Periodically functionalized and grafted copolymers via 1:2-sequence- regulated radical copolymerization of naturally occurring functional limonene and maleimide derivatives

Article abstract of DOI:10.1021/ma401021d

Naturally occurring hydroxy-functionalized limonene analogues, i.e., monoterpene alcohols such as perillyl alcohol and carveol, were radically copolymerized with cyclohexylmaleimide (CyMI) in PhC(CF₃) ₂OH via 1:2-sequence-regulated propagation to obtain periodically functionalized bio-based copolymers possessing one hydroxyl group in every three-monomer unit. Alternatively, a combination of hydroxy-functionalized maleimide (N-2-hydroxyethylmaleimide: HEMI) and limonene resulted in another periodically functionalized copolymer possessing two hydroxyl groups for every three-monomer unit. These copolymerizations were fitted well by the penultimate model, where the hydroxyl functions did not have a significant effect on the selective propagation, as has been reported for a combination of nonfunctionalized limonene and CyMI. The periodic hydroxyl groups can be quantitatively converted into carbamate moieties by a polymer reaction with isocyanate to result in another series of 1:2 and 2:1 periodically functionalized copolymers. Periodically grafted copolymers possessing one or two graft chains repeating in three-monomer units were prepared by radical copolymerization of chlorine-functionalized limonene or maleimide derivatives, which were synthesized from hydroxy-functionalized monomers, followed by ruthenium-catalyzed living radical polymerization of methyl methacrylate initiated from periodically introduced C-Cl bonds in the backbone copolymers.

Full text of DOI:10.1021/ma401021d

Article
pubs.acs.org/Macromolecules
Periodically Functionalized and Grafted Copolymers via 1:2-
Sequence-Regulated Radical Copolymerization of Naturally
Occurring Functional Limonene and Maleimide Derivatives
Masaru Matsuda, Kotaro Satoh, and Masami Kamigaito*
Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603,
Japan
ABSTRACT: Naturally occurring hydroxy-functionalized li-
monene analogues, i.e., monoterpene alcohols such as perillyl
alcohol and carveol, were radically copolymerized with
cyclohexylmaleimide (CyMI) in PhC(CF3)2OH via 1:2-
sequence-regulated propagation to obtain periodically func-
tionalized bio-based copolymers possessing one hydroxyl
group in every three-monomer unit. Alternatively, a combina-
tion of hydroxy-functionalized maleimide (N-2-hydroxyethyl-
maleimide: HEMI) and limonene resulted in another periodi-
cally functionalized copolymer possessing two hydroxyl groups
for every three-monomer unit. These copolymerizations were
fitted well by the penultimate model, where the hydroxyl
functions did not have a significant effect on the selective
propagation, as has been reported for a combination of nonfunctionalized limonene and CyMI. The periodic hydroxyl groups can
be quantitatively converted into carbamate moieties by a polymer reaction with isocyanate to result in another series of 1:2 and
2:1 periodically functionalized copolymers. Periodically grafted copolymers possessing one or two graft chains repeating in three-
monomer units were prepared by radical copolymerization of chlorine-functionalized limonene or maleimide derivatives, which
were synthesized from hydroxy-functionalized monomers, followed by ruthenium-catalyzed living radical polymerization of
methyl methacrylate initiated from periodically introduced C−Cl bonds in the backbone copolymers.
ordered monomer sequence, the controlled sequence is limited
to diads, i.e., an AB alternating fashion.37,38
INTRODUCTION
■
Sequence regulation in synthetic polymers is one of the most
challenging topics in polymer chemistry because polymer
structures and properties depend on not only the monomer
compositions but also their arrangements.1−34 In particular,
arrangements of functional groups in polymer chains are critical
to determining higher-order polymer structures as well as
polymer properties and functions, as is obvious in not only
many synthetic polymers but also natural polymers such as
proteins.35 In polymer synthesis, polar functional groups,
however, often disturb the propagation reaction of growing
chains, particularly in ionic and coordination polymerization,
and are usually protected during the polymerization reaction for
their introduction into polymer chains. In contrast, radical
polymerization is highly tolerant to these functional groups due
to the neutrality of the growing species and can be widely used
for direct polymerization of various functional monomers.36
However, in general, none of the chain-growth polymerization
reactions, including radical polymerization, can achieve control
of the monomer sequence; monomers react statistically, in
most cases, according to their monomer reactivity ratios to
result in statistical or “random” incorporation of the functional
groups into the copolymers. Although alternating radical
copolymerizations are typical exceptions that enable some
Recently, we found that an unprecedented selective 1:2-
sequence-regulated radical copolymerization proceeds between
naturally occurring terpenes, such as limonene (1) and β-
pinene, and maleimide derivatives in fluorinated alcohol
[PhC(CF3)2OH] to give a highly controlled triad sequence in
an ABB fashion, where A and B denote terpenes and maleimide
derivatives, respectively.13 Furthermore, detailed mechanistic
studies revealed that the key to this higher-order monomer
sequence control can be attributed to the bulky and
characteristic structures of naturally occurring terpenes, which
generate relatively electron-rich tertiary carbon radical species
with adjacent cyclohexenyl substituents, and the hydrogen-
bonding interaction between the fluorinated alcohol as a
solvent and the maleimide unit as a comonomer.14,39 Another
important point of this study, particularly with respect to the
sustainable development of polymer materials, is the use of
relatively abundant naturally occurring compounds as renew-
able resources for novel bio-based copolymers40−47 possessing
controlled monomer sequences as well as high glass transition
Received: May 16, 2013
Revised: June 20, 2013
Published: July 3, 2013
© 2013 American Chemical Society
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Scheme 1. Periodically Functionalized and Grafted Copolymers via 1:2-Sequence-Regulated Radical Copolymerization of
Naturally Occurring Functional Limonene and Maleimide Derivatives
temperatures and optical activities originating from the bulky
and chiral characteristics of naturally occurring monomers.
