index (PDI) within 1.45–1.67 as
variation of the feed ratio of COE to 2. The multiblock copolymer
chain containing weak ester linkage can be cleaved under alkali
condition to afford the carboxyl-telechelic Poly(COE) blocks
with much lower molecular weights (Mn,h ¼ 3.6–35.7 ꢀ 103)
and slight higher PDIs (1.65–1.88). The average block number
on multiblock copolymer chain was obtained from the ratio of
C
V
Mn to Mn,h and was reached up to the value of 7–16. 2009 Wiley
Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 380–388,
2010
KEYWORDS: cleavable multiblock copolymer; macrocycles; ring-
opening metathesis copolymerization; telechelics
INTRODUCTION Since the development of a well-defined ru-
thenium catalyst with improved control features and func-
tional group tolerance to acids, alcohols, aldehydes, esters,
and amides,1,2 ring-opening metathesis polymerization
(ROMP) has been widely applied for the synthesis of various
functionalized copolymers, including di- or triblock copoly-
mers,3–10 alternating copolymers,11–15 and random or statis-
tical copolymers.16–23 But the synthesis of multiblock copoly-
mers have been paid relatively limited attentions because it
is still a challenge up to now. Multiblock copolymers are usu-
ally composed of two or more dissimilar repeat blocks or
segments (even groups) arranged in a random or alternating
sequence,24 which can often provide more advantageous
properties such as good biocompatibility and mechanical
properties when compared with diblock or triblock copoly-
mers.25 Moreover, multiblock copolymers can result in for-
mation of unique morphologies, which directly influences
these advantageous properties, especially physical properties.
Increasing attention has recently been devoted to multiblock
copolymers because of interest in their widespread applica-
tion in fields such as adhesives, emulsifiers, barrier materi-
als, impact modifiers, and materials for gene and drug deliv-
ery.25–31 Actually, a few multiblock copolymers24–28 have
been obtained from ROMP process. Watkins and Fox32
reported ABCD-type tetrablock copolymers synthesized by
ROMP of norbornenediol bearing various aryl ketones or
aldehydes. Nomura and Schrock33 synthesized sugar-coated
ABCD- or ABAB-type tetrablock copolymers by Mo-catalyzed
living ROMP techniques. Nomura and coworkers reported
the synthesis of ABAB-type tetrablock copolymers of norbor-
nenes containing acetyl-protected carbohydrates by the liv-
ing ROMP with well-defined ruthenium and molybdenum ini-
tiators,34 and they also prepared amphiphilic ABCBA-type
pentablock copolymers containing acetal-protected sugars
from the coupling of an end-functionalized ROMP copolymer
by molybdenum-alkylidene initiator with poly(ethylene gly-
col).35 Hiff and Kilbinger36 presented a sacrificial approach
to generating cleavable ABABA-type pentablock and ABA-
BABA-type heptablock metathesis copolymers through ROMP
of seven-membered cyclic acetals and N-substituted norbor-
nene dicarboximide derivatives. All the aforementioned
ROMP copolymers were prepared with tedious synthetic pro-
cedures of either sequential monomer addition or the cou-
pling of end-functionalized ROMP polymer. Thus, attempting
to seek the other synthetic strategy for the synthesis of func-
tional multiblock copolymers is becoming significant interest.
Correspondence to: M. Xie (E-mail: mrxie@chem.ecnu.edu.cn)
C
V
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 380–388 (2010) 2009 Wiley Periodicals, Inc.
380
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ARTICLE
Among these reports, however, only two cases were con-
cerned the synthesis of cleavable copolymers. One is the
multiblock copolymer obtained from the controlled/living
polymerization to build the well-defined structure block by
block with sequential addition of cyclic hydrolyzable mono-
mer and stable monomer,36 and the multiblock copolymer
can yield hydroxy-telechelic polymers after acidic hydrolysis,
but the number of blocks is limited. The other is the statisti-
cal copolymer via one-pot monomer feeding technique,16
which is a simple and convenient process, and the copolymer
can also give hydroxy-telechelic polymers after hydrolysis,
but the microstructure and composition of polymer chain is
poor controlled and ill-defined.
and molecular weight distribution (PDI ¼ 1.6) by tuning the
feed ratio of COE and MCO. The cleavage of multiblock long
chain polymeric structure into short chains with the tele-
chelic carboxyl groups under alkaline conditions is also
investigated.
EXPERIMENTAL
Materials
Cyclooctene (99%), benzylidene-bis(tricyclohexylphosphine)-
dichlororuthenium (first generation Grubbs catalyst, Ru1st),
benzylidene[1,3-bis(2,4,6-trimethylphenyl)-2- imidazolidinyli-
dene]dichloro(tricyclohexylphosphine)ruthenium
(second
generation Grubbs catalyst, Ru2nd), and N-phenyldiethanol-
amine (97%) were purchased from Aldrich or Alfa Aesar and
used without purification. 4-Dimethylaminopyridine (DMAP,
98%), n-undecylenic acid (98%), p-aminobenzoic acid
(99.5%), sodium nitrite (99%), 1-[3-(dimethylamino)propyl]-
3-ethylcarbodiimide hydrochloride (EDCIꢁHCl, 99%), and so-
dium acetate (99%) were purchased from Shanghai Chemical
Reagents, and used as received without further purification.
