Synthesis of homopolymers, diblock copolymers, and multiblock polymers by organocatalyzed group transfer polymerization of various acrylate monomers

Article abstract of DOI:10.1021/ma502298v

The group transfer polymerization (GTP) with N-(trimethylsilyl)bis(trifluoromethanesulfonyl)imide (Me₃SiNTf₂) and 1-methoxy-1-triisopropylsiloxy-2-methyl-1-propene (iPr-SKA) has been studied using methyl acrylate (MA), ethyl acrylate (EA), n-butyl acrylate (nBA), 2-ethylhexyl acrylate (EHA), cyclohexyl acrylate (cHA), dicyclopentanyl acrylate (dcPA), tert-butyl acrylate (tBA), 2-methoxyethyl acrylate (MEA), 2-(2-ethoxyethoxy)ethyl acrylate (EEA), 2-(dimethylamino)ethyl acrylate (DMAEA), allyl acrylate (AlA), propargyl acrylate (PgA), 2-(triisopropylsiloxy)ethyl acrylate (TIPS-HEA), and triisopropylsilyl acrylate (TIPSA). Except for tBA and DMAEA, the GTPs of all other monomers described above proceeded rapidly in a living manner and produced well-defined homo acrylate polymers. The living nature of the GTPs of such acrylate monomers was further applied to the postpolymerizations of MA, EA, nBA, and MEA and also to the sequential GTPs of diverse acrylate monomers for preparing di- and multiblock acrylate polymers. In greater detail, the AB and BA diblock copolymers, (ABC)₄ dodecablock terpolymer, (ABCD)₃ dodecablock quaterpolymer, and ABCDEF hexablock sestopolymer were synthesized by sequential GTP methods using various acrylate monomers.

Full text of DOI:10.1021/ma502298v

Article
pubs.acs.org/Macromolecules
Synthesis of Homopolymers, Diblock Copolymers, and Multiblock
Polymers by Organocatalyzed Group Transfer Polymerization of
Various Acrylate Monomers
Kenji Takada, Takahiro Ito, Kodai Kitano, Shinji Tsuchida, Yu Takagi, Yougen Chen, Toshifumi Satoh,
and Toyoji Kakuchi*
Division of Biotechnology and Macromolecular Chemistry, Graduate School of Chemical Sciences and Engineering, Frontier
Chemistry Center, Faculty of Engineering, Hokkaido University, Sapporo, 060-8628, Japan
*
S Supporting Information
ABSTRACT: The group transfer polymerization (GTP) with N-(trimethylsilyl)bis(trifluoromethanesulfonyl)imide
(
(
Me SiNTf ) and 1-methoxy-1-triisopropylsiloxy-2-methyl-1-propene (iPr-SKA) has been studied using methyl acrylate
MA), ethyl acrylate (EA), n-butyl acrylate (nBA), 2-ethylhexyl acrylate (EHA), cyclohexyl acrylate (cHA), dicyclopentanyl
3 2
acrylate (dcPA), tert-butyl acrylate (tBA), 2-methoxyethyl acrylate (MEA), 2-(2-ethoxyethoxy)ethyl acrylate (EEA), 2-
(
(
dimethylamino)ethyl acrylate (DMAEA), allyl acrylate (AlA), propargyl acrylate (PgA), 2-(triisopropylsiloxy)ethyl acrylate
TIPS-HEA), and triisopropylsilyl acrylate (TIPSA). Except for tBA and DMAEA, the GTPs of all other monomers described
above proceeded rapidly in a living manner and produced well-defined homo acrylate polymers. The living nature of the GTPs of
such acrylate monomers was further applied to the postpolymerizations of MA, EA, nBA, and MEA and also to the sequential
GTPs of diverse acrylate monomers for preparing di- and multiblock acrylate polymers. In greater detail, the AB and BA diblock
copolymers, (ABC) dodecablock terpolymer, (ABCD) dodecablock quaterpolymer, and ABCDEF hexablock sestopolymer
4
3
were synthesized by sequential GTP methods using various acrylate monomers.
INTRODUCTION
Hadjichristidis et al. reported the synthesis of poly(2-vinyl-
■
pyridine)-b-polystyrene-b-poly(2-vinylpyridine) (P2VP-b-PS-b-
P2VP), poly(methyl methacrylate)-b-P2VP-b-poly(methyl
methacrylate) (PMMA-b-P2VP-b-PMMA), and PS-b-poly-
Block polymers exhibit various properties in the bulk and
solution phases depending on the type of polymer segments
used and their combinations.
copolymers with various combinations of A and B polymer
segments have been widely designed and synthesized using
many controlled/living polymerization methods to study and
1
−3
For example, AB diblock
9
−12
(
(
dimethylsiloxane)-b-PS (PS-b-PDMS-b-PS).
AB) alternate multiblock copolymer, the ABABAB hexablock,
For the
n
ABABABAB octablock, and ABABABABABAB dodecablock
4
−7
copolymers were synthesized using the α-chain-end-function-
apply their physical properties as polymeric materials.
In
9
−11
alized AB diblock copolymer of PS-b-PMMA.
In addition,
addition, the ABA and BAB triblock copolymers and (AB)n
alternate multiblock copolymers have been synthesized for
comparison with AB diblock copolymers in terms of the
more complicated multiblock polymer objects, such as those
consisting of more than three different polymer segments, have
attracted much attention from the viewpoint of the develop-
ment of advanced nanomaterials. For instance, the ABC
8
−11
interest in their morphologies.
The anionic polymerization
by sequentially and preorderly adding designed monomers, i.e.,
the sequential anionic polymerization, is one of the reliable
methods for preparing multiblock polymers with predictable
molecular weights and narrow molecular weight distributions.
For the ABA and BAB triblock copolymers, Hirao et al. and
Received: November 13, 2014
Revised: December 19, 2014
©
XXXX American Chemical Society
A
DOI: 10.1021/ma502298v
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Article
triblock terpolymers of PS-b-P2VP-b-poly(tert-butyl methacry-
late) (PS-b-P2VP-b-PtBMA) was synthesized by Stadler et al.