This study is focused on the periodic incorporation of
functional moieties into bio-based sequence-regulated copoly-
mers via direct radical copolymerization of functionalized
limonene or maleimide derivatives in fluorinated alcohol
(Scheme 1). More specifically, we first focused on mono-
terpene alcohol, such as perillyl or perilla alcohol (2; p-mentha-
1,8-dien-7-ol) and carveol (3; p-mentha-1,8-dien-6-ol), which
can be obtained from a variety of essential oils, e.g., lavender,
spearmint, and orange,48,49 as hydroxy-functionalized natural
terpene monomers for periodically functionalized copolymers
possessing one hydroxyl group for every three-monomer unit
via radical copolymerization with N-cyclohexylmaleimide
(CyMI) in PhC(CF3)2OH. In addition, nonfunctionalized
limonene (1) was copolymerized with N-2-hydroxyethylmalei-
mide (HEMI) as a hydroxy-functionalized maleimide for
periodically functionalized copolymers possessing two hydroxyl
groups for every three-monomer unit. These incorporated
hydroxyl groups in the obtained periodic copolymers were
further converted into carbamate groups via a polymer reaction
with isocyanate to generate different periodically functionalized
copolymers.
mers.36,50,51 Although 1:1 alternating copolymerization of
styrene and maleimide derivatives has already been employed
for the synthesis of various alternating graft or heterograft
copolymers,52−60 there are no reports on the synthesis of such
periodically grafted copolymers.
EXPERIMENTAL SECTION
■
Materials. (+)-D-Limonene (1) (Aldrich, 97%), (−)-perillyl
alcohol (2) (Aldrich, 96%), (−)-carveol (3) (Aldrich, 97%), methyl
methacrylate (MMA; Tokyo Kasei; >98%), and PhC(CF3)2OH
(Wako, >99%) were distilled from calcium hydride under reduced
pressure before use. N-Cyclohexylmaleimide (CyMI) (Aldrich, 97%)
and 2,2′-azobis(isobutyronitrile) (AIBN) (Kishida, >99%) were
purified by recrystallization from toluene and methanol, respectively.
N-2-Hydroxyethylmaleimide (HEMI) was synthesized according to
the literature.61 Perillyl 2-chloro-2-phenylacetate (2-Cl) and 2-
maleimidoethyl 2-chloro-2-phenylacetate (HEMI-Cl) were synthesized
as below. α-Chlorophenylacetyl chloride (Merck, 98%), Ru(Ind)Cl-
(PPh3)2, (provided from Wako), and Al(acac)3 (acac: acetylacetonate;
Wako, >98%) were used as received. Toluene (Kanto, >99.5%; H2O
<10 ppm) was dried and deoxygenized by passage through columns of
Glass Contour Solvent Systems before use.
Perillyl 2-Chloro-2-phenylacetate (2-Cl). α-Chlorophenylacetyl
chloride (10.0 mL, 0.069 mol) was added dropwise to a solution of 2
(10.8 mL, 0.068 mol) and triethylamine (9.6 mL, 0.069 mol) in dried
CHCl3 (60 mL) at 0 °C. After stirring at ambient temperature, the
solution was washed with water, and all the organic phase was
collected. The obtained crude product was purified by column
chromatography on silica gel with n-hexane/EtOAc = 10/1 and then n-
hexane as an eluent. Perillyl 2-chloro-2-phenylacetate (2-Cl) was
As another application of selective 1:2-sequence-regulated
radical copolymerization, periodically grafted copolymers were
targeted by the copolymerization of functionalized monomers
possessing a reactive C−Cl bond, which were synthesized from
hydroxy-functionalized monomers, followed by the metal-
catalyzed living radical polymerization of vinyl mono-
1
obtained as colorless liquid (5.4 g, yield = 26%, purity >99%). H
NMR (CDCl3, rt): δ 1.33−2.15 (m, 10H), 4.54 (m, 2H, CH2−O),
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4.67−4.71 (m, 2H, CH2C), 5.35 (s, 1H, CH−Cl), 5.70 (m, 1H,
CHC), 7.45−7.49 (m, 3H, m, p-ArH), 7.30−7.40 (m, 2H, o-ArH).
2-Maleimidoethyl 2-Chloro-2-phenylacetate (HEMI-Cl). α-
Chlorophenylacetyl chloride (15.0 mL, 0.103 mol) was added
dropwise to a solution of HEMI (14.033 g, 0.0994 mol) and
triethylamine (14.3 mL, 0.103 mol) in dried CHCl3 (100 mL) at 0 °C.
After stirring at ambient temperature, the solution was washed with
water, and then all organic phase was collected. The obtained crude
product was purified by recrystallization from acetone. HEMI-Cl was
The number-average molecular weight (Mn) and the molecular weight
distribution (Mw/Mn) of the copolymers were determined by size-
exclusion chromatography (SEC) in THF at 40 °C on two polystyrene
gel columns [Shodex KF-805 L (pore size: 20−1000 Å; 8.0 mm i.d. ×
30 cm) × 2; flow rate 1.0 mL/min] for 1-co-CyMI, 2-co-CyMI, 3-co-
CyMI, 2-Cl-co-CyMI, 1-co-HEMI-Cl, and the graft copolymers or in
DMF containing 100 mM LiCl at 40 °C on two polystyrene gel
columns [TSKgel α-M (pore size: 13 μm; 7.8 mm i.d. × 30 cm) and
TSKgel α-3000 (pore size: 7 μm; 7.8 mm i.d. × 30 cm); flow rate 1.0
mL/min] for 1-co-HEMI and its carbamate copolymers, each
connected to a JASCO PU-2080 precision pump and a JASCO RI-
2031 detector. The columns were calibrated against eight standard
poly(MMA) samples (Shodex; Mp = 202−1 950 000; Mw/Mn = 1.02−
1.09). The MALLS analysis was performed in THF on a Dawn
HELEOS photometer (Wyatt Technology; λ = 633 nm). The
refractive index increments (dn/dc = 0.1305 [poly(2-Cl-co-CyMI)],
0.1340 [poly(1-co-HEMI-Cl)], 0.0928 [graft copolymers obtained
from poly(2-Cl-co-CyMI)], and 0.101 [graft copolymers obtained
from poly(1-co-HEMI-Cl) mLg−1] were measured in THF at 40 °C on
Optilab rEX (Wyatt Technology) (λ = 633 nm).
