Regioselective and alternating copolymerization of carbonyl sulfide with racemic propylene oxide

Article abstract of DOI:10.1021/ma401114m

We report the first example of a regioregular and fully alternating poly (propylene monothiocarbonate) (PPMTC) from the well-controlled copolymerization of two asymmetric monomers, carbonyl sulfide and racemic propylene oxide, using (Salen)CrCl in conjunction with bis(triphenylphosphoranylidene)ammonium chloride. The maximum turnover of frequency of this catalyst system was 332 h^-1 at 25 C. The contents of monothiocarbonate and tail-to-head linkages of PPMTC were up to 100% (based on ¹H NMR spectra) and 99.0% (based on ¹³C NMR spectra), respectively. PPMTC samples have number-average molecular weight (M_n) up to 25.3 kg/mol with polydispersity index of 1.41. The very low decomposition temperature of 137 C and high refractive index of 1.63 of PPMTC make it a potential scarifying optical adhesive.

Full text of DOI:10.1021/ma401114m

Article
pubs.acs.org/Macromolecules
Regioselective and Alternating Copolymerization of Carbonyl Sulfide
with Racemic Propylene Oxide
Ming Luo, Xing-Hong Zhang,* Bin-Yang Du, Qi Wang, and Zhi-Qiang Fan
MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang
University, Hangzhou 310027, China
*
S Supporting Information
ABSTRACT: We report the first example of a regioregular and fully
alternating poly (propylene monothiocarbonate) (PPMTC) from the
well-controlled copolymerization of two asymmetric monomers, carbonyl
sulfide and racemic propylene oxide, using (Salen)CrCl in conjunction
with bis(triphenylphosphoranylidene)ammonium chloride. The maxi-
mum turnover of frequency of this catalyst system was 332 h− at 25 °C.
The contents of monothiocarbonate and tail-to-head linkages of PPMTC
1
1
13
were up to 100% (based on H NMR spectra) and 99.0% (based on
C
NMR spectra), respectively. PPMTC samples have number-average
molecular weight (M ) up to 25.3 kg/mol with polydispersity index of
n
1
.41. The very low decomposition temperature of 137 °C and high
refractive index of 1.63 of PPMTC make it a potential scarifying optical
adhesive.
4c
INTRODUCTION
(PDI). Moreover, two special problems will be raised when a
terminated epoxide (herein propylene oxide, PO) is applied, as
shown in Scheme 1.
■
Carbonyl sulfide (COS) is released from the burning of fossil
fuels, coal gas, many chemical processes, volcanic eruption, and
plant or protein corruption. Although the COS concentration
in the troposphere is currently fairly low (∼500 ppt), it causes
acid rain and damage of the ozonosphere by a series of
One is that the oxygen−sulfur exchange reaction (O/S ER)
between COS and PO will generate CO and propylene sulfide
2
8b
(
PS) in the system. The crossed copolymerization of the
1
coexistent species (i.e., PO, COS, CO , and PS; see Table S1 in
2
photochemical reactions. However, as an asymmetric organo-
the Supporting Information) might occur and produce a
copolymer with possible units as 1−4 (and cyclic products 1′−
4′) in Scheme 1, if assuming preferential coordination of the
sulfur atom of COS to the active center (route A in Scheme 1).
The other is the stereochemistry control of COS-PO
copolymerization involving the two asymmetric monomers.
The coordination of the sulfur or oxygen atom of COS to the
active center (route A or B in Scheme 1) will generate −SC(
O)O− and −OC(S)O− units (5) and cyclic byproduct (5′),
respectively. The occurrence of O/S ER will probably cause the
generation of 6 and 6′. Meanwhile, the attacking manner of
propagating species of −OC(O)S− via route A to the carbon
sulfur compound with heterocumulene structure, it is an
resource of CO or CS groups for organic synthetic
2
chemistry. The fixation of COS to chemicals is an intriguing
and promising topic in chemistry, but very few publications are
3
reported to date.
