Cationic polymerization of isobutyl vinyl ether coinitiated with heteropolyacid or its salts in aqueous medium

Article abstract of DOI:10.1002/pola.26431

The suspension cationic polymerization of isobutyl vinyl ether (IBVE) in aqueous medium could be achieved by using H₃PW₁₂O ₄₀, AlPW₁₂O₄₀, FePW₁₂O₄₀, K₃PW₁₂O₄₀, or Na₃PW ₁₂O₄₀ as efficient water-tolerant coinitiators in the presence of HCl. The addition reaction of IBVE with H₂O occurred to form IBVE-H₂O adduct and then subsequent decomposition immediately took place or turned to acetaldehyde diisobutyl acetal (A) in the presence of AlPW₁₂O₄₀, and (A) decomposed rapidly to form 2-isobutanol (B) and acetaldehyde (C). Cationic polymerization of IBVE in aqueous medium was promoted greatly with increasing HCl concentration and proceeded extremely rapidly to get high polymer yield even at low concentration of AlPW ₁₂O₄₀ of 0.3 mM. A sufficient amount of HCl was needed to decrease the hydrolysis of initiator IBVE-HCl and to accelerate the polymerization in aqueous medium simultaneously. The yield and molecular weight of poly(IBVE) increased with increasing concentrations of HCl and AlPW ₁₂O₄₀ or with decreasing temperature. The isotactic-rich poly(IBVE)s with m diad of around 60%, having M_n of 1200-4500 g mol^-1 and monomodal molecular weight distribution could be obtained via cationic polymerization of IBVE in aqueous medium. This is the first example of cationic polymerization of IBVE in aqueous medium coinitiated by heteropolyacid and its salts.

Full text of DOI:10.1002/pola.26431

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Cationic Polymerization of Isobutyl Vinyl Ether Coinitiated with
Heteropolyacid or its Salts in Aqueous Medium
Qiang Huang, Yixian Wu, Jie Dan
State Key Laboratory of Chemical Resource Engineering, Key Laboratory of Carbon Fiber and Functional Polymers
(
Ministry of Education), Beijing University of Chemical Technology, Beijing 100029, China
Correspondence to: Y. Wu (E-mail: yxwu@263.net)
Received 22 June 2012; accepted 13 October 2012; published online 8 November 2012
DOI: 10.1002/pola.26431
ABSTRACT: The suspension cationic polymerization of isobutyl
medium simultaneously. The yield and molecular weight of pol-
y(IBVE) increased with increasing concentrations of HCl and
AlPW12 40 or with decreasing temperature. The isotactic-rich pol-
y(IBVE)s with m diad of around 60%, having M of 1200–4500 g
vinyl ether (IBVE) in aqueous medium could be achieved by using
H
3
PW12
O
40, AlPW12
as efficient water-tolerant coinitiators in the presence of HCl. The
addition reaction of IBVE with H O occurred to form IBVE–H
O
40, FePW12
O
40, K
3
PW12
O
40, or Na
3
PW12
O
40
O
n
ꢀ1
2
2
O
mol and monomodal molecular weight distribution could be
obtained via cationic polymerization of IBVE in aqueous medium.
This is the first example of cationic polymerization of IBVE in
aqueous medium coinitiated by heteropolyacid and its salts.
VC 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.
adduct and then subsequent decomposition immediately took
place or turned to acetaldehyde diisobutyl acetal (A) in the pres-
ence of AlPW12O40, and (A) decomposed rapidly to form 2-isobu-
tanol (B) and acetaldehyde (C). Cationic polymerization of IBVE in
aqueous medium was promoted greatly with increasing HCl con-
centration and proceeded extremely rapidly to get high polymer
2013, 51, 546–556
yield even at low concentration of AlPW12
O
40 of 0.3 mM. A suffi-
KEYWORDS: aqueous medium; cationic polymerization; hetero-
polyacid salts; initiators; poly(isobutyl vinyl ether); poly(vinyl
ethers)
cient amount of HCl was needed to decrease the hydrolysis of ini-
tiator IBVE–HCl and to accelerate the polymerization in aqueous
INTRODUCTION The controlled/living cationic polymeriza-
tions of vinyl monomers, such as isobutylene, styrene (St),
or isobutyl vinyl ether (IBVE) have been achieved by using
initiator/coinitiator initiating system in organic solvent
under strictly anhydrous conditions, in which the coinitiator
is Lewis acid, such as AlCl , TiCl , BF , SnCl , AlEtCl ,
polymerizations of pMOS or IBVE could be induced by using
rare earth metal triflate [Ln(OTf)
; Ln ¼ Yb, Sc, Dy, Sm, Gd,
3
and Nd; OTf ¼ OSO
CF ] in conjunction with hydrogen chlo-
2
3
ride–vinyl monomer adduct in aqueous medium. The cationic
polymerization of pMOS in aqueous medium was quite slow to
reach 98% of monomer conversion after polymerization for
3
4
3
4
2
ꢀ
1
1
200 h, and poly(pMOS) with M of 2000–4000 g mol were
s n
AlMeCl
2
, or ZnI
2
.
