A reactive helix: Synthesis, chemical modification, and polymerization of an optically active polymethacrylate

Article abstract of DOI:10.1021/ma101057j

1-(p-Vinylphenyl)dibenzosuberyl methacrylate (VDBSMA) having two reactive vinyl groups in a molecule was synthesized and polymerized using α,α-azobis(isobutyronitrile) as a radical initiator and using the complexes of 9-fluorenyllithium with (S)-(+)-1-(2-

Full text of DOI:10.1021/ma101057j

5956 Macromolecules 2010, 43, 5956–5963
DOI: 10.1021/ma101057j
A Reactive Helix: Synthesis, Chemical Modification, and Polymerization
of an Optically Active Polymethacrylate
Takeshi Sakamoto,† Toshio Nishikawa,‡ Yasuyuki Fukuda,‡ Shin-ichiro Sato,† and
Tamaki Nakano*,†
†Division of Biotechnology and Macromolecular Chemistry, Faculty of Engineering, Hokkaido University,
Sapporo 060-8628, Japan, and ‡Graduate School of Materials Science, Nara Institute of Science and
Technology (NAIST ), 8916-5 Takayama-cho, Ikoma, Nara 630-0101, Japan
Received May 13, 2010; Revised Manuscript Received June 9, 2010
ABSTRACT: 1-( p-Vinylphenyl)dibenzosuberyl methacrylate (VDBSMA) having two reactive vinyl groups
in a molecule was synthesized and polymerized using R,R0-azobis(isobutyronitrile) as a radical initiator and
using the complexes of 9-fluorenyllithium with (S)-(þ)-1-(2-pyrrolidinylmethyl)pyrrolidine, (-)-sparteine,
and (S,S)-(þ)-2,3-dimethoxy-1,4-bis(dimethylamino)butane as optically active anionic initiators. The free
radical polymerization led to an insoluble material, indicating that both methacrylic and styrenic moieties
participated in the polymerization and a cross-linked gel was produced. In contrast, the anionic polymer-
ization proceeded exclusively through the addition reaction of methacrylic moiety leaving the styrenic vinyl
group intact leading to soluble polymers. The resulting poly(VDBSMA)s having a polymethacrylate-type
main-chain structure were highly isotactic and showed high optical activity and intense circular dichroism
(CD) spectra, indicating that the polymers have a single-handed helical conformation. Thus, a single-handed
helical polymer having side-chain vinyl groups, which can be chemically modified, was successfully syn-
thesized. The side-chain vinyl group was converted to 2-hydroxyethyl group, 1,2-dihydroxyethyl group, and
carboxylic acid group by polymer reaction without seriously deteriorating the single-handed helical
conformation of the polymer. In this way, single-handed helical polymers with side-chain protonic groups
which would be difficult to be prepared by direct asymmetric anionic polymerization of the corresponding
monomers were conveniently synthesized. In addition, radical polymerization of poly(VDBSMA) as a
macromonomer afforded an optically active adduct consisting of single-handed helical chains.
Introduction
might be effective in performing chiral molecular recognition and
in creating novel chiral polymeric materials with a helical chain in
Optically active polymers whose chirality is based on a single-
handed helical conformation is drawing attention because such
polymers have high potentialities in practical applications such as
chiral separation, nonlinear optical devices, and chiral catalysts.1
In this context, various helical polymers have been synthesized,
and their structure-property relation has been investigated.
Optically active, helical polymers can be prepared by poly-
merization of an optically active monomer or by asymmetric
polymerization of a properly designed achiral monomer (helix-
sense-selective polymerization),1a-f or through supramolecular
interaction between an achiral polymer and added chiral
molecules.1 j-m Among various examples of asymmetric poly-
merization, anionic polymerization of designed bulky methacry-
lates and acrylates using the complexes of organolithiums with
chiral ligands as initiators has been studied systematically and
demonstrated to conveniently afford single-handed helical poly-
mers. The first monomer used for such polymerization was
triphenylmethyl methacrylate (TrMA),2-4 and thereafter, many
derivatives and analogues of TrMA were designed and subjected
to asymmetric anionic polymerization.1a-f However, monomer
design was limited to those without protonic functional groups
because the growing species in anionic polymerization is readily
quenched by a protonic group, and hence, it has been difficult to
synthesize a helical polymethacrylate with protonic side chain
groups whose interaction or reaction with added polar molecules
their core part.
Here, we present the synthesis of optically active, single-
handed helical polymethacrylates having protonic side-chain
groups without using monomers protonic groups. Such polymers
(poly-1, poly-2, and poly-3) were synthesized by polymer reac-
tions of single-handed helical poly(1-(p-vinylphenyl)dibenzo-
suberyl methacrylate) (poly(VDBSMA)) which was prepared
by the asymmetric polymerization of 1-(p-vinylphenyl)dibenzo-
suberyl methacrylate (VDBSMA) (Scheme 1). 1-Phenyldibezo-
suberyl methacrylate (PDBSMA), the parent monomer of
VDBSMA without styrenic vinyl group, has been synthesized
and polymerized using chiral complexes to afford a single-handed
helical polymer.5,6
Poly(VDBSMA), the intermediate polymer, was prepared by
asymmetric anionic polymerization of VDBSMA using the com-
plexes of 9-fluorenyllithium (FlLi) with (-)-sparteine (Sp), (S,
S)-(þ)-2,3-dimethoxy-1,4-bis(dimethylamino)butane ((þ)-DDB),
and (S)-(þ)-1-(2-pyrrolidinylmethyl)pyrrolidine (PMP). Each
monomeric unit of poly(VDBSMA) has a reactive side-chain vinyl
group. The vinyl group could be converted to protonic 2-hydro-
xyethyl group, 1,2-dihydroxyethyl group, and carboxylic group by
polymer reaction without seriously deteriorating the single-handed
helix, leading to optically active, single-handed helical polymers
with protonic side chain groups (poly-1, poly-2, and poly-3 in
Scheme 1). Direct synthesis of these polymers from correspond-
ing monomers by asymmetric anionic polymerization would be
impossible unless the protonic groups of such monomers are
*To whom correspondence should be addressed. E-mail: nakanot@
eng.hokudai.ac.jp.
