Crown ether cavity-containing copolymers via controlled alternating cyclocopolymerization

Article abstract of DOI:10.1021/ma201247d

The cyclocopolymerization of difunctional styrenic flexible monomers with maleic anhydride via reversible addition-fragmentation chain transfer (RAFT) has been investigated. The reaction proceeded to yield gel-free copolymers soluble in organic solvents. The kinetic study indicated that the cyclocopolymerization of difunctional styrenic flexible monomer with maleic anhydride proceeded in a controlled manner. The structures of resulting crown ether cavity-containing copolymers were characterized by the use of NMR spectroscopy and MALDI-TOF mass spectrometry. The crown ether cavities in copolymers exhibited a selective recognition for certain dialkylammonium ions.

Full text of DOI:10.1021/ma201247d

ARTICLE
pubs.acs.org/Macromolecules
Crown Ether Cavity-Containing Copolymers via Controlled
Alternating Cyclocopolymerization
Yong-guang Jia,† Ling-yan Liu,† Bin Lei,† Jing Li,*,† and X. X. Zhu*,‡
†State Key Laboratory of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China
‡Dꢀepartement de Chimie, Universitꢀe de Montrꢀeal, C. P. 6128, Succursale Centre-ville, Montreal, QC H3C 3J7, Canada
S Supporting Information
b
ABSTRACT: The cyclocopolymerization of difunctional styre-
nic flexible monomers with maleic anhydride via reversible
additionꢀfragmentation chain transfer (RAFT) has been in-
vestigated. The reaction proceeded to yield gel-free copolymers
soluble in organic solvents. The kinetic study indicated that the
cyclocopolymerization of difunctional styrenic flexible mono-
mer with maleic anhydride proceeded in a controlled manner.
The structures of resulting crown ether cavity-containing
copolymers were characterized by the use of NMR spectrosco-
py and MALDI-TOF mass spectrometry. The crown ether
cavities in copolymers exhibited a selective recognition for certain dialkylammonium ions.
’ INTRODUCTION
five- or six-membered rings or based on monomers possessing
constrained conformation capable of selective ring closure. It is
difficult to construct a cyclo(co)polymerization system forming
larger rings with flexible monomers because of large ring distor-
tion and longer distances for ring closure.
Butler and co-workers demonstrated the formation of water-
soluble linear polymers via cyclopolymerization as compared to
the formation of highly cross-linked quaternary ammonium
polymers during the conventional free-radical polymerization
of diallylquaternaryammonium salts.1,2 The cyclo(co)polymeri-
zation has been considered as one of the most convenient
method for the preparation of a polymer with a cyclic structure
in the main chain because it provides the unique way to generate
cyclic structures in the polymer backbone while making the
polymers efficiently.3,4 Cyclo(co)polymerization generally pro-
duces thermodynamically stable five- or six-membered rings as
the repeating units along the backbone.5ꢀ9 These very compact
rings provide rigidity to the resulting polymers but are too small
for the inclusion of other molecules, making them difficult to be
used, for example, as stationary phases for chromatographic
separation and metal scavengers.10ꢀ12 Larger rings may be
incorporated by the polymerization of properly designed difunc-
tional monomers3,4,13ꢀ20 which contain bulky or orienting
groups joining the two polymerizable groups in such a way to
favor intramolecular cyclization of the growing species in a chain-
addition polymerization process rather than cross-linking. For
instance, Endo’s group16,17 attained selective ring-closure using
the monomer’s constrained conformation and the directing
groups; Kakuchi’s group18ꢀ20 developed the cyclopolymeriza-
tion of difunctional monomers derived from a large series of
optically active diol tethers elaborated as 4-vinyl benzoate esters.