All these Lewis acids are moisture-sensi-
6
2
obtained. The cationic polymerizations of pMOS could also be
carried out with Lewis acid-surfactant combined catalysts,
such as trisdodecyl sulfate ytterbium starting from Lewis acid
tive and decomposed in the presence of water. Conversely,
in general, the presence of water above certain concentration
will terminate the cationic polymerization. Boron trifluoride
2
5,7
YbCl or Yb(OTf) . Photoinitiated cationic polymerization of
3
3
etherate (BF ꢁOEt ) was used for cationic polymerization of
3
2
IBVE in aqueous medium was conducted by using diphenylio-
donium iodide in the presence of Yb(OTf) , resulting in low
styrene and its derivatives only in the presence of a small
3
,4
3
amount of water. However, water is an economically envi-
ronmental-friendly green solvent in chemical reactions. Thus,
the cationic polymerizations in aqueous medium really
ꢀ
1 8
molecular weight (M ꢂ2000 g mol ). Transition metal (Sn,
n
Zn, and Cu) triflates and their tetrafluoroborates were also
used as water-tolerant Lewis acids for emulsion cationic poly-
merization of pMOS in heterogeneous aqueous medium, while
it took long time (ꢂ100 h) to get high monomer conversion of
2
,5
become a big challenge in this area.
Several research groups have focused on the cationic polymer-
5–11
6
ization of vinyl monomer in aqueous medium recently.
90%. The miniemulsion cationic polymerization of pMOS
Lanthanide triflates was introduced as a water-tolerant Lewis
acid in cationic polymerization of certain monomers including
IBVE and p-methoxystyrene (pMOS) in the presence of
could be carried out by dodecylbenzenesulfonic acid and sur-
ꢀ
1
factant (INISURF), leading to low M
(ꢂ1000 g mol ), and M
n
n
increased slowly with monomer conversion due to critical
degree of polymerization (DP) effect when monomer
5
–9
6
water. Sawamoto and his coworkers reported that cationic
V
C
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conversion ꢃ20%. Stable inverse emulsion cationic polymer-
ization of pMOS was conducted in water by using DBSA/
Yb(OTf) system to produce low molecular weight polymers
3
ꢀ
1 9
(
M ¼ 1000–3000 g mol ).
n
Tri(pentafluorophenyl)borane, B(C F ) was also reported as
6
5 3
an effective water-tolerant Lewis acid for cationic polymer-
izations of pMOS, styrene, cyclopentadiene, or isoprene in
aqueous medium to produce the corresponding polymers
ꢀ
1
with low molecular weight (M < 4000 g mol ) and having
n
1
0
hydroxyl terminal groups. The cationic polymerization of
isobutylene in aqueous suspension could be induced
by using chelating diboranes (C F -1,2-[B(C F ) ]) as
6
4
6 5 2
1
1
coinitiatortor.
Heteropolyacid has been widely used in organic synthesis
and in polymerization. Dodecatungstophosphate acid
(
H PW O ) was provided as an efficient catalyst in bulk
3 12 40
cationic polymerization of tetrahydrofuran (THF) using ethyl-
ene oxide as promoter to produce polyTHF with M in the
The bulk or solution poly-
n
ꢀ
1 12
range of 1000–3000 g mol
.
merizations of IBVE, styrene, and IB in dry organic solvents
were carried out with H PW O , resulting in formation of
3
12 40
FIGURE 1 GPC traces of poly(IBVE) obtained from cationic po-
ꢀ
1
12–18
ꢄ
low molecular weight polymers (M < 3000 g mol ).
lymerization of IBVE in CH
2
Cl
2
at different times at 0 C. [IBVE]
n
H PW O , 12-molybdophosporic acid (H MoW O ) and
¼ 1 M, AlPW12 40 ¼ 30 mg, [IBVE–HCl] ¼ 25 mM.
O
3
12 40
3
12 40
their homologous salts (NH
4
)
3
PW12O
4 3 40
40, (NH ) MoW12O
were used to initiate cationic polymerization of styrene in
CH Cl , and H PW O has the highest catalytic activity due
w n
lar weight distribution (MWD) (M /M ) are given in Figure
2
2
3
12 40
1. It can be seen from Figure 1 that cationic polymerization
of IBVE in CH Cl proceeded rapidly to get 30% of polymer
to the acidity strength order of H PW O > H PMo O
>
3
12 40
5,16
3
12 40
2
2
1
(
NH ) PW O > (NH ) PMo O .
The heterogeneous
4
3
12 40
4 3
12 40
yield after 2 min and 100% of polymer yield after 20 min,
living cationic polymerization of IBVE could be achieved by
ꢀ1
and poly(IBVE)s with M of 4100–4700 g mol and mono-
n
ꢄ
17
using H
3
PW12O
40 in the presence of Me
2
S at ꢀ30 C. Very
modal MWD (M /M ¼ 2.4–2.7) could be obtained. The M
w
n
n
recently, living cationic polymerization of IBVE could be
achieved by using HCl in the presence of ether as the
kept almost unchanged and number of polymer chains (N)
ꢀ5
ꢀ5
increased gradually from 1.46 ꢅ 10 mol to 4.76 ꢅ 10
HClꢁEt O acts as protonogen and plays both as an activator
2
mol with prolonging polymerization time from 2 to 20 min.