Scheme 1. Me SiNTf -Catalyzed Group Transfer
3 2
Polymerization of Acrylate Monomers Using iPr-SKA as the
Initiator
13
using sequential anionic polymerization. Recently, the ABCD
tetrablock quaterpolymer of PS-b-polyisoprene-b-PDMS-b-
P2VP (PS-b-PI-b-PDMS-b-P2VP) and the ABCDE pentablock
quintopolymer of PS-b-PI-b-PDMS-b-PtBMA-b-P2VP were
synthesized by the combination of the sequential polymer-
14,15
ization and selective linking methods.
However, the anionic
polymerization of acrylate monomers hardly controlled the
molecular weights and their distributions of the obtained
polymers due to the side reactions of the ester carbonyl group
and the susceptible α-hydrogen with the anionic initiators and
the active chain ends. Therefore, multiblock polymers
containing acrylate polymer segments are limited using the
sequential anionic polymerization method, meaning that the
synthesis of multiblock polymers even though they consist of
only acrylate polymer segments, i.e., multiblock acrylate
polymers, is a remaining and challenging task. The sequential
controlled/living radical polymerization is currently an efficient
technique for the synthesis of well-defined acrylate polymers.
For instance, Whittaker et al. reported that poly(methyl
acrylate)-b-poly(n-butyl acrylate)-b-poly(ethyl acrylate)-b-poly-
(
2-ethylhexyl acrylate)-b-poly(ethyl acrylate)-b-poly(n-butyl
acrylate)-b-poly(n-butyl acrylate)-b-poly(methyl acrylate)
PMA-b-PnBA-b-PEA-b-PEHA-b-PEA-b-PnBA-b-PnBA-b-
(
PMA) and PMA-b-PEA-b-PnBA-b-poly(tert-butyl acrylate)-b-
PMA-b-PEA-b-PnBA-b-poly(tert-butyl acrylate)-b-PMA-b-PEA
were synthesized as octablock and decablock acrylate polymers,
respectively, by the iterative Cu(0)-mediated radical polymer-
(
cHA), dicyclopentanyl acrylate (dcPA), and tBA as alkyl
1
6,17
ization.
acrylates and 2-methoxyethyl acrylate (MEA), 2-(2-
ethoxyethoxy)ethyl acrylate (EEA), allyl acrylate (AlA),
propargyl acrylate (PgA), 2-(triisopropylsiloxy)ethyl acrylate
Group transfer polymerization (GTP), one of the anionic
polymerizations, is well-known as the polymerization method
for (meth)acrylate monomers using conventional Lewis acids
(
TIPS-HEA), and triisopropylsilyl acrylate (TIPSA) as func-
1
8−22
and bases.
Recently, organocatalysts have been found to
tional acrylates, (2) the homopolymer chain extension by the
sequential postpolymerizations (nine times) of MA, EA, nBA,
and MEA, and (3) the synthesis of AB and BA diblock
sufficiently control the GTP, which leads to producing well-
defined (meth)acrylate polymers with predicted molecular
weights and narrow molecular weight distribution. For instance,
Taton et al. and Waymouth et al. reported that N-heterocylic
carbenes efficiently catalyzed the GTPs of methyl methacrylate,
N,N-dimethylaminoethyl methacrylate, N,N-dimethyacryla-
mide, tert-butyl acrylate (tBA), and n-butyl acrylate (nBA) to
produce the respective well-defined homopolymers as well as
copolymers, (PEHA-b-PnBA-b-PEA) dodecablock terpolymer,
(
and PdcPA-b-PnBA-b-PEHA-b-PEA-b-PMA-b-PcHA hexablock
sestopolymer.
4
PnBA-b-PEA-b-PMEA-b-PMA) dodecablock quaterpolymer,
3
EXPERIMENTAL SECTION
23−28
■
their di- and triblock polymers.
In addition, we reported
Materials. Dichloromethane (CH Cl , >99.5%; water content,
2
2
that strong Brønsted acids, such as trifluoromethanesulfonyli-
mide and 1-[bis(trifluoromethanesulfonyl)methyl]-2,3,4,5,6-
pentafluorobenzene, and the Lewis acid of N-(trimethylsilyl)-
bis(trifluoromethanesulfonyl)imide (Me SiNTf ) performed as
<
0.001%), toluene (>99.5%; water content, <0.001%), tetrahydrofuran
(THF, >99.5%; water content, <0.001%), triethylamine (>99.0%),
methanol (>99.5%), and tert-butyl alcohol (>98.0%) were purchased
from Kanto Chemicals Co., Inc. Methyl acrylate (MA, >99.8%), ethyl
acrylate (EA, >99.0%), n-butyl acrylate (nBA, >99.0%), 2-ethylhexyl
acrylate (EHA, 99.0%), cyclohexyl acrylate (cHA, >98.0%),
dicyclopentanyl acrylate (dcPA, >95.0%), tert-butyl acrylate (tBA,
3
2
promoters and organocatalyst, respectively, for the controlled/
29−35
living GTPs of (meth)acrylate and acrylamide monomers.
Particularly, the organic-acid-catalyzed GTP using the initiator
of 1-methoxy-1-triisopropylsiloxy-2-methyl-1-propene (iPr-
SKA) was the most suitable polymerization method for acrylate
monomers, such as methyl acrylate (MA) and nBA, leading to
high-molecular-weight acrylate polymers with the molecular
>
98.0%), 2-methoxyethyl acrylate (MEA, >98.0%), 2-(2-
ethoxyethoxy)ethyl acrylate (EEA, 98.0%), 2-(dimethylamino)ethyl
acrylate (DMAEA, >97.0%), allyl acrylate (AlA, >98.0%), 2-
hydroxyethyl acrylate (>95.0%), acrylic acid (>99.0%), acryloyl
chloride (>95.0%), N-(trimethylsilyl)bis(trifluoromethanesulfonyl)-
3
−1
weight of up to 10 kg mol and those with α,ω-end-functional
groups.
imide (Me SiNTf , >95.0%), and triisopropylsilyl chloride (iPr SiCl)
were purchased from Tokyo Kasei Kogyo Co., Ltd. MA, EA, nBA,
EHA, cHA, dcPA, tBA, MEA, EEA, DMAEA, AlA and CH Cl were
3
2
3
3
3,35
Thus, it is important to elucidate the scope and
limit of this GTP system in terms of applicable acrylate
monomers and synthesis of multiblock acrylate polymers.