Solvents were distilled over drying agents under nitrogen
before use: methylene chloride (CH2Cl2) and chloroform
(CHCl3) from calcium hydride, tetrahydrofuran (THF) and
toluene from sodium/benzophenone. N,N-Dimethyl formam-
ide (DMF) was freshly distilled and dried by sieves.
On the other hand, much attention has been devoted to find
a general and easy approach to make the polymer chain
ends functionality via ROMP. The method for preparation of
end-functionalized ROMP polymers can enable the incorpora-
tion of the functional unit to one end (monotelechelic) or
both ends (telechelic) of a polymer chain, and expand the
applications of ROMP materials. Generally, there have been
three approaches for the synthesis of end-functional poly-
mers. The first approach describes the use of chain transfer
agents to achieve telechelic polymers,37,38 whose disadvant-
age is that the polymer chain is not made in a living fashion,
so a polydisperse product with somewhat broader polydis-
persed index (PDI ¼ 2) is obtained. The second one is typi-
cally carried out by exchanging the benzylidene on the me-
tathesis catalyst for an alkylidene with the desired
functionality, which could be then transfered directly onto
one polymer chain end,39 but this strategy suffers from the
necessity of synthesizing a corresponding catalyst for each
new desired end-functional group. The third is the end-cap-
ping method to yield mono end-functional polymers, utilizing
either the facile route involving the addition of a small mole-
cule onto the end of the polymer chain by the reaction of
terminating agents with the living chain end using ruthe-
nium metathesis catalyst,40–43 or the synthetic route called
as ‘‘sacrificial synthesis’’ based on the cleavage of second
block from diblock copolymer to ensure the high degree of
mono chain end-functionalization.44–49
Characterization
1H and 13C NMR spectra were recorded on a Bruker DPX
spectrometer operated at 500 and 125 MHz, respectively.
Chemical shifts were reported downfield from tetramethylsi-
lane (TMS), all 1H NMR and 13C NMR measurements were
realized in CDCl3. Relative molecular weights and molecular
weight distributions were measured by gel permeation chro-
matography (GPC) system equipped with a Waters 1515 Iso-
cratic HPLC pump, a Waters 2414 refractive index detector,
and a set of Waters Styragel columns (HR3, HR4, and HR5,
7.8 ꢀ 300 mm2). GPC measurements were carried out at
35 ꢂC using THF as the eluent with a flow rate of 1.0 mL/
min. The system was calibrated with polystyrene standards.
Elemental analysis was carried out with an ELEMENTAR
Vario EL 3.
It is well-known that ROMP of strained cyclic olefins is
mainly enthalpy-driven, whereas macrocyclic olefins (MCOs)
are strainless which can undergo entropically driven ring-
opening metathesis polymerization (ED-ROMP). Several
examples have been given in the published literatures for
ED-ROMP of the different size, unstrained MCOs including
the 14-membered cyclic crown ether,50,51 macrocyclic lac-
tones with a range of atoms from 21- to 84-membered
rings,52–54 macrocyclic lactam,55 and bile-acid and ricinoleide
macrocyclic monomers.56,57 However, there seems to be only
one example to form the copolymer by copolymerization of
cyclooctene (COE), norbornene, and the macrocyclic calixar-
ene alkenes with 17- or 19-membered ring.58 To explore the
copolymerization behavior of classical cyclic olefin and MCO,
herein, we report ROMP of COE and cleavable MCO affording
the copolymer with almost the multiblock chain structure,
and comparatively good control over the molecular weight
Polymerizations were carried out in Schlenk tube under dry
nitrogen atmosphere.
Synthesis of Azobenzene Moiety-Containing
a,x-Diolefin (1)
To a Schlenk flask, 4-N,N0-bis(2-hydroxyethyl)amino-40-nitro-
azobenzene (DR19) (4.95 g, 15.0 mmol), n-undecylenic acid
(7.74 g, 42.0 mmol), and DMAP (0.37 g, 3.0 mmol) were dis-
charged and dissolved in 50 mL of dried DMF under a nitro-
gen atmosphere, and then EDCIꢁHCl (6.32 g, 33.0 mmol) was
added at 0 ꢂC with rapid stirring. The reaction mixture was
allowed to warm to room temperature and stirred for an
additional time. After 4 days, the reaction mixture was
poured into water and red solid precipitated. The crude
product was further purified by recrystallization from etha-
nol/ethyl acetate (1:1 v/v). The pure compound 1 was
gained as a red crystal in 85.3% yield (8.5 g, 12.8 mmol).
CLEAVABLE MULTIBLOCK COPOLYMER SYNTHESIZATION, XIE ET AL.