These experimental results indicate that slow initiation and
rapid propagation took place in the heterogeneous cationic
polymerization of IBVE coinitiated by AlPW O in CH Cl .
1
7
and initiator. (NH )
H PW O was used to coinitiate
2.5 0.5 12 40
4
the cationic polymerization of IB in an inert hydrocarbon
18
solvent to produce highly reactive polyisobutylenes.
Aluminum dodecatungstophosphate (AlPW12 40) is a highly
12
40
2
2
O
The chemical structure of terminal groups in poly(IBVE) was
water-tolerant Lewis acid and an efficient catalyst for or-
ganic synthesis, such as protection of thiols and chemoselec-
1
examined by NMR spectroscopy, and the representative
H
13
and C NMR spectra are shown in Figure 2(a,b) respectively.
It can be clearly observed from Figure 2(a) that the charac-
tive synthesis of geminal diacetates (acylals) in CH CN or
3
CH Cl solution but never for cationic polymerization of
2
2
1
9
teristic signal at d ¼ 1.15 ppm is assigned to ACH group
3
vinyl monomer in aqueous medium.
extended our study to the cationic polymerization of IBVE
with AlPW12 40 or other salts, such as FePW12
K PW O , and Na PW O in the presence of large
Therefore, we
(
peak 1) at head group of poly(IBVE) chain. Conversely, the
characteristic resonances at d ¼ 4.56 ppm and d ¼ 9.81
O
40
O ,
ppm are assigned to ACHAOA (peak 7), and ACH ¼¼ O (peak
3
12 40
3
12 40
10) terminal groups, respectively. The content of ACHAOA
amount of water in this current paper.
terminal group was determined to be 74% as polymerization
20,21
RESULTS AND DISCUSSION
was quenched with CH OH or i-BuOH.
There was no sig-
3
nal (d
¼
6.1 ppm) belonging to the structure of
Cationic Polymerization of IBVE with IBVE–HCl/
AlPW12O40 Initiating System in CH Cl
13
ACH ¼¼ CHAOiBu due to b-elimination. The C NMR analysis
in Figure 2(b) was applied to examine stereoregularity of the
resulting poly(IBVE) chains, and the meso diad was
determined to be 67%, which is a similar value to those of
poly(IBVE) obtained with various metal halides in organic
2
2
The control experiments of heterogeneous cationic polymer-
ization of IBVE were performed using AlPW O in conjunc-
1
2 40
ꢄ
tion with IBVE–HCl in CH Cl at 0 C for comparison. Lewis
2
2
acid AlPW12O40 activated the CACl bond in IBVE–HCl to
induce cationic polymerizations. The representative gel
1
solvents.
permeation chromatography (GPC) traces of resulting
Moreover, the cationic polymerization of IBVE in CH Cl2
2
poly(IBVE)s and the data of polymer yield, M , and molecu-
could also be induced with H O/AlPW O initiating system
n
2
12 40
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1
13
ꢄ
3 2 2
FIGURE 2 H and C NMR spectra of poly(IBVE) (P ) in CH Cl at 0 C.
in the absence of IBVE–HCl. Compared to the cationic poly-
could be obtained but oil-like organic phase was formed in
the reaction system. Therefore, it is necessary to get deep
investigation on the reason for no polymerization of IBVE
coinitiated by AlPW12O40 in water. The oil-like organic phase
merization of IBVE with IBVE–HCl/AlPW12O40 initiating sys-
tem in CH Cl , cationic polymerization of IBVE with H O/
2
2
2
AlPW O initiating system in CH Cl proceeded relatively
1
2
40
2
2
1
slowly and produce 33% of polymer after 20 min and 96%
of polymer after 60 min, respectively.
was taken out at different reaction times for H NMR charac-
1
terization, and the corresponding H NMR spectra are given
in Figure 3. The characteristic resonances at d ¼ 0.96 ppm
(peak a), d ¼ 1.98 ppm (peak b), and at d ¼ 3.97 ppm (peak
c) are assigned to methyl, methane, and methylene groups of
IBVE, respectively. Surprisingly, it can be observed that the
characteristic resonances at d ¼ 6.52 ppm (peak d) for
Cationic Polymerization of IBVE coinitiated by
AlPW12O40 in Aqueous Medium
Suspension cationic polymerization of neat IBVE with
AlPW O coinitiator was conducted in aqueous medium in
1
2 40
ꢄ
the absence of IBVE–HCl at 0 C. Unexpectedly, no polymer
ACH ¼¼ and d ¼ 4.16, 3.95 ppm (peak e) for ¼¼ CH of IBVE
2
1
40 at 0 ꢄC. IBVE ¼ 1 mL (7.7 mmol),
FIGURE 3 H NMR spectra of reaction mixtures of IBVE with water in the presence of AlPW12
O
[
AlPW12
O
40] ¼ 26 mM in water. H O ¼ 1 mL.
