Tunable poly(hydroxyl urethane) from CO2-Based intermediates using thiol-ene chemistry

Article abstract of DOI:10.1002/pola.24631

CO₂-based, crosslinked poly(hydroxyl urethane)s (PHUs) are accessed via a set of efficient reactions based on the addition chemistry of thiol-ene and amines-cyclic carbonates. This strategy to utilize 5-membered cyclic carbonates produced from CO₂ is robust, facile, modular, and atomically efficient in nature. The thiol-ene reaction was utilized to access bis(cyclic carbonate), tris(cyclic carbonate), and tetrakis(cyclic carbonate) in quantitative yield from 4-vinyl-1,3-dioxolan-2-one and thiols. Multi-functional cyclic carbonates were simply mixed with diethylenetriamine and/or 1,6-diaminohexane to generate crosslinked PHUs from 25 to 80 °C. These materials are easy to scale-up and are potential candidates in many applications such as coatings, binders, and resins. The resulting polymers have glass transition temperatures between -1 and 16 °C and thermal decomposition temperatures from 190 to 230 °C. 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 CO₂-based, crosslinked poly(hydroxyl urethane)s (PHUs) are accessed via a set of efficient reactions based on the addition chemistry of thiol-ene and amines-cyclic carbonates. The thiol-ene reaction was utilized to access multi-functional cyclic carbonates in quantitative yield from 4-vinyl-1,3-dioxolan-2-one and thiols. These precursors were simply mixed with diethylenetriamine and/or 1,6-diaminohexane to generate crosslinked PHUs. Copyright

Full text of DOI:10.1002/pola.24631

Tunable Poly(hydroxyl urethane) from CO2-Based Intermediates
Using Thiol-Ene Chemistry
CHAU N. TANG,1 HUNAID B. NULWALA,1 KRISHNAN DAMODARAN,2 PALWINDER KAUR,3 DAVID R. LUEBKE1
1National Energy Technology Laboratory, P.O. Box 10940, Pittsburgh, Pennsylvania 15236
2Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
3Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
Received 23 December 2010; accepted 10 February 2011
DOI: 10.1002/pola.24631
Published online 9 March 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: CO2-based, crosslinked poly(hydroxyl urethane)s
(PHUs) are accessed via a set of efficient reactions based on
the addition chemistry of thiol-ene and amines-cyclic carbo-
nates. This strategy to utilize 5-membered cyclic carbonates
produced from CO2 is robust, facile, modular, and atomically
efficient in nature. The thiol-ene reaction was utilized to access
bis(cyclic carbonate), tris(cyclic carbonate), and tetrakis(cyclic
carbonate) in quantitative yield from 4-vinyl-1,3-dioxolan-2-one
and thiols. Multi-functional cyclic carbonates were simply
mixed with diethylenetriamine and/or 1,6-diaminohexane to
generate crosslinked PHUs from 25 to 80 ꢀC. These materials
are easy to scale-up and are potential candidates in many
applications such as coatings, binders, and resins. The result-
ing polymers have glass transition temperatures between ꢁ1
and 16 ꢀC and thermal decomposition temperatures from 190
to 230 ꢀC.
2011 Wiley Periodicals, Inc.† J Polym Sci Part A:
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Polym Chem 49: 2024–2032, 2011
KEYWORDS: amine; carbonate; crosslinked polyurethanes; poly-
(hydroxyl urethane)s; thiol-ene chemistry
INTRODUCTION The observed increase in atmospheric CO2
concentration since the beginning of the industrial era is
mainly due to the burning of fossil fuels.1 This increase in CO2
concentration is believed to be the major cause of global warm-
ing.2–4 To stave off potentially serious changes in the global cli-
mate, it is important to stabilize the CO2 levels in the atmos-
phere. A major effort will be required to reduce CO2 emissions.5
Complete replacement of fossil fuels with renewable energy
sources in the short term is probably not feasible; therefore, a
program of CO2 capture followed by geological storage or utili-
zation is necessary. There is a need to develop processes and
reactions to efficiently store and utilize CO2. The captured CO2
may be thought of as the cheapest raw material available for the
development of polymers, pharmaceuticals, solvents, and other
products. Although the scales of production of these materials
are not sufficient to entirely make use of the CO2, the transfor-
mation of CO2 into useful products can decrease the volume
which must be sequestered and generate revenues to offset the
cost. Many authors have focused on the development of CO2-
based materials via the direct and indirect utilization of CO2.6–10
donating reagents. This makes CO2 an ‘‘anhydrous carbonic
acid,’’ which rapidly reacts with basic compounds. For example,
organometallic reagents such as Grignard reagents readily react
with CO2 even at a low temperature. Similarly, water, alkoxides,
and amines also undergo addition with CO2 to produce com-
pounds with a carboxyl or carboxylate group. These reactions
conveniently produce carbonic and carbamic acids.