Because COS is structurally an analogue of CO (and CS ),
2
2
we were strongly motivated to convert COS into polymers, in a
4
way similar with the CO −epoxide copolymerization,
2
producing poly(thiocarbonate). This polymeric material has
the potential to be applied as photoconductive fiber, heavy
metal scavengers, and adhesives because of its high optical
properties, excellent chemical resistance, and heavy-metal
5
6
of CH or CH of PO will produce four kinds of consecutive
recognition ability. Although polycondensation, ring-opening
2
7
3b,8
monothiocarbonate diads: head-to-tail (H−T), tail-to-head
polymerization (ROP), and alternating copolymerization
Scheme S1 in the Supporting Information) have been utilized
(
T−H), tail-to-tail (T−T), and head-to-head (H−H). Note
(
that T−H diad is different from H−T diad due to asymmetric
monothiocarbonate structure. All predicted units in the
copolymer and cyclic (thio) carbonates are listed in Scheme 1.
Therefore, the selectivity of monothiocarbonate unit 1
depends on the depression extent of O/S ER. We hypothesized
to synthesize poly(thiocarbonate)s, the synthesis of regiore-
gular poly(monothiocarbonate) with asymmetric unit from
direct alternating COS-epoxide copolymerization has, up until
now, not been reported.
The chemistry involved in COS−epoxide copolymerization
process will have all of the issues of CO −epoxide
2
copolymerization, including the activity, copolymer selectivity,
regioselectivity (for terminated epoxides), enantioselectivity,
and control of molecular weight and polydispersity index
Received: May 28, 2013
Revised: July 9, 2013
Published: July 25, 2013
©
2013 American Chemical Society
5899
dx.doi.org/10.1021/ma401114m | Macromolecules 2013, 46, 5899−5904

Macromolecules
Article
a
Scheme 1. Prediction of All Possible Products from COS-PO Copolymerization
a
Upper: If O−S exchange reaction occurs during copolymerization, 1−6 and byproducts 1′-6′ will be formed by the attack of propagating species to
CH of PO. Bottom: Four possible diads of the COS-PO copolymer formed by various regioselective attacks after route A.
2
that metal−OH could result in O/S ER because it was very
active to transform CS (or COS) to COS (or CO ) in the
EXPERIMENTAL SECTION
■
2
2
Method and Materials. All procedures involving air- or moisture-
sensitive compounds were carried out in a glovebox under a dry argon
atmosphere or with the standard Schlenk technique under dry argon.
Propylene oxide (PO) was distilled under a nitrogen atmosphere after
9
presence of water. Because metal−OH could be generated in
our system via chain-transfer reaction of propagating species to
1
0
trace water, O/S ER could be eliminated by depressing the
drying over CaH . COS (99.5%) was purchased from the Mixed Gases
2
chain transfer reaction.
In this work, we report the synthesis of a regioregular and
fully alternating poly(propylene monothiocarbonate)
Company of Hangzhou New Century and used as received. All of the
solvents used were distilled under a nitrogen atmosphere from CaH2
prior to use. Most of other reagents were used without further
1
13
(PPMTC) by using (Salen)CrCl complexes as the catalysts
purification unless otherwise specified. H and C NMR spectra of the
resultant copolymers were performed on a Bruker Advance DMX 400
MHz spectrometer. Chemical shift values were referenced to TMS as
and the confirmation of the above hypothesis. Several
(
Salen)CrCl complexes with various diamine backbones (a−
1
internal standard at 0.0 ppm for H NMR (400 MHz) and against
c) were employed (Figure 1) for COS−PO copolymerization
in the presence of organic bases (Figure 1, Table S2 in the
13
CDCl at 77.0 ppm for C NMR (100 MHz, part of samples was
3
characterized by 125 MHz NMR). Molecular weights and molecular
weight distributions of the resultant copolymers were determined with
a PL-GPC220 chromatograph (Polymer Laboratories) equipped with
an HP 1100 pump from Agilent Technologies. The GPC columns
were eluted with THF with 1.0 mL/min at 40 °C. The sample
concentration was 0.4 wt %, and the injection volume was 100 μL.