381

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 1 Characteristics of Multiblock Copolymers and Telechelic Polymers with Various Molar Ratio of Cyclooctene to
Macrocyclic Olefin or Catalyst
COE:2:Ca
Yieldb (%)
COE:2c
COE:2d
Mn,GPC (103)
PDIe
nf
Mn,h,NMR (103)
Mn,h,GPC (103)
PDIh
mi
e
g
h
Entry
1
2
3
4
5
6
7
8
9
1500:10:1
1500:20:1
1500:30:1
1500:40:1
1500:50:1
300:20:1
600:20:1
900:20:1
1200:20:1
91.3
88.2
90.4
81.4
75.0
70.0
72.0
73.0
75.0
ndj
90
61
45
37
20
36
48
79
177
93
68
49
38
17
39
45
76
249.6
182.7
138.2
124.1
118.1
30.0
1.64
1.61
1.60
1.57
1.62
1.45
1.64
1.67
1.57
161
88
59
43
36
20
35
47
75
18.0
10.0
6.8
5.1
4.3
2.5
4.2
5.5
8.6
35.7
16.6
11.4
8.2
1.65
1.80
1.79
1.78
1.65
1.78
1.80
1.88
1.86
7
11
12
15
16
8
7.5
3.6
71.4
6.8
10
12
9
100.0
112.6
8.2
13.2
f
Polymerization conditions: [C]0 ¼ 1.25 ꢀ 10ꢃ3 mol/L, CHCl3 ¼ 4 mL, po-
lymerization time ¼ 24 h, polymerization temperature ¼ 50 ꢂC.
The number of repeated monomer units (n) in each block of poly(cy-
clooctene) (Poly(COE)) was calculated as follows: n ¼ {[SH(j ꢃ SH(j)]/
þ
o)
a
The molar ratio of cyclooctene (COE) to macrocyclic olefin (2) and cat-
2}/[SH(f)/4] ¼ {[SH(j
ꢃ SH(f)/2]/2}/[SH(f)/4] ¼ [SH(j
ꢃ SH(f)/2]/[SH(f)/2]
þ
o)
þ
o)
alyst (C) in feed.
from the 1H NMR spectrum of the hydrolyzed polymer block Poly(COE).
b
g
Isolated yield based on total mass of COE and 2.
The molar ratio of COE to 2 determined by 1H NMR analysis of the
The molecular weight of the hydrolyzed telechelic polymer
HOOCAPoly(COE)ACOOH was determined by 1H NMR analysis assum-
c
multiblock copolymer, where COE:2 ¼ {[SH(j
ꢃ SH(j)]/2}/[SH(a)/2] ¼
ing Fn ¼ 2.0, i.e., Mn,h,NMR ¼ n ꢀ MCOE þ 2 ꢀ (Mundecylenic
ꢃ 17),
þ
o)
acid
[SH(j þ o) ꢃ SH(a)]/SH(a)
.
where n is the number of repeated monomer units, MCOE ¼ 110 is the
d
The molar ratio of COE to 2 determined by elemental analysis, COE:2
molecular weight of monomer COE, Mundecylenic
¼ 184 is the molec-
acid
¼ {[w ꢃ (w ꢀ x%/(14 ꢀ 4)) ꢀ M2]/MCOE}/(w ꢀ x%/(14 ꢀ 4)) ¼ [56/(MCOE
ꢀ
ular weight of undecylenic acid, and the number 17 is the molar mass
of removed hydroxyl in the esterification process.
x%)] ꢃ (M2/MCOE), where w is the weight of polymer sample, x is the
weight percent of nitrogen, MCOE ¼ 110 is the molecular weight of
monomer COE, and M2 ¼ 634.8 is the molecular weight of 2.
h
Molecular weight and polydispersity index (PDI) of the hydrolyzed tel-
echelic polymer HOOCAPoly(COE)ACOOH determined by GPC analysis.
e
i
The average molecular weight and polydispersity index (PDI) of the
The number of repeated polymer blocks determined by the ratio of
h
multiblock copolymer measured by GPC, calibration with polystyrene
standards.
Mn,GPCe/Mn,h,GPC
.
j
Not determined.
1H NMR (500 MHz, CDCl3), d (TMS, ppm): 8.33 (d, 2H, ArH),
7.92 (t, 4H, ArH), 6.87 (d, 2H, ArH), 5.81 (m, 2H, 2 ꢀ
CH2CH¼¼CH2), 4.96 (m, 4H, 2 ꢀ CH2CH¼¼CH2), 4.31 (t, 4H, 2
ꢀ NCH2CH2O), 3.74 (t, 4H, 2 ꢀ NCH2CH2O), 2.31–2.28 (t, 4H,
2 ꢀ OCOCH2), 2.04–1.99 (m, 4H, CH2CH2CH¼¼CHCH2CH2),
1.58 (t, 4H, 2 ꢀ OCOCH2CH2), 1.36–1.26 (m, 20H, 10 ꢀ
CH2); 13C NMR (125 MHz, CDCl3), d (ppm): 173.63, 156.46,
151.15, 147.60, 144.23, 139.09, 126.18, 124.66, 122.71,
114.14, 111.76, 60.82, 49.59, 34.11, 33.73, 29.24, 29.17,
29.07, 29.02, 28.85, 24.79. Elem. Anal. Calcd. for C38H54N4O6
(662.86): C, 68.85; H, 8.21; N, 8.45. Found: C, 68.93; H, 8.27;
N: 8.41.
CH2CH2CH¼¼CHCH2CH2), 1.62 (t, 4H, 2 ꢀ OCOCH2CH2), 1.35–
1.28 (m, 20H, 10 ꢀ CH2); 13C NMR (125 MHz, CDCl3), d
(ppm): 173.59, 156.52, 150.91, 147.63, 144.32, 130.62,
126.16, 124.64, 122.74, 111.71, 61.20, 50.32, 34.18, 32.03,
29.32, 28.94, 28.83, 28.05, 26.80, 24.86. Elem. Anal. Calcd.
for C36H50N4O6 (634.80): C, 68.11; H, 7.94; N, 8.83. Found:
C, 67.82; H, 7.97; N, 8.78.