More recently, Pasini’s group3,4 achieved the cyclopolymeriza-
tion of difunctional styrenic monomers through the introduction
of pentaerythritol. To date, most examples of cyclo(co)polymeri-
zation are realized through the help of metal catalysts forming
In Butler’s early studies, the cyclocopolymerization of flexible
divinyl ether monomer with maleic anhydride (MAn) was
achieved via radical initiation, resulting in large ring-containing
copolymers,21ꢀ24 but most reports on cyclocopolymerization all
focused on the system of divinyl ether monomers and MAn.25,26
These studies prompted us to study the cyclocopolymerization
of more flexible difunctional styrenic monomers with MAn since
an alternating copolymer is preferentially obtained when styrene
is copolymerized with MAn.27,28 To the best of our knowledge,
difunctional styrenic monomer cyclocopolymerization with
MAn has never been reported. With the development of con-
trolled radical polymerization techniques, reports on the success-
ful application of these methods to cyclo(co)polymerizable
systems have appeared in the literature.16,17,29ꢀ32 The major
objective of this study is to develop a new controlled cycloco-
polymerization system for the common flexible monomers. We
attempted to copolymerize MAn with difunctional styrenic
monomers in which the styrene moieties are covalently linked
to a tri- or tetra(ethylene glycol) (Scheme 1). The copolymer-
ization was achieved with slower propagation via the reversible
additionꢀfragmentation transfer (RAFT) polymerization tech-
nique that would take a thermodynamically favorable process in
Received: March 22, 2011
Revised:
July 7, 2011
Published: July 25, 2011
r
2011 American Chemical Society
6311
dx.doi.org/10.1021/ma201247d Macromolecules 2011, 44, 6311–6317
|

Macromolecules
ARTICLE
Scheme 1. Difunctional Styrenic Monomers with Different
Spacers and Rigidities
Scheme 2. Synthesis of Difunctional Styrenic Monomers M4
and M5 and the Organic Ammonium Salt S1
Synthesis of M5. A mixture of 1,2-(2-hydroxylethoxy)benzene
(990 mg, 5 mmol), synthesized according to the literature,37 and NaH
(288 mg, 12 mmol) in 40 mL of dry THF was stirred in an ice bath for 1 h
and then at room temperature for 2 h. After the addition of a 10 mL of
THF solution of 4-vinylbenzyl chloride (1.82 g, 12 mmol), the mixture
was stirred at room temperature for 1 h and then refluxed for 12 h. The
mixture was cooled down, filtered, and concentrated under reduced
pressure, neutralized by the addition of a dilute acid (50 mL, pH = 2),
and extracted with dichloromethane (3 ꢁ 50 mL). The extract was
washed three times with brine, then dried over MgSO4, and concen-
trated. The product was purified by column chromatography (hexane/
ethyl acetate, 10:1 (v/v)) to afford a viscous liquid of pure M5 (1.74 g,
81%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.37 (d, 4H, J = 8.0 Hz),
7.30 (d, 4H, J = 8.0 Hz), 6.93 (m, 4H), 6.70 (dd, 2H, J1 = 11.2 Hz,
J2 = 17.8 Hz), 5.73 (dd, 2H, J = 17.8 Hz), 5.23 (dd, 2H, J = 11.2 Hz), 4.61
(s, 4H), 4.25 (t, 4H, J1 = 5.2 Hz, J2 = 4.8 Hz), 3.84 (t, 4H, J1 = 4.8 Hz, J2 =
5.2 Hz). 13C NMR (100 MHz, CDCl3, ppm): δ 149.0 (2C), 137.8 (2C),
136.8 (2C), 136.5 (2C), 127.8 (4C), 126.1 (4C), 121.6 (4C), 114.9
(4C), 113.6 (2C), 72.9 (2C), 68.9 (2C), 68.5 (2C). HRMS Calcd for
C26H26O4 [M + Na]+ 453.2042. Found: 453.2036.
Copolymerization of M1 with MAn. All the difunctional
styrenic monomers copolymerizations with MAn were conducted under
the same conditions (Scheme 3). In a typical reaction, benzyl dithio-
benzoate (14 mg, 0.057 mmol), AIBN (3 mg, 0.018 mmol), M1 (354
mg, 1 mmol), and MAn (980 mg, 10 mmol) were added to a dry 100 mL
Schlenk tube equipped with a stirring bar under nitrogen. The tube was
degassed and purged with nitrogen for 1 h. 1,4-Dioxane (50 mL) was
added into the tube under a nitrogen atmosphere. Next, the tube was
sealed with a septum, and residual oxygen in the mixture was removed by
three freezeꢀpumpꢀthaw cycles. The reaction mixture was allowed to
thaw and was immersed in a preheated oil bath at 60 °C for 6 h. The tube
was placed into ice water in order to quench the reaction. The solvent
was mostly removed under reduced pressure. The conversion of M1 was
determined by 1H NMR to be >99%. The reaction mixture was
precipitated in excess methanol. The precipitate was washed several
times with methanol and dried under vacuum to give 525 mg of P1 as a
pink powder. The copolymers P2 (528 mg), P3 (495 mg), P4 (489 mg),
and P5 (546 mg) were obtained from the copolymerization of MAn with
M2, M3, M4, and M5, respectively.
order to attain selective cyclocopolymerization to produce crown
ether cavities on the main chain. In the present study, we
synthesized and used a series of difunctional styrenic monomers
with different spacers and rigidities (Scheme 1) in the prepara-
tion of the copolymers. The characterization and the recognition
with organic ammonium salt of the resulting copolymers have
been investigated.