Specifically, organic carbonates have applications in thermoplas-
tics,11 thermosets,8 electronics12,13 (i.e., electrolytes in lithium
ion battery and sealant), coatings,14–17 solvents, fuel addi-
tives,13,18 and they are used as starting materials for the prepara-
tion of polyurethanes.7,19 The formation of organic carbonates is
an inexpensive method which has been widely studied for CO2
fixation. As carbonates have three oxygen atoms in each mole-
cule, they are relatively suitable synthetic targets for CO2 fixa-
tion.20 Five- and six-membered cyclic carbonates are commer-
cially available and are produced from CO2 in high yields.13,21–23
Figure 1 shows several synthetic pathways to produce five-mem-
bered cyclic carbonate via cycloaddition of CO2 and other con-
ventional routes.20–22,24–41 These cyclic carbonates have found
uses in cycloaddition reaction, but due to their stability, 5-mem-
bered cyclic carbonates are more commonly used as solvent.
Though CO2 is cheap, abundant, and non-toxic, it has found
relatively few uses in industrial processes since it is chal-
lenging to develop chemistry which can activate the highly
oxidized carbon dioxide and transform it into useful prod-
ucts. CO2 has strong affinity toward nucleophiles and electron-
Poly(hydroxyl urethane)s (PHU) presents an opportunity to
directly make polymers from CO2-derived precursors. The poly-
addition of 5-membered and 6-membered bis(cyclic carbonate)s
Additional Supporting Information may be found in the online version of this article. Correspondence to: D. R. Luebke (E-mail: david.luebke@netl.
doe.gov) or H. B. Nulwala (E-mail: hunaid.nulwala@or.netl.doe.gov)
Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 2024–2032 (2011) 2011 Wiley Periodicals, Inc. †This article is a U.S. Government
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work, and as such, is in the public domain in the United States of America.
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Aldrich. Lithium bromide, octylamine, and a Spectroline UV
lamp (Model ENF-280C, 8W) were acquired from Fisher Sci-
entific. Chloroform-d (CDCl3) was purchased from Cambridge
Isotope Laboratory.
Methods
1H (500 or 700 MHz) and 13C (126 or 176 MHz) NMR
spectra were recorded in CDCl3 on a Bruker Avance III 500
or 700 spectrometer. Fourier transform infrared (FT-IR)
spectra were measured using a Nicolet IR100 FT-IR spec-
trometer, equipped with an attenuated total reflectance
(ATR) accessory with a diamond crystal. A Mettler Toledo
TGA/DSC 1 was used to measure the decomposition tem-
perature, which was determined as 5% mass loss, at a heat-
ing rate of 10 ꢀC/min under nitrogen. A TA Instruments
Q200 differential scanning calorimeter equipped with the
Refrigerated Cooling System 40 accessory was used to
determine glass transition temperatures (Tgs), which are
taken as the mean of the second and third heating scans.
The experiments were conducted under nitrogen at a heat-
FIGURE 1 Reported synthetic routes to produce cyclic
carbonates.
ꢀ
ing rate of 10 C/min.
with amines has been reported in the literature7,19 to obtain
PHUs. These polymeric materials have found a wide variety of
applications as adhesives, binders, hydrophilic coatings,42 hydro-
gels, and resins. Materials derived from carbonates offer the
additional advantage of being environmentally friendly.43
Mass spectroscopy was performed using an Agilent 6420 Tri-
ple Quadrupole (QQQ) LC-MS/MS (Agilent Technologies, Santa
Clara, CA). Agilent Mass Hunter software (Version B.02.01)
was used for data acquisition and processing. The samples
were directly infused into the mass spectrometer and eluted
at 0.4 mL/min using ethyl acetate. The flow rate of the drying
Herein, we present crosslinked PHUs which are easily acces-
sible and tunable from commercially available carbonates and
amines. The crosslinked PHUs are accessed via a modular and
facile reaction between amines and multi-functional cyclic car-
bonates, which are prepared from thiol and ene derivatives.