pubs.acs.org/Macromolecules
Published on Web 06/29/2010
r 2010 American Chemical Society

Article
Scheme 1. Polymerization of VDBSMA and Synthesis of
Macromolecules, Vol. 43, No. 14, 2010 5957
Synthesis of 1-(p-Vinylphenyl)dibenzosuberol. Mg turnings
(11.4 g, 471 mmol) were placed in a 500 mL flask equipped with
a dropping funnel and a reflux condenser, and the flask was
evacuated and flame-dried with stirring. Stirring was continued
for 4 h to activate the Mg surface under vacuum. After flushing
the flask with N2 gas, dry THF (160 mL) and a small amount
of I2 were introduced. A solution of 4-chlorostyrene (54.0 g,
390 mmol) in dry THF (100 mL) were added dropwise to the
mixture in the flask from the dropping funnel with stirring. The
color of the reaction mixture slowly changed to dark green.
The reaction mixture was stirred under reflux for 3 h to afford a
THF solution of 4-vinylmagnesium chloride (1.22 M).
Single-Handed Helical Polymethacrylates Bearing Protonic Side-Chain
Groups via Chemical Modification of Poly(VDBSMA)
Dibenzosuberone (48.5 g, 232 mmol) was dissolved in dry
THF (160 mL) in a flame-dried 1-L flask. To this solution
was slowly added the Grignard reagent solution prepared above
(280 mL, 342 mmol) with stirring at 0 °C. After stirring for 16 h
at room temperature, the reaction mixture was quenched by
adding saturated aqueous NH4Cl (50 mL). The product was
extracted with diethyl ether-water, and the organic layer was
dried on MgSO4. Concentration of the dried organic layer
afforded a crude oily material. The crude material was recrys-
tallized from a diethyl ether solution to give colorless crystalline
product (51.3 g, 70.5%). Mp: 87.5-88.2 °C. 1H NMR (500 MHz,
CDCl3, Me4Si) δ 2.29 (s, 1H, -OH), 2.72-2.87 (m, 4H, -CH2-
CH2-), 5.22 (d, 1H, vinyl H), 5.77 (d, 1H, vinyl H), 6.61-6.67
(m, 1H, vinyl H), 6.62-8.05 (m, 12H, aromatic H). Anal. Calcd
for C23H20O: C, 88.43; H, 6.54. Found: C, 88.48; H, 6.49.
Synthesis of VDBSMA. In a 1-L flask equipped with a
dropping funnel and a reflux condenser flushed with N2 gas
was placed NaH (suspension in paraffin) (3.48 g, 145 mmol).
THF (200 mL) was introduced with a syringe to remove paraffin
from NaH, and supernatant THF wash was removed after
stirring. THF (240 mL) was added to the washed NaH, and
1-(p-vinylphenyl)dibenzosuberol (30.2 g, 96.7 mmol) dissolved
in THF (200 mL) was added dropwise with stirring. The reaction
mixture was refluxed for 20 h with stirring to form sodium
alkoxide. Methacryloyl chloride (11.5 mL, 118 mmol) was
slowly added to the reaction mixture cooled to 0 °C, and the
mixture was stirred for 10 min at 0 °C. The mixture was then
warmed to room temperature and further stirred for 4 h. The
reaction mixture was decomposed by adding water. The product
was extracted with CHCl3-water. The organic layer was
washed with saturated aqueous Na2CO3 and with brine in this
order and was then dried on MgSO4. Removal of solvent gave a
crude material. This material was recrystallized from diethyl
ether and then from a benzene-hexane (1/1, v/v) mixture to
afford a colorless crystalline product (19.27 g, 52.4%). Mp:
98.2-98.9 °C. 1H NMR (500 MHz, CDCl3, Me4Si): δ 1.99
(s, 3H, -CH3), 3.19 (s, 4H, -CH2CH2-), 5.20 (d, 1H, styrenic
vinyl H), 5.65 (d, 1H, styrenic vinyl H), 5.67 (d, 1H, methacrylic
vinyl H), 6.28 (d, 1H, methacrylic vinyl H), 6.62-6.66 (m, 1H,
styrenic vinyl H), 7.08-7.40 (m, 12H, aromatic H). Anal. Calcd
for C27H24O: C, 85.23; H, 6.36. Found: C, 88.02; H, 6.39.
Polymerization. Preparation of initiator solution and asym-
metric anionic polymerization were carried out in dry toluene
under dry N2 atmosphere. Polymerization procedure is de-
scribed for run 1 in Table 3 as an example. Fluorene (0.0771 g,
0.464 mmol) was placed in a flame-dried glass ampule sealed
with a three-way stopcock, which was then evacuated on a
vacuum line and was flushed with dry N2 gas. After this proce-
dure was repeated three times, a three-way stopcock was
attached to the ampule and dry toluene (1.10 mL) was intro-
duced with a syringe to dissolve fluorene. n-BuLi in hexane
(0.290 mL, 0.464 mmol) and (þ)-PMP (0.0900 mL, 0.0851 g,
0.552 mmol) were added to the resultant solution with a syringe
in this order, and the mixture was stood at room temperature for
10 min to obtain orange-colored PMP-FlLi complex solution
(0.300 M). In a similar manner to the preparation of the fluorene
solution, VDBSMA (1.0 g, 2.63 mmol) was dried and dissolved
in dry toluene (20 mL) in a flame-dried glass ampule sealed with
protected prior to polymerization. In addition, even if the corre-
sponding protected monomers were used, the protected polar
groups may possibly prevent chiral ligands used for asymmetric
polymerization from effectively coordinating with lithium coun-
tercation at the growing chain end. Evidentially, addition of
achiral coordinating molecules has been reported to reduce helix-
sense selectivity in asymmetric polymerization of a bulky metha-
crylate.7 The synthetic concept presented in this work involving
asymmetric anionic polymerization of a monomer with a reactive
side-chain group and polymer reactions modifying the side-chain
group may open a way to produce single-handed helical polymers
with a variety of polar functional groups which are difficult to
synthesize by direct polymerization of corresponding, designed
monomers. Furthermore, poly(VDBSMA) was effective as a
macromonomer leading to a polymeric adduct consisting of single-
handed helical chains.