General Polymerization Procedure for Synthesis of
Multiblock Copolymers
A typical procedure (Table 1, entry 5) is as follows. In a
nitrogen-filled Schlenk tube, a solution of second generation
Grubbs catalyst (4.3 mg, 5.0 lmol) in 1.0 mL of CHCl3 was
added to a solution of monomers COE (840.0 mg, 7.63
mmol) and MCO 2 (158.7 mg, 0.25 mmol) in 3.0 mL of
CHCl3. The feed ratio of [COE]0:[2]0:[C]0 was 1500:50:1. The
Synthesis of Macrocyclic Olefin Bearing
Azobenzene Moiety (2)
To a solution of 1 (2.65 g, 4.0 mmol) in CH2Cl2 (700 mL)
with N2 sparging was added the solution of first generation
Grubbs catalyst (162 mg, 0.2 mmol) in CH2Cl2 (100 mL) via
a sꢂyringe. The reaction mixture was stirred for 48 h at
45 C. After cooling, the solvent was removed under reduced
pressure, and the residue was purified via column chroma-
tography with CH2Cl2/petroleum ether (2:1 v/v) on silica to
give 2.0 g of 2 as a red solid in 80.0% yield. 1H NMR (500
MHz, CDCl3), d (TMS, ppm): 8.32 (d, 2H, ArH), 7.92 (t, 4H,
ArH), 6.84 (d, 2H, ArH), 5.34 (s, 2H, C H2CH¼¼CHCH2),
4.32 (t, 4H, 2 ꢀ NCH2CH2O), 3.76 (t, 4H, 2 ꢀ NCH2CH2O),
ꢂ
reaction mixture was stirred at 50 C for 24 h. The polymer-
ization was quenched with ethyl vinyl ether, and the polymer
was precipitated by adding dropwise into ethyl acetate. The
polymer was purified by dissolving in THF and reprecipita-
tion in ethyl acetate. The product was dried under vacuum
to give the polymer (750.0 mg) as a red elastomeric solid
1
with 75.0% yield based on total mass of COE and 2. H NMR
(500 MHz, CDCl3), d (ppm): 8.32 (s, ArH), 7.91 (s, ArH), 6.86
(s, ArH), 5.36 (d, CH¼¼ on the polymer chain), 4.30 (s,
NCH2CH2O), 3.73 (s, NCH2CH2O), 2.28 (t, OCOCH2), 2.02–
1.95 (m, CH2CH2CH¼¼CHCH2CH2), 1.68 (t, OCOCH2CH2),
2.34–2.31(m, 4H,
2
ꢀ
OCOCH2), 2.04–1.99 (m, 4H,
382
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ARTICLE
RESULTS AND DISCUSSION
1.31–1.26 (m, CH2 on the polymer chain). All the copolymer-
izations listed in Table 1 were similarly carried out.
Synthesis of Azobenzene Moiety-Containing
a,x-Diolefin 1
The long chain a,x-diolefin 1 was synthesized through the
esterification of n-undecylenic acid with the hydroxyl-con-
taining azobenzene chromophore DR19, which was prepared
by diazo coupling reaction of 4-nitroaniline in the presence
of sodium nitrite with N-phenyldiethanolamine according to
the literature procedure,59 on the basis of dehydration using
EDCI/DMAP as the catalytic system at room temperature for
several days. The synthetic route to this compound was illus-
trated in Scheme 1. The crude product was purified by
recrystallization from ethanol/ethyl acetate to provide the
pure compound 1 as a red crystal with good yield of 85.3%.
The chemical structure of product 1 was confirmed by ele-
mental analysis and NMR spectroscopy.
General Procedure for the Hydrolysis
of Multiblock Copolymers
The copolymer (Mn,GPC ¼ 118,100, Mw/Mn ¼ 1.62; 400 mg)
was dissolved in 20 mL of THF and hydrolyzed by adding
1.0 mL of 40% KOH/methanol solution and 0.5 mL of tri-
ꢂ
ethylamine at 65 C for 48 h. The mixture was concentrated
to about 4 mL and then deposited by dropping into 60 mL
of 2% HCl aqueous solution. The precipitate was washed
with distilled water for two times, dried in vacuo for more
than 24 h to give a sample (330 mg, 85%) composing of
hydrolyzed polymer or oligomer (if existed) for GPC mea-
surements directly. The obtained sample was redissolved in
THF and precipitated in methanol for two times to remove
any likely oligomer, and finally dried in a vacuum oven for
24 h affording pale solid (320 mg, 94.1%), which should be
the pure hydrolyzed polymer, a,x-dicarboxyl-functionalized
telechelic poly(cyclooctene) HOOCAPoly(COE)ACOOH, and
was used for characterizations of NMR and GPC. 1H NMR
(500 MHz, CDCl3), d (ppm): 5.42–5.31 (d, CH¼¼CH, olefinic
protons on the COE unit and MCO segment), 2.35 (t,
CH2CH2CH2COOH), 2.02–1.96 (m, CH2CH¼¼CHCH2), 1.62 (t,
The 1H NMR spectrum of 1 [(Fig. 1(A)] showed the reso-
nance signals of three groups of aromatic protons at 8.33
ppm (Ha), 7.93 ppm (Hb), and 6.88 ppm (Hc), respectively,
and methylene protons at 4.31 ppm for ANCH2CH2OCOA
(He), 3.74 ppm for ANCH2CH2OCOA (Hd), which all ascribed
to the protons from azobenzene chromophore DR19. Mean-
while the signals of alkene protons at 5.77 ppm for
ACH2CH¼¼CH2 (Hj), 4.96 ppm for ACH2CH¼¼CH2 (Hk), and
the signals of the representative alkane protons at 2.29 ppm
for AOCOCH2CH2A (Hf), 2.01 ppm for ACH2CH2CH¼¼CH2
(Hi) were clearly observed. Importantly, the integration area
ratio of these characteristic resonances of 2:2 was well
agreed with the ratio of corresponding protons (He:Hk) of
2:2, which indicated that fully esterification of two hydroxyl
groups had occurred. The result of elemental analysis was
also revealed that the azobenzene moiety-containing a,x-dio-
lefin 1 has been prepared satisfactorily.