Both reactions are atomically efficient and produce solid
materials in high yields. The developed synthetic route is fac-
ile and represents a less-toxic, non-isocyanate pathway to
obtain polyurethanes. The reaction was scaled up to multi-
gram quantities without any need for special equipment or
precaution. The approach allows various properties to be
tuned such as glass transition temperature, modulus, and con-
tent of hydroxyl compounds, which are useful to prepare
polymers for targeted applications. The synthesis of 5- and 6-
membered bis(cyclic carbonate)s using thiol-ene chemistry
and linear PHUs had been reported by Endo et al.7 The syn-
thesis of crosslinked PHUs in a single step without solvents is
reported here for the first time. The multi-functional carbo-
nates were accessed via thiol-ene chemistry, which was
inspired by previous experience and the works of many
authors who used facile, robust, and modular reactions.44–66
These multi-functional cyclic carbonates can serve as mono-
mers, crosslinkers for polymeric materials with terminal and/
or pendant amines, coupling agents, and compatibilizers.
ꢀ
gas (N2) was 11 L/min, and the gas temperature was 350 C.
The MS fragmentor voltage was fixed at 250 V.
Synthesis of 4,40-((Hexane-1,6-diylbis(sulfanediyl))bis-
(ethane-2,1-diyl))bis(1,3-dioxolan-2-one) (Bis-CC)
2,2-Dimethoxy-1,2-diphenylethanone (0.200 g, 0.780 mmol),
4-vinyl-1,3-dioxolan-2-one (10.2 g, 89.4 mmol), and hexane-
1,6-dithiol (6.57 g, 43.7 mmol) were added to an aluminum
pan. The mixture was irradiated for 1 h using a UV lamp
(365 nm). The conversion was quantitative as confirmed
1
using either GC analysis, H NMR, or FTIR spectroscopy. The
1
product was used without further purification. H NMR (700
MHz, CDCl3,d): 1.36 (dt, J1 ¼ 7.25 Hz, J2 ¼ 3.63 Hz, CH2, 4H),
1.47–1.59 (m, CH2, 4H), 1.85–1.95 (m, CH2, 2H), 2.02–2.14 (m,
CH2, 2H), 2.49 (t, J1 ¼ 7.25 Hz, SACH2, 4H), 2.54–2.61 (m,
SACH2, 2H), 2.61–2.71 (m, SACH2, 2H), 4.09 (dd, J1 ¼ 8.67
Hz, J2 ¼ 7.09 Hz, OACH2, 2H), 4.56 (dd, J1 ¼ 8.67 Hz, J2
¼
7.09 Hz, OACH2, 2H), and 4.86 (qd, J1 ¼ 7.78 Hz, J2 ¼ 4.41
Hz, OACH, 2H). 13C NMR (176 MHz, CDCl3, d): 27.11 (SACH2),
28.30 (SACH2), 29.31 (CH2), 32.23 (CH2), 33.93 (CH2), 69.30
(OACH2), 75.71 (OACH(CH2)2), and 154.8 (C¼¼O). ATR-IR
(cmꢁ1): 466, 714, 770, 1054, 1155, 1378, 1437, 1779 (C¼¼O),
2854, and 2927. MS (m/z): calcd for C16H26O6S2, 378.12;
found, 401.11 [MþNa]þ.