Calibration was performed using monodisperse polystyrene standards
covering the molecular-weight range from 580 to 460 000 Da. Infrared
spectra were recorded by using a Bruker Vector 22 FT-IR
Supporting Information) because they could catalyze CS −
2
8
a
8c
epoxides (and PS ) copolymerization and regioselective
10−12
CO −epoxide copolymerization.
2
spectrophotometer. The glass transition temperature (T ) of the
g
resultant copolymer was determined by using a TA DSC-Q200
differential scanning calorimetry (DSC). The sample was heated in
two cycles from room temperature to 80 °C at a rate of 5 °C/min in a
nitrogen atmosphere. Tg was determined from the second run.
Thermogravimetric analysis (TGA) was carried out on a Perkin-Elmer
Figure 1. Binary (Salen)CrCl complex/bis(triphenylphosphoranyl-
idene) ammonium chloride ([PPN]Cl) catalyst system used for COS-
PO copolymerization.
Pyris 1 instrument under a N atmosphere at a heating rate of 10 °C/
2
min from room temperature to 400 °C. Samples for thermal analyses
were all purified. The refractive index (nD) was measured by Abbe
5
900
dx.doi.org/10.1021/ma401114m | Macromolecules 2013, 46, 5899−5904

Macromolecules
Article
a
Table 1. Rac-PO/COS Copolymerization Results
d
copolymer
PPMTC linkages
T-H linkages
(%)
O/S ERe
Mn
(kg/mol)
PDI
w
entry catalyst cocatalyst TOF (h−1)b
selectivity
c
(%)
c
product
f
(M /M )
f
n
1
2
3
4
5
6
7
8
9
a
a
[PPN]Cl
288
N.D.
N.D.
310
332
266
274
290
282
99/1
N.D.
N.D.
99/1
99/1
77/23
97/3
98/2
97/3
100
N.D.
N.D.
100
100
100
100
100
100
98.9
N.D.
N.D.
99.0
98.6
98.1
94.7
95.2
97.6
N.F.
N.D.
N.D.
N.F.
N.F.
F
24.4
N.D.
N.D.
21.9
25.3
12.3
6.6
1.26
N.D.
N.D.
1.35
1.41
1.29
1.06
1.05
1.07
[PPN]Cl
[PPN]Cl
[PPN]Cl
[PPN]Cl
[PPN]Cl
[PPN]Cl
[PPN]Cl
b
c
c
c
c
c
g
h
i
N.F.
N.F.
N.F.
7.3
j
7.5
a
Reaction was performed in neat PO (2.0 mL, 28.6 mmol; catalyst/cocatalyst = 1/1, catalyst/PO = 1/1000, COS/PO = 2/1, all in molar ratio) in a
0 mL autoclave at 25 °C for 3.0 h. (Mol epoxide consumed)/(mol Cr h). Determined by using H NMR spectroscopy (Figure S1−5 in the
b
c
1
1
Supporting Information). The polymer selectivity is the molar ratio of polymer 1/cyclic product. The PPMTC linkages are the molar percentage of
monothiocarbonate linkage in polymer chain. Determined by using C NMR spectroscopy. Determined by using C NMR spectroscopy. O/S
ER = oxygen−sulfur exchange reaction. N.F. = not found and F = found. Determined by gel permeation chromatography in THF, calibrated with
polystyrene standards. Reaction temperature was 60 °C. (S)-PO was used. (R)-PO was used. 75%(S)-PO/25%(R)-PO was used.
d
13
e
13
f
g
h
i
j
1
Figure 2. H NMR spectrum of the crude product of entry 1 in Table 1.
