Copolymerization of propylene oxide with carbon dioxide catalyzed by zinc adipate

Article abstract of DOI:10.1023/A:1020902704652

Copolymerization of carbon dioxide with propylene oxide in the presence of zinc adipate was studied. The effects of the temperature, nature of the solvent, and catalyst concentration on the molecular weight, molecular-weight distribution, and yields of th

Full text of DOI:10.1023/A:1020902704652

Russian Chemical Bulletin, International Edition, Vol. 51, No. 8, pp. 1451—1454, August, 2002
1451
Copolymerization of propylene oxide
with carbon dioxide catalyzed by zinc adipate
A. M. Sakharov,aꢀ V. V. Il´in, V. V. Rusak, Z. N. Nysenko, and S. A. Klimov
a
a
a
b
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
4
7 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7(095) 135 6346. Eꢀmail: as@zelinsky.ru
b
JointꢀStock Company "Kaustik,"
prosp. 40ꢀletiya VLKSM, 400097 Volgograd, Russian Federation.
Fax: +7 (844 2) 66 1184
Copolymerization of carbon dioxide with propylene oxide in the presence of zinc adipate
was studied. The effects of the temperature, nature of the solvent, and catalyst concentration
on the molecular weight, molecularꢀweight distribution, and yields of the copolymer and
propylene carbonate were examined. The structure of the polymer obtained was studied by
13
1
С and Н NMR spectroscopy.
Key words: propylene oxide, carbon dioxide, zinc adipate, copolymerization, poly(propylene
carbonate), propylene carbonate.
One of the promising areas of carbon dioxide utiliꢀ
zation is its use as a reactant for the preparation
of poly(alkylene carbonates), which are ecologically
safe and biodegradable thermal plastics of the new genꢀ
eration.
obtained with this catalyst contains a noticeable number
of ether units.
This disadvantage is much less pronounced for zinc
carboxylates (next in the series of activity), which are
prepared from ZnO and glutaric or adipic acids and alꢀ
low synthesis of PPC with a fairly high molecular weight
(>260000).
Combustion of poly(alkylene carbonates) in air or an
oxygen atmosphere produces СО and water as the only
2
products. They are promising for the solution of technoꢀ
logical, medical, and ecological problems due to a comꢀ
plex of valuable properties, such as a high adhesion to
cellulose substrates in combination with a low oxygen
permeability, oil resistance, easiness of processing, good
compatibility with other polymers to form stable mixꢀ
tures, and others.
The catalysts of this type are characterized by such
advantages as simplicity of synthesis and safety in use.
The preparation of poly(alkylene carbonates) in the presꢀ
ence of zinc carboxylates is presently the single ecoꢀ
nomically and technologically feasible industrial process.
The properties and composition of the polymer are
substantially affected by copolymerization conditions,
namely, temperature, pressure, solvent, and initial conꢀ
Poly(alkylene carbonates) are prepared by the copoꢀ
lymerization of CO with oxiranes in the presence of
centration of reactants. However, only few publications
and they contain only
scanty information for different catalysts.
In this work we studied the effects of the temperature
of the process, catalyst concentration, and nature of the
solvent during propylene oxide (1) copolymerization with
2
are devoted to this problem,9
—12
metal complex catalysts. The copolymer has an alternatꢀ
ing structure of the polymeric chain with a minor conꢀ
tent of ether fragments (≤10 mol.%) randomly incorpoꢀ
rated into the chain. A byꢀproduct, viz., alkylene carꢀ
bonate, is formed along with the copolymer.1
The most part of studies in this area are devoted to a
search for catalytic systems involving no undesirable side
processes and increasing the yield and molecular weight
of the copolymer.2
CO in the presence of zinc adipate on the molecular
weight, molecularꢀweight distribution, and yields of coꢀ
polymer 2 and byꢀproduct 3 (Scheme 1).