Polymer reactions have been widely used to modify material
properties8 and have been applied also for some synthetic helical
polymers. However, examples involving reactive helical polymers
whose conformation is intact through side-chain reactions are
limited.9-13 In addition, almost quantitative side-chain modifica-
tion of a synthetic helical polymer having pendent vinyl group has
not been reported.
Experimental Section
Materials. 4-Chlorostyrene (TCI), Mg turnings (Nacalai
Tesque), I2 (Wako Chemical), dibenzosuberone (TCI), NaH
(suspension in paraffin, assay 60%, Wako Chemical), BH3-
tetrahydrofuran (THF) complex (Aldrich, 1.0 M, a THF
solution), K3Fe(CN)6 (Wako), MeSO2NH2 (Aldrich), and
OsO4 (Wako) were used as received. KMnO4 (Aldrich) was
ground to a fine powder with a mortar. Methacryloyl chloride
(Wako Chemical) was purified by distillation under N2 atmo-
sphere. Fluorene (Nacalai Tesque) was first recrystallized from
ethanol and then from hexane; mp 104.5-105.0 °C. Chiral
ligands, (-)-sparteine (Sp) (Aldrich), (S,S)-(þ)-2,3-dimethoxy-
1,4-bis(dimethylamino)butane ((þ)-DDB), and (S)-(þ)-1-(2-
pyrrolidinylmethyl)pyrrolidine (PMP) (Aldrich) were dried over
CaH2 and distilled under reduced pressure. R,R0-Azobis(iso-
butyronitrile) (AIBN) (Wako) was recrystallized from an etha-
nol solution at room temperature. n-BuLi (Nacalai Tesque,
1.6 M, a hexane solution) was used after titration. Tetrahydro-
furan (THF) (Wako) was refluxed over sodium benzophenone
ketyl and distilled under N2 atmosphere. Toluene used for
polymerization was purified in the usual manner, mixed with a
small amount of n-BuLi, and distilled under high vacuum
immediately before use.

5958 Macromolecules, Vol. 43, No. 14, 2010
Sakamoto et al.
Scheme 2. Synthesis of VDBSMA
a three-way stopcock. The monomer solution was cooled to
-78 °C, and the PMP-FlLi solution (0.438 mL, 0.131 mmoL)
was added with a syringe to initiate the polymerization. After 3 h
of initiation, the reaction was terminated by adding MeOH
(0.05 mL). The reaction mixture was poured into a large excess
of MeOH, and the MeOH-insoluble part was collected with a
centrifuge and was dried under high vacuum at 60 °C for 2 h. The
MeOH-insoluble product was obtained as colorless powder
(0.990 g, yield 97%). The MeOH-insoluble polymer was dis-
solved in CHCl3 (10 mL), and the solution was poured into a
mixture of benzene and hexane (1/1, v/v) (150 mL) to remove
oligomeric products. The MeOH-insoluble, benzene-hexane-
insoluble part was collected with a centrifuge and was dried
under high vacuum at 60 °C for 2 h to afford a colorless product
(0.946 g, 93%). The conversion of poly(VDBSMA) to PMMA
was performed in the same manner as applied for poly(TrMA)
according to the literature.4
(225 mg, 2.12 mmol), and tert-butyl alcohol (0.57 mL). To this
mixture was added THF (95 mL) to dissolve the polymer. The
solution containing suspended Na2CO3 was cooled at 0 °C, and
KMnO4 (1.19 g, 7.51 mmol) dissolved in water (17.8 mL) was
slowly added with a syringe to give a dark purple mixture. The
mixture was warmed to room temperature and was stirred for
4 h to give a dark brown suspension. The mixture was filtrated,
and the filtrate was concentrated to give a pale yellow material
which is considered to be a potassium salt form of the product.
This material was suspended in a MeOH-THF mixture (2/1,
v/v) (150 mL) with an acidic ion-exchange resin, and the mixture
was stirred for 30 min. The mixture was filtrated, and the filtrate
was concentrated to afford a crude polymer. The crude polymer
was washed with an acetone-n-hexane (1/1, v/v) mixture to give
a pale orange product (750 mg, 75.5%).
Measurements. The 1H NMR spectra were recorded on a
1
JEOL JNM-ECP500 spectrometer (500 MHz for H measure-
ment). SEC was carried out using a chromatographic system
consisting of a Hitachi L-7100 pump, an L-7420 UV detector
(254 nm), and an L-7490 RI detector equipped with TOSOH
TSK gel G3000HHR and G6000HHR columns connected in
series (eluent, THF; flow rate, 1.0 mL/min). SEC experiments
were also performed using a chromatographic system with a
JASCO PU2080Plus chromatographic pump with a Viscotek
TDA300 detector system consisting of viscometric, right-angle
laser-light scattering (RALS), and RI detectors and a Wyatt
Technology Dawn E multiangle laser-light scattering (MALLS)
Conversion of the Side-Chain Vinyl Group of Poly(VDBSMA)
to the 2-Hydroxyethyl Group (Synthesis of Poly-1). The reaction
was carried out under N2 atmosphere. Poly(VDBSMA) (DP =
22, Mw/Mn = 1.05, [R]365 þ2038° (THF)) (1.00 g, 2.63 mmol
(monomeric unit)) was dissolved in dry THF (48 mL) in a flame-
dried 200 mL flask. To the polymer solution cooled at 0 °C was
slowly added BH3-THF complex in a THF solution (3.20 mL,
3.20 mmol). The reaction mixture became gradually viscous
within 5 min of completion of the addition. The reaction mixture
was stirred for 1 h at 0 °C and then for 15 h at room temperature.