refractometer. Electrospray ionization-tandem mass spectrometry
appropriate pressure with COS, and the reaction mixture was stirred at
25 °C for 3.0 h. After copolymerization, the autoclave was cooled and
the pressure was slowly vented. The reaction mixture was dried in
vacuum at 50 °C for isolating the unreacted reactants and weighed to
calculate the TOF of the copolymerization. An aliquot was then taken
from the resulting crude product for the determination of the ratio of
(
ESI−MS) analyses were performed on an Esquire3000 plus mass
spectrometer using acetonitrile (CH CN) as a solvent for the
3
copolymer. Raman spectra were recorded by using a RM2000 laser
Raman spectrometer (powder sample, the measurement range was
−
1
−1
1
00−4000 cm resolution of 1 cm ). The catalysts (Salen)CrCl a:
N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-benzenediamino chromium-
1
copolymer 1/cyclic product 1′ by H NMR spectrum. After that, the
(
III) chloride, b: N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-ethylene-
crude product was dissolved in CH Cl (10 mL) and precipitated from
2
2
diamino chromium(III) chloride, and c: (1R,2R) NN′-bis(3,5-di-tert-
,
methanol (100 mL) three more times. Yellowish precipitate was
collected and dried in vacuum at 70 °C to constant weight. The
butylsalicylidene)-1,2-cyclohexanediamino chromium(III) chloride
11
were synthesized according to the literature method.
1
13
obtained copolymer was analyzed by H NMR, C NMR, FT-IR
Copolymerization of PO with COS. The copolymerization of
PO/COS was performed in a 10 mL autoclave equipped with a
magnetic stirrer and a barometer. The (Salen)CrCl complex a (17.9
1
spectroscopy, and GPC. H NMR (CDCl ) δ 5.19−5.13 (m, 1H),
3
13
3
.16−3.00 (m, 2H), 1.37 (d, J = 6.3 Hz, 3H). C NMR (CDCl ) δ
3
−2
−2
1
mg, 2.86 × 10 mmol), [PPN]Cl (16.43 mg, 2.86 × 10 mmol), and
PO (2.00 mL, 28.6 mmol) were transferred into the autoclave, which
was completely dried in advance. The autoclave was pressurized to the
169.58, 73.45, 35.75, 19.01. [propylene monothiocarbonate 1′: H
NMR (CDCl
(m, 1H), 1.54 (d, J = 6.2 Hz, 3H)].
) 4.87−4.79 (m, 1H), 3.57−3.53 (m, 1H), 3.28−3.23
3
5
901
dx.doi.org/10.1021/ma401114m | Macromolecules 2013, 46, 5899−5904

Macromolecules
Article
RESULTS AND DISCUSSION
c/[PPN]Cl was proven to be the best binary catalyst for
producing PPMTC with fully alternating degree and the
complete depression of O/S ER.
The occurrence of O/S ER at 60 °C intrigued us to probe
the structural change of the catalyst during the reaction. As
previously mentioned, [Cr]−OH would be generated in our
system via the chain transfer reaction. The produced [Cr]−OH
could catalyze O/S ER in a proposed way, as shown in Scheme
■
Catalyst a/[PPN]Cl with a molar ratio of 1.0 was successfully
applied to COS-PO copolymerization with a TOF of 288 (i.e.:
PO conversion: 86.4%, entry 1 in Table 1). Blank reactions
showed that a or [PPN]Cl did not solely catalyze COS−PO
copolymerization (entries 2 to 3, Table 1). The selectivity of
copolymer 1/cyclic thiocarbonte was 99/1 based on the H
NMR spectrum (Figure 2). The alternating degree of the
1
2
and Scheme S2 in the Supporting Information. Such chain-
resultant copolymer 1 was estimated to be >99% because no
1
ether units were observed from the H NMR spectrum. No O/
1
3
Scheme 2. Proposed Mechanism of the O/S ER during COS-
PO Copolymerization
S ER had occurred, as confirmed by C NMR spectrum
Figure S1c in the Supporting Information). One peak at
(
1
69.64 ppm was observed, which was ascribed to the carbon
7b,8a
atom of monothiocarbonate linkage (−S(O)CO−, 1).
Hence, the copolymer 1 was fully alternating and named
poly(propylene monothiocarbonate) (PPMTC). The number-
average molecular weight (M ) of copolymer 1 was 24.4 kg/
n
mol with a narrow PDI of 1.26.