Hence, our objective is to establish the Me SiNTf -catalyzed
2
2
distilled from CaH and degassed by three freeze−pump−thaw cycles
2
prior to their use. Toluene was distilled from sodium benzophenone
ketyl. 1-Methoxy-1-triisopropylsiloxy-2-methyl-1-propene (iPr-SKA)
and propargyl acrylate (PgA) were synthesized by previously reported
3
2
GTP using iPr-SKA as a versatile method for synthesizing well-
defined acrylate polymers, as shown in Scheme 1. This article
describes (1) the GTP characteristics of MA, ethyl acrylate
3
6,37
procedures.
A spectra/Por 6 membrane (molecular weight cutoff:
1000) was used for the dialysis. All other chemicals were purchased
(
EA), nBA, 2-ethylhexyl acrylate (EHA), cyclohexyl acrylate
from available suppliers and used without purification.
B
DOI: 10.1021/ma502298v
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Article
Measurements. The H (400 MHz) and 13C NMR (100 MHz)
spectra were recorded using a JEOL JNM-A400II. The polymerization
solution was prepared in an MBRAUN stainless steel glovebox
equipped with a gas purification system (molecular sieves and copper
catalyst) in a dry argon atmosphere (H O, O <1 ppm). The moisture
1
GTP of the acrylates (5.0 mmol) produced PEA (yield, 491 mg, 98%),
PnBA (yield, 612 mg, 96%), PEHA (yield, 892 mg, 97%), PcHA (yield,
748 mg, 97%), PdcPA (yield, 490 mg, 95%; monomer, 2.5 mmol),
PtBA (yield, n.d., no polymerization), PMEA (yield, 638 mg, 98%),
PEEA (yield, 885 mg, 94%), PDMAEA (yield, n.d., no polymer-
ization), PAlA (yield, 522 mg, 93%), PPgA (yield, 518 mg, 94%),
P(TIPS-HEA) (yield, 1.31 g, 96%), and PTIPSA (yield, 1.09 g, 95%)
in a controlled manner.
2
2
and oxygen contents in the glovebox were monitored by an MB-MO-
SE 1 and an MB-OX-SE 1, respectively. Size exclusion chromatog-
raphy (SEC) measurements of the obtained polymers were performed
at 40 °C using a Jasco GPC-900 system equipped with two Shodex
KF-804 L columns (linear, 8 mm ×300 mm) using THF at the flow
rate of 1.0 mL min . SEC measurements for the poly(n-butyl
acrylate)s were performed at 40 °C using a Shodex GPC-101 gel
permeation chromatography (GPC) system (Shodex DU-2130 dual
pump, Shodex RI-71 RI detector, and Shodex ERC-3125SN degasser)
equipped with two Shodex KF-804 L columns (linear, 8 mm ×300
Chain Extension by Postpolymerization. A typical procedure is
as follows. The polymerization of MA (86 mg, 1.0 mmol) with iPr-
SKA (14.4 μL, 50 μmol) and Me SiNTf (10 μL, 1.0 μmol, 0.10 mol
−1
3
2
−1
L
in toluene) in toluene (0.89 mL) at room temperature was carried
out under the condition of [MA] /[iPr-SKA] /[Me SiNTf ] = 20/1/
0
0
3
2 0
−1
0.02 and [MA] = 1.0 mol L for 5 min as the first polymerization
0
((PMA) ). The second polymerization was subsequently started by
1
−1
mm) using THF at the flow rate of 1.0 mL min . The number-
average molecular weight (Mn,SEC) and dispersity (M /M ) of the
polymers were determined by the RI based on PMMA standards with
adding 20 equiv of MA (86.1 mg, 1.0 mmol) in toluene (0.89 mL) to
the polymerization mixture after an aliquot was removed from the
reaction mixture to determine the monomer conversion and the
molecular weight and dispersity of the resulting polymer ((PMA)2).
The continuous postpolymerizations for the synthesis of (PMA)3−10
were carried out by the same procedure after the complete
consumption of MA was confirmed. After all the postpolymerizations,
a small amount of methanol was added to the reaction mixture to
terminate the polymerization. The obtained polymers were purified by
dialysis and preparative SEC to give the (PMA)10 as a clear solid
(yield, 851 mg; 99%). The syntheses of (PEA) , (PnBA) , and
w
n
6
−1
5
−1
the M (M /M )s of 1.25 × 10 g mol (1.07), 6.59 × 10 g mol
w
w
n
5
−1
5
−1
(
×
1.02), 3.003 × 10 g mol (1.02), 1.385 × 10 g mol (1.05), 6.015
4
−1
4
−1
4
10 g mol (1.03), 3.053 × 10 g mol (1.02), and 1.155 × 10 g
1 3 3
−
−1
−1
mol (1.04), 4.90 × 10 g mol (1.10), 2.87 × 10 g mol (1.06),
3
−1
and 1.43 × 10 g mol (1.15). The Mn,NMRs of the polymers were
determined by their H NMR spectra in CDCl based on the initiator
1
3
residue and monomer units. The preparative SEC was performed
−
1
using CHCl (3.5 mL min ) at room temperature (20 ± 5 °C) using
3
10
10
a JAI LC-9201 equipped with a JAI JAIGEL-2H column (20 mm ×
(PMEA)10 were carried out using the same procedure with 1.0 mmol,
2
3
6
00 mm ; exclusion limit, 5 × 10 ) and a JAI RI-50s refractive index
for each polymerization, of acrylates to give the respective acrylate
polymers in quantitative yields ((PEA) , yield, 970 mg, 97%;
detector.
Synthesis of 2-(Triisopropylsiloxy)ethyl Acrylate (TIPS-HEA).
1
0
(
PnBA) , yield, 1.22 g, 95%; (PMEA) , yield, 1.24 g; 95%).