The mixture was cooled to 0 °C again, and 3 N aqueous NaOH
(8.80 mL) and 30% aqueous solution of H2O2 (8.80 mL) were
slowly added in this order. The reaction mixture became yellow.
After stirring for 3 h at 0 °C, brine was added to the mixture. The
product was extracted with THF, and the organic layer was
concentrated to give a crude polymer. The crude product was
washed first with diethyl ether and then with n-hexane to give a
colorless polymer (1.04 g, 99.2%).
detector system equipped with TOSOH TSKgel G3000HHR
,
and G6000HHR columns connected in series (eluent, THF; flow
rate, 1.0 mL/min). IR spectra were measured with a JASCO FT/
IR-420 spectrophotometer using KBr pellet samples. Absorp-
tion spectra were measured with JASCO V-550 and V-570 spec-
trophotometers. Circular dichroism (CD) spectra were taken on
a JASCO J-820 spectrometer. Specific rotation was measured
using a JASCO P-1030 digital polarimeter.
Conversion of the Side-Chain Vinyl Group of Poly(VDBSMA)
to the 1,2-Dihydroxyethyl Group (Synthesis of Poly-2). The
reaction was carried out in the dark. K3Fe(CN)6 (2.60 g, 7.89
mmol), MeSO2NH2 (250 mg, 2.63 mmol), and K2CO3 (1.09 g,
7.89 mmol) were dissolved in a mixture of THF (28 mL) and
water (14 mL) in a 200 mL flask. The solution was cooled to 0 °C
to afford a yellowish orange half-solid mixture. To this mixture
was added OsO4 (66.8 mg, 0.263 mmol), and the mixture was
stirred for 30 min. Poly(VDBSMA) (DP = 22, Mw/Mn = 1.05,
[R]365 þ2038° (THF)) (1.00 g, 2.63 mmol (monomeric unit))
dissolved in THF (20 mL) was added dropwise to the mixture
with stirring. The reaction mixture was warmed to room tem-
perature after completion of the addition and was further stirred
for 24 h to give a reddish brown suspension. The reaction was
then decomposed by adding saturated aqueous NaHSO3 and
brine in this order. The product was extracted with THF, and
the organic layer was concentrated to give a crude polymer. The
crude product washed with a mixture of acetone and hexane
(2/1, v/v) to give a colorless polymer (0.987 g, 89.8%).
Results and Discussion
Synthesis and Stability of VDBSMA Monomer. VDBSMA
was synthesized by a two-step reaction according to Scheme 2
starting from dibenzosuberone (cf. Experimental Section) and
was purified by recrystallization to give a material pure enough
to be used for anionic polymerization.
Triarylmethyl methacrylates are known to be prone to
hydrolysis of the ester bonding by protonic solvents or
moisture in the air. This often leads to degradation of helical
structure of poly(triarylmethyl methacrylate)s. Hence, it is
important to test the stability of ester bonding of a newly
made monomer. The stability of VDBSMA was examined by
monitoring its methanolysis reaction carried out in a mixture
of CDCl3 and CD3OD (1/1, v/v) at 35 °C in an NMR sample
1
tube by H NMR spectroscopy by the reported method.6
The first-order methanolysis rate constant and half-life
period of VDBSMA are indicated in Table 1 together
with those of other methacrylate monomers with a similar
backbone. VDBSMA was slightly less stable compared
with PDBSMA, its parent compound without a vinyl group,
Conversion of the Side-Chain Vinyl Group of Poly(VDBSMA)
to the Carboxylic Group (Synthesis of Poly-3). In a 200 mL flask
were placed poly(VDBSMA) (DP=22, Mw/Mn =1.05, [R]365
þ2038° (THF)) (950 mg, 2.50 mmol (monomeric unit)), Na2CO3

Article
Macromolecules, Vol. 43, No. 14, 2010 5959
but was more stable than TrMA.14 This result combined
with the fact that optically active poly(TrMA) has been
commercialized as a chiral selector material for HPLC15-17
indicates that poly(VDBSMA) would have sufficient stability
as a polymeric material. The lower stability of VDBSMA in
comparison to PDBSMA may arise from higher stability of
1-(p-vinylphenyl)dibenzosuberyl cation than 1-(p-vinylphenyl)-
dibenzosuberyl cation, which are considered to be an intermedi-
ate species of solvolysis, because of the larger π-conjugation
system in VDBSMA delocalizing and stabilizing the positive
charge involving a vinyl group than that of PDBSMA.
Polymerization of VDBSMA. The conditions and results
of free-radical polymerization using AIBN and asymme-
tric aninoic polymerization using Sp-FlLi, DDB-FlLi, and
PMP-FlLi at [M]/[I] = 20 are summarized in Table 2. The
free-radical polymerization with AIBN in THF afforded a
mostly insoluble material, suggesting that both methacrylic
and styrenic vinyl groups of VDBSMA monomer reacted
during the polymerization leading to a cross-linked gel. In
contrast, the anionic polymerizations using the three opti-
cally active complexes in toluene gave soluble polymers.