Catalysts b and c could also catalyze COS-PO copolymeriza-
tion in the presence of [PPN]Cl at 25 °C with high TOFs
(
entries 4 and 5 with TOFs of 310 and 332, respectively, Table
). For the copolymer of entry 5, only one peak at 169.64 ppm
1
1
3
was observed from C NMR spectrum (curve A in Figure 3),
transfer reaction can be accelerated by either increasing
reaction temperature or introducing greater amounts of water
(
or compounds with active protons) into the system. Herein,
the generation of CO was confirmed by the observation of
2
carbonate unit −OC(O)O− and cyclic carbonate (curve B in
Figure 3, Figures S4 and S7 in the Supporting Information),
which may support the occurrence of chain-transfer reaction
and the production of [Cr]−OH.
For further clarifying the structural change of (Salen)CrCl
complex and following O/S ER induced by chain-transfer
reaction during copolymerization, a series of control experi-
ments were carried out by adding certain amounts of water to
1
13
the reaction system, as shown in Table 2 ( H and C NMR
spectra, see Figures S9−13 in the Supporting Information).
When the molar ratios of H O/PO were 1/200 to 1/33, the
2
TOFs, the selectivity, and the alternating degrees of the
Figure 3. 13C NMR spectra of carbonyl region of the crude products
resultant copolymers remained nearly the same, while M of the
n
(
entries 5 and 6 in Table 1). The formation of 1−4 and 1′-4′ is shown
resultant copolymers decreased clearly and PDI remained
narrow. These phenomena were typical for the copolymeriza-
in Scheme 1 and Table S1 in the Supporting Information.
tion with predominant chain-transfer reaction, which was
8
a
10,13
which could be ascribed to −SC(O)O− (1 and/or 4).
similar to CO −PO copolymerization.
We also observed
that O/S ER took place when the H O/PO molar ratio ≥1/50
2
However, when the COS/PO copolymerization was catalyzed
by c/[PPN]Cl system at 60 °C (entry 6), considerable amounts
of cyclic products (23 wt %) were collected, which were evident
by the 13C NMR and H NMR spectra (curve B in Figure 3,
Figure S4 in the Supporting Information) of the crude product.
As seen in curve B in Figure 3, the products mentioned in
Scheme 1 such as −SC(O)S− (188.04 ppm, 3), −OC(
O)O− (153.48 ppm, 2), −SC(O)O− (169.64 ppm, 1 and/
or 4), and cyclic byproducts of 3′ (197.59 ppm), 1′ and 4′
2
(entries 3−5 in Table 2). The FT-IR (Figure S14 in the
Supporting Information) and Raman (Figure S15 in the
Supporting Information) spectra of the copolymer from entry
1
−1
5 of Table 2 showed that it contained end −OH (3540 cm in
−1
FT-IR) and −SH groups (2665 cm in Raman spectrum). ESI-
MS spectrum (Figure S16 in the Supporting Information) of
this copolymer showed that it had three kinds of m/z species,
which represented three copolymers of (i) H-PO-(COS-PO) -
n
8
a
+
+
(
172.59 ppm), and 2′ (154.92 ppm) were observed.
SH + Na , (ii) H-PO-(COS-PO) -OH + Na , and (iii) H-PO-
(COS-PO) -(COS-PS)-SH+ Na with relative abundance ratio
n
+
Moreover, 4′ was confirmed by GC-MS technique (Figure S7
in the Supporting Information). These results indicated that the
high reaction temperature will cause the occurrence of O/S ER
and weaken the selectivity of the monothoicarbonate units.
A series of COS/PO copolymerization were also investigated
with various COS/PO molar ratios, solvents, and cocatalysts
n
of 100:18:7. No observation of copolymer with −Cl end group
indicated that the chain-transfer reaction was very fast in the
presence of considerable amounts of water.