CH2CH2CH2COOH),
1.33–1.28
(m,
CH2CH2CH2COOH,
CH2CH2CH¼¼CHCH2CH2CH2); 13C NMR (125 MHz, CDCl3), d
(ppm): 207.22 (COOH), 130.49, 130.03, 32.75, 31.04, 29.90,
29.79, 29.54, 29.45, 29.33, 29.19, 28.86, 27.37, 24.86
(HOOCCH2).
Synthesis of a,x-Dianthracene Moiety-Containing
Telechelic Poly(cyclooctene)
To
a
Schlenk flask, the carboxyl-telechelic polymer
HOOCAPoly(COE)ACOOH (Mn,NMR ¼ 4300; 108.0 mg, 0.025
mmol), 9-anthracenemethanol (313.0 mg, 1.5 mmol), and
DMAP (18 mg, 0.15 mmol) were discharged and dissolved in
9 mL of CH2Cl2 and 4 mL of THF under a nitrogen atmo-
sphere, and then EDCIꢁHCl (288 mg, 1.5 mmol) was added at
Synthesis of Macrocyclic Olefin 2
Olefin metathesis provides an efficient methodology for car-
bon-carbon double bond (C¼¼C) formation and has received
a great deal of attention for the synthesis of middle or large
rings from acyclic diene precursors,60,61 and many macro-
cycles62–66 or macrocyclic polymers67–69 have been ingeni-
ously achieved by ring-closing metathesis (RCM) method.
The unsaturated macrocycle 2 with 27-membered ring was
readily prepared by RCM reaction of long chain acyclic diene
precursor 1 at refluxing in high dilution dichloromethane so-
lution (0.005 mol/L concentration) with good yield of 80.0%
as a red solid after carefully purifying by silica gel column
chromatography using a mixture of CH2Cl2/petroleum ether
as eluent (Scheme 1). The resulting RCM product 2 was
0
ꢂC with rapid stirring. The reaction mixture was allowed
to warm to room temperature and stirred for an additional
time. After 5 days, the reaction mixture was poured into
methanol and solid precipitated, which was further purified
by precipitatation from methanol for two times, and finally
the pure product a,x-dianthracene-functionalized telechelic
poly(cyclooctene) was gained as a solid in a yield of 87.8%
(102 mg, 0.022 mmol). 1H NMR (500 MHz, CDCl3), d (ppm):
8.50 (s, 2H, ArH), 8.34 (d, 4H, ArH), 8.04 (d, 4H, ArH), 7.56
(t, 4H, ArH), 7.49 (t, 4H, ArH), 6.15 (s, 2H, Ar-CH2OCO), 5.37
(t, 2H, CH¼¼CH on the polymer chain), 2.32 (t, 4H, 2 ꢀ
OCOCH2), 2.01–1.96 (m, CH2CH2ACH¼¼CHACH2CH2 on the
polymer chain), 1.60 (t, 4H, 2 ꢀ OCOCH2ACH2), 1.32–1.19 (t,
CH2 on the polymer chain); 13C NMR (125 MHz, CDCl3), d
(ppm): 173.79 (COOCH2Ar), 131.4, 131.04, 130.33, 129.87,
129.09, 126.58, 125.08, 123.97, 58.64, 34.31, 32.59, 29.74,
29.62, 29.53, 29.38, 29.29, 29.17, 29.07, 29.03, 28.70, 27.20,
25.0 (CH2COOCH2Ar). GPC: Mn ¼ 7780, Mw/Mn ¼ 1.88;
NMR: Mn ¼ 4700.
1
characterized by H NMR spectroscopy and elemental analy-
sis, from which the results were in full agreement with the
structure. The newly formed internal C¼¼C double bond in
macrocycle 2 has a favorable trans configuration of the
alkene protons of ACH2CH¼¼CHCH2A (Hj) observed at 5.34
1
ppm in H NMR spectroscopy as shown in Figure 1(B). While
the signals of alkene protons at 5.77 ppm for ACH2CH¼¼CH2
(Hj) and 4.96 ppm for ACH2CH¼¼CH2 (Hk) from the original
long chain acyclic diene 1 was completely disappeared after
CLEAVABLE MULTIBLOCK COPOLYMER SYNTHESIZATION, XIE ET AL.