10 10
iPr SiCl (16.6 g, 86.1 mmol) was dropwise added to a solution of 2-
hydroxyethyl acrylate (10.0 g, 86.1 mmol) and triethylamine (8.71 g,
6.1 mmol) in CH Cl (150 mL) at 0 °C. The reaction mixture was
stirred overnight at room temperature and sequentially washed with 1
mol L HCl (100 mL × 2), conc. aq. NaHCO (100 mL), and
distilled water (100 mL). The organic phase was dried over anhydrous
MgSO . After filtration and evaporation, the residue was purified by
distillation under reduced pressure to give TIPS-HEA as a transparent
3
Synthesis of Di- and Multiblock Acrylate Polymers. The
diblock copolymerizations were carried out using nBA (160 mg, 1.25
mmol) with MEA (162 mg, 1.25 mmol), AlA (140 mg, 1.25 mmol),
and PgA (137 mg, 1.25 mmol). The multiblock polymerizations of MA
(86 mg, 1.0 mmol), EA (100 mg, 1.0 mmol), nBA (128 mg, 1.0
mmol), EHA (184 mg, 1.0 mmol), cHA (154 mg, 1.0 mmol), dcPA
(206 mg, 1.0 mmol), and MEA (130 mg, 1.0 mmol) were carried out
8
2 2
−1
3
4
using iPr-SKA (28.8 μL, 100 μmol) and Me SiNTf (20 μL, 2.0 μmol,
1
3
2
liquid. Yield: 12.51 g (53.3%). Bp: 67 °C/0.02 mmHg. H NMR (400
−1
0
.1 mol L in toluene) to produce (PHEA-b-PnBA-b-PEA) (1.57 g,
4
MHz, CDCl ): δ (ppm) 6.40 (dd, J = 17.4, 1.4 Hz, 1H, −CH
3
9
5%), (PnBA-b-PEA-b-PMEA-b-PMA) (1.28 g, 96%), and PdcPA-b-
E
Z
E
Z
3
C H H), 6.12 (dd, J = 17.4, 10.6 Hz, 1H, −CHC H H), 5.81 (dd, J
PnBA-b-PEHA-b-PEA-b-PMA-b-PcHA (842 mg, 98%).
E
Z
=
10.4, 2.0 Hz, −CHC H H), 4.26 (t, J = 5.2 Hz, 2H,
−
1
COCH CH OSi-), 3.93 (t, J = 5.2 Hz, 2H, −COCH CH OSi-),
2
2
2
2
13
.01−1.13 (m, 21H, -OSi[CH(CH ) ] ). C NMR (100 MHz,
RESULTS AND DISCUSSION
3
2
3
■
CDCl ): δ (ppm) 166.2, 130.8, 128.4, 65.9, 61.5, 17.9, 11.9. Anal.
3
Me SiNTf -Catalyzed GTP of Alkyl Acrylates. The group
3
2
Calcd for C H O Si (272.46): C, 61.72; H, 10.36. Found: C, 61.40;
14
28
3
transfer polymerization (GTP) of the acrylate monomers was
H, 10.30.
c a r r i e d o u t u s i n g N - ( t r i m e t h y l s i l y l ) b i s -
Synthesis of Triisopropylsilyl Acrylate (TIPSA). iPr SiCl (30.1
g, 156 mmol) was dropwise added to a solution of acrylic acid (11.3 g,
3
(
trifluoromethanesulfonyl)imide (Me SiNTf ) and 1-methoxy-
3 2
1
56 mmol) and triethylamine (15.8 g, 156 mmol) in CH Cl (150
1-triisopropylsiloxy-2-methyl-1-propene (iPr-SKA) as the orga-
nocatalyst and initiator, respectively. We initially determined
the GTP characteristics of the alkyl acrylates, such as methyl
acrylate (MA), ethyl acrylate (EA), n-butyl acrylate (nBA), 2-
ethylhexyl acrylate (EHA), cyclohexyl acrylate (cHA),
dicyclopentanyl acrylate (dcPA), and tert-butyl acrylate (tBA).
In order to compare their polymerization rates, the polymer-
izations of MA, EA, nBA, EHA, cHA, and dcPA were carried out
under the conditions of the fixed monomer (M)-to-initiator
2
2
mL) at 0 °C. The following procedure was similar to that for
synthesizing TIPS-HEA, which gave TIPSA as a transparent liquid.
Yield: 19.5 g (54.6%). Bp: 87 °C/6.0 mmHg. H NMR (400 MHz,
1
E
Z
CDCl ): δ (ppm) 6.37 (dd, J = 17.4, 1.4 Hz, 1H, −CHC H H),
3
E
Z
6
1
.12 (dd, J = 17.2, 10.4 Hz, 1H, −CHC H H), 5.84 (dd, J = 10.2,
E
Z
.4 Hz, −CHC H H), 1.01−1.13 (m, 21H, −OSi[CH(CH ) ] ).
3 2 3
1
3
C NMR (100 MHz, CDCl ), δ (ppm) 165.8, 130.8, 130.3, 17.8, 12.0.
3
Anal. Calcd for C H O Si (288.40): C, 63.10; H, 10.59. Found: C,
12
24
2
63.02; H, 10.57.
Me SiNTf -Catalyzed GTP of Acrylates Initiated by iPr-SKA.
molar ratio ([M] /[iPr-SKA] ) of 200 in toluene at room
0 0
3
2
A typical procedure is as follows. A stock solution of Me SiNTf (10
temperature. The kinetic experiments exhibited a distinct first-
order relationship between the reaction time and monomer
conversion, as shown in Figure 1. There was no significant
difference in the polymerization rates among MA, EA, and nBA,
whose rates were higher than that of EHA. Although the
loading amount of the catalyst was greater than that used for
the polymerizations of MA, EA, nBA, and EHA, no polymer-
ization proceeded for cHA and dcPA within the polymerization
time of 30 min. There was an obvious difference in the
3
2
−1
μL, 1.0 μmol, 0.10 mol L in toluene) was added to a solution of MA
430 mg, 0.449 mL, 5.0 mmol) and iPr-SKA (14.4 μL, 12.9 mg, 50.0
(
μmol) in toluene (4.48 mL) under an argon atmosphere at room
temperature (23 ± 5 °C). After stirring for 1 h, the polymerization was
quenched by adding a small amount of methanol. The crude product
was purified by reprecipitation in n-hexane, dialysis, and preparative
size exclusion chromatography (SEC) in CHCl3 to give the
poly(methyl acrylate) (PMA) as a white solid. Yield: 425 mg (99%).