1
obtained as white solid (23.3 g, yield = 80%, purity >99%). H NMR
(CDCl3, rt): δ 3.73−3.85 (t, 2H, N−CH2), 4.23−4.38 (m, 2H, CH2−
O), 5.29 (s, 1H, CH−Cl), 6.63 (s, 2H, CHCH), 7.38−7.44 (m, 3H,
m, p-ArH), 7.32−7.36 (m, 2H, o-ArH).
Radical Copolymerization in PhC(CF3)2OH. Polymerization was
carried out by the syringe technique under dry nitrogen in oven-dried
and sealed glass tubes. A typical example for 2 and CyMI
copolymerization with AIBN in PhC(CF3)2OH is given below. In a
50 mL round-bottomed flask were placed PhC(CF3)2OH (0.87 mL),
PhC(CF3)2OH solution of CyMI (3.0 mL of 1200 mM, 3.6 mmol), 2
(0.27 mL, 1.7 mmol), and PhC(CF3)2OH solution of AIBN (0.36 mL,
0.036 mmol) at room temperature. The total volume of the reaction
mixture was 4.5 mL. Immediately after mixing, aliquots (0.6 mL each)
of the solution were distributed via a syringe into baked glass tubes,
which were then sealed by flame under nitrogen atmosphere. The
tubes were immersed in thermostatic oil bath at 60 °C. In
predetermined intervals, the polymerization was terminated by cooling
the reaction mixture to −78 °C. Monomer conversion was determined
RESULTS AND DISCUSSION
■
Periodically Hydroxy-Functionalized Copolymers.
Naturally occurring hydroxy-functionalized limonene ana-
logues, monoeterpene alcohols (2 and 3), were copolymerized
with a nonfunctionalized maleimide, CyMI, in PhC(CF3)2OH
at 60 °C, where the initial monomer feed ratio of the two
monomers was [Lim]0/[CyMI]0 = 1/2 (Figure 1). Alter-
1
from the concentration of residual monomer measured by H NMR
spectroscopy. The quenched reaction solutions were evaporated to
dryness to give poly(2-co-CyMI).
Polymer Reaction between Hydroxy-Functionalized Copoly-
mers and Isocyanate. The polymer reaction between the hydroxy-
functionalized copolymers and isocyanate was carried out under a dry
nitrogen atmosphere in a 50 mL round-bottom flask. A typical example
for poly(2-co-CyMI) is given below. Phenyl isocyanate (0.21 mL, 1.9
mmol) and dibutyltin dilaurate (1.17 mL, 1.9 mmol) as a catalyst were
added to a solution of poly(2-co-CyMI) (0.20 g) in anhydrous THF
(10 mL), and then the mixture was stirred for 24 h at 40 °C to give a
turbid solution. After the removal of the solvent by evaporation, the
product was purified by precipitation (0.19 g, yield 78%).
Ruthenium-Catalyzed Living Radical Graft Polymerization
of MMA. A typical example for the graft polymerization of MMA from
poly(2-Cl-co-CyMI) with Ru(Ind)Cl(PPh3)2/Al(acac)3 is given below.
In a 50 mL round-bottomed flask was placed poly(2-Cl-co-CyMI)
(87.6 mg, 0.13 mmol C−Cl bonds), Ru(Ind)Cl(PPh3)2 (10.1 mg,
0.013 mmol), Al(acac)3 (0.1686 g, 0.52 mmol), toluene (9.98 mL),
and MMA (2.78 mL, 26 mmol) at room temperature. The total
volume of reaction mixture was 13 mL. Immediately after mixing,
aliquots (1.0 mL each) of the solution were distributed via a syringe
into baked glass tubes, which were then sealed by flame under nitrogen
atmosphere. The tubes were immersed in thermostatic oil bath at 80
°C. In predetermined intervals, the polymerization was terminated by
cooling the reaction mixture to −78 °C. Monomer conversion was
determined from the concentration of residual monomer measured by
1H NMR spectroscopy. The quenched reaction solutions were
Figure 1. Radical copolymerization of limonene analogues (Lim) and
maleimide derivatives (MI) in PhC(CF3)2OH at 60 °C; [Lim]0/[MI]0
= 400/800 mM, [AIBN]0 = 8.0 mM.
natively, a hydroxy-functionalized maleimide, HEMI, was
similarly copolymerized with a nonfunctionalized limonene
(1) under the same conditions. In all cases, both terpene and
maleimide derivatives were consumed at the same rate in a
manner similar to that for the copolymerization of 1 and CyMI
(red symbols in Figure 1),13,14 suggesting that similar 1:2
copolymerizations occur irrespective of the presence of
hydroxyl groups in the monomers. In particular, the
consumption rates of 1 and HEMI were almost the same as
those of 1 and CyMI, whereas the rates were much smaller for
2 and 3. The molecular weights of the products decreased with
decreasing polymerization rate; i.e., 1 > 2 > 3, most likely
because the chain-transfer reactions via the allylic hydrogen
abstraction became more pronounced in the order of methyl or
primary (1) < primary alkoxy (2) < secondary alkoxy (3) via
the formation of more stable allylic radical species.
precipitated into n-hexane and isolated by centrifugation. After two
times of the precipitation, the precipitate was evaporated to dryness to
yield the product, which was subsequently dried overnight in vacuo at
room temperature.
Measurements. Monomer conversion was determined from the
1
concentration of residual monomer measured by H NMR spectros-
1
copy with reaction solvent as an internal standard. H NMR spectra
for monomer conversion were recorded in CDCl3 at 25 °C on a
Varian Mercury 300 spectrometer, operating at 300 MHz, and 1H
NMR spectra for the product copolymer were recorded in CDCl3 at a
55 °C on a JEOL ECS-400 spectrometer, operating at 400 MHz.
MALDI-TOF-MS spectra were measured on a Shimazu AXIMA-CFR
Plus mass spectrometer (linear mode) with trans-2-[3-(4-tert-
butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) as
the ionizing matrix and sodium trifluoroacetate as the ion source.