EXPERIMENTAL
Synthesis of 2-Ethyl-2-(((3-((2-(2-oxo-1,3-dioxolan-4-yl)-
ethyl)thio)propanoyl)oxy) methyl)propane-1,3-diyl bis(3-
((2-(2-oxo-1,3-dioxolan-4-yl)ethyl)thio)propanoate) (Tris-CC)
The procedure was the same as above using trimethylol-
propane tris(3-mercaptopropionate) (6.70 g, 16.8 mmol),
4-vinyl-1,3-dioxolan-2-one (5.85 g, 51.3 mmol), and 2,2-
dimethoxy-2-phenylacetophenone (12.5 mg, 48.8 lmol). 1H
Materials
Diethylenetriamine (DETA), 4-vinyl-1,3-dioxolan-2-one (99%),
1,6-hexanedithiol (>97%), trimethylolpropane tris(3-mercapto-
propionate), pentaerythritol tetrakis(3-mercaptopropionate)
(97%), 1,6-diaminohexane (98%), and 2,2-dimethoxy-2-phe-
nylacetophenone (99%) were used as received from Sigma-
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
NMR (500 MHz, CDCl3, d): 0.88 (t, J1 ¼ 7.41 Hz, CH3CH2,
3H), 1.48 (q, J1 ¼ 7.36 Hz, CH3CH2, 2H), 1.88 – 1.96 (m, CH2,
3H), 2.00 – 2.17 (m, CH2, 3H), 2.46 – 2.66 (m, CH2, 6H), 2.66
– 2.78 (m, CH2, 12H), 4.03 (br. S, OACH2C, 6H), 4.10 (t, J1 ¼
8.50 Hz, OACH2CH, 3H), 4.57 (t, J1 ¼ 8.35 Hz, OACH2CH,
3H), and 4.87 (qd, J1 ¼ 7.83 Hz, J2 ¼ 4.26 Hz, OACH, 3H).
13C NMR (126 MHz, CDCl3, d): 7.46 (CH3), 23.03 (CH2CH3),
27.11 (SACH2), 27.26 (SACH2), 33.79 (CH2), 34.56
(CH2AC¼¼O), 40.84 (CCH2CH3), 64.00 (CH2CO2), 69.29
(OCH2CH), 75.58 (OCH2CH), 154.8 (CO3), and 171.4
(CH2CO2). ATR-IR (cmꢁ1): 468, 714, 770, 1055, 1153, 1236,
1286, 1352, 1382, 1476, 1725 (OC¼¼O), 1783 (O2C¼¼O),
2926, and 2962. MS (m/z): calcd for C30H44O15S3, 740.18;
found, 763.18 [MþNa]þ.
Synthesis of 2,2-Bis(((3-((2-(2-oxo-1,3-dioxolan-4-yl)ethyl)-
thio)propanoyl)oxy) methyl)propane-1,3-diyl bis(3-((2-(2-
oxo-1,3-dioxolan-4-yl)ethyl)thio)propanoate) (Tetra-CC)
The procedure was the same as above using pentaerythritol
tetrakis(3-mercaptopropionate) (8.40 g, 17.2 mmol), 4-vinyl-
1,3-dioxolan-2-one (7.95 g, 69.6 mmol), and 2,2-dimethoxy-
2-phenylacetophenone (11.9 mg, 46.4 lmol). 1H NMR (500
MHz, CDCl3, d): 1.89 – 1.96 (m, CH2, 4H), 2.04 – 2.11 (m,
CH2, 4H), 2.58 – 2.65 (m, CH2, 12H), 2.69 – 2.78 (m, CH2,
12H), 4.09 – 4.16 (m, 12H), 4.58 (t, J1 ¼ 8.35 Hz, OCH2CH,
4H), and 4.87 (qd, J1 ¼ 7.88, J2 ¼ 4.41 Hz, OCH2CH, 4H). 13C
NMR (126 MHz, CDCl3, d): 27.06 (SACH2), 27.25 (SACH2),
33.74 (CH2), 34.47 (CH2AC¼¼O), 42.21 [(CH2)4AC], 62.36
(CH2CO2), 69.31 (OCH2CHO), 75.63 (OCH2CH), 154.9 (CO3),
and 171.3 (CH2CO2). ATR-IR (cmꢁ1): 714, 769, 1054, 1154,
1236, 1352, 1382, 1478, 1728 (OC¼¼O), 1781 (O2C¼¼O),
2926, and 2962. MS (m/z): calcd for C37H52O20S4, 944.19;
found, 967.18 [MþNa]þ.
(hydroxyl urethane)s (PHUs) were characterized by ATR-IR
spectroscopy and thermal analyses.
PHU-1s were synthesized from Bis-CC (0.583 g, 1.54 mmol)
and DETA (0.166 g, 1.61 mmol) without a catalyst for 24 and
72 h and with LiBr as a catalyst for 48 h. In addition, the poly-
addition of Bis-CC and DETA was conducted at room tempera-
ture for 24 h. The mixture became viscous after several hours.
PHU-2 was synthesized from Tris-CC (1.18 g, 1.60 mmol)
and DETA (0.180 g, 1.75 mmol) without a catalyst for 24 h.