With DDB and PMP as chiral ligands, the polymer yield
was nearly quantitative in the reaction time of 3 h. The
relatively low polymer yield in the system with Sp may mean
that the reaction was slower when this ligand was used. The
same tendency has been reported for TrMA polymerization
using the same initiators.4 The anionic polymerization pro-
ducts contained a small amount of oligomers which were
removed from the polymers by washing with a mixture
benzene and hexane (1/1, v/v). The polymers obtained using
PMP and DDB had rather narrow molecular weight dis-
tributions, implying that the reaction systems with PMP and
DDB may have a living nature.
monomer and the poly(VDBSMA) obtained by anionic
polymerization using DDB-FlLi (run 2 in Table 1). In the
spectrum of the polymer, the signals based on methacrylic-
type vinyl group completely disappeared and those based on
styrene-type vinyl group were quantitatively observed. These
results clearly indicate that the polymer has a polymethacry-
late structure having the unreacted styrenic vinyl group in the
side chain. In addition, the upfield-shifted R-methyl signal
in the range of 0-0.5 ppm suggests a helical conformation
of the poly(VDBSMA).18
The polymethacrylate structure of poly(VDBSMA) was
further supported by the fact that the poly(VDBSMA) was
converted to PMMA by hydrolysis of ester bonding using
MeOH containing a small amount of HCl and methylation
of the hydrolysis products using CH2N2. 1H NMR analyses of
the products confirmed the chemical and stereostructure of the
PMMA (Figure 2). The polymers obtained by asymmetric
anionic polymerization were nearly completely isotactic as
found by 1H NMR spectra of PMMAs derived from the
poly(VDBSMA)s. As an example, the spectrum of PMMA
derived from the polymer obtained using DDB-FlLi (run 2 in
Table 1) is shown in Figure 2. The spectrum shows a typical AB
quartet splitting of the methylene protons based on the mmm
tetrad and the R-methyl signal based exclusively on mm triad.
In addition, the polymers obtained by asymmetric anionic
polymerization showed large dextrorotation. The degree of
optical rotation was greater than those of single-handed
helical poly(TrMA) and poly(PDBSMA),6 the parent poly-
mer of poly(VDBSMA) without vinyl group. These results
strongly suggests that the poly(VDBSMA) obtained in this
work has a single-handed helical structure.
In the anionic polymerizations, only the methacrylic vinyl
group reacted leaving the styrenic vinyl group intact
(Scheme 1). This was evidenced by H NMR spectral ana-
1
1
lyses. Figure 1 shows the H NMR spectra of VDBSMA
Table 1. First-Order Rate Constants and Half-Life Periods in
Methanolysis Reaction of Methacrylatesa
run
monomer
k/h-1
half-life period/min
1
2
3
VDBSMA
PDBSMAb
TrMAc
0.61
0.46
2.86
69.3
89.0
14.5
a Solvolysis reactions were carried out in a mixture of CDCl3 and
CD3OD (1/1, v/v) at 35 °C. b Cited from ref 6. c Cited from ref 14.
Figure 1. 1H NMR spectra of VDBSMA (A) and poly(VDBSMA)
prepared using DDB-FlLi (run 2 in Table 2) (B) [500 MHz, CDCl3].
Table 2. Polymerization of VDBSMA Using Various Initiatorsa
benzene-hexane(1/1)-insoluble part
yieldb (%)
content (%)
[R]25 c (deg)
DPd
Mw/Mn
mme (%)
d
run
initiator
solvent
[M]/[I]
temp (°C)
time (h)
365
1
2
3
4
AIBN
DDB-FlLi
Sp-FlLi
THF
50
20
20
20
60
-78
-78
-78
24
24
24
3
95 f
>99
61
toluene
toluene
toluene
82
þ1900
-1920h
þ1975i
30
38
23
1.07
1.33
1.07
>99
>99
>99
82g
93
PMP-FlLi
97
a Conditions: VDBSMA, 300 mg (runs 1-3), 1.0 g (run 4), [VDBSMA]o = 0.15 M. b MeOH-insoluble part. c Measured in THF (concentration
0.5 g/dL, cell length 0.1 dm). d Determined by SEC of PMMA derived from poly(VDBSMA). e Determined by 1H NMR of PMMA derived from
poly(VDBSMA). f Not precipitated in methanol. Yield was estimated by 1H NMR analysis of THF-soluble part (32%) of the product (unreacted
monomer content 84%) assuming that THF-insoluble product (68%) contains no monomer. g Consisted of THF-soluble (18%) and -insoluble (82%).
h THF-soluble part. i [R]25435 þ892°, [R]25546 þ485°, [R]25577 þ422°, [R]25589 þ411° (in THF, concentration 0.3 g/dL, cell length 0.1 dm).

5960 Macromolecules, Vol. 43, No. 14, 2010
Sakamoto et al.
Among the three optically active anionic initiator com-
plexes, PMP-FlLi gave the polymer with the largest optical
activity and the DP closest to the [M]/[I] ratio in feed. This
means that PMP-FlLi among the three initiators best con-
trols the polymerization of VDBSMA from the views of
stereochemistry and livingness. Using PMP-FlLi, polymer-
izations were further conducted at different [M]/[I] ratios
(Table 3). In the polymerizations for 3 h, polymer yield
decreased with an increase in [M]/[I] ratio (Table 3, runs
1-4). This suggests that the reaction time of 3 h is not long
enough to achieve complete monomer consumption at
[M]/[I] = 40 and larger. When the polymerization time was
extended to 48 h, the polymer yield at [M]/[I] = 40 was nearly
quantitative and that at [M]/[I] = 80 reached 84%. These
two systems gelled during the polymerization due to low
solubility of the products: most part of the isolated products
in these two systems were insoluble in THF or CHCl3. The
observed gelation and insolubility of the products are due
not to reactions of the side-chain vinyl groups but to
molecular aggregations as discussed below.