The observation of copolymer with end −SH group
confirmed the generation of [Cr]−SH, which initiated the
COS−PO copolymerization. As a result, the transformation of
[Cr]−Cl of (Salen)CrCl complex to [Cr]−OH, which could be
converted to [Cr]−SH by O/S ER, was resulted from the
(
Table S2 in the Supporting Information). The polymerization
kinetics showed a linear increase in M with increasing reaction
times (Figure S8 in the Supporting Information). The catalyst
n
5
902
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Macromolecules
Article
a
Table 2. Rac-PO/COS Copolymerization in the Presence of Various Amounts of Water
b
c
d
f
f
H O
H O:PO
TOF
copolymer
c
PPMTC linkages
(mol %)
T-H linkages
(%)
O/S ERe
product
Mn
PDI
w
2
2
−
1
entry
(μL)
(molar ratio)
(h
)
selectivity
(kg/mol)
(M /M )
n
1
2
3
4
5
2.5
5.0
1/200
1/100
1/50
274
282
288
266
157
99/1
99
99
99
98
86
97.6
97.1
92.8
90.9
76.0
N.F.
N.F.
F
9.5
8.1
5.2
3.9
1.2
1.12
1.08
1.06
1.06
1.15
99/1
10.0
15.0
30.0
98/2
1/33
90/10
86/14
F
1/17
F
a
Reaction was performed in neat PO (2.0 mL, 28.6 mmol; a/[PPN]Cl = 1/1, catalyst/PO = 1/1000, COS/PO = 2/1, all in molar ratio) in a 10 mL
b
c
1
autoclave at 25 °C for 3.0 h. (Mol epoxide consumed)/(mol Cr h). Determined by using H NMR spectroscopy (Figures S9−13 in the Supporting
Information). The polymer selectivity is the molar ratio of polymer 1/cyclic product. The PPMTC linkages are the molar percentage of
d
13
monothiocarbonate linkage in polymer chain. Determined by using C NMR spectroscopy (Figure S9−13 in the Supporting Information).
e
Determined by using 13C NMR spectroscopy (Figure S9−13 in the Supporting Information). O/S ER = oxygen−sulfur exchange reaction. N.F. =
f
not found and F = found. Determined by gel permeation chromatography in THF, calibrated with polystyrene standards.
chain-transfer reaction (Scheme S2 in the Supporting
Information).
copolymer. GC-MS measurements were then carried out to
clearly differentiate 1′ and 4′, and the diads of the copolymer
could be deduced. The GC-MS results showed that the molar
ratio of cyclic monothiocarbonates 1′ to 4′ was 40 for the
system of entry 6 in Table 1, as shown in Figure S7 in the
Supporting Information, indicating that the −OC(O)S
CH CH (CH )O− unit was the main structure of the
Under the premise of the complete depression of O/S ER,
the stereochemistry of COS-PO copolymerization can be
clarified. The units of −OC(S)O− (5), −SC(S)O− (6),
and corresponding cyclic products of 5′ and 6′ were not
13
observed in C NMR spectra of all copolymers listed in Tables
2
3
1
and 2. It indicated that the insertion path B in Scheme 1 was
copolymer even if O/S ER had occurred. Furthermore, the
content of T−H diad of copolymer 6 was estimated to be
97.6% from the molar ratio of 1′/(1′ + 4′), which was
totally prohibited. That is, the coordination of the sulfur atom
of COS to the active center was completely selective. As a
−
13
result, only one propagating species (−OC(O)S , via route
consistent with that of 98.1% calculated from C NMR
A) existed before PO insertion. The nucleophilic attack of
spectrum (entry 6 in Table 1). The multiple peaks at 169.64
ppm could be then assigned to the T-H diad. The content of T-
H diad in all copolymers in Table 1 was calculated as 98.1 to
99.0%, indicating that the copolymerization was highly
regioselective.
−
−
OC(O)S to CH2 or CH of PO determines the
regioregularity of the resultant copolymer (Scheme 1 and
Scheme S3 in the Supporting Information).
