Quantitative synthesis of bis(cyclic carbonate)s by iron catalyst for non-isocyanate polyurethane synthesis

Article abstract of DOI:10.1039/c4gc01294a

Bis(cyclic carbonate)s were quantitatively prepared with high efficiency via the coupling reaction of carbon dioxide (CO₂) with diglycidyl ethers by a [Fe(BPMCDAC)]/TBAB catalytic system, where glycol diglycidyl ether (1a) could be completely converted to the corresponding bis(cyclic carbonate) (2a) with a turnover number of 1000 at 100 °C and 3 MPa in 4 h. The obtained bis(cyclic carbonate) (2a) could be used to prepare hydroxyl-functional polyurethanes via reaction with diamines, which may be one alternative for obtaining conventional polyurethanes without the use of toxic phosgene or isocyanates. The number-average molecular weights of the obtained non-isocyanate polyurethanes (NIPUs) were up to 25.4-30.2 kg mol-1, and the polydispersity indexes (PDIs) were relatively narrow between 1.18 and 1.22. A typical NIPU showed a glass transition temperature of 9 °C and an initial degradation temperature (Td 5%) of 206 °C.

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Polyurethanes were prepared from the polyaddition of diamines and bis(cyclic
carbonate)s which were obtained via complete carbonation of diepoxides.

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ARTICLE TYPE
Quantitative Synthesis of Bis(cyclic carbonate)s by Iron Catalyst for
Non-isocyanate Polyurethane Synthesis
Xingfeng Sheng,a,b Guanjie Ren,a,b Yusheng Qin,*a Xuesi Chen,a Xianhong Wang,**a Fosong Wanga
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
Bis(cyclic carbonate)s were prepared quantitatively in high efficiency via the coupling reaction of
carbon dioxide (CO2) with diglycidyl ethers by [Fe(BPMCDAC)]/TBAB (Fig. 1) catalytic system,
where glycol diglycidyl ether (1a) could be completely converted to the corresponding bis(cyclic
o
carbonate) (2a) with turn over number of 1000 at 100 C and 3 MPa in 4 h. The obtained bis(cyclic
10 carbonate) (2a) could be used to prepare hydroxyl-functional polyurethanes via reaction with
diamines, which may be one alternative for conventional polyurethanes without toxic phosgene or
isocyanates. The number-average molecular weights of obtained non-isocyanate polyurethanes
(NIPUs) were up to 25.4
between 1.18 and 1.22. A typical NIPU showed glass transition temperature of 9 C and initial
15 degradation temperature (Td 5%) of 206 oC.
~
30.2 kg mol-1 and the polydispersity indexes (PDIs) were relatively narrow
o
reaction of limonene dioxide, epoxidized linseed and soybean oil
with CO2 at 120-140 oC, and the limonene dioxide could be
completely converted to the corresponding bis(cyclic carbonate)
at 140 oC and 3 MPa within 43 h. Recently, Zhang13 reported that
50 bis(cyclic carbonate)s could be prepared via the coupling reaction
of diepoxides with CO2 catalyzed by zinc-cobalt double metal
cyanide complex, conversion of 81% could be obtained at 120 oC
and 5 MPa CO2 pressure within 9 h. Furthermore, Guillaume14
Introduction
Carbon dioxide (CO2) is regarded as the main reason for global
warming,1 but it is abundant, cheap and non-toxic, and its specific
molecular structure makes it important C1 feedstock in industry.
20 Employing CO2 as a raw material to prepare large scale
chemicals may create a new way to high value-added utilization
of CO2. Among all the reported CO2 fixation routes, synthesis of
cyclic carbonates via the coupling reaction of CO2 with epoxides
is one of the most attractive processes.2
Because cyclic carbonates are widely used as green solvents,
electrolytes, fuel additives and intermediates for the production of
biodegradable polymers,3 numerous catalyst systems have been
developed to promote this transformation.4 Prominent among
these are salen complexes of cobalt,5 chromium,6 zinc7 and
prepared carbonate-end functionalized PTMCs through
a
55 complex series of reactions with suitable solvents. However,
according to the above literatures, the complete conversion of
diepoxide in the coupling reaction needed suitable solvent,
relatively long time and harsh reaction conditions. Hence, though
some investigations about the diepoxide/CO2 coupling reaction
60 have been carried out, the convenient synthesis of bis(cyclic
carbonate) via the diepoxide/CO2 coupling reaction with the
complete conversion of diepoxide still remained a challenge
before this work.