The structures of the resultant copolymers were analyzed by
1H NMR spectroscopy (Figure 2). Figure 2 shows the 1H NMR
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Figure 2. 1H NMR spectra [(A−C) in CDCl3 at 55 °C, (D) in DMSO-d6 at 80 °C] of the copolymers obtained in PhC(CF3)2OH at 60 °C; [Lim]0/
[MI]0 = 400/800 mM, [AIBN]0 = 8.0 mM.
Figure 3. Copolymer composition curves for the copolymerization of limonene analogues (M1) and maleimide derivatives (M2) in PhC(CF3)2OH at
60 °C; [M1]0 + [M2]0 = 1200 mM, [M1]0/[M2]0 = 1/7, 1/3, 1/1, 3/1, 7/1, [AIBN]0 = 8.0 mM. M1/M2: 1/CyMI (A), 2/CyMI (B), 3/CyMI (C), 1/
HEMI (D). The dotted lines were fitted by the modified Kelen−Tudos method for (A−C) or curve-fitting method for (D), assuming that the values
̈
̃
of r11 and r21 are 0.
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Figure 4. MALDI-TOF-MS spectra of poly(1-co-CyMI) (Mn = 2100, Mw/Mn = 1.55) (A), poly(2-co-CyMI) (Mn = 1700, Mw/Mn = 1.79) (B), and
poly(1-co-HEMI) (Mn = 1900, Mw/Mn = 1.67) (C) obtained with CBTC in PhC(CF3)2OH at 60 °C; [Lim]0/[MI]0 = 400/800 mM, [CBTC]0 = 10
mM, [AIBN]0 = 5.0 mM. The calculated molar masses are those of the expected copolymer structures with sodium ion from the salt (CF3CO2Na)
for the MALDI-TOF-MS analysis.
spectra of poly(1-co-CyMI) (A), poly(2-co-CyMI) (B), poly(3-
co-CyMI) (C), and poly(1-co-HEMI) (D). In all of the spectra,
the strong signals near 1−3 ppm can be assigned to aliphatic
protons of the limonene analogue and cyclohexyl maleimide
units including the pendent and main-chain groups. In addition
to these signals, several characteristic protons, i.e., olefinic
protons (e) in the limonene analogue units and methine
protons (l) adjacent to the nitrogen in CyMI units, appeared
near 5−6 and 4 ppm, respectively. For the copolymers with
HEMI (Figure 2D), two methylene groups (q and r) both
adjacent to the heteroatoms appeared at 3.3−3.6 ppm along
with the emergence of hydroxyl protons (s) at 4.3−4.5 ppm.
The copolymer compositions, i.e., limonene analogues/
maleimide derivatives [Lim/MI(NMR)], were then calculated
from the peak intensity ratios of these characteristic protons (e
for 1, 2, and 3; l for CyMI; q and r for HEMI). The obtained
compositions agreed well with the values calculated from the
initial charge ratio and conversions of the two monomers,
indicating that all of the consumed monomers were
incorporated into the copolymers. Furthermore, all of these
values were very close to 1:2. These results indicate that 1:2
copolymers possessing hydroxy groups were similarly obtained
in the radical copolymerization of limonene analogues and
maleimide derivatives at 1:2 feed ratios in PhC(CF3)2OH.
To obtain monomer sequence information, the monomer
reactivity ratio of limonene analogues (M1) and maleimide
derivatives (M2) was determined by copolymerization at
various monomer feed ratios in PhC(CF3)2OH at 60 °C.
Figure 3 shows the resultant copolymer composition curves, in
which the incorporated ratios of limonene derivatives in the
resulting copolymers are plotted against the monomer feed
ratios. All composition ratios are nearly constant at 0.33,
irrespective of the presence of hydroxyl groups in the
monomers (2, 3, and HEMI). Similar to reports for
nonfunctionalized monomer pairs (1 and CyMI),13,14 the
monomer reactivity ratios were best fitted by a penultimate
model, which was used to calculate r12 and r22 based on the
modified Kelen−Tudos or curve-fitting method, assuming that
̈
̃
radical homopropagation of unconjugated limonene analogues
does not occur (r11 = r21 = 0). The r12 and r22 values were
calculated to be 14 and 0.017 for 2 and CyMI, 12 and 0.017 for
3 and CyMI, and 14.5 and 0.0060 for 1 and HEMI, respectively.
•
Thus, irrespective of the hydroxyl functions, the ∼∼M1M2
•
radical favors M2 (r12 > 10) to result in ∼∼M2M2 , which
•
exclusively reacts with M1 (r22 < 0.02) to give ∼∼M2M1 , and
•
the resulting ∼∼M2M1• selectively adds to M2 (r21 = 0) to
generate the ∼∼M1M2 radical again. These results indicate
that these three consecutive selective radical propagations also
occur for limonene analogues with similar skeletons or
maleimide derivatives irrespective of additional functional
groups. Thus, specific structures of limonene with isoprope-
nylcyclohexene units, maleimide comonomers, and fluoroalco-
hol are crucial for 1:2-sequence-regulated radical copolymeriza-
tion.13,14
The RAFT copolymerization of 2 and CyMI or 1 and HEMI
was also investigated using S-cumyl S′-butyl trithiocarbonate
(CBTC) as a RAFT agent to obtain chain-end-defined
copolymers for the analysis of monomer sequences in the
hydroxy-functionalized copolymers by MALDI-TOF-MS (Fig-
ure 4).13,14,36 The main series of peaks in the hydroxy-
functionalized copolymers (Figure 4B,C) are separated by the
total molar masses for one limonene analogue (L or P) and two
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Figure 5. 1H NMR spectra (DMSO-d6, 80 °C) of the carbamate-functioned copolymers obtained by the polymer reaction of poly(2-co-CyMI) (A)
or poly(1-co-HEMI) (B) with phenyl isocyanate.
maleimide derivative (M or H) units, similar to those reported
for limonene (L) and CyMI (M) (Figure 4A), and can be
assigned to a series of end-to-end sequenced copolymers [C-
(M-M-P)n-M-S or C-(H-H-L)n-H-S] (C: cumyl group; S:
trithiocarbonyl group) with well-defined initiating and capping
terminals along with the M-M-P or H-H-L repeating sequence.