It seems hard to accurately assign the multiple peaks of
−SC(O)O− unit [curve (A), Figure 4] to the various
For further demonstrating the unique regioregularity of
PPMTC, (S)-PO, (R)-PO, and 75%(S)-PO/25%(R)-PO were
copolymerized with COS by using the catalyst c/[PPN]Cl
(
7
entries 7−9, Table 1). Note that (S)-PO, (R)-PO, and
5%(S)-PO/25%( R)-PO were used without further purifica-
tion. The (S) [or (R)]-configuration of methine carbon of (S)
or (R)]-PO was expected to be retained after copolymeriza-
[
tion if just a−a propagating manner took place. Hence, the
isotactic T−H diad would be the only configuration of the
1
3
resultant copolymer and will cause one single peak in its
C
1
3
NMR spectrum. This expectation was proved by the C NMR
spectrum of COS/(S)-PO copolymer and COS/(R)-PO
copolymer, as shown in curves (B) and (C) in Figure 4.
Moreover, the copolymer from COS with 75% (S)-PO/25%
(
R)-PO presented similar multiple peaks as those observed for
rac-PO/COS copolymer [curve (A), Figure 4], and the sharp
peak at right-hand [(S) isotactic T-H diad, curve (D)] became
relative stronger because of greater amounts of (S)-PO in the
system.
Figure 4. Carbonyl region of the 13C NMR spectra of PPMTC
resulted from (A) rac-PO/COS (entry 6, Table 1) and (B) (S)-PO/
COS (entry 7, Table 1); (C) (R)-PO/COS (entry 8, Table 1) and (D)
The obtained PPMTC is highly soluble in common solvents,
such as, CH Cl , CHCl , and THF. The glass-transition
2
2
3
75%(S)-PO/25%(R)-PO/COS (entry 9, Table 1). Note that (S)-PO,
temperature (T ) of PPMTC of entry 7 in Table 1 was 22.4
g
(R)-PO, and 75%(S)-PO/25%(R)-PO were used without further
°
C (Figure S17 in the Supporting Information). Interestingly,
the initial decomposition temperature of this copolymer was
37 °C and rather low (Figure 5). Refractive index (nD) of this
purification.
1
microstructures (i.e., H−T, T−H, T−T, and H−H diads) of
the copolymer 6 (entry 6, Table 1). If the cyclic
monothiocarbonate could be predominantly generated via the
copolymer was measured to be 1.63(22 °C, cast film), which
can be classified into polymers with large refractive index. Such
low decomposition temperature and high refractive index of
PPMTC make it a potential scarifying optical adhesive.
In conclusion, the regioselective and alternating copoly-
merization of COS and PO are reported for the first time using
the binary (Salen)CrCl/[PPN]Cl catalyst system. The O/S ER
10
backbiting from the anionic alkoxy−chain end, as shown in
Scheme 3, then the molar ratio of cyclic monothiocarbonates 1′
to 4′ could represent the molar ratio of the units −OC(O)
SCH CH(CH )O− to −OC(O)SCH(CH )CH O− in the
2
3
3
2
5
903
dx.doi.org/10.1021/ma401114m | Macromolecules 2013, 46, 5899−5904

Macromolecules
Article
Scheme 3. Proposed Production of Cyclic Monothiocaarbonate 1′ and 4′ by “Backbiting” Mechanism
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Figure 5. TGA curve of the COS-PO copolymer (entry 1, Table 1).
(
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could be completely inhibited at 25 °C. The resultant
copolymers had 98.1 to 99.0% T−H linkages and full
alternating asymmetric monothiocarbonate units. Importantly,
it also presented a new copolymerization model involved two
asymmetric monomers.
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ASSOCIATED CONTENT
Supporting Information
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(11) Darensbourg, D. J.; Mackiewicz, R. M.; Rodgers, J. L.; Fang, C.-
*
S
Text, figures, and tables giving general experimental procedures
and characterization data for PO−COS copolymers. This
material is available free of charge via the Internet at http://
pubs.acs.org.
C.; Billodeaux, D. R.; Reibenspies, J. H. Inorg. Chem. 2004, 43, 6024−
034.
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AUTHOR INFORMATION
Corresponding Author
Tel/Fax: +86-571 87953732. E-mail: xhzhang@zju.edu.cn.
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*
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful for financial support by the National Science
Foundation of the People’s Republic of China (nos. 21274123
and 21074106) and the Science and Technology Plan of
Zhejiang Province (no. 2010C31036).
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