Synthesis of stable and soluble one-handed helical poly(substituted acetylene)s without chiral pendant groups via polymer reaction in membrane state

Article abstract of DOI:10.1016/j.polymer.2012.03.022

A soluble and stable one-handed helical conjugated polymer without the coexistence of any other chiral moieties was successfully synthesized by asymmetric-induced polymerization of a chiral monomer having two hydroxyl groups followed by desubstitution of

Full text of DOI:10.1016/j.polymer.2012.03.022

Polymer 53 (2012) 2129e2133
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Polymer
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Polymer communication
Synthesis of stable and soluble one-handed helical poly(substituted acetylene)s
without chiral pendant groups via polymer reaction in membrane state
,
b
c
d
a
Yunosuke Abe a, Toshiki Aoki a , Hongge Jia , Shingo Hadano , Takeshi Namikoshi , Yuriko Kakihana ,
*
Lijia Liu a, Yu Zang a, Masahiro Teraguchi a, Takashi Kaneko a
a Department of Chemistry and Chemical Engineering, Graduate School of Science and Technology, Center for Transdisciplinary Research, Venture Business Laboratory,
and Center for Instrumental analysis, Niigata University, Ikarashi 2-8050, Nishi-ku, Niigata 950-2181, Japan
b Department of Polymeric Material and Engineering, Qiqihar University, Wenhua street 42, Qiqihar, China
c Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
d Material Science and Engineering, Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A soluble and stable one-handed helical conjugated polymer without the coexistence of any other chiral
moieties was successfully synthesized by asymmetric-induced polymerization of a chiral monomer
having two hydroxyl groups followed by desubstitution of the chiral groups in a solid membrane state.
The reason for the success was the polymer reaction was carried out in the membrane state. This is an
alternative method to obtain such a unique chiral polymer which was obtained only by the helix-sense-
selective polymerization (HSSP) we reported before. In addition the efficiency of the chiral induction was
higher than that of the HSSP. It is interesting that the “Membrane state” acted like as if a protecting group.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 10 December 2011
Received in revised form
22 February 2012
Accepted 8 March 2012
Available online 20 March 2012
Keywords:
One-handed helical polyacetylenes
Polymer reaction
Membrane state
1. Introduction
conformation. One is HSSP [36e48] of an achiral monomer by using
a chiral catalyst as a chiral source and the other is asymmetric-
Conjugated polymers like polyacetylenes have aroused interest
because of their noteworthy physical properties such as conduc-
tivity, organomagnetism, and optical non-linear susceptibility.
Recently chiral polyacetylenes [1e25] have attracted much atten-
tion since the chiral structure can enhance the unique properties
and add new functions.
Many kinds of polymers having chiral structures in their main
chains and/or pendant groups have been synthesized. Among
them, soluble chiral conjugated polymers whose chiral structures
arise solely from the one-handed helical conformation of the
conjugated main chains (therefore, they have no asymmetric
carbons) and are stable alone in solution have so far only been
synthesized by the helix-sense-selective polymerization (HSSP) of
an a chiral phenylacetylene monomer by using a chiral catalytic
system developed in our laboratory [26e35].
induced polymerization(AIP), by using achiral catalysts, of mono-
mers having a chiral group as a chiral source, followed by removing
the chiral groups by a polymer reaction in solution (R) where the
chiral groups were desubstituted from the resulting one-handed
helical polymers (AIP-R) [41,49e59].
However, the examples where the two methods, HSSP and
AIP-R, have been applied to conjugated polymers are very few
[26e35,49,59]. In fact there has been only one example by using
HSSP by our group [26e35] and no examples of the use of AIP-R for
obtaining soluble chiral conjugated polymers [59,60]. Therefore, so
far our HSSP synthesis of achiral substituted acetylenes by a chiral
catalytic system [26e35] was the only method available to obtain
soluble chiral conjugated polymers whose chiral structures arise
only from the one-handed helical conformation of their conjugated
main chains [61e63]. However, the HSSP needed large amounts of
chiral cocatalysts [64,65].
In general, there exist two methods to synthesize soluble chiral
polymers whose chiral structures are present alone in the main
chain as asymmetric carbons and/or as a one-handed helical
* Corresponding author. Tel./fax: þ81 25 262 7280.