The small series of peaks, of which the molar mass differences
compared with the main series are close to those of the
monomer units, can be assigned to other copolymer series with
one additional maleimide and one additional limonene
analogue unit at the capping terminals, as has been reported
for copolymers of 1 and CyMI.13 However, much smaller
peaks, which are observed for the copolymers of 2, might be
due to irreversible chain-transfer reactions originating from the
primary alkoxy allyl hydrogen in 2 as mentioned above. These
results again indicate that the copolymerization of these
hydroxy-functionalized monomers proceeds in the ABB-
sequence fashion irrespective of the functional groups to result
in periodically functionalized copolymers with one or two
hydroxyl groups repeating in three-monomer units.
To synthesize other periodically functionalized copolymers
by utilizing the resulting hydroxy-functionalized copolymers,
the polymer reaction between poly(2-co-CyMI) or poly(1-co-
HEMI) and phenyl isocynate was investigated in THF in the
presence of a tin catalyst at 40 °C. The reaction between
alcohol and isocyanate generally proceeds at a high yield and is
often effectively used for polymer reactions. Figure 5 shows the
1H NMR spectra of the copolymers obtained after the polymer
reaction, in which phenyl (u) and carbamate protons (t) clearly
appeared along with downfield shifts of methylene protons (i′
and r′) originally adjacent to the hydroxyl moieties. The
polymer reaction proceeded almost quantitatively, and the
ratios of limonene analogues and maleimide units were nearly
1:2, as calculated from the peak intensity ratios based on the
phenyl groups, indicating the formation of another series of
periodically functionalized copolymers possessing one or two
carbamate moieties for each three-monomer unit.
Periodically Grafted Copolymers. As another series of
functional monomers for synthesizing periodically grafted
copolymers, limonene and maleimide derivatives, 2-Cl and
HEMI-Cl, possessing reactive C−Cl bonds as initiating
moieties for living radical polymerization, were prepared from
2 and HEMI, respectively, via esterification of their hydroxyl
groups with α-chlorophenylacetyl chloride.62,63 Free radical
copolymerizations of 1:2 mixtures of 2-Cl and CyMI or 1 and
HEMI-Cl were then conducted in PhC(CF3)2OH at 60 °C
(Figure 6). In both cases, the comonomers were consumed at
the same rate to give copolymers similar to those obtained for 1
and CyMI (red circles in Figure 6), whereas the consumption
rates of 2-Cl and CyMI were low (blue circles), similar to the
result for 2 and CyMI (see above). These results suggest that
the presence of C−Cl bonds does not have a significant effect
on copolymerization in fluorinated alcohol.
To obtain more detailed information regarding the monomer
sequence in radical copolymerization of C−Cl-containing
monomers, monomer reactivity ratios were analyzed by varying
the comonomer feed ratios ([Lim (M1)]0/[MI (M2)]0 = 1/7,
1/3, 1/1, 3/1, 7/1) in PhC(CF3)2OH at 60 °C. As shown in
Figure 7, the copolymer composition ratios are almost constant
at 0.33, irrespective of the comonomer feed ratios, as was
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obtained from their parent hydroxy-functionalized monomers,
respectively, whereas several peaks (i″ in Figure 9A and r″ in
Figure 9B) shifted downfield, along with the emergence of new
peaks (v and w) due to esterification by the α-chloropheny-
lacetyl moiety. The copolymer compositions, 2-Cl/CyMI-
(NMR) or 1/HEMI-Cl(NMR), were then calculated from
the peak intensity ratios of phenyl (w for 2-Cl) to methine
protons adjacent to nitrogen (j for CyMI) or olefin (e for 1) to
phenyl (w for HEMI-Cl) protons, respectively, and were
observed to be nearly 1/2, which agrees well with the values
calculated from the initial charge ratio and conversion of the
two monomers. Thus, the obtained copolymers, poly(2-Cl-co-
CyMI) and poly(1-co-HEMI-Cl), possess one and two C−Cl
bonds in each repeating three-monomer unit, respectively.
Furthermore, the number-average initiating sites [Fn(C−Cl)]
per backbone polymer chain were calculated by absolute Mn
values determined by MALLS [Mn(MALLS)] and their
copolymer compositions [M1/M2(NMR)] and were found to
be 23.6 for poly(2-Cl-co-CyMI) and 40.4 for poly(1-co-HEMI-
Cl) (Table 1).
Figure 6. Copolymerization of limonene analogues (Lim) and
maleimide derivatives (MI) possessing a reactive C−Cl bond for the
metal-catalyzed living radical polymerization in PhC(CF3)2OH at 60
°C; [Lim]0/[MI]0 = 400/800 mM, [AIBN]0 = 8.0 mM.
observed for their precursors; i.e., hydroxy-functionalized
monomers, 2, or HEMI (see Figure 3B,D). The monomer
reactivity ratios were calculated by the modified Kelen−Tudos
̈
̃
The metal-catalyzed living radical graft polymerization of
MMA was then examined using the periodically chlorine-
functionalized copolymers as macroinitiators in conjunction
with Ru(Ind)Cl(PPh3)2 as a catalyst in the presence of
Al(acac)3, which was used as a cocatalyst.64−68 As shown in
Figure 8C,D, the SEC curves shifted to higher molecular
weights while retaining unimodal shapes as the MMA was
consumed. Although the Mn(SEC) values measured by the RI
detector were lower than the calculated values, assuming that
the consumed MMA was polymerized from the C−Cl bonds,
due to the difference in the hydrodynamic volumes between
MMA and the PMMA standard as well as the branched
structures of the resulting graft copolymers, the absolute Mn
values determined by MALLS were close to the calculations
(Table 1).
method for the penultimate model, assuming that homopro-
pagation of unconjugated olefin does not occur. These ratios
are r12 = 17 and r22 = 0.036 for 2-Cl/CyMI and r12 = 15 and r22
= 0.028 for 1/HEMI-Cl and are similar to those for the
hydroxy-functionalized monomers. Thus, a similar 1:2 mono-
mer sequence also forms for the radical copolymerization of
C−Cl-containing monomers.