’ EXPERIMENTAL SECTION
The chain transfer agent (CTA) benzyl dithiobenzoate was synthe-
sized according to the literature.33 2,20-Azobis(isobutyronitrile) (AIBN)
(>98%, Tianjin Chemical Co.) was recrystallized from methanol twice,
and maleic anhydride (>99%, Tianjin Guangfu Fine Chemical Research
Institute) was recrystallized from CHCl3 twice before use. 1,4-Dioxane
was dried by sodium, distilled, and stored under nitrogen. Ethyl acetate,
hexane, chloroform, and methanol were all purchased from Tianjin
Chemical Co. and purified by distillation. Other reagents were used
as received. The difunctional styrenic monomers 1,2-bis(2-(4-vinylphe-
noxy)ethoxy) ethane (M1),34 1,2-bis(2-(4-vinylbenzyloxy)ethoxy)-
ethane (M2), and 1-((2-(2-(2-(2-(4-vinylbenzyloxy)ethoxy)ethoxy)-
ethoxy)ethoxy)methyl)-4-vinylbenzene (M3)35 were synthesized according
to the literature. The syntheses of 1,2-bis(2-(4-vinylphenoxy)ethoxy)-
benzene (M4) and 1,2-bis(2-(4-vinylbenzyloxy)ethoxy)benzene (M5) are
shown in Scheme 2.
Synthesis of M4. A mixture of catechol (0.72 g, 6 mmol), K2CO3
(3.00 g), 1-(2-bromoethoxy)-4-vinylbenzene (4.52 g, 20 mmol), synthe-
sized according to the literature,36 and dimethylformamide (10 mL) was
stirred at 75 °C for 24 h. The mixture was diluted with water; the
precipitate was collected and washed with cold water. The crude product
was crystallized from ethyl acetate twice (2.03 g, 84%). 1H NMR (400
MHz, CDCl3, ppm): δ 7.23 (d, 4H, J = 8.8 Hz), 6.90 (m, 4H), 6.69 (d,
4H, J = 8.8 Hz), 6.57 (dd, 2H, J1 = 10.8 Hz, J2 = 17.6 Hz), 5.53 (dd, 2H,
J = 17.6 Hz), 5.05 (dd, 2H, J = 10.8 Hz) 4.29 (t, 4H, J1 = 4.0 Hz, J2 = 4.8
Hz), 4.22 (t, 4H, J1 = 4.8 Hz, J2 = 4.0 Hz). 13C NMR (100 MHz, CDCl3,
ppm): δ 158.0 (2C), 148.7 (2C), 135.7 (2C), 130.3 (2C), 126.9 (4C),
121.7 (4C), 115.4 (4C), 114.3 (4C), 111.2 (2C), 67.9 (2C), 66.3 (2C).
HRMS Calcd for C26H26O4 [M + Na]+ 425.1729. Found: 425.1723.
Synthesis of N-n-Butylbenzylammonium Hexafluoropho-
sphate (S1). S1 was synthesized according to the literature procedure
with minor modifications (Scheme 2).38 Butan-1-amine (10 mmol) was
added to a solution of benzaldehyde (10 mmol) in anhydrous toluene
(20 mL). The resulting mixture was heated at 110 °C for 3 h and then
evaporated to dryness. Then the crude product was dissolved in MeOH
6312
dx.doi.org/10.1021/ma201247d |Macromolecules 2011, 44, 6311–6317

Macromolecules
ARTICLE
Scheme 3. Difunctional Styrenic Monomers Copolymerized with MAn
(15 mL). NaBH4 (30 mmol) was then added to the solution at 0 °C,
which was stirred for 8 h after warming to room temperature. Water
(10 mL) was added carefully to quench the excess NaBH4. The solvent
was then evaporated, and the residue was partitioned between water and
CHCl3. The organic extracts were dried, and the solvent was removed in
vacuo. The residue was dissolved in THF, and 10 mmol of HPF6 was
added to the solution. THF was removed after the mixture was dried
over MgSO4. The solid was washed by CHCl3 to yield S1 (2.78 g, 90%)
as a white powder.
Characterization. The number-average (Mn) and the weight-
average molecular weights (Mw) and the polydispersity index (PDI)
of the polymers were determined by size exclusion chromatography
(SEC) by the use of an Agilent Technologies 1200 series SEC equipped
with a G1362A differential refractive index detector, with THF as eluent
at a flow rate of 1.0 mL/min. Polystyrene standards were used for the
calibration of molecular weight. 1H and 13C NMR spectra were recorded
on a 400 MHz Bruker Avance spectrometer at room temperature, with
TMS as the internal standard. Thermogravimetric analysis (TGA) was
performed on a Q500 thermogravimetric analyzer under nitrogen
atmosphere (60 mL/min) at a heating rate of 10 K/min. FT-IR spectra
were recorded with KBr pellets of solid samples on a Bruker Tensor 27.