In the polymerizations at [M]/[I] = 20-60 for 3 h, mostly
soluble products with relatively narrow molecular weight
distributions were obtained. DP of the obtained polymer was
higher at a higher [M]/[I] ratio, suggesting again that these
reaction systems may have a living nature. The specific
rotation of the polymers with DP of 40 and 57 were larger
than þ2000°. These may be the highest specific rotations ever
observed for single-handed helical (meth)acrylic polymers.
Also, these polymers indicated intense circular dichroism
(CD) spectra, supporting their single-handed helical struc-
ture (Figure 3). The CD spectral patterns of the polymers
slightly differed depending on DP. This might reflect mole-
cular aggregation of the polymer chain as discussed below.7
Although the polymers obtained in runs 1-3 of Table 3
had relatively narrow molecular weight distributions as
determined as PMMA derived from the original form, the
SEC curve of the original poly(VDBSMA)s obtained at
[M]/[I] = 40 and 60 indicated broader or multi modal dis-
tributions (Figure 4). This indicate that poly(VDBSMA)
forms aggregates when its DP is 40 or greater.
Side-Chain Modification of Poly(VDBSMA). In order to
obtain single-handed helical, optically active polymethacry-
lates bearing protonic side-chain groups, the side-chain vinyl
group of the single-handed helical poly(VDBSMA) prepared
using PMP-FlLi at [M]/[I]=20 (DP = 22, Mw/Mn=1.05,
[R]365 þ2038° (THF)) was converted to 2-hydroxyethyl, 1,2-
dihydroxyethyl, and carboxylic acid groups (poly-1, poly-2,
and poly-3, respectively, in Scheme 1). The conversion of
vinyl to 2-hydroxyethyl was conducted by hydroboration
followed by hydrolysis, that of vinyl to 1,2-dihydoxyethyl by
oxidation with OsO4 followed by decomposition using aqu-
eous NaHCO3, and that of vinyl to carboxylic acid by
oxidation with KMnO4 followed by treatment with an acidic
ion-exchange resin. These reactions were confirmed by FT-
1
IR and H NMR spectra of the products (Figures 5 and 6,
respectively).
In the FT-IR spectra (Figure 5), the relatively weak but
clearly observed bands based on the vinyl CdC around
1650 cm-1 for poly(VDBSMA) was not observed for poly-
1, poly-2, and poly-3. In addition, the IR bands due to O-H
stretching around 3500 cm-1 which were absent in the
spectrum of poly(VDBSMA) emerged for poly-1, poly-2,
and poly-3. Further, all polymers indicated CdO bands of
ester group around 1730 and 1150 cm-1. Also, poly-3
indicated a CdO band around 1690 cm-1 based on carbo-
xylic acid group. These results support the conversion of the
Figure 3. CD (top panel) and UV (bottom panel) spectra of poly-
(VDBSMA) having different degrees of polymerization:run 1 in Table 3
(A), run 2 in Table 3 (B), and run 3 in Table 3 (C) [in THF, at room
temperature].
Figure 2. 1H NMR spectra of PMMA derived from the poly-
(VDBSMA) prepared using DDB-FlLi (run 2 in Table 2) [500 MHz,
CDCl3].
Table 3. Asymmetric Anionic Polymerization of VDBSMA with PMP-FlLi in Toluene at -78 °Ca
THF-sol., benzene-hexane(1/1)-insol. part
yieldb (%)
THF-insol. part content
content (%)
[R]25 c (deg)
DPd
Mw/Mn
mme (%)
d
run
[M]/[I]
time (h)
365
1
2
3
4
5
6
20
40
60
80
40
80
3
3
3
3
48
48
97
76
63
53
96
84
∼0
2
3
28
89
>99
96
89
90
þ1975 f
þ2170
þ2140
23
40
57
1.07
1.10
1.19
>99
>99
>99
DP = 99, Mw/Mn = 1.53, mm > 99%g
DP = 149, Mw/Mn = 1.59, mm > 99%g
a Conditions: VDBSMA, 1.0 g (run 1), 500 mg (runs 2-6); [VDBSMA] = 0.15 M. b MeOH-insoluble part. c Measured in THF (concentration
0.5 g/dL, cell length 0.1 dm). d Determined by SEC of poly(MMA) derived from poly(VDBSMA). e Determined by 1H NMR of poly(MMA) derived
from poly(VDBSMA). f [R]25 þ892°, [R]25 þ485°, [R]25 þ422°, [R]25 þ411° (in THF, concentration 0.3 g/dL, cell length 0.1 dm). g Values
435
546
577
589
corresponding to the MeOH-insoluble part without fractionation using THF.

Article
Macromolecules, Vol. 43, No. 14, 2010 5961
vinyl group of poly(VDBSMA) to the corresponding proto-
nic groups of poly-1, poly-2, and poly-3 and clearly indicate
that the reagents used for the side chain vinyl group conver-
sion did not affect (hydrolyze) the ester linkage in the side
chain.