2
—7
The structure of zinc adipate is likely similar to that
1
Carbon dioxide is a stable compound, and its copolyꢀ
merization with olefin oxides needs a highly active cataꢀ
lyst. A study of more than a hundred of catalytic systems
of zinc glutarate studied elsewhere.
8
based on metal (Zn, Со, Cr, Mg, Ca, Al, Y) complexes
showed that zinc coordination compounds exhibit the
highest activity, and Zn [Fe(CN) ] is the most active
among them. However, poly(propylene carbonate) (PPC)
The influence of the CO pressure (pCO2) on copolyꢀ
3
6 2
2
1
0,12
merization has earlier been described.
However, data
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1339—1342, August, 2002.
066ꢀ5285/02/5108ꢀ1451 $27.00 © 2002 Plenum Publishing Corporation
1

1452
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 8, August, 2002
Sakharov et al.
Scheme 1
Table 2. Effect of the catalyst concentration (CCat) on the yield
and properties of PPC 2
M •10– M •10
3
–3
M /M
CCat
mol L–1
Yield of 2
w
n
w
n
/
(%)
0
0
0
0
0
0
.077
.154
.191
.203
.303
.400
23.0
25.0
29.0
38.0
63.5
61.0
250.0
335.0
326.0
221.0
207.0
171.0
45.0
5.55
7.98
5.09
4.02
5.17
4.17
42.0
64.0
55.0
40.0
41.0
Note. Catalyst is zinc adipate, reaction time is 10 h, T =
1—83 °C, solvent is CH Cl , p = 25—27 atm.
8
2
2
CO
2
only source of its formation is the polymeric chain, whose
decomposition decreases the molecular weight14 (degraꢀ
dation, depolymerization). It seems more probable that
Cat is zinc adipate
on the molar ratios of СО2 and propylene oxide are
lacking, and it seems impossible to conclude about the
influence of the pressure on the yield and molecular
weight of the copolymer.
Our experiments were carried out at pCO2
5—27 atm, which ensured approximately twofold CO2
15
compound 3 is additionally formed due to the direct
interaction of the comonomers on the catalyst active
sites, which differ from the active site of polymerization.
The data in Table 2 reflect the effect of the catalyst
concentration on the yield and molecularꢀweight charꢀ
acteristics of PPC 2 and show that the maximum moꢀ
lecular weight of the polymer corresponds to a relatively
=
2
molar excess over oxide 1.
The yields of PPC 2 and propylene carbonate 3, numꢀ
–1
low catalyst concentration (0.154 mol L ). The maxiꢀ
berꢀaverage (M ) and weightꢀaverage (M ) molecular
n
w
mum yield of the polymer is achieved at higher catalyst
weights, and molecularꢀweight distribution (M /M ) at
–1
w
n
concentrations (0.303 mol L ).
different temperatures of the process (T) are presented
in Table 1. The yield of PPC 2 increases, its molecular
weight decreases, and the yield of byꢀproduct 3 increases
with the temperature T (see Table 1).
The dynamics of changing the characteristics of PPC
2
0
during copolymerization at a catalyst concentration of
–1
.29 mol L is shown in Table 3.
It follows from the data presented that under the
The found increase in the yield of PPC 2 with T
contradicts earlier theoretical calculations.1 In the auꢀ
thors´ opinion, the copolymerization of oxide 1 with
indicated conditions (pCO2 = 25—27 atm and T =
5—87 °С) the maximum yield of copolymer 2 is achieved
in 10—12 h and remained at a constant level for the next
10—12 h, although such a behavior is accompanied by a
decrease in the molecular weight.
The influence of the solvent nature on the yield of
the polymer and its molecularꢀweight characteristics is
determined by several factors, in particular, the basicity
3
8
CO is accompanied by a decrease in the entropy and
2
enthalpy, due to which this process should have the upꢀ
per limiting temperature. It is known that for such transꢀ
formations the equilibrium is shifted toward a decrease
in the yield of the reaction products with T.