PHU-3 was synthesized from Tetrakis-CC (1.154 g, 1.22 mmol)
and DETA (0.174 g, 1.69 mmol) without a catalyst for 24 h.
The polymerization of Bis-CC and 1,6-diaminohexane using
10 and 24 mol % DETA (mole ratio of DETA to cyclic car-
bonate) were conducted for 24 h to generate PHU-4a and
PHU-4b, respectively. For example, PHU-4a was produced from
Bis-CC (1.143 g, 3.02 mmol), 1,6-diaminohexane (0.247 g,
2.13 mmol), and DETA (74.4 mg, 0.721 mmol).
RESULTS AND DISCUSSION
Monomer Syntheses
Thiol-ene chemistry was employed as the general synthetic
route to produce CO2-based multi-functional cyclic carbo-
nates. This chemistry is appealing due to the robust and or-
thogonal nature of the reaction and the synthetically power-
ful characteristics such as lack of byproducts, quantitative
yields, and optional use of solvents. In addition, it offers the
ability to construct multiple chemical intermediates from
commercially available reagents by changing the thiol-ene
combination. We chose 4-vinyl-1,3-dioxolan-2-one (VEC),
which has been extensively explored in the literature,9,29–32
as the CO2-based starting material due to its availability and
synthetic attributes such as high yield and abundant catalyst
selection.
Model Reaction
Bis-CC (0.539 g, 1.42 mmol) and octylamine (0.381 g, 2.95
mmol) were added to a 40 mL vial. The mixture was placed
ꢀ
Following the synthetic route outlined in Scheme 1, we dem-
onstrated that bis(cyclic carbonate) (Bis-CC), tris(cyclic car-
bonate) (Tris-CC), and tetrakis(cyclic carbonate) (Tetra-CC)
were successfully synthesized using the thiol-ene reaction of
VEC with 1,6-hexanedithiol, trimethylolpropane tris(3-mer-
captopropionate), or pentaerythritol tetrakis(3-mercaptopro-
pionate), respectively, at room temperature under UV light
using 2,2-dimethoxy-2-phenylacetophenone as an initiator.
These multi-functional cyclic carbonates were characterized by
FTIR, 1H NMR, 13C NMR, and mass spectroscopies. Figure 2
shows the 1H NMR spectra of starting reagents (1,6-hexane-
dithiol and VEC) and Bis-CC after the reaction. In every
thiol-ene reaction, the conversion of the limiting reagent (thi-
ols in all of the reactions) was quantitative after a short pe-
riod (30–60 min) of exposure to UV light. For example, we
observed the disappearance of the SAH resonance (1.31
ppm) and a shift of the SACH2 resonance (2.49 ppm) in
Figure 2 for the reaction between 1,6-hexanedithiol and VEC
after 30 min. 1H NMR spectra of the Bis-CC shows new
peaks for the CHACH2ACH2 resonance (1.93 and 2.14 ppm),
for the ACH2ASACH2A resonance (2.54 ppm), for the
ACH2ASACH2 resonance (2.64 and 2.72 ppm), and for the
into an oil bath at 80 C for 21 h. Because of the possibility
of four isomeric products, the assignment for the 1H NMR
listed only the methyl group and the methylene unit con-
nected to the nitrogen atom; similarly, only the methyl,
CH2N, and carbonyl resonances in the 13C NMR were pro-
vided. 1H NMR (500 MHz, CDCl3, d): 0.88 (t, J ¼ 6.78 Hz,
CH3, 6H) and 3.16 (q, J ¼ 6.83 Hz, 4H). 13C NMR (126 MHz,
CDCl3, d): 14.22 (CH3), 41.26 (CH2NH), and 156.9 (NC¼¼O).
ATR-IR (cmꢁ1): 540, 722, 776, 1042, 1141, 1250, 1458,
1536, 1668 (C¼¼O), 2852, 2921, and 3296 (OH and NH).
The reaction was also conducted using a catalyst. Bis-CC
(0.533 g, 1.41 mmol), octylamine (0.390 g, 3.02 mmol), and
LiBr (21.4 mg, 0.246 mmol) were added to a 40 mL vial. The
ꢀ
reaction was placed into an oil bath at 80 C for 2 h.