The periodically chlorine-functionalized copolymers were
then used as a backbone or as stem polymers, from which
subsequent metal-catalyzed living radical graft polymerization
of MMA was initiated for the synthesis of periodically grafted
copolymers based on the “grafting-from” method.36,50,51 Prior
to graft polymerization, a relatively large amount of periodically
chlorine-functionalized copolymers was synthesized by radical
copolymerization of 2-Cl/CyMI or 1/HEMI-Cl in PhC-
(CF3)2OH and was characterized by SEC (Figure 8A,B) and
1H NMR (Figure 9A,B). The obtained copolymers show
molecular weights similar to those presented in Figure 8, where
the Mn values measured by MALLS are slightly higher than
those obtained by an RI detector equipped with SEC, most
likely due to difference between the hydrodynamic volumes of
the copolymers and those of standard PMMA.
1
The H NMR spectra of the graft copolymers primarily
exhibited the characteristic signals of the methyl (c), methylene
(d), and methoxy (b) of the PMMA graft chains in addition to
the weaker signals of phenyl (w) protons originating from the
initiating moieties of the backbone (Figure 9C,D). The
number-average degrees of polymerization of MMA
[m(NMR)], as calculated from the initiating moiety (w/5) to
the main chain MMA (b/3) unit, were found to be m(NMR) =
96 (Figure 9C) and 40 (Figure 9D), which are comparable to
those calculated from the MMA conversion and initial
The resultant poly(2-Cl-co-CyMI) and poly(1-co-HEMI-Cl)
1
show H NMR spectra that are similar to those of poly(2-co-
CyMI) (Figure 2B) and poly(1-co-HEMI) (Figure 2D)
Figure 7. Copolymer composition curves for the copolymerization of Lim and MI in PhC(CF3)2OH at 60 °C; [Lim]0 + [MI]0 = 1200 mM, [Lim]0/
[maleimide] = 1/7, 1/3, 1/1, 3/1, 7/1, [AIBN] = 8.0 mM. The dotted lines were fitted by the modified Kelen−Tudos method assuming that the
̈
̃
0
0
values of r11 and r21 are 0.
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Figure 8. SEC curves of periodically chlorine-functionalized copolymers obtained by radical copolymerization of 2-Cl/CyMI (A) or 1/HEMI-Cl (B)
and periodically grafted copolymers obtained by ruthenium-catalyzed living radical polymerization of MMA initiated from poly(2-Cl-co-CyMI) (C)
and poly(1-co-HEMI-Cl) (D). Polymerization condition: [M1]0/[M2]0/[AIBN]0 = 400/800/8.0 mM in PhC(CF3)2OH at 60 °C for (A) and (B);
[MMA]0/[C−Cl]0/[Ru(Ind)Cl(PPh3)2]/[Al(acac)3]0 = 2000/10/1.0/40 mM in toluene at 80 °C for (C); [MMA]0/[C−Cl]0/[Ru(Ind)Cl-
(PPh3)2]/[Al(acac)3]0 = 2000/10/0.50/20 mM in toluene at 40 °C for (D).
Figure 9. 1H NMR spectra of periodically chlorine-functionalized copolymers (CDCl3, 55 °C) obtained by radical copolymerization of 2-Cl/CyMI
(A) or 1/HEMI-Cl (B) and periodically grafted copolymers (acetone-d6, 50 °C) obtained by ruthenium-catalyzed living radical polymerization of
MMA initiated from poly(2-Cl-co-CyMI) (C) and poly(1-co-HEMI-Cl) (D). Polymerization condition: [M1]0/[M2]0/[AIBN]0 = 400/800/8.0 mM
in PhC(CF3)2OH at 60 °C for (A) and (B); [MMA]0/[C−Cl]0/[Ru(Ind)Cl(PPh3)2]/[Al(acac)3]0 = 2000/10/1.0/40 mM in toluene at 80 °C for
(C); [MMA]0/[C−Cl]0/[Ru(Ind)Cl(PPh3)2]/[Al(acac)3]0 = 2000/10/0.50/20 mM in toluene at 40 °C for (D).
Table 1. Periodically Chlorine-Functionalized Copolymers by Radical Copolymerization of Limonene Analogues (M1) and
Maleimide Derivatives (M2) and Periodically Grafted Copolymers by Ruthenium-Catalyzed Living Radical Graft Polymerization
of MMA
Mn
m
d
conv (%)
M1/M
2e
Mw
Mw/Mn
g
f
g
f
h
i
j
k
entry Lim (M1) MI (M2)
M1/M2 or MMA (NMR)
(MALLS)
SEC
MALLS
calcd
n/a
(SEC)
Fn(C−Cl) calcd NMR
a
1
2
3
4
2-Cl
n/a
1
CyMI
n/a
49/48
44
33/67
n/a
24 200
410 500
37 200
9 000
96 100
7 300
15 900
246 300
14 800
1.74
1.71
2.47
1.74
23.6
n/a
40.4
n/a
n/a
88
n/a
96
b
a
c
247 500
n/a
HEMI-Cl
n/a
91/88
20
35/65
n/a
n/a
40
n/a
40
n/a
331 400
86 000
167 100
176 600
a
b
Polymerization condition: [M1]0/[M2]0/[AIBN]0 = 400/800/8.0 mM in PhC(CF3)2OH at 60 °C. Polymerization condition: [MMA]0/[C−Cl]0/
c
[Ru(Ind)Cl(PPh3)2]0/[Al(acac)3]0 = 2000/10/1.0/40 mM in toluene at 80 °C. Polymerization condition: [MMA]0/[C−Cl]0/[Ru(Ind)Cl-
(PPh3)2]0/[Al(acac)3]0 = 2000/10/0.50/20 mM in toluene at 40 °C. Determined by H NMR analysis of residual monomers in the reaction
mixture. Determined by H NMR analysis of the isolated copolymers. Measured by multiangle laser light scattering (MALLS) detector equipped
d
1
e
f
1
g
h
with size-exclusion chromatography (SEC). Determined by SEC. Mn(calcd) = Mn(backbone polymer, MALLS) + m × Fn × MW(MMA).
i
j
k
1
Determined by Mn(MALLS) and M1/M2(NMR). ([MMA]0/[C−Cl]0) × conv(MMA). Determined by H NMR.