Matrix-assisted laser desorption ionization time-of-flight (MALDI-
TOF) mass spectrometry was performed on a Bruker Biflex III spectro-
meter equipped with a 337 nm nitrogen laser. 2,5-Dihydroxybenzoic
acid was used as the matrix. The mass spectra were acquired in a
linear mode at an acceleration voltage of +19 kV. High-resolution
mass spectrometry (HRMS) was performed on a Varian QFT-ESI
instrument.
formation of the charge transfer complex and to enhance
intramolecular cyclization. We also tried to decrease the molar
ratio of MAn to difunctional styrenic monomer. Precipitation
occurred during the polymerization when the molar ratio of MAn
to difunctional styrenic monomer was lower than 5. When this
molar ratio was 7, the conversion of difunctional styrenic
monomers reached 99% in 48 h. The molar ratio of MAn to
difunctional styrenic monomers was optimized to be 10, which
afforded high cyclization yields even under dilute conditions. All
resulting copolymers are soluble in organic solvents such as
acetone and THF, which indicates that the cyclizations were
efficient enough to prevent cross-linking. The 1H NMR spectra
of the copolymers are listed in Figure S1. The complete
disappearance of the vinyl proton resonances indicates an effi-
cient cyclocopolymerization and rules out the presence of
detectable vinyl pendant groups within the copolymer backbone.
The existence of MAn was confirmed by FT-IR spectra (Figure
S2), showing two new strong absorption peaks at 1857 and
1780 cmꢀ1 assigned to the characteristic carbonyl absorption of
MAn. In this work, the copolymers were precipitated in methanol
at the room temperature. Concerns of possible opening of the
anhydride ring are eased by the attenuated total reflection (ATR)
FT-IR spectra of the polymers obtained without the use of KBr,
where no absorption was observed in the region of 3000ꢀ
3500 cmꢀ1. The small absorption observed in this region in
the FT-IR spectra may be caused by the water moisture in the
KBr used. The IR spectra are shown in the Supporting Informa-
tion (Figure S2).
Good agreements between the Mn,SEC measured by SEC and
the Mn,NMR by NMR were observed, while the PDIs were not
very narrow (Table 1). The PDI increased with an increase in the
monomer’s spacer length from P1 to P2 and to P3 even under
the same reaction conditions, indicating that the cyclization
becomes increasingly difficult to control as the spacer group
becomes longer. The duration of cyclizations also increased from
P1 to P2 and to P3 with increasing spacer length of the mono-
mers. In contrast, the yield decreased with the increase in the
spacer length, which may be explained by the increased flexibility
of the copolymer backbone caused by the spacer length. The
resulting copolymers also have a higher solubility in methanol.
For the same reason, solubility of the copolymers in chloroform
also increased from P1, P2 to P3. In previous reports,12,39,40 the
broadening of the PDI from the appearance of the shoulder on
the high-molecular-weight side of the SEC curve is rather
common in the course of cyclopolymerization of divinyl ether
monomers, especially at high monomer conversions, where a
’ RESULTS AND DISCUSSION
Synthesis and Characterization of the Copolymers. Com-
pared with M1 and M2, M4 and M5 are more rigid due to the
presence of an aromatic ring. The length of the spacer increases
from M1 to M2 and to M3 to increase the ring size in the
resulting copolymers (Scheme 1). A low initial monomer con-
centration ([monomer]0 = 0.02 M) was used to favor intramo-
lecular propagation and to suppress any intermolecular
propagation that may lead to uncyclized repeating units. It well
established that an alternating copolymer will be preferentially
obtained when styrene is copolymerized with MAn.27,28 Increas-
ing the concentration of the comonomers can generally promote
the formation of charge transfer complex between the
comonomers,27 which facilitates the formation of an alternating
copolymer. Since a high concentration of difunctional styrenic
monomer may lead to potential problems of cross-linking, we
opted to increase the concentration of MAn to promote the
6313
dx.doi.org/10.1021/ma201247d |Macromolecules 2011, 44, 6311–6317

Macromolecules
ARTICLE
Table 1. Results of the RAFT Copolymerization of the
Difunctional Styrenic Monomers M1ꢀM5 with Maleic An-
hydride in 1,4-Dioxane
the presence of minor peaks on the left side (for P1 in Figure 2A
and P2 in Figure S7) or on both sides (for P5 in Figure 2B) of
each of main peaks. In the enlarged figure, one can clearly note
that the interval between main peaks and the minor peaks are all
98 Da, which can be assigned to one unit of MAn (such as the
interval between peaks D and E in Figure 2A). These differences
can be attributed to the different terminal monomer patterns
during polymerization (Scheme 4). Pattern A: the ends of
polymer chain are different, being maleic anhydride and styrenic
monomer, respectively. Pattern B: both ends terminate with the
styrenic monomer (one MAn unit less). Pattern C: both ends
terminate with MAn (one MAn unit extra). Patterns B and C
may be less abundant than pattern A, even though all three
patterns in the same group may contain the same number of
styrenic monomers. In Figure 2A, the interval between peaks B
and E (18 Da) correspond to a water molecule, since some of the
anhydride groups may undergo a hydrolysis or absorb one water
molecule at a high temperature with traces of moisture during
the ionization experiments. The interval between peaks B and E
(16 Da) may be caused by the different cationization or terminal
chain transfer agent groups. In the MALDI-TOF mass spectrum
of P5 (Figure 2B), other minor peaks are present on both sides
of the main peaks. The interval between main peaks A and B
(626 Da) is fragment mass of structural pattern A. The intervals
between peaks B and D or B and F are both 98 Da, corresponding
to one unit of MAn, which can be also explained by the different
terminal monomer patterns. Peaks B, D, and F correspond to the
patterns A, C, and B in Scheme 4, respectively.