2
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FIGURE 4 IBVE conversion (a) and A% (b) with reaction time in aqueous medium at different concentrations of AlPW12
O40. IBVE ¼
ꢄ
7
.7 mmol, H
2
O ¼ 1 mL, T
p
¼ 0 C.
reduced gradually with prolonging reaction time and finally
disappeared. It means that IBVE had been converted to other
compounds in the presence of AlPW O . The extremely
molecules had been converted to A, B, and C in 3.8 h when
concentration of AlPW12 40 was 26 mM, while complete
conversion of IBVE took 10 h when concentration of
AlPW12 40 was 6 mM. The experimental results indicate that
IBVE conversion was significantly accelerated by increasing
AlPW12 40 concentration in the reaction system. On the ba-
O
1
2 40
unstable hemiacetal (IBVE–H O) formed by addition of dou-
O
2
ble bond of IBVE with H O catalyzed by AlPW O and then
2
12 40
rapidly decomposed to 2-isobutanol (B) and acetaldehyde
C). The decomposition of unstable hemiacetal to acetalde-
hyde was also observed in termination under the similar
O
1
(
sis of H NMR spectra, the molar percents of acetaldehyde
diisobutyl acetal A (A%) in organic phase with reaction time
2
0
at different concentrations of AlPW12
O40 are given in Figure
conditions in ref.
3
The characteristic resonances at d ¼
4(b). It can be seen from Figure 4(b) that all the A% was
.35 ppm (peak m) for ACH
2
A in 2-isobutanol (B) and at d
less than 100% since A was further decomposed to 2-isobu-
¼
2.21 ppm (peak n) and d ¼ 9.80 ppm (peak o) for ACH
3
1
tanol (B) and acetaldehyde (C) in the presence of AlPW12O
and ACH ¼¼ O in acetaldehyde (C) could be observed in
H
40
in aqueous medium according to the Ref. 22. When
NMR spectra. Conversely, IBVE–H O could also immediately
2
AlPW O concentration was 26 mM, A% was 40% within
12 40
react with 2-isobutanol (B) to create the relatively stable ac-
etaldehyde diisobutyl acetal (A). It can be also seen from
Figure 3 that the characteristic resonances at d ¼ 4.67 ppm
2
h and then decreased to 3% after prolonging reaction time
to 4.3 h. The similar results obtained at AlPW12 40 concen-
O
trations of 15 mM and 6 mM were shown in Figure 4(b).
(
peak i), d ¼ 3.35 ppm (peak h), and d ¼ 1.31 ppm (peak j)
The formation of adduct (A) in the presence of AlPW O in
12 40
are assigned to ACHA, ACH A, and ACH of acetaldehyde
2
3
water was elucidated in Scheme 1.
diisobutyl acetal (CH ACHA(OACH ACH(CH ) ) (A). The
3
2
3 2 2
conversions of IBVE with reaction time at different concen-
The cationic polymerization of IBVE in aqueous medium was
also conducted with IBVE–HCl/AlPW12O4 initiating system.
trations of AlPW O are shown in Figure 4(a). All the IBVE
1
2 40
4
SCHEME 1 Possible mechanism for reaction of IBVE in aqueous medium catalyzed by AlPW12O .
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FIGURE 5 H NMR spectra of IBVE–HCl and the organic mixtures after IBVE–HCl was added into water containing AlPW12
40
O .
IBVE–HCl ¼ 1 mL, [AlPW12 40] ¼ 26 mM in water. H O ¼ 1 mL.
O
2
However, no polymer could be obtained as well. The possible
reason for no polymerization of IBVE in aqueous medium
conjunction with AlPW O , a large amount of HCl ([HCl] ¼
1
2 40
3.56 M) was introduced into the aqueous medium. As
expected, the cationic polymerization of IBVE coinitiated by
was that the sensitive CACl dormant bond of CH ACH(Oi-
3
ꢄ
Bu)Cl reacted with water to form hemiacetal and then the
AlPW O could be achieved in aqueous medium at 0 C in
12 40
unstable hemiacetal decomposed to form 2-isobutanol (B)
the presence of HCl. The influence of polymerization time on
poly(IBVE) yield, number average molecular weight (M ),
and MWD (M /M ) and the first-order kinetic plot (insert) is
and acetaldehyde (C) in the presence of AlPW12
O
40, which is
n
6
(a)
similar to the results reported by Sawamoto et al.
To con-
w
n
firm the hydrolysis of IBVE–HCl adduct, IBVE–HCl adduct
shown in Figure 6. It can be seen from Figure 6 that cationic
polymerization of IBVE proceeded extremely rapidly and
reached polymer yield of 62% within 30 s. The addition
reaction of HCl with IBVE occurred immediately to form
IBVE–HCl adduct and hydrolysis of IBVE–HCl was decreased
or even suppressed in the presence of a large amount of
HCl. Then, IBVE–HCl formed in situ could be used as an ini-
tiator in conjunction with AlPW O to induce the cationic
1
was added into water in the presence of AlPW O .