E-mail address: toshaoki@eng.niigata-u.ac.jp (T. Aoki).
0032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2012.03.022

2130
Y. Abe et al. / Polymer 53 (2012) 2129e2133
2.1.2. Synthesis of 2-acetoxy-1,3-bis(acetoxymethyl)-5-
bromobenzene (4) [70]
Acetic anhydride (24.3 mL, 257 mmol) was added dropwise to
a solution of 3 (10.0 g, 42.9 mmol) in pyridine at 5 ꢀC. The solution
was stirred at room temperature for 2 h. The resulting solution was
washed with 10 wt% copper sulfate pentahydrate aqueous solution
and brine. The organic layer was dried with magnesium sulfate
overnight. After filtration, the solvent was evaporated and the
crude product was purified by silica-gel column chromatography
(hexane: ethyl acetate ¼ 2:1) to give 4 as a white solid. Yield: 83.4%
(12.9 g). Rf: 0.29 (hexane: ethyl acetate ¼ 2:1). IR (KBr): 1780e1700
(C¼O), 3000e2800 (CH), 1000e1200 (CO) cmꢁ1; 1H NMR(270 MHz,
Scheme 1. Two synthetic routes to one-handed helical copoly[(de-1)/2] by
asymmetric-induced polymerization followed by a polymer reaction (desubstitution)
in
a membrane(AIP-RIM) in this study and helix-sense-selective polymerization
(HSSP) in our previous report [26]. (1) a. [Rh(nbd)Cl]2, Et3N, [1]/[1 þ 2] ¼ 0.10 (AIP), b.
HCl/CH3OH in membrane state (RIM), (2) c. [Rh(nbd)Cl]2, (S)-PEA, [(S)-PEA]/[(de-1)þ
2] ¼ 0.10 (HSSP).
CDCl3, ppm)
d
: 7.54(s, 2H, PhH), 4.98(s, 4H, (CH2OC(¼O)CH3)2),
2.32(s, 3H, OC(¼O)CH3), 2.07(s, 6H, (CH2OC(¼O)CH3)2).
2.1.3. Synthesis of 2-acetoxy-1,3-bis(acetoxymethyl)-5-
In this communication, we report that such a soluble and stable
chiral conjugated polymer was successfully obtained by an AIP-R
synthesis in a polymer membrane (¼ AIP-RIM) for the first time
(Scheme 1). In addition, we report that this AIP-RIM [66e69]
method is an alternative synthetic route which has a better effi-
ciency of asymmetric induction than our HSSP.
(trimethylsilylethynyl)benzene (5) [26]
Trimethylsilylacetylene (6.46 mL, 45.7 mmol) was added with
a syringe to a mixture of 4 (11.7 g, 32.6 mmol), triphenylphosphine
(0.606 g, 2.31 mmol), copper iodide (0.752 g, 3.95 mmol) and bis(-
triphenylphosphine)palladium (II) chloride (0.470 g, 0.670 mmol) in
triethylamine (130 mL). The mixture was stirred at 48 ꢀC for 24 h. The
formed salt was removed by filtration and the solvent was concen-
trated. After addition of ethyl acetate (50 mL), the resulting solution
was washed with brine. The organic layer was dried with magnesium
sulfate overnight. The solvent was evaporated and the crude product
was purified by silica-gel column chromatography (hexane: ethyl
acetate ¼ 3:1) to give 5 as a white solid. Yield: 83.4% (12.9 g). Rf: 0.26
(hexane: ethyl acetate ¼ 3:1). IR (KBr): 3700e3000 (OH), 3000e2800
(CH), 1759 (C¼O), 1250 (SiCH), 847 (SiCH) cmꢁ1; 1H NMR(270 MHz,
2. Experimental section
Acetone and toluene were distilled from CaH2, and tetrahydro-
furan was distilled from Na. Formalin 35 vol% solution stabilized
with 5% methanol purchased from Junsei Chemical was used as
received. The polymerization initiator, [Rh(nbd)Cl]2 (nbd ¼ 2,5-
norbornadiene), purchased from Aldrich Chemical was used as
received.