reaction
time (h)
yield
(%)a
Mn,
Mn,
Td
(°C)d
b
c
copolymer
PDIc
NMR
SEC
P1
P2
P3
P4
P5
6
24
48
6
95
89
78
80
86
9600
9200
8000
8400
12900
6500
9500
1.33
1.52
1.86
1.51
1.53
313
296
275
316
310
11400
8000
24
10800
a Yield calculated from the soluble portion in methanol. The conversion
of the difunctional styrenic monomers was >99% as determined by
b
1H NMR. Mn,NMR = [M]0/[CTA]0 ꢁ conversion (%) ꢁ molecular
weight of monomer + molecular weight of CTA. c Determined by SEC.
d The decomposition temperature is defined as the temperature at 5%
weight loss, measured by TGA.
In this study, the design of the polymers is based on the well-
known fact that styrenic monomers and MAn copolymerize to
yield alternating copolymers with a regular sequence of the type
M1M2M1M2.... This work is the first attempt to introduce
relatively large crown ether rings on the main chain of polymers
by the alternating copolymerization of difunctional styrenic
monomers with MAn. It is known that comonomer pairs in
the form of charge transfer complex M1M2 may be formed before
the initiation, which helps the copolymerization of the mono-
mers spontaneously in an alternating fashion.27 Furthermore, if
one considers the following reactions
Figure 1. SEC curves of P1, P2, P3, P4, and P5.
minor extent of cross-linking and/or branching reactions may
occur to consume the pendant unreacted vinyl groups and
broaden the PDIs of the produced polymers. In this study, there
is no apparent shoulder on the high-molecular-weight side of the
SEC curves (Figure 1).
1
k11
k12
From the H NMR spectra of P1 and P3, molar ratio of
•
•
•
•
oM1 þ M1 f o M1M1 oM1 þ M2 f o M1M2
difunctional styrenic monomers and MAn can be calculated
directly by the relative integration of the proton resonances
(Figures S3 and S4). They are both close to 1:2, indicating the
good match between the observed and the proposed alternating
structures of the comonomers. On the basis of the reactivity of
the propagating radical and the comonomers, an alternating
copolymer is preferentially obtained when styrene is copolymer-
ized with MAn.27,28 Charge transfer complexes should be formed
between the monomers. Once the polymerization is initiated, the
comonomer pair in the complex copolymerizes spontaneously to
yield an alternating copolymer.
The MALDI-TOF mass spectrometric results in Figure 2 are
also in accordance with the structure of an alternating polymer.
In the spectra, the main peaks are separated by a fragment mass
corresponding to a repeating unit consisting of one difunctional
styrenic monomer and two MAn monomers (structural pattern
A in Scheme 4). For example, peaks A and B (Figure 2A) both
correspond to the products of Na+ cationization, and the interval
between them correspond to the fragment mass of one difunc-
tional styrenic monomer and two MAn (550 Da) as shown in
pattern A in Scheme 4. In the enlarged spectra, one can observe
r1 ¼ k11=k12
k22
k21
•
•
•
•
oM2 þ M2 f o M2M2 oM2 þ M1 f o M2M1
r2 ¼ k22=k21
where M1 and M2 represent MAn and styrene, respectively; the
reactivity ratios r1 and r2 of the two monomers at 50 °C are 0.005
and 0.050, repectively.41 These values indicate clearly that the
two types of propagating species preferentially add the other
monomer, not the monomer of its own kind. Under the dilute
conditions (0.02 M) used in our study, which is lower than the
concentration used by others in the cyclopolymerization of
difunctional monomers,3,17 it is even harder for the difunctional
styrenic monomers to homopolymerize. Chances of any intra-
molecular cyclization of the two styrene moieties should be very
low. Both the MALDI-TOF mass spectrometric data and the 1H
NMR spectroscopic data point to the formation of alternating
copolymer structures as the major products. Theoretically, we
cannot exclude the probability of adjacent identical monomer
6314
dx.doi.org/10.1021/ma201247d |Macromolecules 2011, 44, 6311–6317

Macromolecules
ARTICLE
Figure 2. MALDI-TOF mass spectra of P1 (A) and P5 (B) and the enlarged regions of the spectra.