25
30 aluminium,8 which show high activities under mild conditions.
However, most studies have focused on the coupling reaction of
CO2 with mono-epoxides, while epoxides with two or more
epoxy groups were rarely used in the literature. Lee and co-
workers9 synthesized bis(cyclic carbonate)s via the addition
35 reaction of carbon dioxide with diglycidyl ether derivatives in N-
methyl-pyrrolidone (NMP) in the presence of phase transfer
catalyst, and the conversion of diepoxides was below 60% at 100
oC within 6 h. Endo et al.10 prepared bis(cyclic carbonate)s via
o
the coupling reaction of CO2 with diepoxides in NMP at 100 C
40 under CO2 atmosphere. Furthermore, Wilkes11 found that
epoxidized soybean oil could be effectively converted to
carbonated soybean oil containing five-membered cyclic
carbonates via reaction with CO2 employing tetrabutylammonium
bromide (TBAB) as catalyst at 110 oC. Mülhaupt and co-
45 workers12 reported that TBAB could catalyze the coupling
65
Fig. 1 Structure of Fe(BPMCDAC).
Bis(cyclic carbonate)s can react with di- or polyfunctional
primary alkyl amines, leading to non-isocyanate polyurethanes
(NIPUs), which is an alternative route for polyurethanes without
toxic phosgene or isocyanates.10-15 In this process, the ratio of
70 carbonate to amine group is a major factor influencing the
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property of NIPUs, whose accuracy is significantly affected by 35 purity were used as received.
the conversion of diepoxides, and the ideal ratio is 1:1. That is to
say, if the epoxy groups were not completely carbonated, the
Characterization
1
Nuclear magnetic resonance spectra. All H-NMR and 13C-
NMR measurements were recorded on a Bruker ARX-300
spectrometer at room temperature in deuterated chloroform
40 (CDCl3) or dimethyl sulfoxide (DMSO) with tetramethylsilane
(TMS) as internal reference.
product was the mixture containing mono-cyclic carbonate, bis-
cyclic carbonate and diepoxide, which are difficult to separate
each other, resulting in the error of the carbonate/amine group
ratio. Thus, highly efficient and quantitative synthesis of
bis(cyclic carbonate)s is extremely significant.
5
Differential scanning calorimetry analysis. DSC analysis
was performed on a Perkin-Elmer DSC-7 instrument under a N2
atmosphere. The samples were first heated from -50 °C to 50 °C
45 at 10 °C/min and then rapidly quenched to -50 °C, followed by
the second heating process in the same way as the first. The glass
transition temperature (Tg) was defined as the value of midpoint
of transition in the second heating process.
Fourier tansform infrared spectroscopy. Fourier transform
50 infrared (FTIR) spectra were recorded on a Bruker Optics Tensor
27 spectrometer. The spectral resolution is
2
cm-1. The
characteristic IR absorptions mentioned in the text are strong
bands in wavenumber (cm-1).
10
Scheme 1 Coupling reaction of CO2 and diepoxides.
In this work, we report that an iron complex (Fig. 1), [N,N-
Thermogravimetry analysis. TGA test was performed on a
bis-2-pyridinylmethyl-cyclohexane-1,2-diamine]iron(II) chloride 55 Perkin-Elmer Pyris 1 TGA thermal analyzer under a N2
[Fe(BPMCDAC)] shows high catalytic activity in combination
with TBAB towards the coupling reaction of CO2 and diglycidyl
atmosphere at a heating rate of 10 °C/min from ambient
temperature to 500 °C.