CDCl3, ppm)
d
: 7.50(s, 2H, PhH), 4.97(s, 4H, (CH2OC(¼O)CH3)2), 2.32(s,
3H, OC(¼O)CH3), 2.06(s, 6H, (CH2OC(¼O)CH3)2), 0.23(s, 9H, Si(CH3)3).
2.1. Monomer synthesis (Scheme 2)
2.1.4. Synthesis of 4-hydroxy-3,5-bis(hydroxymethyl)
phenylacetylene (de-1)
2.1.1. Synthesis of 4-bromo-2,6-bis(hydroxymethyl)phenol (3) [26]
Formalin stabilized with 5 vol% methanol (35 vol%, 600 mL,
8.00 mmol) was added dropwise to a solution of 4-bromophenol
(125 g, 723 mmol) and potassium hydroxide (44.7 g, 950 mmol)
in 2-propanol (200 mL) at 5 ꢀC. The solution was heated and stirred
at room temperature for a week. The resulting solution was poured
into 0.1 mol/L hydrochloric acid (2 L) with stirring. The solution was
allowed to stand for 6 h to precipitate a red viscous solid. After
removing the red solid by decantation, the supernatant solution
was allowed to stand for 2 days to precipitate a white solid. The
solid was filtered, washed with chloroform, and dried to give 3 as
a white solid. Yield: 48.9% (82.3 g). IR (KBr): 3700e3000 (OH),
Lithium aluminum hydride (1.17 g, 30.8 mmol) was added
slowly to tetrahydrofuran (45.2 mL) at 0 ꢀC. A solution of 5 (5.18 g,
15.4 mmol) in THF (6.17 mL) was added dropwise to the solution at
0
ꢀC. The solution was stirred at room temperature for 2 h. After
addition of water to the solution, the resulting solution was
concentrated. Ethyl acetate (50 mL) was added to the solution and
the resulting solution was washed with 2 N hydrochloric acid and
brine. The organic layer was dried with magnesium sulfate over-
night. After filtration, the solvent was evaporated and the crude
product was purified by silica-gel column chromatography
(hexane: ethyl acetate ¼ 2:3) to give de-1 as a white solid. Yield:
70.6% (2.74 g). Rf: 0.33 (hexane: ethyl acetate ¼ 1:1). IR (KBr):
3000e2800 (CH), 1000e1200 (CO) cmꢁ1
DMSO-d6) : 8.76 (s, 1H, PhOH), 7.29 (s, 2H, PhH), 5.32 (s,
2H,(CH2OH)2), 4.51 (s, 4H, (CH2OH)2).
;
1H NMR(270 MHz,
d
3700e3000 (OH), 3300 (^CH), 1338(OH), 1000e1200 (CeO) cmꢁ1
;
1H NMR(270 MHz, DMSO-d6, ppm)
d: 8.98(s, 1H, PhOH), 7.25(s, 2H,
OAc
OAc
OAc
OAc
c
OH
OH
OH
a
b
Si
Br
OAc
OAc
Br
OH
Br
3
4
5
OH
OH
OH
OH
O
e
d
O
OH
de-1
1
Scheme 2. Synthetic routes of de-1 and 1. a. HCHO aq., KOH/2-propanol, b. acetic anhydride/pyridine, c. trimethylsilylacetylene, PPh3, CuI, PdCl2(PPh3)2/triethylamine, d. 1. LiAlH4/
THF, 2. NaOH, H2O, e. (ꢁ)-chloromethyl menthyl ether, K2CO3/acetone.

Y. Abe et al. / Polymer 53 (2012) 2129e2133
2131
PhH), 5.29(s, 2H, (CH2OH)2), 4.50(s, 4H, (CH2OH)2), 3.89(s, 1H,
HC^C). 13C NMR(67.5 MHz, DMSO-d6, ppm)
: 152.2, 129.3, 128.9,
9.66. Found. C, 75.78; H, 9.55. The ratio of de-1 unit to 2 unit in
copoly[(de-1)/2] was 1:9 determined by the elemental analysis.
d
112.0 (Ph), 84.5, 78.2(C^C), 58.8 (CH). Anal. Calcd for C10H10O3: C,
67.41; H, 5.66. Found. C, 66.24; H, 5.60.