Scheme 4. Different Structural Patterns of the Copolymers Observed in MALDI-TOF Mass Spectrometry
units in the copolymers obtained, but the data obtained indicates
that the difunctional styrenic monomers preferentially copoly-
merize with MAn, yielding alternating copolymers. In the case of
M5 copolymerization with MAn, there may be trace amounts of
adjacent MAn units close to the baseline noise of the enlarged
part of the MALDI-TOF spectrum of P5 (Figure 2B). This is not
observed, however, for the other copolymers obtained as shown
in Figure 2A for P1 and Figure S7 for P2. Indeed, reports on the
homopolymerization of MAn are rare due to MAn’s very low
homopolymerization reactivity.
molecular region. It is possible that copolymer has a lower
solubility in the mixture of THF and methanol, which may lead
to insufficient mixing of the polymer and matrix, causing
difficulty in the ionization of the polymer.42
To demonstrate the controlled character of these polymeriza-
tions, M1 copolymerization with MAn was used as a model for
the kinetic study at 60 °C. The samples were withdrawn from the
copolymerization mixtures at prefixed time intervals, quenched
in an ice bath, and promptly analyzed by SEC and 1H NMR. As
shown in Figure 3A, a nearly linear increase of Mn with conver-
sion as well as the relatively narrow PDI values (1.3ꢀ1.5) reveals
a constant number of propagating chains throughout the poly-
merization and the absence of nondegenerative chain transfer
Other matrices were also tested for the MALDI-TOF mass
spectrometry of the copolymers, but the result was not satisfac-
tory due to the low intensity of the signals, especially in the higher
6315
dx.doi.org/10.1021/ma201247d |Macromolecules 2011, 44, 6311–6317

Macromolecules
ARTICLE
possessing a cumyl R group.46 These results indicate that the
cyclocopolymerizations of M1 with MAn proceeded in a con-
trolled manner via RAFT. In contrast, in the case of conventional
radical polymerization, precipitation was observed from the
copolymerization mixture after 5 min, yielding a cross-linked
polymer. This significant difference in the polymers obtained
indicates that the slower propagation in the presence of CTA
favors the selective cyclopolymerization process. If the efficiency
of the cyclization were low, the number of the propagating
ends per polymer chain would have increased by branching as
the polymerization progressed. The polymer obtained did
1
not contain any double bond moiety, as confirmed by H
NMR, which also supports the good selectivity of the cyclo-
copolymerization.
We also examined the interplay between the structure and the
thermal properties of copolymers by TGA. The Td decreases
with increasing ring size and with decreasing ring rigidity
(Table 1). In other words, a smaller ring size and a more rigid
ring both lead to an increased stability of the copolymers.
Formation of Inclusion Complexes. The interaction be-
tween crown ether cavities and organic ammonium salts (S1)
can help to establish the relative ring sizes and can be monitored
by 1H NMR spectroscopy as reported previously.38,47,48 The 1H
NMR spectra were recorded after mixing S1 and a copolymer
sample for 30 min (Figure 4). No chemical shift change can be
observed when P5 is mixed with S1. When another copolymer
P3 with a larger ring on the chain is mixed with S1, the 1H NMR
spectra reveals that the characteristic peaks of Ha and Hb of the
methylene group of S1 shifts upfield from 4.11 and 2.94 ppm to
3.91 and 2.78 ppm, respectively. A portion of the proton signals
of the crown ether units also shifts upfield from 3.55 to 3.33 ppm.
These results suggest that the dialkylammonium ions are en-
circled by the crown ether cavities on the polymer backbone and
that the match of ring size with the organic ammonium ion is
crucial in the formation of inclusion complexes.
Figure 3. Kinetic study of M1 cyclocopolymerization with MAn in 1,4-
dioxane at 60 °C: (A) plot of Mn as a function of M1 conversion; (B)
plot of ln([M]0/[M]) as a function of reaction time.
’ CONCLUSION
The cyclocopolymerizations of difunctional styrenic flexible
monomers with MAn have been successfully carried out in high
yield. The expected ratio of difunctional styrenic monomers to
1
MAn in the H NMR spectra of the resultant polymers, the
MALDI-TOF mass spectrometric results, and their solubility in
common organic solvents all indicate the formation of crown
ether cavity-containing cyclocopolymers on the main chain. This
cyclocopolymerization strategy provides a favorable condition to
obtain alternating copolymers in high yields even in high dilution
and without cross-linking products. The crown ether cavities in
the copolymers exhibited a selective recognition for certain
dialkylammonium ions and may be useful for other size selective
complexations. This method leads a new path for cyclocopoly-
merization. In addition, the MAn moiety may be easily trans-
formed into other functional groups, which is a subject of further
studies.