15 ethers (Scheme 1), whose iron active site is environmentally
friendly alternative to toxic central metal like cobalt and
Gel permeation chromatography. GPC measurements were
performed on Waters 410 GPC instrument. The GPC columns
chromium. Under solvent-free condition, glycol diglycidyl ether 60 were eluted with DMF solution containing 0.03 M LiBr at 1.0 mL
(1a) could be completely converted to the corresponding
bis(cyclic carbonate) (2a) with turn over number of 1000 under
20 relatively mild conditions (100 oC and 3 MPa) in 4 h, which
could be conveniently purified by flash column chromatography
using CH2Cl2 as the eluent. Furthermore, the obtained bis(cyclic
carbonate) (2a) could react with 1,2-ethane diamine (EDA), 1,3-
propane diamine (PDA) or 1,6-hexane diamine (HDA) to produce
25 NIPUs (Scheme 2) in accurate ratio of carbonate to amine group.
min-1 at 50 oC. Calibration was performed using mono-dispersed
polystyrene.
Synthesis of bis(cyclic carbonate)s
Diglycidyl ethers (1a-1e in Scheme 1), Fe(BPMCDAC) and
65 TBAB were added to a stainless-steel autoclave with a magnetic
stirrer in a glove box. CO2 was pressurized to this mixture and the
reaction was operated under determined conditions. After
reaction, the autoclave was cooled to room temperature, and the
CO2 pressure was released by opening the outlet valve. Then the
70 crude reaction mixture was obtained to calculate the conversion
by 1H NMR spectroscopy in CDCl3. The catalysts were removed
by flash column chromatography using CH2Cl2 as the eluent and
the obtained pure bis(cyclic carbonate) could be used for NIPU
preparation.
1
75
1a: H-NMR (CDCl3, TMS, 300 MHz): δ (ppm) = 3.72 (m,
2H), 3.62 (m, 4H), 3.36 (m, 2H), 3.10 (m, 2H), 2.72 (m, 2H),
2.54 (m, 2H).
1
1b: H-NMR (CDCl3, TMS, 300 MHz): δ (ppm) = 3.60 (m,
2H), 3.40 (m, 4H), 3.26 (m, 2H), 3.03 (m, 2H), 2.68 (m, 2H),
80 2.50 (m, 2H), 1.55 (m, 4H).
1
1c: H-NMR (CDCl3, TMS, 300 MHz): δ (ppm) = 3.61 (m,
Scheme 2 Synthesis of NIPUs from 2a and diamines.
2H), 3.41 (m, 4H), 3.26 (m, 2H), 3.03 (m, 2H), 2.68 (m, 2H),
2.48 (m, 2H), 1.48 (m, 4H), 1.26 (m, 4H).
1d: H-NMR (CDCl3, TMS, 300 MHz): δ (ppm) = 3.66 (m,
Experimental
1
Materials
85 2H), 3.35 (m, 2H), 3.21 (m, 4H), 3.09 (m, 2H), 2.73 (m, 2H),
2.56 (m, 2H), 0.86 (m, 6H).
30 Glycol diglycidyl ether (GDE) (1a) and other diglycidyl ether
derivatives (1b-1e) were purchased from Ruipu Material Co.
(China) and distilled over CaH2 under reduced pressure before
use. [Fe(BPMCDAC)] was prepared following a literature
procedure developed in this lab.16 Other reagents with analytical
1
1e: H-NMR (CDCl3, TMS, 300 MHz): δ (ppm) = 7.17 (m,
1H), 6.51 (m, 3H), 4.21 (m, 2H), 3.91 (m, 2H), 3.34 (m, 2H),
2.88 (m, 2H), 2.74 (m, 2H).
1
90
2a: H-NMR (CDCl3, TMS, 300 MHz): δ (ppm) = 4.80 (m,
2H), 4.49 (m, 2H), 4.40 (m, 2H), 3.62-3.79 (m, 8H).
2
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1
2b: H-NMR (CDCl3, TMS, 300 MHz): δ (ppm) = 4.76 (m,
between 2.54 and 3.10 ppm were ascribed to the methylene and
methine protons of epoxy group. Due to the decreased signal
intensity at δ = 2.54-3.10 ppm, the conversion of 1a could be
2H), 4.43 (m, 2H), 4.30 (m, 2H), 3.44-3.63 (m, 8H), 1.55 (m, 4H).