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(13) Satoh, K.; Matsuda, M.; Nagai, K.; Kamigaito, M. J. Am. Chem.
Soc. 2010, 132, 10003−10005.
monomer feed ratios, m(calcd) = 88 and 40, respectively. These
results suggest that the graft polymerization successfully
proceeded to afford periodically grafted copolymers with one
or two PMMA grafting chains for every repeating three-
monomer unit.
(14) Matsuda, M.; Satoh, K.; Kamigaito, M. J. Polym. Sci., Part A:
Polym. Chem. 2013, 51, 1774−1785.
(15) Yamamoto, D.; Matsumoto, A. Macromol. Chem. Phys. 2012,
213, 2479−2485.
(16) Hisano, M.; Takeda, K.; Takashima, T.; Jin, Z.; Shiibashi, A.;
Matsumoto, A. Macromolecules 2013, 46, 3314−3323.
(17) Yokota, K. Prog. Polym. Sci. 1999, 24, 517−563.
(18) Cho, I. Prog. Polym. Sci. 2000, 25, 1043−1087.
(19) Lehman, S. E.; Wagener, K. B.; Baugh, L. S.; Rucker, S. P.;
Schulz, D. N.; Varma-Nair, M.; Berluche, E. Macromolecules 2007, 40,
2643−2656.
CONCLUSION
■
In conclusion, functionalized limonene or maleimide derivatives
possessing hydroxyl and other related groups were employed in
1:2- or 2:1-sequence-regulated radical copolymerization with
nonfunctionalized maleimide or limonene in fluorinated alcohol
to achieve periodically functionalized copolymers with one or
two functional moieties in repeating three-monomer units,
respectively. The periodic hydroxyl groups can be quantitatively
converted into carbamate groups by a polymer reaction with
isocyanate to result in another series of periodically function-
alized copolymers. Periodically grafted copolymers with one or
two graft chains in repeating three-monomer units can also be
prepared via the 1:2- or 2:1-sequence-regulated radical
copolymerization of chlorine-functionalized monomers fol-
lowed by metal-catalyzed living radical polymerization. Thus,
naturally occurring functional limonene analogues are useful
building blocks for sequence-regulated functional bio-based
copolymers, which can exhibit novel functions and properties
originating from the regulated sequence distribution of
functional groups and other structural features such as rigidity
and chirality.13,14
(20) Boz, E.; Wagener, K. B. Polym. Rev. 2007, 47, 511−541.
(21) Kobayashi, S.; Pitet, L. M.; Hillmyer, M. A. J. Am. Chem. Soc.
2011, 133, 5794−5797.
(22) Zhang, J.; Matta, M. E.; Hillmyer, M. A. ACS Macro Lett. 2012,
1, 1383−1387.
(23) Brudno, Y.; Liu, D. R. Chem. Biol. 2009, 16, 265−276.
(24) Niu, J.; Hill, R.; Liu, D. R. Nat. Chem. 2013, 5, 282−292.
(25) Stayshich, R. M.; Meyer, T. Y. J. Am. Chem. Soc. 2010, 132,
10920−10934.
(26) Li, J.; Stayshich, R. M.; Meyer, T. Y. J. Am. Chem. Soc. 2011, 133,
6910−6913.
(27) Stayshich, R. M.; Weiss, R. M.; Li, J.; Meyer, T. Y. Macromol.
Rapid Commun. 2011, 32, 220−225.
(28) Li, J.; Rothstein, S. N.; Little, S. R.; Edenborn, H. M.; Meyer, T.
Y. J. Am. Chem. Soc. 2012, 134, 16352−16359.
(29) Li, Z.-L.; Li, L.; Deng, X.-X.; Zhang, L.-J.; Dong, B.-T.; Du, F.-S.;
Li, Z.-C. Macromolecules 2012, 45, 4590−4598.
(30) Deng, X.-X.; Li, L.; Li, Z.-L.; Lv, A.; Du, F.-S.; Li, Z.-C. ACS
Macro Lett. 2012, 1, 1300−1303.
AUTHOR INFORMATION
Corresponding Author
*E-mail: kamigait@apchem.nagoya-u.ac.jp (M.K.).
Notes
■
(31) Natalello, A.; Hall, J. N.; Eccles, E. A. L.; Kimani, S. M.;
Hutchings, L. R. Macromol. Rapid Commun. 2011, 32, 233−237.
́
(32) Brule, E.; Guo, J.; Coates, G. W.; Thomas, C. M. Macromol.
Rapid Commun. 2011, 32, 169−185.
The authors declare no competing financial interest.
(33) Robert, C.; de Montigny, F.; Thomas, C. M. Nat. Commun.
2011, 2, 586.
ACKNOWLEDGMENTS
(34) Ito, S.; Noguchi, M.; Nozaki, K. Chem. Commun. 2012, 48,
■
10481−10483.
This work was supported in part by the Funding Program
(Green Innovation GR051; Precision Polymerization of Plant-
Derived Vinyl Monomers for Novel Bio-Based Polymers) for
Next-Generation World-Leading Researchers from the Cabinet
Office, Government of Japan and Program for Leading
Graduate Schools “Integrative Graduate Education and
Research Program in Green Natural Sciences”.
(35) Schmidt, B. V. K.; Fechler, N.; Falkenhagen, J.; Lutz, J.-F. Nat.
Chem. 2011, 3, 234−238.
(36) Moad, G.; Solomon, D. H. The Chemistry of Radical
Polymerization, 2nd ed.; Elsevier Science: Oxford, 2006.
(37) Cowie, J. M. G. Alternating Copolymers; Plenum Press: New
York, 1985.
(38) Hagiopol, C. Copolymerization: Toward a Systematic Approach;
Kluwer Academic/Plenum Publishers: New York, 1999.
(39) Matsuda, M.; Satoh, K.; Kamigaito, M. KGK-Kautschuk Gummi
Kunststoffe 2013, 66 (5), 51−56.