−1
−1
Mn,NMR = 8600 g mol ; M
= 9700 g mol ; M /M = 1.03. The
n,SEC
w n
C
DOI: 10.1021/ma502298v
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Article
with the predicted values (Mn,calcd.s) of 86 100, 100 200,
−1
1
28 300, and 184 400 g mol , respectively. For the polymer-
ization of cHA, the monomer conversion was 90.5% even after
−
1
2
4 h. Although the Mn,SEC of 166 700 g mo−l approximately
1
agreed with the Mn,calcd. of 139 700 g mol , the molecular
weight distribution slightly increased for the M /M of 1.15.
w
n
Though the polymerization of dcPA needs long polymerization
time as 24 h, it proceeded to produce well-defined PdcPA with
Mn,NMR (M /M ) of 10 670 (1.08). On the other hand, the
w
n
polymerization of tBA did not proceed at all even though given
a polymerization time of 20 h, which was caused by the ester
cleavage of the monomer in the presence of the strong Lewis
acid of Me SiNTf . These results indicated that the polymer-
Figure 1. Kinetic plots for the Me SiNTf −catalyzed GTP of MA, EA,
3
2
nBA, EHA, cHA, and dcPA using iPr-SKA in toluene ([M] /[iPr-
0
3
2
−1
SKA] /[Me SiNTf ] , 200/1/0.02; [M] , 1.0 mol L ; temperature, 27
0
3
2
0
0
ization ability of the primary alkyl acrylate was much higher
than that of the secondary alkyl acrylate, and the tertiary alkyl
acrylate possessed no polymerization ability for the Me SiNTf -
°C).
3
2
catalyzed GTP using the iPr-SKA initiator.
Me SiNTf -Catalyzed GTP of Functional Acrylates. In
polymerization ability between the primary and secondary alkyl
acrylates for the Me SiNTf -catalyzed GTP using iPr-SKA.
3
2
3
2
In order to ensure the synthesis of the targeted molecular
weight polymers, which is one of the important characteristics
for the living polymerization system, the polymerizations of
MA, EA, nBA, EHA, and cHA were carried out under the
conditions with the [M] /[iPr-SKA] s of 100, 400, and 1000 in
toluene at room temperature. All the polymerization results are
listed in Table S1. The loading amount of the catalyst, i.e., the
order to elucidate the scope and limit of the applicable
monomers, we examined the polymerization of functional
acrylates, such as 2-methoxyethyl acrylate (MEA), 2-(2-
ethoxyethoxy)ethyl acrylate (EEA), 2-(triisopropylsiloxy)ethyl
acrylate (TIPS-HEA), 2-(dimethylamino)ethyl acrylate
(DMAEA), allyl acrylate (AlA), propargyl acrylate (PgA), and
triisopropylsilyl acrylate (TIPSA) using the iPr-SKA initiator.
Table 1 summarizes the polymerization results. The polymer-
0
0
[
Me SiNTf ] /[iPr-SKA] , was 0.02 for the [M] /[iPr-SKA] s
3 2 0 0 0 0
of 100 and 400, whereas a higher amount of catalyst was
izations of MEA with the [MEA]
/[iPr-SKA] s of 100, 400, and
0 0
required for the [Me SiNTf ] /[iPr-SKA] of 0.05 and the
1000 produced the targeted molecular weight PMEAs, such as
3
2 0
0
−
1
[
M] /[iPr-SKA] of 1000. The polymerization time increased
the Mn,SECs of 14 400, 58 800, and 140 300 g mol ,
respectively, which well agreed with the Mn,calcd.s of 13 100,
0
0
with the increasing [M] /[iPr-SKA] , and all of the monomers
0
0
−1
were consumed except for cHA. The number-average molecular
weights of the obtained polymers estimated using SEC
measurements (Mn,SECs) linearly increased with the increasing
52 200, and 130 200 g mol , respectively (runs 1−3). In
addition, the molecular weight distributions of the PMEAs were
as narrow as M
hydrophilic acrylate polymers relative to PMEA, the GTPs of
EEA and TIPS-HEA were examined. For the polymerization
/M
of 1.03−1.05. In order to more
w
n
[
M] /[iPr-SKA]0 (Figure 2), and the molecular weight
0
distributions (M /M s) of the obtained polymers were as low
w
n
as 1.02−1.06, as shown in Figure S1. For the [M] /[iPr-SKA]
condition of [M]
/[iPr-SKA] /[Me SiNTf ] = 100/1/0.02,
0 0 3 2 0
0
0
−1
of 1000, the M
s (M /M s) were 97 500 g mol (1.04) for
the Mn,SEC of poly(2-(2-ethoxyethoxy)ethyl acrylate) (PEEA)
n,SEC
w n
−1
−1
−1
PMA, 108 400 g mol (1.04) for PEA, 141 900 g mol (1.05)
was 18 900 g mol
and the Mn,NMR of poly(2-
−
1
for PnBA, and 220 000 g mol (1.06) for PEHA, which agreed
(triisopropylsiloxy)ethyl acrylate) (P(TIPS-HEA)) was 26 700
−1
g mol , which agreed with the Mn,calcd.s of 18 900 and 27 300 g
−1
mol , respectively (runs 4 and 5). The M /M of PEEA was
w
n
1
.06 even though a small peak was observed in the high
molecular weight region, and that of P(TIPS-HEA) was 1.02.
On the other hand, the polymerization of DMAEA did not
proceed after 20 h, which should have been caused by the
incentive that the dimethyamino group in the monomer
deactivating the catalytic performance of Me SiNTf (run 6).
3
2
The deprotection of the triisopropylsilyl group in the P(TIPS-
HEA) using tetra-n-butylammonium fluoride smoothly pro-
ceeded to produce the well-defined poly(2-hydoxyethyl
acrylate). The Me SiNTf -catalyzed GTPs of AlA and PgA
3
2
under the condition of [M] /[iPr-SKA] = 100/1 produced gel-
0
0
−1
free polymers with the Mn,NMRs of 11 800 and 11 000 g mol ,
respectively, which agreed with the predicted values by the
initial monomer-to-initiator ratio (runs 7 and 8). The
characteristic proton signals of the allyl and ethynyl groups
were observed at 5.91, 5.30−5.15, and 2.55 ppm respectively,
together with those of the acrylate polymer main-chain at
1
2
.60−2.40 ppm, in the H NMR spectra, indicating that the
polymerization of AlA and PgA proceeded through a
controlled/living GTP mechanism in even in the presence of
the reactive allyl and ethynyl groups (Figures S10 and S12). In
addition, the GTP of TIPSA proceeded without cleavage of the
Figure 2. Plots for the molecular weights (Mn,SEC) of the obtained
polymers vs the initial molar ratios of the monomer and initiators
(
[M] /[iPr-SKA] ) MA, EA, nBA, EHA, and cHA along with the value
0 0
of molecular weight and molecular weight distribution.