H
1
2 40
NMR spectra of IBVE–HCl and the organic mixtures after
IBVE–HCl was added into water containing AlPW O for
12 40
1
0 min are given in Figure 5. The characteristic resonances
at d ¼ 0.93 ppm (peak p), d ¼ 1.89 ppm (peak q), and d ¼
.23, 3.67 ppm (peak r) are assigned to isobutyl group of
3
IBVE–HCl. It can be clearly observed that the characteristic
12 40
resonances at d ¼ 5.71 ppm (peak s) for ACHClA and at d
polymerization of IBVE in aqueous medium. The polymeriza-
tion was first order with respect to IBVE concentration
within 20 s and the apparent constant of propagation rate
¼
1.79 ppm (peak t) for CH ACHClA in IBVE–HCl disap-
3
peared after IBVE–HCl mixed with water for 10 min in the
A
ꢀ1
presence of AlPW12 40. The characteristic resonances of the
O
(k ) was determined to be 0.0503 s . The number average
p
organic mixture for compounds of acetaldehyde diisobutyl
acetal (A), isobutanol (B), and acetaldehyde (C) are gener-
ated in Figure 5. Therefore, it can be concluded that IBVE–
HCl was rapidly hydrolyzed in water in the presence of
AlPW O , leading to formation of IBVE–H O and acetalde-
hyde diisobutyl acetal (A), and then decomposed to isobuta-
nol (B) and acetaldehyde (C). Very importantly, it can be
recognized that hydrolysis of IBVE–HCl resulted in formation
of HCl.
molecular weights and MWDs of the resulting poly(IBVE)
polymers were almost independent on polymerization time.
The cationic polymerization of IBVE coinitiated by
AlPW O in aqueous medium was further conducted at dif-
12 40
1
2
40
2
1
ferent concentrations of HCl, and the H NMR characteriza-
tion on the reaction mixtures in organic phases is presented
in Figure 7. It can be found that IBVE was consumed com-
pletely and the products in organic phases were the mixtures
of poly(IBVE), acetaldehyde diisobutyl acetal (A), isobutanol
(B), and acetaldehyde (C). The cationic polymerization pro-
ceeded accompanied with side reactions, such as hydrolysis
To decrease or even suppress the hydrolysis of IBVE–HCl
and to induce the cationic polymerization by IBVE–HCl in
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n w n
FIGURE 6 Effect of polymerization time on polymer yield, M and M /M and first-order kinetic plot (insert) for cationic polymer-
ization of IBVE coinitiated by AlPW12
O
40 in aqueous medium in the presence of HCl at 0 ꢄC. IBVE ¼ 3.85 mmol, [AlPW12
40] ¼ 2.6
O
mM, [HCl]¼ 3.56 M.
1
FIGURE 7 H NMR spectra of organic mixtures of poly(IBVE), IBVE–H
2
O (A), isobutanol (B) and acetaldehyde (C) at different
concentrations of HCl at 0 ꢄC. IBVE ¼ 3.85 mmol [AlPW12
O40] ¼ 2.6 mM, t ¼ 5 min.
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FIGURE 8 Effect of HCl concentration on poly(IBVE) yield and molar percent of IBVE–H
2
O (C
A
%) (a) and GPC traces of the corre-
sponding poly(IBVE) products obtained at different HCl concentrations (b). IBVE ¼ 3.85 mmol, [AlPW12
5 min.
O
40] ¼ 2.6 mM, T ¼ 0 ꢄC, t
¼
of some IBVE–HCl to form acetaldehyde diisobutyl acetal (A)
and then partial decomposition of (A) to create isobutanol
aqueous medium as well, leading to increases in polymer
yield and molecular weight of polymer.
(
B) and acetaldehyde (C) in the presence of AlPW O .
12 40
Conversely, AlPW12O40 was considered as a coinitiator to
Effect of HCl concentration on poly(IBVE) yield and molar
percent of acetaldehyde diisobutyl acetal (A) (C %) and GPC
traces of the corresponding poly(IBVE) products obtained at
different HCl concentrations are given in Figure 8. It can be
clearly observed that no polymer could be obtained at HCl
concentration of 0.94 M while the poly(IBVE) yield increased
generate initiating species to induce cationic polymerization
of IBVE in aqueous medium containing a large amount of
HCl as no polymer could be obtained without AlPW O in
A
12 40
the control experiment at high HCl concentration of 5 M
within 10 min. The result is similar to the previous report
in which CH ACH(OiBu)Cl alone did not induce polymeriza-
3
from 10% to 83% and C % in organic mixtures decreased
A
tions at all or polymerization of IBVE by dry HCl gas in hex-
from 42.0% to 1.2% with increasing concentration of HCl in
water from 1.6 M to 6.3 M. Therefore, the hydrolysis of
some IBVE–HCl in the presence of AlPW O could be effec-
tively decreased by increasing HCl concentration, leading to
improvements in polymerization and polymer yield. As
shown in Figure 8, all the GPC traces of the resulting
poly(IBVE)s at four different concentrations of HCl exhibit
monomodal molecular weight distributions. The number av-
6(a),17(b)
ꢄ
ane or toluene at ꢀ40 C did not proceed.