1
2c: H-NMR (CDCl3, TMS, 300 MHz): δ (ppm) = 4.74 (m,
2H), 4.41 (m, 2H), 4.28 (m, 2H), 3.56 (m, 2H), 3.50 (m, 2H), 60 monitored. New signals at δ = 4.40-4.80 ppm were attributed to
5
3.40 (m, 4H), 1.47 (m, 4H), 1.26 (m, 4H).
2d: H-NMR (CDCl3, TMS, 300 MHz): δ (ppm) = 4.78 (m,
the methylene and methine protons of cyclic carbonate group.
1
Table 1 Coupling reaction of 1a/CO2 in Fe(BPMCDAC)/TBAB catalytic
systema
2H), 4.42 (m, 4H), 3.62 (m, 2H), 3.52 (m, 2H), 3.18 (m, 4H),
0.86 (m, 6H).
1
Temperature
(oC)
Pressure Time Conversion
TOF
(h-1)d
2e: H-NMR (CDCl3, TMS, 300 MHz): δ (ppm) = 7.20 (m,
Entry
TONc
(MPa)
(h)
(%)b
10 1H), 6.52 (m, 3H), 5.02 (m, 2H), 4.59 (m, 2H), 4.49 (m, 2H),
4.20 (m, 2H), 4.10 (m, 2H).
1
2
3
4
5
6
7
8
100
100
100
100
80
3
3
3
3
3
3
1
2
1
2
3
4
2
2
2
2
73
91
730 730
910 455
960 320
1000 250
520 260
1000 500
910 455
900 450
Synthesis of NIPUs
96
NIPUs could be synthesized through the polyaddition of the
bis(cyclic carbonate) (2a) and diamines (Scheme 2). 2a (60 mmol)
15 and diamine (60 mmol) were added in a flask under N2
atmosphere. The mixture was stirred at 60 oC for 20 min, then the
temperature was raised to 80 oC and maintained for 2 h. All of the
procedures were performed under N2 atmosphere.
100
52
120
100
100
100
91
90
NIPU 1: 1H-NMR (d6-DMSO, TMS, 300 MHz): δ (ppm) =
20 7.12-6.75 (-NH), 4.65 (-OCH(CH2OH)CH2-), 3.36-3.91 (-
OCH(CH2OH)CH2-, -CH2O-, -OCH2CH(OH)CH2-), 3.00 (-
NHCH2). 13C-NMR (d6-DMSO, TMS, 75 MHz): δ (ppm) =
156.42, 156.06, 73.43, 72.33, 70.22, 69.79, 67.80, 65.69, 60.15,
40.22.
a
Reaction conditions: 0.1 mol-% Fe(BPMCDAC), 0.1 mol-% TBAB
b
65 (relative to epoxy group). Conversion was determined by 1H NMR
spectroscopy. Moles of epoxy group per mole of catalyst. Moles of
epoxy group produced per mole of catalyst per hour.
c
d
25
NIPU 2: 1H-NMR (d6-DMSO, TMS, 300 MHz): δ (ppm) =
7.09-6.72 (-NH), 4.66 (-OCH(CH2OH)CH2-), 3.36-4.05 (-
OCH(CH2OH)CH2-, -CH2O-, -OCH2CH(OH)CH2-), 2.97 (-
NHCH2), 1.50 (-CH2-). 13C-NMR (d6-DMSO, TMS, 75 MHz): δ
(ppm) = 156.46, 156.12, 73.37, 72.39, 70.28, 69.85, 67.89, 65.67,
30 60.25, 38.03, 29.90.
NIPU 3: 1H-NMR (d6-DMSO, TMS, 300 MHz): δ (ppm) =
7.09-6.75 (-NH), 4.66 (-OCH(CH2OH)CH2-), 3.36-3.88 (-
OCH(CH2OH)CH2-, -CH2O-, -OCH2CH(OH)CH2-), 2.93 (-
NHCH2), 1.50-1.22 (-CH2-). 13C-NMR (d6-DMSO, TMS, 75
35 MHz): δ (ppm) = 156.33, 155.97, 73.14, 72.37, 70.20, 69.77,
67.84, 65.48, 60.19, 40.23, 29.43, 26.03.