Figure 4. 1H NMR spectra (400 MHz, CDCl3/CD3CN, 5:1, v/v) of (A)
P5, (B) S1 mixed with P5 (C) S1, (D) P3, and (E) S1 mixed with P3. S1
was added in equimolar amounts as the crown ether units in the polymers.
reaction. The linearity of the first-order kinetic plot (Figure 3B)
for the copolymerization indicates a constant free radical con-
centration and the absence of significant termination reactions.
Figure 3B also indicates the consumption of M1 starting after
an induction period of 1 h. The induction periods are often
observed with CTAs in which the substitution group R reinitiates
slowly43ꢀ45 or preferentially adds back to CTA, such as the CTA
’ ASSOCIATED CONTENT
S
Supporting Information. Figures showing IR, NMR, and
b
MALDI-TOF mass spectra and TGA curves of the copolymers.
This material is available free of charge via the Internet at http://
pubs.acs.org.
6316
dx.doi.org/10.1021/ma201247d |Macromolecules 2011, 44, 6311–6317

Macromolecules
ARTICLE
’ AUTHOR INFORMATION
(27) Cowie, J. M. G. In Alternating Copolymers; Plenum Press: New
York, 1985.
(28) Seymour, R. B.; Garner, D. P. Polymer 1976, 17, 21–24.
(29) Erkoc, S.; Mathias, L. J.; Acar, A. E. Macromolecules 2006, 39,
8936–8942.
Corresponding Author
*E-mail: lijing@nankai.edu.cn (J.L.) or julian.zhu@umontreal.ca
(X.X.Z.).
(30) Erkoc, S.; Acar, A. E. Macromolecules 2008, 41, 9019–9024.
(31) Assem, Y.; Chaffey-Millar, H.; Barner-Kowollik, C.; Wegner,
G.; Agarwal, S. Macromolecules 2007, 40, 3907–3913.
(32) Assem, Y.; Greiner, A.; Agarwal, S. Macromol. Rapid Commun.
2007, 28, 1923–1928.
(33) Vosloo, J. J.; De Wet-Roos, D.; Tonge, M. P.; Sanderson, R. D.
Macromolecules 2002, 35, 4894–4902.
(34) McCairn, M. C.; Tonge, S. R.; Sutherland, A. J. J. Org. Chem.
2002, 67, 4847–4855.
(35) Feng, S. J.; Wang, Q.; Gao, Y.; Huang, Y. G.; Qing, F. L. J. Appl.
’ ACKNOWLEDGMENT
The financial support from the National Natural Science
Foundation of China (20774045) and the Canada Research
Chair program is gratefully acknowledged. We thank Professor
Zhi-hong Wang and Dr. Ying-jun Chen (both of Nankai Uni-
versity) for their help with the 13C NMR and the MALDI-TOF
mass measurements. Y.G.J. thanks the China Scholarship Coun-
cil for a scholarship.
Polym. Sci. 2009, 114, 2071–2078.
(36) Motoi, M.; Saito, E.; Kyoda, S.; Takahata, N.; Nagai, S.; Arano,
A. Polym. J. 1991, 23, 1225–1241.
(37) Bogaschenko, T.; Basok, S.; Kulygina, C.; Lyapunov, A.;
Lukyanenko, N. Synthesis 2002, 15, 2266–2270.
’ REFERENCES
(38) Xiong, X. Q.; Chen, Y. M.; Feng, S.; Wang, W. J. Polym. Sci., Part
A: Polym. Chem. 2010, 48, 3515–3522.
(39) Hashimoto, T.; Watanabe, K.; Kodaira, T. J. Polym. Sci., Part A:
Polym. Chem. 2004, 42, 3373–3379.
(40) Hashimoto, T.; Takagi, H.; Hasegawa, Y.; Matsui, H.; Urushisaki,
M.; Sakaguchi, T. J. Polym. Sci., Part A: Polym. Chem. 2010, 48, 952–958.
(41) Odian, G. Principles of Polymerization, 4th ed.; Wiley: New
York, 2004; Chapter 6.
(42) Zou, Y.; Brooks, D. E.; Kizhakkedathu, J. N. Macromolecules
2008, 41, 5393–5405.
(43) Chong, Y. K.; Krstina, J.; Le, T. P. T.; Moad, G.; Postma, A.;
Rizzardo, E.; Thang, S. H. Macromolecules 2003, 36, 2256–2272.
(44) Vana, P.; Davis, T. P.; Barner-Kowollik, C. Macromol. Theory
Simul. 2002, 11, 823–835.