The increase in the yield of propylene carbonate 3
with T cannot be explained in terms of concepts that the
and polarity, solubility of CO (depending on the exꢀ
2
Table 3. Change in the characteristics of PPC 2 during copolyꢀ
merization of propylene oxide (1) with CO (concentration of
2
Table 1. Yield of PPC 2 and its properties as functions of the
reaction temperature
zinc adipate is 0.29 mol L–
1
)
Mw•10–3
Mn•10–3
Mw/Mn
–
3
–3
Reaction
time/h
Yield of 2
T/°С
Yield (%)
M •10
M •10
M /M
w
n
w
n
(%)
2
3
6
48.87
64.69
67.33
63.85
62.31
62.54
287.8
218.9
159.9
146.9
130.7
130.3
57.4
52.8
33.1
25.7
26.9
27.6
5.01
4.15
4.84
5.71
4.85
4.72
6
7
8
9
5
5
5
0
23.0
28.8
64.7
46.0
5.5
8.5
10.0
16.0
300.1
268.1
218.5
122.2
34.3
31.6
28.7
37.5
8.73
8.48
7.61
3.26
10
13
16
19
2
2
Note. Catalyst is zinc adipate (0.308 mol L–1), reaction time
is 10 h, solvent is CH Cl , p = 25—27 atm.
Note. T = 85—87 °C, solvent is CH Cl , p = 25—27 atm.
CO
2
2
2
CO
2
2
2

Copolymerization of propylene oxide with CO2
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 8, August, 2002
1453
Table 4. Effect of the solvent nature on the copolymerization of propylene oxide (1) with CO in the presence of zinc adipate
2
(
T = 75—78 °C, pCO2 = 26—28 atm, 10 h)
M •10–3 M •10
–3
M /Mn
Basicity
parameter
Polarity
parameter
Solvent
Yield (%)
w
n
w
1
6
17
2
3
Perfluorodecalina
67.1
67.0
66.4
65.4
57.8
56.2
54.1
52.2
50.0
38.2
27.0
13.7
4.1
5.5
6.0
6.0
8.0
5.5
6.0
4.0
5.5
4.0
5.5
16.0
5.0
30.0
30.0
50.0
0
180.0
158.0
194.0
299.0
152.0
202.0
282.0
172.0
216.0
95.7
60.0
161.0
15.0
—
67.0
2.69
4.82
2.50
5.26
2.18
2.97
11.49
2.94
2.94
7.19
3.89
8.18
—
—
—
b
oꢀXylene
33.0
77.0
57.0
70.0
68.0
25.0
59.0
73.0
13.0
15.0
20.0
—
—
—
—
—
—
—
0.157
0.128
0.178
0.078
0.124
0.444
0.056
0.038
—
0.641
0.655
0.876
0.563
0.667
0.701
0.519
0.616
—
0.795
—
0.838
0.895
—
b
Toluene
b
CH Cl
2
2
a
Methylcyclohexane
b
Benzene
b
1
,4ꢀDioxane
a
nꢀHexane
Freonꢀ113
a
b
Toluene—AcOEt (1 : 1)
AcOEtb
0542
—
b
Benzyl chloride
THF
b
0.591
0.286
0.636
0.623
0.482
0.613
0.341
MeCN
Monoglyme
Diglyme
1.5
Traces
0
0
0
—
—
—
—
—
—
—
—
—
—
—
Cyclohexanone
0
0
—
0.874
0.970
0.930
1
ꢀMethylpyrrolidinꢀ2ꢀone
Propylene carbonate
0
—
a
The final reaction mixture exhibits syneresis.
The final reaction mixture is a viscous heterogeneous paste.
b
perimental conditions and composition of the reaction
mixture), and others.