Effect of
concentration of AlPW O on cationic polymerization of
12 40
1
2 40
IBVE in aqueous medium in the presence of sufficient
ꢄ
amount of HCl ([HCl] ¼ 5M) at 0 C was investigated. Inter-
estingly, the cationic polymerization of IBVE in aqueous me-
dium could be induced even at very low AlPW12O40 concen-
tration of 0.3 mM with polymer yield of 54% within 10 min
and accelerated to 95% of polymer yield by increasing
erage molecular weight (M ) of poly(IBVE) increased from
1
persity index (M /M ) increased from 2.3 to 4.4 with
n
[
AlPW O ] to 3 mM, which was far less than that of
12 40
ꢀ
1
200 to 4500 g mol , MWD became broader and polydis-
Ln(OTf) ([Ln(OTf) ] ¼ 150 or 300 mM) in the cationic pol-
3
3
w
n
6
ymerizations of IBVE or pMOS in aqueous medium. The
increasing HCl concentration from 2.2 M to 7.8 M. These
results further support that cationic polymerization of IBVE
in aqueous medium could be accelerated by increasing HCl
concentration in reaction system. HCl played very important
roles in reacting with IBVE to form IBVE–HCl initiator, and
conversely, in decreasing or even suppressing the hydrolysis
of CACl bond in IBVE–HCl and poly(IBVE) chain ends. The
hydrolysis of initiating species IBVE–HCl should be pre-
vented prior to polymerization by increasing the concentra-
tion of HCl in the presence of large amount of water. A large
amount of HCl was also needed to decrease the termination
of the resulting poly(IBVE) propagating species via route B
during polymerization in the presence of a large amount of
water (medium). Therefore, the large amount of HCl is
needed to suppress the initial hydrolysis of the initiating
species IBVE–HCl and to promote IBVE polymerization in
molecular weight slightly increased from 3300 to 3700 g
ꢀ1
mol with increasing AlPW12
O
40 concentration from 0.3 to
3
mM.
The chemical structures of head or terminal groups and ster-
eoregularity of the resulting poly(IBVE) chains obtained via
cationic polymerization of IBVE coinitiated by AlPW12O in
40
aqueous medium containing sufficient amount of HCl was
1
13
examined by H and C NMR spectroscopy. The representa-
tive spectra of poly(IBVE) are given in Figure 9. Poly(IBVE)
with ACH3 head group (d ¼1.15 ppm, peak 1) indicating
that the cationic polymerization of IBVE was initiated from
IBVE–HCl adduct. The growing polymer chain could not be
terminated by adding CH OH as the characteristic resonance
3
at (d ¼ 4.56 ppm (peak 7) for ACHAOA terminal group was
undetectable, which is different from that in poly(IBVE)
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1
13
ꢄ
FIGURE 9 H and C NMR spectra of ploy(IBVE) (P ) obtained in aqueous medium at 0 C.
6
obtained via cationic polymerization in organic solvent
CH Cl ). All the growing polymer chains were terminated
containing a sufficient amount of HCl was terminated by H2O
in aqueous phase and both aldehyde and alkenal terminal
groups existed in poly(IBVE) chains via elimination of 2-
isobutanol.
(
2
2
by water to create ACH ACH(OiBu)OH terminal group. How-
2
ever, the unstable ACH ACH(OiBu)OH terminal group was
2
immediately transferred to ACH ACH ¼¼ O aldehyde terminal
2
As well known, polymerization temperature (T) is a critical
factor in cationic polymerization. To examine the effect of po-
lymerization temperature, cationic polymerizations of IBVE
coinitiated with AlPW O were conducted at various tem-
group by elimination of 2-isobutanol and further to
ACH ¼¼ CHACH ¼¼ O alkenal terminal group by elimination of
20,21
another 2-isobutanol from aldehyde terminal group.
12 40
Therefore, poly(IBVE)s with terminal groups containing 76%
ꢄ
peratures ranging from 0 to 50 C. The polymer yield
of ACH ACH ¼¼ O (d ¼9.81 ppm, peak 10) and 24% of
2
decreased from 63% to 21% and Mn of poly(IBVE)
ACH ¼¼ CHACH ¼¼ O (d ¼ 9.5 ppm, peak 16) could be obtained
ꢀ1
decreased from 4500 to 1800 g mol with increasing tem-
via cationic polymerization of IBVE coinitiated by AlPW12O
40
ꢄ
perature from 0 to 50 C. Higher temperature might acceler-
13
in aqueous medium. It can be determined from C NMR
analysis that poly(IBVE) chains with 60% of meso diad (m)
could be obtained via cationic polymerization of IBVE in
aqueous medium containing sufficient amount of HCl, which
is similar to that in poly(IBVE) obtained via cationic poly-
merization of IBVE coinitiated in CH Cl (shown in Fig. 2).
ate the side reactions, such as chain transfer and termina-
tion. The inverse effect of polymerization temperature on
molecular weight has been quantitatively expressed by
23–25
Arrhenius equation, that is, ln M ¼ ln A ꢀ DE/RT.
The
n
overall activation energy difference (DE or E ) was calcu-
from the slope of the linear
Arrhenius plot of ln(M ) versus 1/T for the temperature
DP
2
2
ꢀ1
lated to be ꢀ13.5 kJ mol
On the basis of the above observations and experimental
results, a possible mechanism of cationic polymerization of
IBVE coinitiated by AlPW O in aqueous medium contain-
n
ꢄ
interval from 0 to 50 C, shown in Figure 10.