D
DOI: 10.1021/ma502298v
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Table 1. Me SiNTf -Catalyzed Group Transfer Polymerization of MEA, EEA, TIPS-HEA, DMAEA, AlA, PgA, and TIPSA Using
3
2
a
the iPr-SKA Initiator
b
Mn,calcd./g mol−1
c
Mn,SEC (Mn,NMR )/g mol−1
b
d
d
run
monomer (M)
[M] /[iPr-SKA] /[Me SiNTf ]
time/h
conv/%
M /M
w n
0
0
3
2
0
1
2
3
4
5
6
7
8
9
MEA
100/1/0.02
400/1/0.02
1000/1/0.05
100/1/0.02
100/1/0.02
100/1/0.02
100/1/0.02
100/1/0.05
100/1/0.02
1
3
>99
>99
>99
>99
>99
<1
13 100
52 200
130 200
18 900
27 300
−
14 400 (13 700)
58 800
1.03
1.03
1.05
1.06
1.02
−
1.04
1.10
1.15
MEA
MEA
18
1
140 300
EEA
18 900
TIPS-HEA
DMAEA
AlA
3
21 200 (26 700)
−
11 000 (11 800)
18 600 (11 000)
10 700 (23 520)
20
1
>99
>99
91.5
11 300
PgA
3
11 100
TIPSA
21
21 000
a
−1
b
1
c
Argon atmosphere; solvent, toluene; [M] , 1.0 mol L ; temperature, room temperature. Determined by H NMR in CDCl . Calculated from
0
3
(
[M] /([iPr-SKA] ) × (conv) × (MW of monomer; MEA, 130.14; EEA, 188.22; TIPS-HEA, 272.46; DMAEA, 143.19; AlA, 112.13; PgA, 110.11;
0 0
d
TIPSA, 228.40) + (MW of initiator residue, 102.13). Determined by SEC in THF using poly(methyl methacrylate) standard.
silyl ester linkage to produce the poly(triisopropylsilyl acrylate)
−1
(
PTIPSA) with the Mn,NMR of 23 520 g mol though the
polydispersity slightly increased for the M /M of 1.15 (run 9).
w
n
PTIPSA was also deprotected using tetra-n-butylammonium
fluoride to produce poly(acrylic acid), which could be used as
8
the hydrophilic polymer segment in amphiphilic materials.
For the GTP of the functional acrylates, the GTP
characteristics of MEA were similar to those of the primary
alkyl acrylate. The GTPs of EEA, TIPS-HEA, AlA, PgA, and
TIPSA could be controlled at any initial monomer-to-initiator
ratio not more than 100. The amino group containing the
acrylate of DMAEA possessed no GTP reactivity. Importantly,
AlA, PgA, and TIPSA are new functional monomers applicable
for the anionic polymerization method, and their polymers
should be expected to serve as precursors for producing various
macromolecular architectures.
Figure 3. Chain extensions of MA, EA, nBA, and MEA produced by
the sequential GTPs (PMA (●), PEA (red ■), PnBA (violet ▲), and
PMEA (green ▼)).
the postpolymerizations were carried out nine times, which
promises the synthesis of various block acrylate polymers.
For the synthesis of block acrylate polymers, we synthesized
the AB and BA diblock copolymers using the alkyl acrylate of
nBA and the functional acrylates of MEA, AlA, and PgA. Table
S6 summarizes the results of the block copolymerization under
the condition of the ([Mfirst + Msecond]0/[iPr-SKA]0/
Synthesis of Di- and Multiblock Acrylate Polymers.
The Me SiNTf -catalyzed GTP using the initiator of iPr-SKA
3
2
was an efficient controlled/living system for producing well-
defined acrylate homopolymers, which should be applicable to
the synthesis of acrylate block polymers. Thus, we first
investigated the stability of the propagating chain end of the
acrylate polymer by a chain extension experiment. For the
postpolymerizations of MA, EA, nBA, and MEA, the first GTP
[
L
Me SiNTf ] , of 25 + 25/1/0.02 and the [M] of 1.0 mol
3 2 0 0
−1
in toluene at room temperature. In the case of nBA with
was carried out under the conditions for the [M]first/[iPr-SKA]
0
MEA, MEA was added as the second monomer to the reaction
mixture after the first GTP of nBA was completed. The product
of the first GTP showed a monomodal molecular weight
distribution in the SEC trace, which shifted to a higher
molecular weight region in the SEC trace of the product of the
second GTP, while keeping a narrow polydispersity, as shown
in Figure 5a. The Mn,NMR increased from 3360 to 6640 g mol−
and the M /M s decreased from 1.09 to 1.04 after the block
−1
of 20 and the [M] of 1.0 mol L in toluene at room
0
temperature, after all the first monomer was consumed, the
second GTP was sequentially started by adding the second
monomer with [M]second/[iPr-SKA] , and the same procedure
0
was repeated for another eight times. The postpolymerization
results for MA, EA, nBA, and MEA are listed in Tables S2, S3,
S4, and S5, respectively. The molecular weight (Mn,NMR) of the
obtained polymers linearly increased with the increasing
1
w
n
copolymerization. The structure of PnBA-b-PMEA was
1
number of GTPs, as shown in Figure 3; from the M
of
n,NMR
confirmed by a H NMR measurement (Figure S7).