383

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Multiblock copolymer via ring-
opening metathesis copolymerization of
cyclooctene and macrocyclic olefin and its
hydrolysis to give carboxyl-telechelic poly-
mers. [Color figure can be viewed in the
online issue, which is available at www.
interscience.wiley.com.]
RCM, which meant the expected 27-membered dilactone 2
was successful produced. The elemental analysis of 2 also
gave a good result matched with the theoretical value.
process of strained COE and unstrained MCO displayed better
control over the polymer composition and chain structure
than those of classical statistical copolymerization of strained
cyclic olefin monomers, where the random copolymer is
formed.16
Preparation of Cleavable Multiblock Copolymer by
Ring-Opening Metathesis Copolymerization of
The obtained [Poly(COE)–2]m was characterized via 1H NMR
spectroscopy [Fig. 1(C)]. Upon ring-opening and subsequent
polymerization, the resonance signals of the olefinic protons
in monomer COE and in macrocycle 2 shifted upfield to 5.37
and 5.30 ppm from the original 5.42 and 5.34 ppm, respec-
tively. The methylene proton signals from COE units and
macrocycle segments were appeared at 1.95 ppm (Hp,i) and
1.26 ppm (Hh,q,r), and other specific aromatic and alkane
protons from macrocycle segments were clearly observed at
8.32 ppm (Ha), 7.92 ppm (Hb), 6.87 ppm (Hc), 4.30 ppm
(He), 3.73 ppm (Hd), 2.29 ppm (Hf), and 1.58 ppm (Hg)
orderly. This observation indicated that the copolymerization
had occurred, and the monomer COE and MCO 2 had turned
to be the corresponding polymer block and segment on the
multiblock copolymer chain. The interesting results of ROMP
are summarized in Table 1. It was seen obviously, when the
molar feed ratio of monomer COE to MCO 2 and catalyst (C)
(COE:2:C) is 1500:10:1, that the number average molecular
weight (Mn,GPC) of the copolymer measured by GPC is up to
249.6 ꢀ 103 g/mol (entry 1, Table 1), while Mn,GPC decreased
with increasing of MCO 2 in the feed ratio of COE:2:C rang-
ing from 1500:10:1 to 1500:50:1 (entries 1–5, Table 1), and
all the copolymers have a reasonable PDI value around 1.60
concerning second generation Grubbs catalyst used. The vari-
ation of Mn,GPC was also shown as GPC traces in Figure 2.
Additionally, the value of Mn,GPC increased with enlarging the
feed ratio of COE:2 from 300:20 to 1200:20 (entries 6–9,
Table 1). Furthermore, the composition of the multiblock
Strained Stable Cyclic Olefin and Strainless
Degradable Macrocyclic Olefin
To explore the copolymerization behavior of conventional
cycloolefin monomer such as COE and MCO monomer, the
27-membered MCO 2 containing bulky azobenzene moiety
was selected as comonomer, which is crucial to tune the
composition of copolymer chain and also will facilitate both
the NMR characterization as many aromatic protons offering
strongly resonance signals at 8.33–6.88 ppm and nitrogen
elemental analysis to identify the molar ratios of COE units
and MCO units of copolymers. Unlike the alternating
ROMP,11–15 where the restricted alternating momomer units
A and B from the conventional cyclic olefin monomer COE,
cyclopentene, or norbornene (derivative) formed on the
polymer chain, the monomer pairs of COE and MCO 2 in this
case undergo ROMP in a comparatively good controlled man-
ner to provide almost the multiblock copolymer architecture,
in which the segment of ring-opened 2 bridged the homopoly-
mer Poly(COE) block by block affording multiblock copoly-
mer [Poly(COE)–2]m as shown in Scheme 1. It is possible to
construct such a multiblock coplymer chain as [Poly(COE)–
2]m in the copolymerization process based on the much dis-
crepancy in reactivity ratios of COE (r > 1) to MCO (r ! 0)
and in the feed ratio of monomer pairs, allowing for the for-
mation of Poly(COE) blocks and prevention of long runs of
Poly(2). This is the observed phenomenon in ROMP that the
reactivity of cycloolefin is usually reduced with the increasing
of ring size.58 As a result, it is understandable that the ROMP
384
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
DR19 in Figure 1(C) were disappeared completely in Figure
1(D) after the hydrolysis reaction, whereas all the signals
corresponding to the polymer backbone Poly(COE) block and
the macrocycle residue attached to the n-undecylenic acid
segment including the olefinic proton signals at 5.42–5.31
ppm (Hj,o), and the methylene proton signals at 2.02–1.96
ppm (Hp,i) and 1.33–1.28 ppm (Hh,q,r), especially the signals
of the methylene protons adjacent to the end group carboxyl
which derived from the cleaved ester bond at 1.62 ppm (Hg)
and the next at 2.35 ppm (Hf) were still well remainded and
clearly observed in the spectrum even after hydrolysis. This
investigation revealed that the structure of Poly(COE) with
CAC bond was kept strongly,70 whereas the segment within
2 bearing the comparative weak ester linkage (CH2OCO) was
cleaved off the multiblock copolymer chain under the hydro-
lyzed conditions, affording the carboxyl-telechelic Poly(COE)
with a high degree of functionality (Fn ¼ 2). However, the
end group carboxyl of telechelic polymer was not detectable
1
easily in the H NMR spectrum, owing to its too low propor-
tion occupied in the polymer chain, but could be observed in
13C NMR spectrum at 207.22 ppm for the carbon atom of
COOH, and 24.86 ppm for the carbon atom of CH2COOH
shown in Figure 3(A), confirming the polymer chain struc-
ture as expected.