Results and discussion
Fig. 2 IR spectra of bis(cyclic carbonate) (2a) and diepoixde (1a).
Reactions of carbon dioxide with glycol diglycidyl ether
Bis(cyclic carbonate)s were prepared by the cycloaddition
40 reaction of diepoxides and CO2 catalyzed by Fe(BPMCDAC).
Moreover, the selection of suitable co-catalysts was extensively
investigated, and TBAB was found to be an effective co-catalyst
in activating the iron catalytic system for cycloaddition of
epoxides and CO2 (in Supplementary Table S1), which was
45 consistent with our recent work.16 With TBAB as the co-catalyst,
Fe(BPMCDAC) could effectively catalyze the coupling reaction
of glycol diglycidyl ether (1a) and CO2 to generate the
corresponding carbonate (2a). The data were listed in Table 1.
The formation of the cyclic carbonate groups was monitored
50 quantitatively via IR spectroscopy and 1H-NMR spectroscopy.
Fig.2 displayed the IR spectra of diepoxide (1a) before and after
carbonation (2a). The strongest peak at 1795 cm-1 was ascribed to
the carbonyl group of 2a. The 1H-NMR analysis was used to track
70
Fig.3 1H-NMR spectra of the coupling products at different time at 100 oC
and 3MPa using Fe(BPMCDAC)/TBAB as catalyst.
1
the conversion of 1a to 2a at various time. Fig.3 showed the H-
o
55 NMR spectra of coupling products at 100 C and 3 MPa (Entries
The signals between 2.54 and 3.10 ppm disappeared completely
1-4) using Fe(BPMCDAC)/TBAB as catalyst. The signals
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at 100 oC and 3 MPa after 4 h, indicating that 1a could be
converted to 2a completely under the reaction conditions, i.e.,
quantitative synthesis of bis(cyclic carbonate) (2a) could be
possible reaction pathway for the coupling reaction of diepoxides
and carbon dioxide. It is possible that a chloride ligand which is
able to ring-open epoxy group dissociate from the iron centre
realized. This is extremely important for preparation of NIPUs 40 forming a cationic iron species, which can coordinate and activate
5
with high molecular weight.
epoxide.19 Furthermore, the cocatalyst (TBAB) has two key roles
in the catalytic cycle,17a one is to provide bromide for the ring-
opening of the epoxide, and the other to form tributylamine
which reacts with CO2 to form a carbamate salt for better CO2
The reaction temperature was an important factor to the
catalytic activity. As shown in Table 1, the catalytic activity
increased significantly when the temperature increased from 80 to
120 oC. 1a was completely converted into the corresponding 45 activation. The activated CO2 can insert into the metal alkoxide
o
o
10 carbonate in 2 h at 120 C (Entry 6), while it took 4 h at 100 C
(entry 4). Higher temperature was beneficial for the conversion of
bond to give a metal carbonate which experiences ring-closing to
form the cyclic carbonate.
17
quaternary ammonium salt into amine, the amine subsequently
Reactions of carbon dioxide with a series of diglycidyl ether
derivatives
formed a carbamate salt with carbon dioxide, therefore, the
activation of carbon dioxide was accelerated, leading to faster
15 coupling reaction.
50 To evaluate the versatility of Fe(BPMCDAC) catalyst for other
diepoxides, cycloaddition of CO2 with a variety of diepoxides
(1b-1e) were investigated, the results were summarized in Table 2.
In some cases it was necessary to use dichloromethane as the
solvent during the conversion to avoid high viscosity and/or solid
55 nature of the reaction mixture.
The reactions with the iron catalyst were also conducted under
different pressures. Using Fe(BPMCDAC) as catalyst, the
catalytic activities varied insignificantly when CO2 pressure
increased from 1 MPa to 3 MPa, indicating that the rate of the
20 coupling reaction was independent of CO2 pressure in this range.