þ333° for poly-1 (in THF, concentration 0.5 g/dL, cell length
0.1 dm), [R]25
577
þ1463°, [R]25
þ844°, [R]25
þ469°,
365
435
546
[R]25
(1/1, v/v), concentration 0.5 g/dL, cell length 0.1 dm), and
þ407°, [R]25
þ394° for poly-2 (in THF-MeOH
589
[R]25
þ1221°, [R]25
þ697°, [R]25
þ384°, [R]25
365
435
546
577
1
The H NMR spectra (Figure 6) of poly-1, poly-2, and
þ336°, [R]25589 þ321° for poly-3 (in THF-MeOH (1/1, v/v),
concentration 1.0 g/dL, cell length 0.1 dm), suggesting that
single handedness of the polymer helix was maintained
during the polymer reaction of poly(VDBSMA) leading to
poly-1, poly-2, and poly-3. Hence, the helical polymethacry-
lates having protonic side-chain groups with single-handedness
poly-3 indicated no signal of the styrenic vinyl group of
poly(VDBSMA). For poly-1 and poly-2, proton signals
arising from the 2-hydroxyethyl and 1,2-dihydroxyethyl
groups were clearly observed. Furthermore, it is important
to note that R-methyl signals appeared in the range 0-0.5
ppm, indicating that the helical structure of poly(VDBSMA)
was not deteriorated by the side-chain modification reac-
tions. Helical polymethacrylates with bulky side groups
have been reported to indicate the R-methyl signals around
0.5 ppm.18 In the spectrum of poly-3, several minor signals
marked by an asterisk were observed in the range 4.5-
5.5 ppm. These signals might arise from 1,2-dihydroxyethyl
groups that may exist to a minor extent.
Chirality of poly-1, poly-2, and poly-3 was assessed by CD
spectra and optical activity measurements. Figure 7 shows
the CD and UV spectra of the three polymers along with that
of poly(VDBSMA). The UV spectra of poly-1, poly-2, and
poly-3 lacked the absorption band around 260 nm, confirm-
ing that π-conjugation systems of the three polymers are
smaller than that of poly(VDBSMA) because of the con-
sumption of the vinyl group of poly(VDBSMA) by the
polymer reactions. The three polymers indicated intense
CD and exhibited large dextrorotation: [R]25
þ1276°,
365
þ350°, [R]25
[R]25
þ735°, [R]25
þ403°, [R]25
435
546
577
589
Figure 6. 500 MHz 1H NMR spectra of poly(VDBSMA) (run 1 in
Table 3) in CDCl3, (A), poly-1 in CDCl3-pyridine-d5 (5/1, v/v), (B),
poly-2 in DMSO-d6 (C), and poly-3 in DMSO-d6 (D). Key (ꢀ) impurity
signals; (/) see text.
Figure 4. SEC curves of poly(VDBSMA)s having different degrees of
polymerization: run 1 in Table 3 (A), run 2 in Table 2 (B), and run 3 in
Table 3.
Figure 5. FT-IR spectra of poly(VDBSMA) (run 1 in Table 3) (A), poly-1 (B), poly-2 (C), and poly-3 (D) (KBr pellet).

5962 Macromolecules, Vol. 43, No. 14, 2010
Sakamoto et al.
Figure 8. First-order plots for methanolysis reactions of poly(VDBSMA)
(run 1 in Table 3) (A), poly-1 (B), and poly-3 (C) in a mixture of CDCl3,
CD3OD, and C5D5N (2/1/1, v/v/v) at 60 °C.
Table 5. First-Order Rate Constants and Half-Life Periods in
Methanolysis Reaction of Polymethacrylatesa
Figure 7. CD (top panel) and UV (bottom panel) spectra of poly-
(VDBSMA) (run 1 inTable 3) in THF (A), poly-1 inTHF-MeOH (1/1,
v/v) (B), poly-2 in THF-MeOH (1/1, v/v) (C), and poly-3 in
THF-MeOH (1/1, v/v) (D).
run
polymerb
k/h-1
half-life period/min
1
2
3
poly(VDBSMA)c
poly-1
poly-3
0.15
0.14
0.077
20 700
21 540
39 120
Table 4. Solubilities of Poly(VDBSMA), Poly-1, Poly-2, and Poly-3a
polymer
a Solvolysis reactions were carried out in a mixture of CDCl3,
CD3OD, and C5D5N (1/1/2, v/v/v) at 60 °C. b [Monomeric unit]o
=
solvent
CHCl3
poly(VDBSMA)
poly-1
poly-2
poly-3
0.0195 M. c Run 1 in Table 3.
S
S
I
I
I
I
I
I
I
I
I
I
I
S
S
S
S
S
I
I
I
I
S
S
S
S
S
I
indicating that these two polymers have similar stabilities.
The side-chain -OH groups of poly-1 do not seem to accele-
rate decomposition under the reaction conditions employed
in this work. The rate constant of decomposition of poly-3
was approximately half that of poly(VDBSMA), meaning
that poly-3 is twice more stable than poly(VDBSMA). This is
probably because the triarylmethyl cation originating from
the side-chain group of poly-3, which may be an intermediate
species of decomposition, is destabilized by the electron-
withdrawing effect of the -COOH group. This effect is con-
sidered to predominate over acidic catalysis effects of the
-COOH group. These results clearly indicate that the poly-
methacrylates having protonic side-chain groups have suffi-
cient stability for applications.
Radical Polymerization of Poly(VDBSMA). Reactivity of
poly(VDBSMA) was investigated from the view of an inter-
molecular (interhelix) reaction. Poly(VDBSMA) (run 1 in
Table 3) was subjected to free-radical polymerization reac-
tion with AIBN (Table 6). Here, the polymer may be recogni-
zed as a polyfunctional, helical macromonomer. At [AIBN]o =
0.004 M (run 2 in Table 6), consumption of the side-chain vinyl
group was incomplete and the product was mostly insoluble in
THF, indicating that a gel was formed. However, at [AIBN]o =
0.02 (run 1 in Table 6), the side-chain vinyl group was almost
quantitatively consumed and the product was mostly soluble in
THF. From the comparison of absolute molecular weights
(Mw’s determined by MALLS) of the source poly(VDBSMA)
(10 580) and the poly[poly(VDBSMA)] (325 200), the poly-
[poly(VDBSMA)] is considered to consist of approximately
30 helical chains. In addition, the much smaller Mark-
Houwink-Sakurada constant (0.19) of the poly[poly(VDB-
SMA)] than that of the source poly(VDBSMA) (0.76) suggests
that the constituent poly(VDBSMA) chains in the poly[poly-
(VDBSMA)] have a relatively random arrangement and the
poly[poly(VDBSMA)] has a rather globule-like shape.19,20 The
poly[poly(VDBSMA)] indicated intense CD ([θ]245 þ32000 deg
cm2 dmol-1 in THF). This indicates that single-handed helicity
of poly(VDBSMA) is maintained in the course of radical
polymerization in the formation an optically active macromo-
lecular adduct.