2.3. Polymer reaction
2.1.5. Synthesis of 3,5-bis(hydroxymethyl)-4-(L-menthoxymethyloxy)
phenylacetylene (1) [71]
2.3.1. Preparation of one-handed helical copoly[(de-1)/2] by
polymer reaction in membrane state (RIM) of the chiral groups in
copoly(1/2) [68] (Scheme 1 (1))
(ꢁ)-Chloromethyl menthyl ether (0.352 mL, 1.69 mmol) was
added with a syringe to a solution of de-1 (300 mg, 1.68 mmol) and
potassium carbonate (232 mg,1.68 mmol) in acetone (4.20 mL). The
solution was refluxed for 3 h and then was cooled to room
temperature. Unreacted potassium carbonate was filtered by Celite.
The solvent was evaporated. The crude product was purified by
silica-gel column chromatography (hexane: ethyl acetate ¼ 5:1
A solution of copoly(1/2) in chloroform (100 mg/5 mL) was cast
on a poly(tetrafluoroethylene) sheet, and the solvent was evapo-
rated for 24 h at room temperature. The resulting free-standing
membrane was detached from the sheet and dried in vacuo for
24 h. After the membrane was immersed in solution of methanol/
2 N hydrochloric acid (1/1 (v/v)) at 0 ꢀC for 3 days. It was neutral-
ized in 28 wt% aqueous ammonia for 12 h, washed with methanol
and dried in vacuo for 24 h. The weight loss (%), calcd: 4.9, found:
then 3:1) to give 1 as a white solid. Yield: 58.0% (169 mg). Rf: 0.27
D
(hexane: ethyl acetate ¼ 3:1). [
a
]
20ꢁ22.59ꢀ (c ¼ 0.500, THF). IR
4.9. 1H NMR(270 MHz, CDCl3/DMSO-d6 ¼ 1/1, ppm)
d
: 6.77(s, 2H,
(KBr): 3700e3100(OH), 3312(HC^), 3000e2800(CH), 951(cyclo-
hexane ring). 1H NMR(270 MHz, CDCl3, ppm)
d：7.45(s, 2H, PhH),
PhH), 5.77(s, 0.80H, CH2¼CH(cis)), 4.77e4.46(b, 2H, PhOCH2),
4.42e4.03(b, 4H, (CH2OH)2), 3.72e3.41(b, 2H, (CH2OH)2), 1.74e0.85
(m, 21H, dodecyl groups, (no 0.95(menthyl group) and no
0.78(menthyl group)). IR (film): 3700e3070(OH), 3000e2800(CH),
1464(Ph), (no 947(cyclohexane ring in menthyl group)). Anal. Calcd
for copoly[(de-1)/2]: C, 75.78; H, 9.66, Found. C, 75.72; H, 9.61.
5.14 (2dd, 2H, PhOCH2), 4.58(s, 4H, (CH2OH)2), 3.01(s, 1H, HC^C),
3.41e0.71 (m, 19H, menthoxy group). 13C NMR(67.5 MHz, CDCl3,
ppm) d: 155.4, 134.7, 133.4, 118.7 (Ph), 82.8, 77.１(C^C), 99.0, 60.8,
47.8, 42.0, 34.1, 31.7, 25.7, 23.3, 22.3, 20.9, 16.2 (CH). Anal. Calcd for
C21H30O4: C, 72.80; H, 8.73. Found. C, 72.68; H, 8.73.
2.2. Polymerization
2.3.2. Removal of the chiral groups from copoly(1/2) in THF (R)
Copoly(1/2) (40.0 mg, 0.115 mmol) was dissolved in THF/12 N
HCl (63/1 (v/v)) 3.20 mL for a week at room temperature. The
solution was poured into a large amount of methanol to precipitate
a red solid, which was filtered and dried in vacuo.