General Procedures for the Preparation of
Poly(hydroxyl urethane)s
In a typical example, an equimolar of total reactive groups
from
a carbonate (Bis-CC, Tris-CC, and Tetra-CC) and
amine(s) were added to a vial containing a stir bar. The reac-
ꢀ
tion was heated at 80 C for the desired amount of time and
allowed to cool to room temperature. The crosslinked poly-
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SCHEME 1 Synthetic route to multi-functional cyclic carbonates via thiol-ene reaction of 4-vinyl-1,3-dioxolan-2-one with several thiols.
CH resonance (4.86 ppm) of the cyclic carbonate. 1H NMR
spectra of Tris-CC and Tetra-CC are provided in the Support-
ing Information as Figures S1 and S2, respectively.
and 1781 cmꢁ1, respectively. In all of the multi-functional
cyclic carbonate, we observed the disappearance of the
vibrations due to the vinyl group (942 and 986 cmꢁ1).
Figure 3 shows the FTIR spectra of VEC, Bis-CC, Tris-CC, and
Tetra-CC. The m(C¼¼O) vibration of Bis-CC is at 1779 cmꢁ1. In
the case of Tris-CC, the peaks at 1725 and 1783 cmꢁ1 are
assigned to the m(C¼¼O) vibrations of the ester and carbonate
linkages, respectively. Similarly, the carbonyl groups of the
ester and carbonate linkages for Tetra-CC appear at 1728
To investigate the potential of side reactions, a equimolar
mixture of propylene carbonate and 1,6-hexanedithiol was
subjected to the same conditions as the thiol-ene reaction
(UV irradiation for 1 h) and the polyaddition (80 ꢀC for
24 h). If the thiol undergoes addition with the cyclic carbon-
ate during these experiments, then the product is a thio-
carbonate. However, no thiocarbonate was produced for
both conditions as confirmed by 1H NMR spectroscopy (see
Fig. S3 of the Support Information). The results further dem-
onstrated the modularity of the chemistry.
Model Reaction
To increase our understanding of the carbamate formation,
we reacted octylamine with Bis-CC in the presence and ab-
sence of LiBr as a catalyst to generate the urethane DOU.
Scheme 2 shows only one of four possible isomeric products
ꢀ
for this reaction. The conversion at 80 C for the uncatalyzed
reaction was quantitative after 21 h, and it was quantitative
after 2 h for the catalyzed reaction. These observations are
similar to results obtained in the literature.15,67–69 Besides
LiBr, other catalysts such as lithium oxide,67 lithium meth-
oxide,67 and potassium t-butoxide15,67 are effective for the
addition of carbonates and amines. Carbamate formation was
confirmed via FTIR and NMR spectroscopies. Figure 4
FIGURE 2 1H NMR spectra of 4-vinyl-1,3-dioxolan-2-one (top),
1,6-hexanedithiol (middle), and bis(cyclic carbonate) (bottom).
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FIGURE 4 FTIR spectra of bis(cyclic carbonate) (top) and DOU
(bottom).
the appearance of a methyl group at 0.89 ppm and a CH2AN
resonance at 3.19 ppm.
Polymerization
In the previous section, we have exploited thiol-ene chemis-
try to make CO2-based multi-functional cyclic carbonates. To
study their thermal properties and to identify potential
application of the polymers, we conducted the ring-opening
polyadditions of Bis-CC, Tris-CC, and Tetra-CC with DETA for
24 h at 80 ꢀC to generate CO2-based, crosslinked PHU-1,
PHU-2, and PHU-3 (Scheme 3), respectively. Many authors6,19
have prepared linear PHUs from bis-functional cyclic carbo-
nates and diamines. All of the polymerizations were per-
formed in bulk to avoid solvent trapping and elaborate the
facile nature of this chemistry. These PHUs were character-
ized using FTIR spectroscopy, differential scanning calorime-
try (DSC), and thermogravimetric analysis (TGA).