Therefore, considering the catalytic performance, the easiness
of operation as well as economical efficiency, the optimal
conditions for the coupling reaction of diepoxides/CO2 catalyzed
Table 2 Coupling reaction of CO2/ diglycidyl ether derivatives a
Time
（h）
Conversion
（%）
TOF
(h-1)
Entry Epoxide
Product
TON
o
by Fe(BPMCDAC) should be carried out at 100 C and 3 MPa
1b
2b
3
1a
1a
1b
1b
1c
1c
1d
1d
1e
1e
1e
1e
1b
1b
2a
2a
2b
2b
2c
2c
2d
2d
2e
2e
2e
2e
2b
2b
2
4
91
100
81
97
46
68
75
85
93
100
39
55
74
82
910 455
1000 250
810 405
970 243
460 230
680 170
750 188
850 213
930 465
1000 250
390 195
550 138
25 for 4 h, in molar ratio [epoxy group/Fe(BPMCDAC)/TBAB] of
1000:1:1.
2
4
4
5
2
6
4
7
2
8
4
9
2
10
11c
12c
13d
14e
4
2
4
72
9
132
--f
1.8
--f
a
Reaction conditions: 0.1 mol-% Fe(BPMCDAC), 0.1 mol-% TBAB
(relative to epoxy group), 3 MPa, 100 oC. Entry 2 and Entry 4 from
b
Table 1 were reproduced here for reference. c Dichloromethane as solvent,
d
e
60 and the ratio of epoxide to solvent was 1:1 (v/v). Data from ref 10c.
Data from ref 13.
f
TON and TOF cannot be calculated due to
heterogeneous catalysts.
Low loadings of catalyst (0.1 mol %) and co-catalyst (0.1
o
mol %) were generally effective at 100 C and 3 MPa. All
65 diepoxides can be effectively converted into the corresponding
organic carbonates, and conversion of over 50% was achieved,
indicating the good versatility of this catalytic system. It should
be noted that all diepoxides could be completely converted into
the corresponding organic carbonates in enough reaction time. As
70 anticipated, the conversions were time-dependent, it increased
with longer reaction periods while the turnover frequencies
(TOFs) decreased. Furthermore, the catalyst system could not
only catalyze the cycloaddition of the linear diepoxides and
carbon dioxide, but also tolerate the diepoxides which contain
75 side chains or aromatic rings. Under the applied conditions, on
Scheme 3 Proposed reaction mechanism for diepoxide/CO2 coupling.
Furthermore, a reaction mechanism was proposed (Scheme 3).
30 As reported in the literatures,8c, 17-18 coupling reaction of carbon
dioxide with epoxides to generate corresponding cyclic
carbonates requires activation, i.e., the Lewis acid activates the
epoxide while the Lewis base acts as a nucleophile to open the
epoxide ring. Besides, the cocatalyst also plays a key role in the
35 catalytic cycle. Based on the molecular structure of the
complexes and the coupling reaction results, we propose a
4
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prolonging the carbon chains, the conversions gradually
decreased (Entries 1, 3 and 5). A 91% conversion was obtained in
2 h for 1a, while it decreased to 81% for 1b, and only 46% was
converted for 1c. Besides, a 75% conversion of 1d with side
were relatively narrow between 1.18 and 1.22. Though the
number-average molecular weights showed a slight decrease in
comparison with the literature,14 the procedure to synthesis of
NIPUs was simple without any solvent. Interestingly, the degrees
5
chain was obtained in 2 h (Entry 7), though it was much lower 55 of polymerization (DPs) of the resultant NIPUs were similar
than that of 1a. Therefore we assumed that the catalytic activity
was affected by aliphatic chain length in the monomer.9 As
aliphatic chain length increased, addition of carbon dioxide was
hindered because of chain folding or the fluidity of chains and the
[m(NIPU 1) = 78.8, m(NIPU 2) = 82.9, m(NIPU 3) = 79.8]
(Scheme 2), which were independent of the chain length of
diamines.