2.2.1. Synthesis of copoly(1/2) by asymmetric-induced
polymerization (AIP) of 1 with 2 [26] (Scheme 1 (1))
Triethylamine (0.484 mL, 72.2
solution (3.61 mL) of [Rh(nbd)Cl]2 (8.00 mg, 17.4
of the solution (0.340 mL, 4.25 mol) of the catalytic system were
added with a syringe to a toluene solution (1.1 mL) of 1 (5.00 mg,
14.4 mol) and 2 (45.0 mg, 130 mol). After the reaction solution
m
mol) was added to a toluene
1H NMR(270 MHz, CDCl3/DMSO-d6 ¼ 1/1, ppm)
d: 6.77(s, 2H,
mmol) and aliquots
m
PhH), 5.77(s, 0.80H, CH2¼CH(cis)), 4.79e4.48(b, 2H, PhOCH2),
4.45e4.05(b, 4H, (CH2OH)2), 3.74e3.40(b, 2H, (CH2OH)2), 1.74e0.85
(m, 21H, dodecyl groups, (no 0.95(menthyl group) and no
0.78(menthyl group)). IR (film): 3700-3070(OH), 3000-2800(CH),
1464(Ph). Anal. Calcd for copoly[(de-1)/2]: C, 75.78; H, 9.66. Found.
C, 75.63; H, 9.57.
m
m
was stirred at room temperature for 6 h, the solution was diluted
with toluene. The solution was poured into a large amount of
methanol to precipitate a red solid, which was filtered and dried in
D
vacuo. copoly(1/2): Yield 94.6% (47.3 mg). [
a
]
20ꢁ88.9ꢀ (c ¼ 0.100,
THF). 1H NMR(270 MHz, CDCl3/DMSO-d6 ¼ 1/1, ppm)
d: 6.77(s, 2H,
3. Results and discussion
PhH), 5.77(s, 0.81H, CH2¼CH(cis)), 4.80e4.50(b, 2H, OCH2),
4.45e4.05(b, 4H, (CH2OH)2), 3.74e3.40(b, 2H, (CH2OH)2),
2.30e2.14(b, 0.2H, menthyl group), 1.74e0.70(m, 23H, menthyl
group and dodecyl group). Cis% ¼ 81%. IR (film): 3700e3100(OH),
3000-2800(CH), 1464(Ph), 947(cyclohexane ring in menthyl
group). Anal. Calcd for copoly(1/2): C, 75.91; H, 9.77. Found. C,
75.87; H, 9.75. The molar ratio of 1 unit to 2 unit in copoly(1/2) was
1:9 determined by the elemental analysis.
The new two-step AIP-RIM synthetic route is shown in Scheme
1(1). First, we performed a standard AIP: a chiral monomer (1)
having a chiral substituent via an acetal group and two hydroxyl
groups was copolymerized with an achiral monomer (2) having
a dodecyl group via an ether group and two hydroxyl groups to
yield a one-handed helical copoly(1/2) having chiral pendant
Table 1
One-handed helical copoly[(de-1)/2] synthesized by asymmetric-induced poly-
merization followed by a polymer reaction(desubstitution) in membrane (AIP-RIM)
of 1 and 2 and helix-sense-selective polymerization (HSSP) of de-1 and 2.a
2.2.2. Synthesis of one-handed helical copoly[(de-1)/2] by helix-
sense-selective polymerization (HSSP) of de-1 with 2 [26] (Scheme 1
(2))
copoly(1/2)
copoly[(deL1)/2]
yield Mw
(S)-Phenylethylamine (63.0
a triethylamine(1.31 mL, 1.27 mmol) and tetrahydrofuran (10.4 mL)
solution of [Rh(nbd)Cl]2 (22.8 mg, 49.3 mol). Aliquots of the
solution (2.15 mL, 9.00 mol) of the catalytic system were added
with a syringe to a tetrahydrofuran solution (6.85 mL) of de-1
(4.81 mg, 27.0 mol) and 2 (302 mg, 873 mol). After the reaction
ml, 0.493 mmol) was added to
b
b
No. Mw
Mw/Mn
g
Mw/Mn
g
( ꢂ 106)b
( ꢂ 10ꢁ8
)
(%)d ( ꢂ 105)
( ꢂ 10ꢁ8
)
c
b
c
m
1
1.91
1.91
e
4.7
4.7
e
2.69
2.69
98.3 2.05
97.6 3.68
58.9 2.10
96.5 2.26
7.0
4.8
5.3
6.8
1.90
0
0.42
0
m
2e
3f
4g
m
m
1.83
6.5
0.288
solution was stirred at room temperature for 12 h, the solution was
diluted with tetrahydrofuran. The solution was poured into a large
amount of methanol to precipitate a red solid, which was filtered
and dried in vacuo. copoly[(de-1)/2]: Yield 58.9% (170.4 mg). 1H
a
Nos. 1, 2, 4: at room temperature for 6 h in toluene. [1D2] ¼ 0.1 mol/L, [1D2]/
[[Rh(nbd)Cl]2] ¼ 100.[Et3N]/[[Rh(nbd)Cl]2] ¼ 200; no. 3: at room temperature for
12 h in THF; [(de-1)D2] ¼ 0.1 mol/L, [(de-1)D2]/[[Rh(nbd)Cl]2] ¼ 100. [Et3Nþ(S)-
PEA]/[[Rh(nbd)Cl]2] ¼ 200. [(S)-PEA]/[[Rh(nbd)Cl]2] ¼ 200.