FIGURE 3 FTIR spectra of (top to bottom) 4-vinyl-1,3-dioxolan-
2-one, bis(cyclic carbonate), tris(cyclic carbonate), and tetrakis-
(cyclic carbonate).
compares the FTIR spectra of Bis-CC and DOU. The m(C¼¼O)
vibration shifted to a lower wavenumber when the cyclic
carbonate linkage (1779 cmꢁ1) was converted into the ure-
thane linkage (1688 cmꢁ1). Furthermore, there are peaks for
the carbamate that appears at 1250 and 1536 cmꢁ1 for the
NAH bending and CAN stretching and at 3296 cmꢁ1 for
NAH and OH stretchings. Endo et al.68 reported that the
m(C¼¼O) and m(NAH) vibrations are at around 1700 and
3240 cmꢁ1, respectively, for the urethanes produced from
hexylamine with different cyclic carbonates. The m(C¼¼O)
vibration is consistent with Endo et al., whereas the m(NAH)
vibration appear at higher wave number. Similarly, the 1H
NMR spectra (Fig. 5) shows the disappearance of the methyl-
ene and ethane moieties from the cyclic carbonate ring and
The polymerizations of Bis-CC and DETA were performed
with and without LiBr as a catalyst to evaluate the polymer-
ization behavior of this materials. Figure 6 shows the FTIR
spectrum of crosslinked PHU-1 as well as those for DOU and
crosslinked PHU-4. In PHU-1, hydroxyl urethane linkages are
observed at 1690 cmꢁ1 for the C¼¼O stretching and at 3305
cmꢁ1 for the NAH and OH stretchings whereas the m(C¼¼O)
vibration of cyclic carbonate in the crosslinked polymer is at
1794 cmꢁ1. Under similar conditions, it was found, as
SCHEME 2 The reaction between bis(cyclic carbonate) and
octylamine with and without LiBr as a catalyst (note: scheme
shows only one of four isomeric products).
FIGURE 5 1H NMR spectra of bis(cyclic carbonate) (top) and
bis-urethane (bottom).
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SCHEME 3 Synthetic route to CO2-based, crosslinked poly(hydroxyl urethane)s.
expected, that materials without LiBr take longer to polymer-
ize than those in which the catalyst was present; however, the
former materials have slightly higher Td. For example, when
the catalyzed polymerization was monitored with FTIR at 4,
24, and 48 h, the m(C¼¼O) vibration of the cyclic carbonate
decreased relative to the intensity of the carbonyl stretching
due to the urethane linkage. In addition, the intensity of the
NH and OH stretchings at 3305 cmꢁ1 increased with time.
However, both the catalyzed and uncatalyzed polymerizations
failed to convert all the carbonate linkages into the urethane
linkages unlike the small molecule model reaction (Fig. 4) due
to the restriction in chain mobility with increasing conversion.
ate linkages (ꢂ1790 cmꢁ1) present in these polymers after
24 h. On the basis of a total equimolar mixture of amine and
carbonate functional groups, the theoretical gelation point pc
(pc ¼ 2/favg, where pc is the critical extent of reaction at the
gel point and favg is the average functionality of the polymer-
ization system) for the polymerization of DETA with Bis-CC,
Tris-CC, and Tetra-CC occurs at 82%, 67%, and 58% conver-
sions, respectively. Thus, the gelation point of the polymeriza-
tion is reached at lower conversion as functionality increases.
The conversion was qualitatively monitored using the inten-
sity of the carbonyl stretching for the carbonate moiety in the
FTIR spectra. We determined that the conversion of the poly-
merization reaction for Tris-CC and DETA was greater than
that for the polymerization of Tetra-CC and DETA (see Fig. 7).
This result followed the theoretical prediction.
Figure 7 shows the FTIR spectra of PHU-2 and PHU-3. In
PHU-2 and PHU-3, the C¼¼O stretching of the carbamates
overlaps with the carbonyl group of the ester. There is a
broad peak at 3361 cmꢁ1 for the NH and OH stretchings of
the carbamate linkage for PHU-2 and PHU-3, and additional
peaks for the carbamate linkage appear at 1238 and 1527
cmꢁ1 for the NAH bending and CAN stretching. From the
FTIR analyses, it appears that there are residual cyclic carbon-
As a concrete demonstration of the robust and facile nature
of the polyaddition, we added equimolar mixtures of a multi-
functional cyclic carbonate and DETA to a Teflon dish and
placed these mixtures in an oven at 80 ꢀC for 24 h to pro-
duce the PHUs. The multi-functional cyclic carbonates were
TUNABLE POLY(HYDROXYL URETHANE), TANG ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 8 Pictures of crosslinked poly(hydroxyl urethane) pro-
duced from Bis-CC, Tris-CC, and Tetra-CC with DETA.
of DOU and PHU-1. The profiles of the three spectra are sim-
ilar, except for the presence of a m(C¼¼O) vibration of the
cyclic carbonate (1794 cmꢁ1) in PHU-1.