1
−1
1
920 g mol− for (PMA) to the M
of 17 380 g mol for
1
n,NMR
Alternatively, MEA was first polymerized to form the PMEA
−
1
−1
−
1
(
(
(
PMA) , from 2100 g mol for (PEA) to 20 230 g mol for
PEA) , from 2800 g mol for (PnBA) to 26 100 g mol for
PnBA) , and from 2770 g mol for (PMEA) to 26 760 g
with the Mn,NMR of 3480 g mol , and nBA was then
subsequently polymerized to produce the PMEA-b-PnBA with
1
0
1
−1
−1
10
1
−1
−1
1
0
1
the Mn,NMR of 6860 g mol and the M /M of 1.05. For the
w
n
−1
mol for (PMEA) . All the Mn,NMRs of the obtained acrylate
block copolymerization of nBA with AlA, the PnBA-b-PAlA and
PAlA-b-PnBA diblock copolymers had the well-controlled
1
0
polymers well agreed with the Mn,calcds. In addition, Figure 4
−1
shows the monomodal SEC traces of (PMA) , (PEA) ,
Mn,NMRs of 6240 and 6580 g mol , respectively. The M /M
n
n
w n
(
PnBA) , and (PMEA) , and the molecular weight distributions
of PnBA-b-PAlA was as low as 1.07, while that of PAlA-b-PnBA
was relatively high at 1.13 due to a small peak observed in the
low molecular weight region of the SEC trace (Figure 5b). This
small peak was attributed to the unreacted PAlA, meaning that
the second GTP of nBA initiated by the propagating PAlA
n
n
were as narrow as the M /M s of 1.02−1.10 for (PMA) , 1.02−
w
n
n
1
.09 for (PEA) , 1.03−1.11 for (PnBA) , and 1.02−1.11 for
n
n
(
PMEA) . These results strongly indicated that the propagating
n
chain end should retain the structure of iPr-SKA even though
E
DOI: 10.1021/ma502298v
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Figure 4. SEC traces of (a) (PMA) , (b) (PEA) , (c) (PnBA) , and (d) (PMEA) obtained from the sequential GTPs of MA, EA, nBA, and MEA
n
n
n
n
−1
(
eluent, THF; flow rate, 1.0 mL min ).
−1
PEHA-b-PnBA-b-PEA triblock terpolymer with 4390 g mol ,
which agreed with the Mn,calcd.s of 1940, 3220, and 4220 g
−1
mol , respectively. The SEC traces of the homo, diblock, and
triblock polymers were monomodal and the polydispersity
(
M /M ) decreased from 1.11 to 1.07, as shown in Figure 6a.
w n
This procedure was repeated three more times. The SCE traces
of the multiblock polymers shifted to a higher molecular weight
region with the increasing number of sequential GTPs.
Similarly, the (PnBA-b-PEA-b-PMEA-b-PMA)3 dodecablock
quaterpolymer was synthesized by the sequential Me SiNTf -
3
2
catalyzed GTP of nBA, EA, ME, and MA. Table S6 summarizes
the results of the sequential GTPs. With the increasing number
of sequential GTPs, the Mn,NMR of the multiblock polymers
theoretically increased and their SCE traces shifted to the
higher molecular weight region while maintaining a mono-
modal and narrow polydispersity (Figure 6b). For the synthesis
of the PdcPA-b-PnBA-b-PEHA-b-PEA-b-PMA-b-PcHA hexa-
block sestopolymer, the sequential Me SiNTf -catalyzed GTP
3
2
of dcPA, nBA, EHA, EA, MA, and cHA produced the homo-,
co-, ter-, quarter-, quinto-, and sestopolymers with predictable
M
s and narrow M /M s (Table S9). Figure 7 shows the
n,NMR
w n
1
H NMR spectra of the homo-, co-, ter-, quarter-, quinto-, and
sestopolymers in the polymerization mixtures after all the
monomers were consumed. The characteristic signal a observed
at 4.55 ppm was attributed to the methyne proton of the dcPA
unit and that at 3.63 ppm to the methoxy proton b of the
initiator residue (Figure 7a), that at 4.04 ppm to the methylene
proton c of the nBA unit (Figure 7b), that at 3.96 ppm to the
methylene proton d of the EHA unit (Figure 7c), that at 4.09
ppm to the methylene proton e of the EA unit (Figure 7d), that
at 3.64 ppm to the methoxy proton f of the MA unit (Figure
7e), and that at 4.73 ppm to the methyne proton g of the cHA
unit (Figure 7f). Similarly, the syntheses of (PEHA-b-PnBA-b-
PEA) and (PnBA-b-PEA-b-PMEA-b-PMA) were also con-
Figure 5. SEC traces of the diblock copolymers of (a) nBA and MEA,
(
b) nBA and AlA, and (c) nBA and PgA ([Mfirst + M
second
]0/[iPr-
−1
SKA] /[Me SiNTf ] , 25 + 25/1/0.02; [M] , 1.0 mol L ) (dashed
0
3
2
0
0
line, first polymer; solid line, block copolymer; eluent, THF; flow rate,
−
1
1
.0 mL min ).
chain end was slightly insufficient. The block copolymerization
of nBA and PgA produced the structurally defect-free PnBA-b-
−1
PPgA with the Mn,NMR and M /M of 6320 g mol and 1.07,
w
n
and the PPgA-b-PnBA with values of 6120 and 1.05,
respectively. These results indicated that amphiphilic and
reactive di- and multiblock acrylate copolymers can be
synthesized using the Me SiNTf -catalyzed GTP by the
4
3
firmed by the same method (Figures S13 and S14), and the
structures of the multiblock polymers were assigned as the final
3
2
1
products by the H NMR spectra (Figures S15−S17). Finally,
appropriate combinations of acrylate monomers.
we obtained the (PEHA-b-PnBA-b-PEA) dodecablock terpol-
Finally, multiblock acrylate polymers were synthesized by the
sequential Me SiNTf -catalyzed GTP using various acrylate
4
ymer with the Mn,NMR of 16 890 g mol− and the M /M of
1
w
n
3
2
1
.03, the (PnBA-b-PEA-b-PMEA-b-PMA) dodecablock qua-
monomers, as shown in Scheme 2. The synthetic result of the
3
−1
terpolymer with the Mn,NMR of 13 520 g mol and the M /Mn
(
PEHA-b-PnBA-b-PEA) dodecablock terpolymer is listed in
w
4
Table S7. Each GTP was carried out under the condition of the
of 1.02, and the PdcPA-b-PnBA-b-PEHA-b-PEA-b-PMA-b-
PcHA hexablock sestopolymer with the Mn,NMR of 9240 g
[
0
M] /[iPr-SKA] of 10 and the [Me SiNTf ] /[iPr-SKA] of
0 0 3 2 0 0
−1
.02. The first series of the sequential GTPs of EHA, nBA, and
mol and the M /M of 1.05 (Table 2). These results clearly
w n
−1
EA produced the PEHA with the Mn,NMR of 1980 g mol , the
PEHA-b-PnBA diblock copolymer with 3350 g mol , and the
indicated that the sequential GTP was an efficient method for
the syntheses of the well-defined multiblock acrylate polymers.