10 hindrance of methyl groups. The diepoxide 1e containing
aromatic ring had a relatively higher conversion, it reached 93%
in 2 h, which was even higher than that for 1a (91%). The
existence of aromatic ring could increase the rigidity of chains
and decrease the chain folding. Furthermore, phenoxy group
15 could increase the Lewis acidity of epoxy group to activate
diepoxide. Dichloromethane was used as solvent due to the solid
nature of the product (2e) at room temperature (Entries 11 and
12). Unfortunately, the conversion of 1e decreased significantly
compared to that without solvent, since the solvent may reduce
20 the diepoxide density leading to slow reaction rate. Furthermore,
for diepoxides like 1b, Fe(BPMCDAC) exhibited great catalytic
activity, a 97% conversion of 1b could be obtained in 4 h, which
was much higher than the data in the literature (Entries 4, 13 and
14).10c, 13
25 Preparation of NIPUs
60
Fig.4 IR spectra of various NIPUs from diamine and 2a.
The obtained bis(cyclic carbonate)s could be applied to
synthesize poly(hydroxyurethane)s via polyaddition reaction with
diamines. The polyaddition reactions of 2a with 1,2-ethane
diamine (EDA), 1,3-propane diamine (PDA) and 1,6-hexane
30 diamine (HDA) to produce NIPUs were carried out by a solvent-
free and catalyst-free method, resulting in three polyurethanes
with different backbones. The results were summarized in Table
3.
The thermal properties of the NIPUs were characterized by
DSC and TGA. The DSC thermograms are shown in Fig. S1 and
the evaluated data are presented in Table 3. The Tg values depend
on the chemical structure of NIPUs. As expected, NIPU 1 had the
o
65 highest Tg (9 C) among the synthesized materials because of its
smaller spacer length that limited the mobility of polymer chain
segments for higher Tg.20 The thermal decomposition analysis
under nitrogen of various NIPUs was investigated by TGA from
ambient temperature to 500 oC. As shown in Fig. S2, these NIPUs
70 demonstrated initial degradation (Td = 5%) temperature between
Table 3 Polyaddition reaction of 2a with EDA, PDA and HADa
b
c
d
d
PDIb
Tg Td 5% Td max
o
Mn
206 and 266 C, and maximum decomposition rate between 241
Entry Diamine NIPU
(kg mol-1) (Mw/Mn) (oC) (oC) (oC)
and 319 oC. NIPU 3 having longest carbon chain possessed the
o
highest initial degradation temperature at 266 C, its maximum
1
2
3
EDA
PDA
HAD
NIPU 1
NIPU 2
NIPU 3
25.4
27.9
30.2
1.18
1.19
1.22
9
4
206
234
241
276
319
rate of degradation occurred at relatively high temperature (319
75 oC), which was very interesting for this kind of NIPUs, where
NIPU containing longest spacer length showed highest thermal
stability.
-2 266
35 a Reaction conditions: 2a:diamine (mol/mol) = 1:1, 60 oC for 20min, then
80 oC for 2 h. b Determined by GPC using dimethyl formamide (DMF) as
eluent. c Measured by DSC. d Measured by TGA.
Acknowledgements
The polyadditon reactions of 2a and diamines were monitored
by FT-IR spectroscopy. The FT-IR spectra in Fig.4 showed the
40 vibration peak at 1795 cm-1 which was assigned to the carbonyl
group of the cyclic carbonate. After polyaddition, the vibration
peak at 1795 cm-1 disappeared , and new peaks at 1700, 1540 and
3340 cm-1 appeared, which were typical for the carbonyl IR
absorption of the urethane groups, N-H deformation of the
45 urethane groups, and hydroxyl groups, respectively.
As shown in Table 3, GPC analysis showed that the number-
average molecular weights of the obtained NIPUs were between
25.4 and 30.2 kg mol-1, which were remarkable under solvent-
free and catalyst-free condition. Moreover, compared with the
50 data in the literature10, 12a, 13, 15b, the polydispersity indexes (PDIs)
The authors thank financial support from the National Natural
80 Science Foundation of China (Grant No. 51321062, 51273197
and 21134002).
Notes and references
a Key Laboratory of Polymer Ecomaterials, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun 130022,
85 People’s Republic of China. Fax: +86 431 85262252; Tel: +86 431
85262252; E-mail: ysqin@ciac.jl.cn. Fax: +86 431 85689095; Tel: +86
431 85262250; E-mail: xhwang@ciac.jl.cn
b University of Chinese Academy of Sciences, Beijing 100039, People’s
Republic of China
90
†
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