1
2 40
ing a sufficient amount of HCl was proposed, as shown in
Scheme 2. IBVE–HCl adduct first formed by addition reaction
of IBVE with HCl. The hydrolysis of IBVE–HCl in the pres-
ence of AlPW O via route A could be effectively decreased
Cationic Polymerization of IBVE Coinitiated by
H PW12O40 and its Salts in Aqueous Medium
3
A series of heteropolyacid and its salts, such as H PW O ,
3
12 40
AlPW O , FePW O , K PW O , or Na PW O , were
1
2
40
12 40
12 40
3
12 40
3
12 40
by introduction of a sufficient amount of HCl. In the pres-
ence of a sufficient amount of HCl, the initiating species was
formed from IBVE–HCl in conjunction with AlPW O to
used as coinitiators for the cationic polymerizations of IBVE
in aqueous medium containing a large amount of HCl
([HCl]¼ 4 M and 6 M). The polymer yield, M , and polydis-
12
40
n
induce cationic polymerization of IBVE via route B. A large
amount of HCl was needed to promote the polymerization
coinitiated by AlPW O and to decrease the hydrolysis of
persity index (M /M ) of poly(IBVE)s obtained by
w
n
H PW O and it salts are presented in Figure 11. The ex-
3
12 40
perimental results illustrate that all heteropolyacid
H PW O and its salts were efficient to coinitiate the cati-
1
2 40
IBVE–HCl catalyzed by AlPW O . The initiation, propaga-
1
2
40
3
12 40
tion, and termination of IBVE polymerization proceeded at
the interface between organic IBVE droplet and aqueous
phase containing AlPW O and HCl. The cationic polymer-
onic polymerization of IBVE in aqueous medium, in which
polymer yield could reach about 80% by using H PW O
3
12 40
or AlPW12O40 as a coinitiator at [HCl] ¼ 6 M. The number
1
2 40
ization of IBVE coinitiated by AlPW O in aqueous medium
average molecular weights of the resulting poly(IBVE)s
1
2 40
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SCHEME 2 Possible mechanism of cationic polymerization of IBVE coinitiated by AlPW12
O40 in aqueous medium containing a suf-
ficient amount of HCl.
obtained in aqueous medium were in the range of 2000–
tungstophosphate (K PW O ), sodium dodecatungstophos-
3 12 40
phate (Na PW O ) were synthesized with quantitative
3 12 40
ꢀ
1
3
800 g mol , and the polydispersity indexes of polymers
kept at around 3.0, which are closed to those of polymers
obtained in organic solvent CH Cl . We proposed the similar
results were due to the same PW O
yields by reaction of H PW O
with Al(NO ) ꢁ9H O,
3
12 40
3 3
2
2
2
Fe(NO
3
27
)
3
ꢁ9H
2
O, K
2
CO
3
2 3
, or Na CO aqueous solution, respec-
3
ꢀ
anion in the poly-
tively. IBVE–HCl adduct was synthesized by bubbling dry
HCl gas through a solution of IBVE in hexane (1.0 M) at
1
2 40
merization system with a sufficient amount of HCl.
ꢄ
20
0
C. HCl was generated by dropping concentrated sulfuric
EXPERIMENTAL
acid into powdery sodium chloride and dried by passing it
Materials
IBVE (98%, Aldrich) was washed with 10% aqueous sodium
hydroxide and then with water, dried overnight by potassium
hydroxide, and distilled twice from calcium hydride (CaH
2
)
before use. Dichloromethane (CH Cl ; AR; Beijing Yili Fine
2
2
Chemical Co.), n-hexane (n-Hex; AR.; Beijing Yili Fine Chemi-
cal Co.), and THF (AR; Beijing Yili Fine Chemical Co.) were
26
distilled from CaH2 before use as described previously.
Dodecatungstophosphoric acid hydrate (H PW O ꢁnH O;
3
12 40
2
AR., Aldrich, H
2
O ¼ 6 wt %), aluminum nitrate nonahydrate
(
Al(NO ) ꢁ9H O; AR, Beijing Chemical Co.), potassium car-
3
3
2
bonate (K CO , AR, Beijing Chemical Co.), sodium carbonate
2
3
(
(
(
Na CO ; AR; Beijing Chemical Co.), iron nitrate nonahydrate
2 3
Fe(NO ) ꢁ9H O; AR; Beijing Chemical Co.), and methanol
3
3
2
MeOH; AR; Beijing Yili Fine Chemical Co. ) were used as
received.
Procedures
Aluminum dodecatungstophosphate (AlPW O ), iron
FIGURE 10 Arrhenius plot of ln(M ) versus 1/T for IBVE poly-
1
2
40
n
dodecatungstophosphate (FePW O ), potassium dodeca-
merization in aqueous medium.
1
2 40
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FIGURE 11 Cationic polymerization of IBVE coinitiated by various heteropolyacid and its salts in aqueous medium. IBVE ¼ 3.85
ꢄ
mmol, t ¼ 5 min, T ¼ 0 C, [heteropolyacid/salts] ¼ 2.6 mM.
ꢄ
1
through a column packed with calcium chloride. After 30
min, excess HCl in solution was removed by bubbling dry
CDCl as a solvent at 25 C. H NMR spectra of sample solu-
3
tions in CDCl were calibrated to tetramethylsilane as inter-
3
ꢄ
nitrogen at 0 C for 30 min, and the clean and quantitative
nal standard (d ¼ 0.00).