Along with the main signals, the spectrum also conꢀ
tains minor signals with chemical shifts at 1.05—1.41
The results of studying the effect of the solvent naꢀ
ture on the copolymerization of CO2 with propylene
oxide (1) (Table 4) suggest that the yield (>50%) of
(m, СН(Me)), 3.33—3.88 (m, CH ), and 4.81—5.23 ppm
2
(m, CH(Me)) corresponding to the ether fragments of
the polymeric chain with structure B. Their content could
be determined from the ratio of integral intensities of
PPC 2 with М = 150000—300000 and the low content
w
of byꢀproduct 3 are achieved by the use of solvents with
mainly low basicity and polarity. In solvents with high
polarity and basicity the process is inhibited or comꢀ
pletely suppressed likely due to the competition between
the solvent and oxide 1 for the active site of polymerꢀ
ization.
signals from the carbonate and ether СН groups beꢀ
2
cause the identification of the ether fragments from other
signals is impeded due to their superposition. In the
presented example, the content of the ether fragments
was 9%.
Analysis of the 13С NMR spectra shows that all posꢀ
sible types of addition of the monomer units are accomꢀ
plished in PPC 2, viz., "headꢀtoꢀhead" (HH), "tailꢀtoꢀ
tail" (TT), and "headꢀtoꢀtail" (HT). Based on the asꢀ
sumption that the relaxation times of the C atoms of the
Advantages of fluorinated solvents are worth of speꢀ
cial mentioning. They are nontoxic and incombustible,
and СО is highly soluble in them. In addition, syneresis
2
is observed in the reaction mixture at the final stage of
copolymerization to considerably simplify solvent regenꢀ
eration. Despite the polymer precipitates from the reacꢀ
tion mixture at the final stage of polymerization, the
molecular weights of PPC 2 are rather high.
1
3
carbonyl groups in the С NMR spectra are approxiꢀ
mately the same for the three variants of addition (HH,
1
8
TT, and HT, 153.0—155.0 ppm ), the content of these
fragments in the chain of PPC 2 can quantitatively be
estimated from the integral intensities of their signals. In
the case considered, the ratio is HH : TT : HT =
0.817 : 1.000 : 3.142. The multiplicity of signals from
other C atoms also points to different types of addition
of the monomers.
The structure of polymer 2 obtained at 75 °С in the
1
presence of zinc adipate (see Table 1) was studied by Н
and 1 С NMR spectroscopy.
3
1
The Н NMR spectrum of 2 contains signals with
chemical shifts at 1.28—1.74 (m, СН(Me)), 4.04—4.38
(
m, CH ), and 4.95—5.13 ppm (m, CH(Me)) and a ratio
The data presented completely coincide with the reꢀ
sults of studies of the structure of PPC obtained with the
2
of integral intensities of 3 : 2 : 1, which corresponds to
the PPC fragments with structure A (see Scheme 1).
1
8
catalytic system based on the Et Zn derivatives.
2

1454
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 8, August, 2002
Sakharov et al.
Experimental
2. S. Inoue, H. Koinuma, and T. Tsuruta, Makromol. Chem.,
1
969, 130, 210.
Carbon dioxide was stored for 72 h at ∼20 °C in an autoꢀ
3. W. Kuran, S. Pasynkiewicz, and J. J. Skupinska, Makromol.
Chem., 1976, 177, 1283.
4. W. Kuran and T. Listos, Makromol. Chem. Phys., 1994,
195, 401.
clave filled with activated silica gel (pressure 55 atm).
Zinc adipate was synthesized using a known procedure
1
9
and activated for 40 h at 130 °С (2 Torr), decomposition point
4
25—450 °С (cf. Ref. 19: decomposition point 425—450 °С).
5. T. Aida, M. Ishikawa, and S. Inoe, Macromolecules,
1986, 19, 8.
6. M. Cheng, E. B. Lobkovsky, and G. W. Goates, J. Macromol.
Sci. Chem., 1995, 32A, 393.
–
1
Its IR spectrum (Specord IRꢀ75, 1540 cm
1
sented previously.
(Zn→О=С),
–
1
585 cm (terminal acidic groups)) coincides with that preꢀ
1
Propylene oxide was refluxed above CaH2 until gas evoluꢀ
tion ceased and distilled.