The molecular weights (Mn,h,GPC) of the hydrolyzed polymers
HOOCAPoly(COE)ACOOH were shown in Table 1, and all
have the same tendency as those of their corresponded mul-
tiblock copolymers with the variation of the feed ratio of
COE:2:C from 1500:10:1 to 1500:50:1 (entries 1–5, Table 1)
or the feed ratio of COE:2 from 300:20 to 1200:20 (entries
6–9, Table 1). The values of Mn,h,GPC were much lower than
those (Mn,GPC) of the multiblock copolymers, and their GPC
traces were shifted down to the lower molecular weight
positions as depicted in Figure 2, which revealed the obvious
difference in the length of the polymer chain and these
multiblock copolymers yielded telechelic polymers after
FIGURE 1 1H NMR spectra of (A) a,x-diolefin 1, (B) azobenzene
moiety-containing macrocyclic olefin 2, (C) representative
cleavable multiblock copolymer, (D) a,x-dicarboxyl-fonctional-
ized telechelic poly(cyclooctene), and (E) a,x-dianthracene-fonc-
tionalized telechelic poly(cyclooctene).
copolymer can be determined by both 1H NMR and elemen-
tal analysis, although the molecular weight of the copolymer
was hard to get from these two different mesearments, and
the ratios of COE:2 incorporated in the multiblock copolymer
chain were very similar with each other, which were also
close to the feed ratio of COE:2 as shown in Table 1.
Determination of Cleavable Multiblock Copolymer
Structure by Hydrolysis
To validate the multiblock architecture and molecular weight
of the copolymer, the hydrolysis was carried out under alka-
line conditions as shown in Scheme 1. It turned out that
the multiblock copolymer chain [Poly(COE)–2]m was broken
with removing the moiety 2 from the polymer structure
and shortened to be telechelic polymer blocks HOOCA
1
Poly(COE)ACOOH. Figure 1(D) showed typical H NMR spec-
trum of HOOCAPoly(COE)ACOOH with two carboxyl-termi-
nated end groups obtained from the hydrolysis of multiblock
copolymer [Poly(COE)–2]m. The signals of the aromatic and
alkane protons at 8.32 ppm (Ha), 7.92 ppm (Hb), 6.87 ppm
(Hc), 4.30 ppm (He), and 3.73 ppm (Hd) from precursor
FIGURE 2 GPC traces for multiblock copolymers [Poly
(COE)–2]m (left group, MP 1–5), and hydrolyzed homopolymers
Poly(COE) (right group, HP 1–5).
CLEAVABLE MULTIBLOCK COPOLYMER SYNTHESIZATION, XIE ET AL.
385

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
that of Mn,h,GPC for each hydrolyzed polymer as displayed in
Table 1. More important, the degree of polymerization (n) or
the number of repeat monomer units in each Poly(COE)
block was calculated from the 1H NMR spectrum of the
hydrolyzed polymer, which was well agreed with the molar
ratio of COE:2 in the multiblock copolymer for each counter-
part. Therefore, the average number of 2 in each [Poly(-
COE)–2] repeat unit on the multiblock copolymer chain
should be one, otherwise, Mn,h,NMR of Poly(COE) would be
increased in proportion to the enlarged number of 2 with
keeping the constant ratio of COE:2. Consequently, a conclu-
sion could be made from these results that the Poly(COE)
block should be connected one by one with the segment of
ring-opened 2 as a bridged linker, and the multiblock copoly-
mer chain was cleavable as the incorporation of moiety 2 in
the chain structure.
FIGURE 3 13C NMR spectra of (A) a,x-dicarboxyl-fonctionalized
telechelic poly(cyclooctene), and (B) a,x-dianthracene-fonction-
alized telechelic poly(cyclooctene).
Transformation of a,x-Dicarboxyl End Group Into
Anthracene Moiety of the Fonctionalized Telechelic
Poly(cyclooctene)
To further confirm the telechelic polymer chain structure,
the presence of functionalized end groups was verified by
the dehydration reaction of carboxyl group on the polymer
chain end with anthracenemethanol, and the esterification
process was shown as Scheme 2.
hydrolysis. Additionally, the values of PDI of the hydrolyzed
polymers were within the range of 1.65–1.88, which were all
slightly higher after hydrolysis compared with the original
values of the corresponded multiblock copolymers. It is
worth to note that all the samples of the hydrolyzed poly-
mers for GPC measurements were collected directly with an
excellent yield of 94% by dealing with the simple precipita-
tion only from acidic water after hydrolyzation, meaning all
the water-insoluble organic components including telechelic
polymer or any others preserved. All these hydrolyzed poly-
mers presented a monomodal distribution in GPC chromato-
gram given in Figure 2, which indicated that the composition
of the hydrolyzed polymer was still homogeneous compara-
tively, in despite of their slightly higher PDIs than those of
multiblock copolymers. Importantly, the water-insoluble frac-
tion is also almost whole methanol-insoluble as described in
experimental section, which is further confirmed the good
uniformity of Poly(COE) blocks in original multiblock copoly-
mer chain architecture, and is different from that of statisti-
cal degradable cyclooctadiene/cleavable seven-membered
acetal copolymers,16 where the methanol-soluble fraction
was more than 30% after hydrolysis of copolymer.