b
By GPC.
NMR(270 MHz, CDCl3/DMSO-d6 ¼ 1/1, ppm)
d: 6.75(s, 2H, PhH),
c
g ¼ ([
q]/3300)/ 3 .
Methanol insoluble part.
5.76(s, 0.87H, CH2¼CH (cis)), 4.66(b, 2H, PhOCH2), 4.31(b, 4H,
(CH2OH)2), 3.74e3.40(b, 2H, (CH2OH)2), 1.74e0.85 (m, 21H, in
dodecyl groups). Cis% ¼ 87%, IR (KBr): 3700e3100(OH), 3000-
2800(CH) 1463(Ph). Anal. Calcd for copoly[(de-1)/2]: C, 75.78; H,
d
e
f
The chiral groups were removed in THF solution(AIP-R).
HSSP.
The corresponding monomer(1’) without any hydroxyl groups was used instead of 1.
g

2132
Y. Abe et al. / Polymer 53 (2012) 2129e2133
Fig. 1. CD and UVevis spectra of the copolymers in THF. (A) (a) Copoly (1/2) (see Scheme 1(1a)), (b) copoly[(de-1)/2] by AIP-RIM(see Scheme 1(1b)), (c) copoly[(de-1)/2] (where the
chiral groups was removed in THF solution.), and (B) copoly[(de-1)/2] synthesized by (a) AIP-RIM (see Scheme 1(1)) and (b) HSSP(see Scheme 1(2)).
groups. Second, a solid membrane form of the chiral copoly(1/2)
was prepared by solvent casting and we removed the chiral
pendant groups completely by a polymer reaction while the poly-
mer remained in a membrane state(RIM). Finally we obtained the
target soluble molecule, copoly(de-1/2) by AIP-RIM. For compar-
ison, in order to obtain copoly(de-1/2) which has the same chemical
structure and chemical composition (1 unit/2 unit) as that by AIP-
RIM, de-1 and 2 were copolymerized by using a chiral catalytic
system (HSSP) as shown in Scheme 1(2). The characteristic of the
copolymers are listed in Table 1 (for the detail of the synthesis, see
Supporting Information (SI)).
There are the following four reasons why such a unique soluble
chiral conjugated polymer having a one-handed helical confor-
mation supported by intramolecular hydrogen bonds was
successfully prepared by AIP-RIM. (1) the polymer reaction i.e.,
desubstitution reaction should be carried out not in solution but
with the polymer in the form of a membrane (RIM). In fact, when
this reaction was carried out in solution, the resulting polymer
showed no CD peaks (Fig. 1(A)c and Table 1, no. 2). The intra-
molecular hydrogen bonds were retained during the desubstitution
reaction only when the polymer was in a membrane state. (2) The
monomer (1) having two hydroxy groups should be used for AIP. In
fact, when the monomer (1’) having no hydroxy groups was used
instead of 1, the resulting polymer did not maintain the chiral main
chain (Table 1, no 4). (3) The comonomer (2) having a hydrophobic
substituent which would not be affected by the conditions used in
RIM should be used. In fact, when the comonomer (2) was not used
for AIP-RIM, i.e., in the case of homopolymerization of 1, the
resulting polymer was insoluble. (4) Since the chiral source is the
chiral substituent connected with the monomer via a covalent bond
in case of AIP-RIM, the effect was higher than that in case of HSSP
where the chiral source was just added to the polymerization
system as a cocatalyst.