THF
S
S
S
S
S
S
I
CHCl3-pyridineb
THF-MeOHc
pyridine
DMF
DMSO
MeOH
H2O
I
a Polymer 1 mg, solvent 0.1 mL. S = soluble, I = insoluble. b 5/1, v/v.
c 1/1, v/v.
were successfully prepared by polymer reaction of poly-
(VDBSMA). It is difficult to discuss at this point whether
or not the differences in CD intensity and optical activity of
the three polymers may mean differences in the degree of
single handedness because their chemical structures are
different.
Solubilities of Poly(VDBSMA), Poly-1, Poly-2, and Poly-3.
Solubilities of the four polymers in various solvents are
summarized in Table 4. Although poly(VDBSMA) (run 1
from Table 3) was soluble only in CHCl3 and in THF among
the tested solvents, poly-1, poly-2, and poly-3 derived from
poly(VDBSMA) were soluble in more polar solvents. This
suggests that the three polymers effectively interact with
solvent molecules through hydrogen bonding. Thus, intro-
duction of protonic groups to the side chain of helical
polymethacrylate was demonstrated to expand the appli-
cability of polymer for polar solvent systems.
Stabilities of Poly(VDBSMA), Poly-1, and Poly-3. The
introduced protonic groups of the side-chain might possibly
induce decomposition of the ester linkage of the polymers. In
order to address this point, stabilities of poly(VDBSMA)
(run 1 in Table 3), poly-1, and poly-3 were tested by
monitoring methanolysis reactions of these polymers carried
out in a mixture of CDCl3, CD3OD, and C5D5N (2/1/1, v/v/
1
v) at 60 °C in an NMR sample tube by H NMR spectra
(Figure 8, Table 5). From the plots shown in Figure 8, the
first-order decomposition rate constants and half-life peri-
ods for the three polymers were estimated and summarized in
Table 5. The first-order decomposition rate constants and
half-life periods of poly(VDBSMA) and poly-1 were close,

Article
Macromolecules, Vol. 43, No. 14, 2010 5963
Table 6. Radical Polymerization of Poly(VDBSMA) Using AIBN in THF at 60 °C for 39 ha
THF-insol. part
yield(%)
THF-soluble part
run [poly(VDBSMA)]o (M) [AIBN]o (M) convnb (%)
yield (%) Mw
Mw/Mn Mark-Houwink-Sakurada constant (a)d
c
c
1
2
0.01e
0.01e
0.02
0.004
>99
49
13
78
87
22
325 200
n.d.
1.49
n.d.
0.19
n.d.
a Poly(VDBSMA) (run 1 in Table 3) 50 mg. Mw = 10 580, Mw/Mn = 1.05 as determined by SEC with multiangle light-scattering (MALLS) detec-
tion. Mark-Houwink-Sakurada constant (a) 0.76 as determined by SEC equipped with online viscometer and RI and right-angle light-scattering
detectors. b Conversion ratio of the side-chain vinyl group estimated by FT-IR. c Determined by SEC with MALLS detection. d Determined by SEC
equipped with online viscometer and RI and right-angle light-scattering detectors. e Monomeric unit.
Conclusions
Macromol. Rapid Commun. 2000, 21, 603. (f ) Okamoto, Y.; Nakano,
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Single-handed helical, optically active poly(VDBSMA) bear-
ing reactive vinyl side groupswas obtainedbyasymmetricanionic
polymerization of the corresponding monomer. Simple chemical
modifications of the side-chain vinyl group of this polymer
afforded poly-1, poly-2, and poly-3 having protonic side-chain
groups without seriously deteriorating the helical structure. In
this way, without laborious monomer syntheses and protection/
deprotection chemistry, single-handed helical polymethacrylates
with protonic side-chain groups were readily obtained. In addi-
tion, radical polymerization of poly(VDBSMA) as a macromo-
nomer afforded a novel optically active material consisting of
helical chains whose helicity was maintained through the reac-
tion.
The synthetic concept introduced in this work is not limited to
the three protonic groups described here as representative exam-
ples but can be extended to a wide range of functional, protonic
groups. Also, the concept is applicable for a wide variety of helical
(meth)acrylic and related polymers, and facile introduction of
protonic side-chain groups will greatly widen the scope of appli-
cation of helical polymers.
(2) Okamoto, Y.; Suzuki, K.; Ohta, K.; Hatada, K.; Yuki, H. J. Am.
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Acknowledgment. This paper is dedicated toProfessor Toyoji
Kakuchi on the occasion of his 60th birthday (“Kanreki”). We
thank Professor Yoshio Okamoto (Nagoya University) for valu-
able advises and Professor Takeshi Ohkuma and Associate
Professor Noriyoshi Arai (Hokkaido University) for the access
to the FT-IR spectrometer. This study was supported in part by
Grant-in-Aid No. 22350047, No. 21655037, and No. 22350047
and the Global COE Program (Project No. B01: Catalysis as the
Basis for Innovation in Materials Science) from the Ministry of
Education, Culture, Sports, Science, and Technology, Japan, and
in part by the Asahi Glass Foundation.
(10) Ito, Y.; Miyake, T.; Suginome, M. Macromolecules 2000, 23, 4034.
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