(45) Coote, M. L. Macromolecules 2004, 37, 5023–5031.
(46) Thomas, D. B.; Convertine, A. J.; Myrick, L. J.; Scales, C. W.;
Smith, A. E.; Lowe, A. B.; Vasilieva, Y. A.; Ayres, N.; McCormick, C. L.
Macromolecules 2004, 37, 8941–8950.
(47) Clemente-Leꢀon, M.; Pasquini, C.; Hebbe-Viton, V.; Lacour, J.;
Dalla Cort, A.; Credi, A. Eur. J. Org. Chem. 2006, 105–112.
(48) Jiang, W.; Sch€afer, A.; Mohr, P. C.; Schalley, C. A. J. Am. Chem.
Soc. 2010, 132, 2309–2320.
(1) Butler, G. B.; Bunch, R. L. J. Am. Chem. Soc. 1949, 71, 3120–3122.
(2) Butler, G. B. In Cyclopolymerization and Cyclocopolymerization;
Marcel Dekker: New York, 1992.
(3) Edizer, S.; Veronesi, B.; Karahan, O.; Aviyente, V.; Deꢁgirmenci,
I.; Galbiati, A.; Pasini, D. Macromolecules 2009, 42, 1860–1866.
(4) Sharma, A. K.; Cornaggia, C.; Pasini, D. Macromol. Chem. Phys.
2010, 211, 2254–2259.
(5) Park, S.; Takeuchi, D.; Osakada, K. J. Am. Chem. Soc. 2006,
128, 3510–3511.
(6) Okada, T.; Takeuchi, D.; Osakada, K. Macromolecules 2010,
43, 7998–8006.
(7) Park, S.; Okada, T.; Takeuchi, D.; Osakada, K. Chem.—Eur. J.
2010, 16, 8662–8678.
(8) Takeuchi, D.; Matsuura, R.; Park, S.; Osakada, K. J. Am. Chem.
Soc. 2007, 129, 7002–7003.
(9) Takeuchi, D.; Matsuura, R.; Fukuda, Y.; Osakada, K. Dalton
Trans. 2009, 8955–8962.
(10) Urushisaki, M.; Kodaira, T.; Furuta, T.; Yamada, Y.; Oshitani, S.
Macromolecules 1999, 322–327.
(11) Sakai, R.; Satoh, T.; Kakuchi, R.; Kaga, H.; Kakuchi, T.
Macromolecules 2004, 37, 3996–4003.
(12) Rahman, M. S.; Hashimoto, T.; Kodaira, T. J. Polym. Sci., Part A:
Polym. Chem. 2003, 41, 281–292.
(13) Costa, A. I.; Barata, P. D.; Prata, J. V. React. Funct. Polym. 2006,
66, 465–470.
(14) Kim, T. H.; Dokolas, P.; Feeder, N.; Giles, M.; Holmes, A. B.;
Walther, M. Chem. Commun. 2000, 2419–2420.
(15) Wulff, G.; Matussek, A.; Hanf, C.; Gladow, S.; Lehmann, C.;
Goddard, R. Angew. Chem., Int. Ed. 2000, 39, 2275–2277.
(16) Nagai, A.; Ochiai, B.; Endo, T. Macromolecules 2005,
38, 2547–2549.
(17) Ochiai, B.; Ootani, Y.; Endo, T. J. Am. Chem. Soc. 2008, 130,
10832–10833.
(18) Kakuchi, T.; Narumi, A.; Kaga, H.; Ishibashi, T.; Obata, M.;
Yokota, K. Macromolecules 2000, 33, 3964–3969.
(19) Kakuchi, T.; Narumi, A.; Kaga, H.; Yamauchi, Y.; Obata, M.;
Uesaka, T.; Yokota, K. Macromolecules 2001, 34, 38–43.
(20) Narumi, A.; Sakai, R.; Ishido, S.; Sone, M.; Satoh, T.; Kaga, H.;
Nakade, H.; Kakuchi, T. Macromolecules 2007, 40, 9272–9298.
(21) Butler, G. B.; Lien, Q. S. ACS Symp. Ser. 1982, 195, 149–165.
(22) Butler, G. B.; Wu, C. C. Macromol. Synth. 1982, 8, 89–94.
(23) Butler, G. B.; Campus, A. F. J. Polym. Sci., Part A-1 1970,
8, 523–532.
(24) Guilbault, L. J.; Butler, G. B. J. Macromol. Sci., Chem. 1971,
5, 1219–1228.
(25) Kunitake, T.; Tsukino, M. J. Polym. Sci., Polym. Chem. Ed. 1979,
17, 877–888.
(26) Tsukino, M.; Kunitake, T. Polym. J. 1981, 13, 671–678.
6317
dx.doi.org/10.1021/ma201247d |Macromolecules 2011, 44, 6311–6317