Figure 1(E) showed 1H NMR spectrum of the functionalized
polymer with two detectable anthracene-terminated end
groups. The signals of the aromatic protons from anthracene
groups were appeared at the range of 8.50–7.49 ppm, and
the signals of methylene protons (ArCH2OCOCH2) were
observed at 6.15 ppm (Hz) after esterification of anthracene-
methanol, which was usually in the position around 5.7 ppm.
At the same time, the variation of signal for carbon atom of
COOCH2Ar was observed at 173.79 ppm in Figure 3(B), com-
paring with that for carbon atom of COOH at 207.22 ppm in
Figure 3(A) before esterification of carboxyl end groups. This
result indicated that the transformation of a,x-dicarboxyl
end group into anthracene moiety was conducted indeed.
The efficiency of transformation from end group carboxyl to
anthracene group was estimated roughly by comparing the
integration of the signal from the diagnostic methylene pro-
tons at 6.15 ppm (Hz) on the polymer chain end to a signal
of the methylene protons at 2.32 ppm (Hf) from the polymer
backbone, SH(z)/SH(f) ¼ 4/4.92, and thus the value was
81.3% under the reaction conditions; or the anthracene-func-
The average number of blocks (m) on the copolymer chain
could thus be calculated from the ratio of molecular weight
of original multiblock copolymer (Mn,GPC) to that of hydro-
lyzed polymer (Mn,h,GPC), that is, m ¼ Mn,GPC/Mn,h,GPC, and the
value was reached at least to seven or even up to 16 (Table
1). These inspiring results confirmed that the hydrolysis of
the multiblock copolymer was proceeded successfully, and
the polymer structure changed from multiblock copolymer
[Poly(COE)–2]m to functional telechelic homopolymer
HOOCAPoly(COE)ACOOH with the decrease of molecular
weight and chain length of polymer. Contrary to indetermina-
tion of molecular weights of the multiblock copolymer, the
tionalized telechelic Poly(COE) has
a lower degree of
molecular weights of the hydrolyzed polymers (Mn,h,NMR
)
could be determined by 1H NMR spectroscopy based on the
SCHEME 2 Transformation of a,x-dicarboxyl group into anthra-
end group analysis, and the value of Mn,h,NMR was lower than
cene moiety on the telechelic poly(cyclooctene) ends.
386
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ARTICLE
8 Bertin, P. A.; Gibbs, J. M.; Shen, C. K.; Thaxton, C. S.; Russin, W. A.;
functionality (Fn ¼ 1.63) than that of original carboxyl-tele-
chelic Poly(COE), which exhibited a Fn near 2.
Mirkin, C. A.; Nguyen, S. T. J Am Chem Soc 2006, 128, 4168–4169.
9 Switek, K. A.; Chang, K.; Bates, F. S.; Hillmyer, M. A. J Polym Sci Part
A: Polym Chem 2007, 45, 361–373.
CONCLUSIONS
10 Gabert, A. J.; Verploegen, E.; Hammond, P. T.; Schrock, R. R. Macro-
This work aimed at reporting the synthesis of cleavable mul-
tiblock copolymer by ROMP of COE and MCO. First, the MCO
with 27-membered ring was prepared via RCM reaction of
its long chain alkyldiene precursor catalyzed by ruthenium-
based catalyst, and then the prepared MCO 2 was well-con-
ducted ROMP reaction with monomer COE to provide a new
type of cleavable multiblock copolymer [Poly(COE–2)]m con-
sisting of Poly(COE) blocks and ring-opened 2 segments. The
multiblock copolymer containing weak ester linkage can be
cleaved under alkali conditions and converted effectively into
carboxyl-telechelic Poly(COE) blocks with obvious shortened
chain length and slight broadening molecular weight distri-
bution. The average block number on the multiblock copoly-
mer chain was thus calculated by the ratio of molecular
weights before and after hydrolysis of the multiblock copoly-
mer, which was reached up to the value of 7–16. The func-
tional carboxyl group on the telechelic polymer ends can be
changed further to anthracene moiety by esterification.
Therefore, the usage of flexible MCO 2 with quite low activ-
ity would provide an alternative method toward the forma-
tion of cleavable multiblock copolymer by ROMP process and
functional telechelic polymer after hydrolysis. Additionally,
this technique of MCO-tuned ROMP is expected to facilitate
the preparation of any type of multiblock ROMP copolymers
via one-pot procedure by changing the ring type and size of
MCO, to make for expanding applications of functionalized
multiblock ROMP copolymers. The use of these multiblock
copolymers in the measurements of their physical properties
is presently under investigation.
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