Thermal Analysis
FIGURE 6 FTIR spectra of DOU (top), PHU-1 (middle), and
Table 1 summarizes the glass transition temperatures (Tg)
and thermal decomposition temperatures (Td), which were
determined as the 5% mass loss, of different PHUs. From the
DSC analysis, PHU-1s have Tg between 3 and 12 C. The Tg of
PHUs produced with and without a catalyst (polymerization
PHU-4a (bottom).
immediately used after the thiol-ene reaction without purifica-
tion of unreacted starting material and initiator. Figure 8 shows
photos of the resulting polymers after the polymerization. We
are not concerned about the tendency of the monomeric rea-
gent to limit the molecular weight of the polymer formed since
it will be a crosslinked material. The robustness of the ring-
opening polyaddition of amine to carbonate eliminates the need
for purification prior to polymerization. Hence, the simplicity of
this reaction allows for easy scale-up in an industrial setting.
ꢀ
time ¼ 72 h) are similar. PHU-2 and PHU-3 have similar Tg
To tune the chemical and thermal properties of the poly(hy-
droxyl urethane)s, Bis-CC and 1,6-diaminohexane were poly-
merized with various contents of DETA to produce PHU-4
(Scheme 4). This polymerization provided an opportunity to
compare PHU-1 with PHU-4 and to access different materials
for thermal analyses. PHU-4a and PHU-4b were generated
using 10 and 24 mol % DETA, respectively, relative to the
mole of Bis-CC. The conversion of the cyclic carbonate was
quantitative in the polymerization of Bis-CC, 1,6-diaminohex-
ane, and 10 mꢀol % DETA (relative to the mole of cyclic car-
bonate) at 80 C for 24 h in the absence of a catalyst. Using
24 mol % DETA in the polymerization, we found that full
conversion was hindered by a lower value for the theoretical
gelation point (94% conversion for this system vs. 98% con-
version for the former). Figure 6 shows the FTIR spectrum
of the resulting polymer PHU-4a, which is compared to those
SCHEME 4 Synthesis of CO2-based, crosslinked poly(hydroxyl
urethane) using bis(cyclic carbonate), 1,6-diaminohexane, and
diethylenetriamine.
FIGURE 7 FTIR spectra of PHU-2 (top) and PHU-3 (bottom).
2030
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ARTICLE
TABLE 1 Decomposition Temperatures (Td) of Poly(hydroxyl
between VEC and different thiols produced multi-functional
cyclic carbonates (i.e., Bis-CC, Tris-CC, and Tetra-CC) in quan-
titative yield. The polyaddition of DETA (and 1,6-diaminohex-
ane in some cases) with the multi-functional cyclic carbo-
nates provided an easy and effective technique for producing
polymeric materials with tunable properties. The thermal
properties of the crosslinked polymers were characterized
by DSC and TGA. PHU-2 and PHU-3 have the highest Tg
whereas PHU-4 showed the best thermal stability. From the
physical and thermal properties, these materials are poten-
tial candidates in adhesive and sealant applications. Overall,
we showed a simple method to incorporate CO2 into poly-
mer via the use of cyclic carbonate chemistry.
urethane)sa
b
Polymers
Td (ꢀC)
Tg (ꢀC)
PHU-1c
PHU-1d
PHU-1
PHU-1e
PHU-2
PHU-3
PHU-4a
PHU-4b
a
–
3
11
5
190
217
208
193
186
230
231
12
16
16
ꢁ1
7
Polymerization was conducted at 80 ꢀC for 24
unless noted otherwise.
h
without catalyst
This work was funded and supported by U.S. Department of
Energy’s Office of Fossil Energy. The authors thank Dr. Sheila
Hedges and Dr. Jeffrey Culp for the training and use of differ-
ential scanning calorimeter and thermogravimetric analyzers.
b
Determined as 5% mass loss.
c
Polymerization was conducted at room temperature.
Used LiBr as a catalyst and polymerization time 48 h.
Polymerization time 72 h.
d
e
even though the functionality of these cyclic carbonates is dif-
ferent. Furthermore, the Tg of poly(hydroxyl urethane)s pro-
duced from Bis-CC, 1,6-diaminohexane, and DETA ranges from
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