H
1
formation of IBVE–HCl adduct was confirmed by H NMR
Percent of acetaldehyde diisobutyl acetal (A%) is defined as
the ratio of acetaldehyde diisobutyl acetal (A) in the prod-
ucts from IBVE in aqueous medium in the presence of
AlPW O according to eq 1. SA is the integral value of
around 4.67 ppm of acetaldehyde diisobutyl acetal. SIBVE0 is
the integral value of around 0.92 ppm of initial IBVE and SIB-
spectroscopy.
Polymerizations
12 40
All the polymerization reactions were carried out under a
nitrogen atmosphere in glass tubes. A typical cationic poly-
merization of IBVE in aqueous medium (water) was con-
ducted as follows: AlPW O was dissolved in water, and
is the integral value of around 6.49 ppm for a period of
VEt
1
2 40
time.
then HCl aqueous was added. The neat monomer IBVE (0.5
mL; 3.85 mmol) was added into the above aqueous phase
SA
(
3.0 mL) to start the polymerization. The polymerization was
A% ¼
ꢅ 100
(1)
ꢄ
SIBVE0=6 ꢀ SIBVEt
carried out under thermal regulation (typically at 0 C) with
severe magnetical stirring at speed of around 300 rpm. After
predetermined time, 1 mL of methanol was injected to ter-
minate the polymerization and 5 mL CH Cl was added in to
Concentration of acetaldehyde diisobutyl acetal (A, C % ) is
defined as the molar ratio of acetaldehyde diisobutyl acetal
A to original IBVE in the reaction mixture according to eq 2.
A
2
2
dissolve the resulting poly(IBVE). Organic phase was sepa-
rated, transferred, and evaporated to obtain poly(IBVE)
SA
products. A typical cationic polymerization of IBVE in CH
2
Cl
2
CA% ¼
ꢅ 100
(2)
SIBVE0=6
was carried out as follows: IBVE solution in CH Cl (2 mL, 1
2
2
M) and IBVE–HCl solution in hexane (0.05 mL, 1 M) were
successively introduced into polymerization reactor with
CONCLUSIONS
ꢄ
AlPW O at 0 C under magnetic stirring. After predeter-
1
2 40
Suspension cationic polymerization of IBVE coinitiated by
H PW O , AlPW O , FePW O , K PW O , or Na PW O
mined time, 1 mL of methanol was injected to terminate po-
lymerization. Poly(IBVE) was obtained by removing residue
catalyst via centrifugation and evaporating organic solvents.
The resulting poly(IBVE) was dried in a vacuum oven at 40
C to a constant weight. Poly(IBVE) yield was determined
gravimetrically.
3
12 40
12 40
12 40
3
12 40
3
12 40
in aqueous medium could be achieved up to more than 83% of
poly(IBVE) yield in the presence of a large amount of HCl. The
number average molecular weights of the resulting isotactic-rich
poly(IBVE)s with m diad of 60% obtained in aqueous medium
ꢄ
ꢀ
1
were in the range of 1200–4500 g mol and the polydispersity
indexes of polymers kept at around 3.0, which are similar to
those of polymers obtained in organic solvent CH Cl . A suffi-
Characterization
Number average molecular weight (M
n
), weight average mo-
) of poly(IBVE) were
2
2
lecular weight (M ), and MWD (M /M
w
w
n
cient amount of HCl ([HCl] ꢃ 1.6 M) was needed to decrease or
suppress the hydrolysis of initiator IBVE–HCl and to accelerate
the cationic polymerization of IBVE in aqueous medium. The cat-
ionic polymerization of IBVE in aqueous medium in the presence
of HCl proceeded extremely rapidly with apparent constant of
determined with a Waters 515-2410 GPC system equipped
with four Waters styragel columns connected in the follow-
3
4
5
ꢄ
ing series: 500, 10 , 10 , and 10 at 30 C. THF served as
solvent, poly(IBVE) with a concentration of 20 mg of poly(-
IBVE)/10 mL of THF, and THF was also used as mobile
A
p
ꢀ1
propagation rate (k ) of 0.0503 s . The yield and molecular
ꢀ
1
phase at a flow rate of 1.0 mL min . The calibration of mo-
lecular weight was based on polystyrene standards. NMR
characterization of the reaction mixtures and poly(IBVE) was
performed on a Bruker AV400 MHz spectrometer using
weight of poly(IBVE) could be increased by increasing the
amount of HCl and AlPW O concentration or by decreasing
12 40
polymerization temperature. The elementary reactions for the
cationic polymerization, including initiation, propagation, and
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termination happened at the interface between IBVE droplet
and aqueous phase. All the poly(IBVE) growing chains were ter-
A. Deffieux, C. Absalon, J. E. Puskas, F. Ganachaud, Macromo-
lecules 2011, 44, 1372–1384.
minated by H O and further transferred to aldehyde and alkenal
terminal groups in polymer chains by elimination of 2-
isobutanol.
11 (a) S. P. Lewis, N. J. Taylor, W. E. Piers, S. Collins, J. Am. Chem.
Soc. 2003, 125, 14686–14687; (b) S. P. Lewis, L. D. Henderson, B. D.
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ACKNOWLEDGMENTS
The authors are grateful to the financial support from National
Natural Science Foundation of China (Grant 20934001).
1
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