−1
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DOI: 10.1021/ma502298v
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Scheme 2. Synthesis of (PEHA-b-PnBA-b-PEA) Dodecablock Terpolymer, (PnBA-b-PEA-b-PMEA-b-PMA) Dodecablock
4
3
Quaterpolymer, and PdcPA-b-PnBA-b-PEHA-b-PEA-b-PMA-b-PcHA Hexablock Sestopolymer, as (ABC) , (ABCD) , and
4
3
ABCDEF Block Polymers by Sequential Group Transfer Polymerization
Figure 6. SEC traces for the synthesis of (a) (PEHA-b-PnBA-b-PEA) dodecablock terpolymer, (b) (PnBA-b-PEA-b-PMEA-b-PMA) dodecablock
4
3
−1
quaterpolymer, and (c) PdcPA-b-PnBA-b-PEHA-b-PEA-b-PMA-b-PcHA hexablock sestopolymer (eluent, THF; flow rate, 1.0 mL min ).
CONCLUSION
acrylate polymers. These GTP characteristics were caused by
the living nature that the triisopropylsilyl ketene acetal of the
initiator and the propagating chain-end efficiently reacted with
the acrylate monomer activated by the strong organic Lewis
acid, which was proved by the sequential GTP leading to the
polymer chain extension. In addition, the (PEHA-b-PnBA-b-
■
The organocatalyzed group transfer polymerization (GTP) of
acrylate monomers was studied in order to clarify its scope and
limits. The primary alkyl acrylate possessed a high GTP ability
compared to the secondary alkyl acrylate, and the tertiary alkyl
acrylate exhibited no polymerization ability. The GTPs of the
allyl acrylate and propargyl acrylate proceeded without gelation
and that of the triisopropylsilyl acrylate without cleavage of the
silyl ester linkage, correspondingly producing their well-defined
PEA)
PMA)
dodecablock terpolymer, (PnBA-b-PEA-b-PMEA-b-
dodecablock quaterpolymer, and PdcPA-b-PnBA-b-
4
3
PEHA-b-PEA-b-PMA-b-PcHA hexablock sestopolymer were
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1
Figure 7. H NMR spectra of the hexablock sestopolymer obtained by sequential Me SiNTf -catalyzed GTP; (a) PdcPA, (b) PdcPA-b-PnBA, (c)
3
2
PdcPA-b-PnBA-b-PEHA, (d) PdcPA-b-PnBA-b-PEHA-b-PEA, (e) PdcPA-b-PnBA-b-PEHA-b-PEA-b-PMA, and (f) PdcPA-b-PnBA-b-PEHA-b-PEA-b-
PMA-b-PcHA (solvent, CDCl3).
Table 2. Synthesis of (PEHA-b-PnBA-b-PEA) Dodecablock Terpolymer, (PnBA-b-PEA-b-PMEA-b-PMA) Dodecablock
4
3
Quaterpolymer, and PdcPA-b-PnBA-b-PEHA-b-PEA-b-PMA-b-PcHA Hexablock Sestopolymer by Sequential Me SiNTf -
3
2
a
Catalyzed Group Transfer Polymerization of EHA, nBA, EA, MEA, MA, dcPA, and cHA
1
c
Mn,NMR/g mol−1
b
d
n
block polymer
PEHA-b-PnBA-b-PEA)4
PnBA-b-PEA-b-PMEA-b-PMA)3
Mn,calcd./g mol−
M /M
w
(
(
16 580
13 420
16 890
13 520
9 240
1.03
1.02
1.05
PdcPA-b-PnBA-b-PEHA-b-PEA-b-PMA-b-PcHA
8 680
a
−1
Argon atmosphere; solvent, toluene; initiator, iPr-SKA; [M] , 1.0 mol L ; [M] /[iPr-SKA] , 10; [Me SiNTf ] /[iPr-SKA] , 0.02; temperature,
0
0
0
3
2
0
0
b
1
c
room temperature; polymerization time, 5 min; monomer conversion, > 99%. Determined by H NMR in CDCl . Calculated from ([M] /([iPr-
3
0
SKA] ) × (conv) × (MW of monomer); dcPA, 206.29; nBA, 128.17;EHA, 184.28; EA, 100.12; MA, 86.09; cHA, 154.21; MEA, 130.14) + (MW of
0
d
the initiator residue, 102.13). Determined by SEC in THF using poly(methyl methacrylate) standards.
synthesized by the sequential GTP method. To the best of our
knowledge, the synthesis of the multiblock acrylates polymers
was the first reliable demonstration of the precisely designed
acrylate polymers using the living anionic polymerization, i.e.,
the organocatalyzed GTP.
AUTHOR INFORMATION
■
*
Corresponding Author
(T.K.) Telephone and Fax: +81-11-706-6602. E-mail:
kakuchi@poly-bm.eng.hokudai.ac.jp.
Notes
The authors declare no competing financial interest.
ASSOCIATED CONTENT
■
ACKNOWLEDGMENTS
*
S
Supporting Information
■
Additional data for the polymerizations of MA, EA, EHA, nBA,
cHA, dcPA, and tBA (tables and SEC traces), postpolymeriza-
tions of MA, EA, nBA, and MEA (tables and H NMR spectra),
diblock copolymerizations (tables and H NMR spectra), and
multiblock polymerizations (tables and H NMR spectra). This
material is available free of charge via the Internet at http://
pubs.acs.org.
This work was financially supported by the MEXT (Japan)
program “Strategic Molecular and Materials Chemistry through
Innovative Coupling Reactions” of Hokkaido University and
the MEXT Grant-in-Aid for Scientific Research on Innovative
Areas “Advanced Molecular Transformation by Organo-
catalysts”. K.T. and Y.C. were supported by the Grant-in-Aid
for the Japan Society for the Promotion of Science (JSPS)
Fellows.
1
1
1
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Article
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DOI: 10.1021/ma502298v
Macromolecules XXXX, XXX, XXX−XXX