(40) Coppen, J. J. W.; Hone, G. A. Gum Naval Stores: Turpentine and
Rosin from Pine Resin; Natural Resource Institute, Food and
Agriculture Organization of the United Nations: Rome, 1995.
(41) Braddock, R. J. Handbook of Citrus By-Products and Processing
Technology; John Wiley & Sons: New York, 1999.
(42) Wool, R. P.; Sun, X. S. Bio-Based Polymers and Composites;
Elsevier: Oxford, 2005.
(43) Gandini, A. Macromolecules 2008, 41, 9491−9504.
(44) Gandini, A.; Belgacem, M. N. Monomers, Polymers and
Composites from Renewable Resources; Elsevier: Oxford, 2005.
(45) Williams, C. K.; Hillmyer, M. A. Polym. Rev. 2008, 48, 1−10.
(46) Coates, G. W.; Hillmyer, M. A. Macromolecules 2009, 42, 7987−
7989.
(47) Yao, K.; Tang, C. Macromolecules 2013, 46, 1689−1712.
(48) Breitmaier, E. Terpenes; Wiley-VCH: Weinheim, 2006.
(49) Connolly, J. D.; Hill, R. A. Dictionary of Terpenoids; Chapman &
Hall: London, 1991.
REFERENCES
■
(1) Ouchi, M.; Badi, N.; Lutz, J.-F.; Sawamoto, M. Nat. Chem. 2011,
3, 917−924.
(2) Badi, N.; Lutz, J.-F. Chem. Soc. Rev. 2009, 38, 3383−3390.
(3) Lutz, J.-F. Nat. Chem. 2010, 2, 84−85.
(4) Lutz, J.-F. Polym. Chem. 2010, 1, 55−62.
(5) Zamfir, M.; Lutz, J.-F. Nat. Commun. 2012, 3, 1138.
(6) Lutz, J.-F.; Schmidt, B. V. K. J.; Pfeifer, S. Macromol. Rapid
Commun. 2011, 32, 127−135.
(7) Ida, S.; Terashima, T.; Ouchi, M.; Sawamoto, M. J. Am. Chem.
Soc. 2009, 131, 10808−10809.
(8) Ida, S.; Ouchi, M.; Sawamoto, M. J. Am. Chem. Soc. 2010, 132,
14748−14750.
(9) Hibi, Y.; Ouchi, M.; Sawamoto, M. Angew. Chem., Int. Ed. 2011,
50, 7434−7437.
(10) Hibi, Y.; Tokuoka, S.; Terashima, T.; Ouchi, M.; Sawamoto, M.
Polym. Chem. 2011, 2, 341−347.
(11) Ida, S.; Ouchi, M.; Sawamoto, M. Macromol. Rapid Commun.
2011, 32, 209−214.
(50) Kamigaito, M.; Ando, T.; Sawamoto, M. Chem. Rev. 2001, 101,
3689−3746.
(12) Satoh, K.; Ozawa, S.; Mizutani, M.; Nagai, K.; Kamigaito, M.
Nat. Commun. 2010, 1, 6.
5481
dx.doi.org/10.1021/ma401021d | Macromolecules 2013, 46, 5473−5482

Macromolecules
Article
(51) Matyjaszewski, K.; Xia, J. Chem. Rev. 2001, 101, 2921−2990.
(52) Cianga, L.; Sarac, A.; Ito, K.; Yagci, Y. J. Polym. Sci., Part A:
Polym. Chem. 2005, 43, 479−492.
(53) Cakir, T.; Serhatli, I. E.; Onen, A. J. Appl. Polym. Sci. 2006, 99,
1903−2001.
(54) Zhang, Y.; Li, X.; Deng, G.; Chen, Y. Macromol. Chem. Phys.
2006, 207, 1394−1403.
(55) Shi, Y.; Fu, Z.; Yang, W. J. Polym. Sci., Part A: Polym. Chem.
2006, 44, 2069−2075.
(56) Ishizu, K.; Yamada, H. Macromolecules 2007, 40, 3056−3061.
(57) Zhu, H.; Deng, G.; Chen, Y. Polymer 2008, 49, 405−411.
(58) Yin, J.; Ge, Z.; Liu, H.; Liu, S. J. Polym. Sci., Part A: Polym. Chem.
2009, 47, 2608−2619.
(59) Deng, G.; Chen, Y. J. Polym. Sci., Part A: Polym. Chem. 2009, 47,
5527−5533.
(60) Li, S.; Ye, C.; Zhao, G.; Zhang, M.; Zhao, Y. J. Polym. Sci., Part
A: Polym. Chem. 2012, 50, 3135−3148.
(61) Heath, W. H.; Palmieri, F.; Adams, J. R.; Long, B. K.; Chutte, J.;
Holcombe, T. W.; Zieren, S.; Truitt, M. J.; White, J. L.; Willson, C. G.
Macromolecules 2008, 41, 719−726.
(62) Baek, K.-Y.; Kamigaito, M.; Sawamoto, M. J. Polym. Sci., Part A:
Polym. Chem. 2002, 40, 1937−1944.
(63) Baek, K.-Y.; Kamigaito, M.; Sawamoto, M. J. Polym. Sci., Part A:
Polym. Chem. 2002, 40, 1972−1982.
(64) Takahashi, H.; Ando, T.; Kamigaito, M.; Sawamoto, M.
Macromolecules 1999, 32, 3820−3823.
(65) Ueda, J.; Matsuyama, M.; Kamigaito, M.; Sawamoto, M.
Macromolecules 1998, 31, 557−562.
(66) Miura, Y.; Satoh, K.; Kamigaito, M.; Okamoto, Y. Polym. J. 2006,
38, 930−939.
(67) Miura, Y.; Satoh, K.; Kamigaito, M.; Okamoto, Y.; Kaneko, T.;
Jinnai, H.; Kobukata, S. Macromolecules 2007, 40, 456−473.
(68) Miura, Y.; Kaneko, T.; Satoh, K.; Kamigaito, M.; Jinnai, H.;
Okamoto, Y. Chem.Asian J. 2007, 2, 662−672.
5482
dx.doi.org/10.1021/ma401021d | Macromolecules 2013, 46, 5473−5482