7. M. Super, E. Berenche, C. Costello, and E. Beckman, Macꢀ
romolecules, 1997, 30, 368.
8. M. Ree, J. Y. Bac, J. H. Jung, and T. J. Shin, Korea
Polym. J., 1999, 7, 333.
9. X. Chen, Z. Shen, and Y. Zhang, Macromolecules, 1991,
24, 5305.
10. C.ꢀS. Tan and T.ꢀJ. Hsu, Macromolecules, 1997, 30, 3147.
11. L.ꢀB. Chen, Makromol. Chem., Macromol. Symp.,
1992, 59, 75.
Solvents were purified using known procedures.20
The molecular weights of polymers were determined by gel
permeation chromatography on a Gilson instrument (colꢀ
umns AMꢀGel 500A, 2 Linear (300×7 mm), eluent velocity
–
1
1
mL min , eluent CHCl ). NMR spectra were recorded on a
3
Bruker DRXꢀ500 spectrometer (500 MHz) in CDCl3.
Copolymerization (general procedure). A solvent (50 mL)
was loaded to a 200ꢀmL steel reactor (maximum pressure 50 atm)
with a heated jacket and a mechanical stirrer, and the catalyst
12. K. Soga, K. Hyakkoku, K. Izumi, and S. Ikeda, J. Polym.
Sci., Polym. Chem. Ed., 1978, 16, 2383.
(
3 g) and propylene oxide (1) (15 g) were added with stirring.
13. M. A. Markevich, L. I. Pavlinov, and Yu. A. Lebedev,
Dokl. Akad. Nauk SSSR, 1982, 262, 652 [Dokl. Chem., 1982
(Engl. Transl.)].
14. W. Kuran and P. Gorecki, Makromol. Chem., 1983, 184, 907.
15. S. Inoe, K. Matsumoto, and Y. Yoschida, Makromol. Chem.,
1980, 181, 2287.
16. J. Catalan, C. Diaz, V. Lopez, P. Perez, J.ꢀL. G. de Paz,
and J. G. Rodriguez, Liebigs Ann., 1996, 1785.
17. J. Catalan, V. Lopez, P. Perez, R. MartinꢀVillamil, and
J. G. Rodriguez, Liebigs Ann., 1995, 241.
18. P. W. Lednor and N. C. Rol, J. Chem. Soc., Chem. Commun.,
1985, 598.
19. US Pat. 5,026,676; Chem. Abstrs., 1991, 115, 93209.
20. D. D. Perrin, W. L. F. Armarego, and D. R. Perrin, Purifiꢀ
cation of Laboratory Chemicals, 2nd ed., Pergamon Press
Ltd., 1980.
The reactor was sealed at ∼20 °C, and CO2 was conveyed with
stirring until the pressure reached 16 atm. Then the reaction
mixture was heated to the reaction temperature and stirred for
a specified time (pCO2 = 26±1 atm). After the end of the reacꢀ
tion, a heterogeneous mixture of the catalyst and a viscous
solution of the polymer was unloaded and treated with a
6
% solution of HCl to decompose the catalyst. The transparent
organic layer was washed to the neutral reaction and slowly
added with stirring to MeOH (200 mL) to precipitate the polyꢀ
mer. The precipitated polymer was additionally washed with
MeOH (100 mL), and the precipitate was separated and dried
at 80—90 °С (5 Тorr) to a constant weight.
Poly(propylene carbonate) 3. 1H NMR, δ: 1.28—1.74 (m,
3
H, Me); 4.04—4.38 (m, 2 H, CH ); 4.95—5.13 (m, 1 H, CH).
2
13
C NMR, δ: 16.10—16.40 (m, Me); 68.80—69.40 (m, OCH );
2
7
1.90—72.50 (m, OCH); 153.00—155.00 (m, C=O).
References
Received June 13, 2001;
1
. J. M. Bronk and J. S. Rifle, Polym. Prepr., 1994, 35, 815.
in revised form December 28, 2001