Copoly(1/2) made by AIP was found to have one-handed helical
structure from its CD (Fig.1(A)a and Table 1, no.1). The completeness
of removing of the chiral groups from the polymer membrane (RIM)
(Scheme 1b) was confirmed by solution NMR, elementary analysis,
IR, and the weight loss (See SI). Since the resulting copoly(de-1/2)
was soluble, we could measure and detect the CD of the AIP-RIM
product in solution for the first time [60,69]. Since the copolymer
without any chiral groups prepared by AIP-RIM showed CD signals
(Fig.1(A)b) in the main chain region, the polymer was found to have
a one-handed helix. We had therefore successfully synthesized
a soluble chiral conjugated polymer whose chiral structure arises
only from the one-handed helical conformation of its conjugated
main chain. This is the first such example except for the HSSP
synthesis we previously reported [26]. When DMSO was added to
a THF solution of copoly(de-1/2) prepared by AIP-RIM, the strength
of the CD decreased and then disappeared (see Fig. S1 in SI). This
observation proved that the main-chain chirality was maintained by
intramolecular hydrogen bonds. The phenomenon is exactly the
same as that occurred in chiral polymers prepared by our HSSP
method that we reported before [26e35]. Therefore, copoly(de-1/2)
prepared by AIP-RIM has the same chiral structure as the polymers
made by HSSP. To compare the efficiency of asymmetric polymeri-
zation between AIP-RIM and HSSP, copoly(de-1/2) with the same
chemical structure and monomer unit/commoner unit composition
was prepared by copolymerization of de-1 and 2 by using a chiral
catalytic system (HSSP) (Scheme 1(2)). A soluble and CD active
polymer was obtained but the CD strength was much smaller than
that of the same polymer made by AIP-RIM (Fig. 1(B)b and Table 1,
no.3). Therefore, the efficiency of AIP-RIM in asymmetric induction
was found to be much higher than that of HSSP.
O
O
1'
In conclusion, by using the AIP-RIM approach, where a chiral
monomer was used as a starting monomer in AIP, followed by
desubstitution of the chiral groups from a polymer membrane
(RIM), a unique soluble chiral conjugated polymer which has the
same chemical structure as that obtained by HSSP was synthesized
more effectively.
The most important feature of this method is that the desub-
stitution of the chiral groups was carried out with the polymer as
a solid membrane. In the membrane, quantitative desubstitution
was realized with maintenance of the one-handed helical confor-
mation and the intramolecular hydrogen bonds. It is interesting
that the “membrane state” acted like as if a protecting group and
this function was removed by dissolving the membrane. There are
several important implications of this work. First, it may be possible
to synthesis new unique chiral polymers by AIP-RIM which cannot
be prepared by HSSP. Second, the resulting membranes are likely to
function as optical resolution membranes [8,66,67]. Lastly, this
new concept of “Membrane Protection” may be applicable to other
reactions.
In summary, only when the polymer was a solid membrane, the
one-handed helical conformation retained during the polymer
reaction i.e., desubstitution reaction (R). Furthermore, it is only by
using monomers having hydroxyl groups (1 and 2) and a como-
nomer having a dodecyl group (2) that the resulting copolymer was
soluble and showed CD in solution. In addition, the CD (g ¼ 1.90)
was much stronger than that (g ¼ 0.42) of the corresponding
copolymer made by HSSP (Table 1).

Y. Abe et al. / Polymer 53 (2012) 2129e2133
2133
hydrogen bonds the helicity disappears in a polar solvent which can scission
the hydrogen bonds.
Acknowledgment
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Partial financial support through a Grant-in-Aid for Scientific
Research in a Priority Area "Super-Hierarchical Structures" (No.
18039011 and 19022009) from the Ministry of Education, Culture,
Sports, Science and Technology, Japan is gratefully acknowledged.
Appendix A. Supplementary material
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Supplementary material associated with this article can be
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