Upgrading castor oil: From heptanal to non-isocyanate poly(amide-hydroxyurethane)s

Article abstract of DOI:10.1016/j.polymer.2017.07.070

Intensive research has recently been carried out to synthesize non-isocyanate polyurethanes (NIPUs) from five-membered cyclic carbonates and amines as a sustainable route to industrial relevant polyurethanes. Herein, an activated disubstituted cyclic carbonate and methyl ester containing monomer CE was prepared using castor oil based heptanal and CO₂. Good results for the catalytic cycloaddition have been obtained using renewable sugar cane bagasse in combination with TBAB, and this system has been shown to be recyclable. A novel poly(amide-hydroxyurethane) (PAHU) was obtained by bulk ring-opening and amidation polymerization of high reactive CE with 1,6-diaminohexane at low temperature and in absence of catalyst. PAHU contains aliphatic pendant moieties allowing its self-assembling into nanoparticles in aqueous solution, showing potential application in catalysis or drug delivery among other applications.

Full text of DOI:10.1016/j.polymer.2017.07.070

Accepted Manuscript
Upgrading castor oil: From heptanal to non-isocyanate poly(amide-hydroxyurethane)s
L. Ruiz, A. Aghmiz, A.M. Masdeu-Bultó, G. Lligadas, J.C. Ronda, M. Galià, V. Cádiz
PII:
S0032-3861(17)30745-0
10.1016/j.polymer.2017.07.070
JPOL 19882
DOI:
Reference:
To appear in: Polymer
Received Date: 13 June 2017
Revised Date: 20 July 2017
Accepted Date: 25 July 2017
Please cite this article as: Ruiz L, Aghmiz A, Masdeu-Bultó AM, Lligadas G, Ronda JC, Galià M, Cádiz
V, Upgrading castor oil: From heptanal to non-isocyanate poly(amide-hydroxyurethane)s, Polymer
(2017), doi: 10.1016/j.polymer.2017.07.070.
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Graphical Abstract
SCB

ACCEPTED MANUSCRIPT
Upgrading castor oil: from heptanal to non-isocyanate
poly(amide-hydroxyurethane)s
L. Ruiza, A. Aghmizb, A.M. Masdeu-Bultóc,*, G. Lligadasa, J.C. Rondaa, M. Galiàa,*, V.
Cádiza
aDepartament de Química Analítica i Química Orgànica, Universitat Rovira i Virgili,
Marcel.lí Domingo 1, 43005 Tarragona, Spain.
E-mail: marina.galia@urv.cat
bA. Aghmiz, Faculté des Sciences, University Addelmalek Essaadi, Mhannech II, B.P.
Tétouan, Morocco
cA. M. Masdeu-Bultó, Departament de Química Física i Inorgànica, Universitat Rovira i
Virgili, Marcel.lí Domingo 1, 43005 Tarragona, Spain.
E-mail: annamaria.masdeu@urv.cat
Abstract
Intensive research has recently been carried out to synthesize non-isocyanate
polyurethanes (NIPUs) from five-membered cyclic carbonates and amines as a
sustainable route to industrial relevant polyurethanes. Herein, an activated
disubstituted cyclic carbonate and methyl ester containing monomer CE was prepared
using castor oil based heptanal and CO2. Good results for the catalytic cycloaddition
have been obtained using renewable sugar cane bagasse in combination with TBAB,
and this system has been shown to be recyclable. A novel poly(amide-
hydroxyurethane) (PAHU) was obtained by bulk ring-opening and amidation
polymerization of high reactive CE with 1,6-diaminohexane at low temperature and in
absence of catalyst. PAHU contains aliphatic pendant moieties allowing its self-
assembling into nanoparticles in aqueous solution, showing potential application in
catalysis or drug delivery among other applications.
Introduction
Polyurethanes (PUs) are one of the most important classes of polymers. Due to
their versatile properties, they can be used as thermoplastics, thermosets or
elastomers in a multitude of everyday life applications such as foams, coatings,
sealants, adhesives or fibbers.1 Despite this wide range of applications, there
1

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has been increased concern for the use of isocyanates, as they are toxic
compounds being made from even more toxic reagents.2 Another issue
regarding the use of isocyanates is their sensitivity to moisture that can be
problematic for their storage stability. Moreover, isocyanates and polyols are
currently synthesized from petrochemical resources. Stimulated by strict
regulations and the quest for sustainable development, latest advances in PU
research have been driven by a growing demand for greener processes
exploiting renewable resources and reducing potential hazards.
Consequently, intensive research on alternative synthesis pathways to non-
isocyanate PUs (NIPUs) has been carried out.3 These studies concluded that the
aminolysis of cyclic carbonates is one of the most promising alternatives. Even
though six- and seven-membered cyclic carbonates are more reactive than five-
membered carbonates, the focus has been placed on the last ones which are
readily available from the carbonation of epoxide groups. The generation of
cyclic carbonates by this route enables the fixation of the greenhouse gas
carbon dioxide in a 100% atom economical reaction. CO2 is an abundant
renewable C1-building block for the synthesis of a wide range of organic
chemicals.4 As a matter of fact, there are yet commercial industrial processes to
obtain aliphatic cyclic carbonates such as ethylene and propylene carbonates
using CO2 and a wide range of epoxides can be transformed in the
corresponding cyclic carbonates by means of different catalytic systems.5
Moreover, it has been shown that cyclic carbonate materials can be readily
obtained from renewable resources such as plant oils,6 fatty acids,7 limonene8 or
lignocellulose.9 Quaternary ammonium salts, such as tetrabutylammonium
bromide (TBAB), catalyses this transformation with catalysts loadings 3-5 %.6
Heterogeneous catalysts such as Keggin heteropolyacids Pt doped were also
active but the catalyst was not recyclable.10 Two points have been identified as
possibility of improvement of the catalytic activity. Firstly, it has been observed
that binary catalysts improve the activity. For example, the combination
SnCl4·5H2O/TBAB showed a synergic effect achieving a 94 % conversion in the
reaction of soybean oil and CO2 in 20h at 140°C.6h In this case, toxic
dimethylformamide was used as a solvent. In another example, a cooperative
effect was observed using the combination of TBAB and polyoxometalates
containing chromium6g or TBAB and aluminium complexes in the cycloaddition of
CO2 to methyl oleate.11 A second factor is the use of supercritical or condensed
carbon dioxide. This has been attributed to an increase of the oil-CO2 solubility
2

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due to the increased pressure.6g Nevertheless, the solubility of the catalyst in the
condensed CO2 phase was also important, since as the density of the CO2
phase increased, the ionic catalyst became insoluble and the conversion
dropped. Thus, it is necessary to find more sustainable catalytic systems which
can be reused and to optimize the pressure conditions to the optimum substrate-
CO2 versus catalyst solubility.
Soybean oil and castor oil fatty acid derivatives, containing internal double
bonds, have been investigated for the production of NIPUs.12 The resulting
disubstituted carbonates are less reactive than monosubtituted cyclic carbonates
and elevated temperatures and long reaction times are needed to obtain high
conversions. Undecylenic acid, a castor oil derivative having a terminal double
bond, has also been investigated.13 Undecylenic acid is obtained from the
thermal cracking of ricinoleic acid and in this process heptanal is also obtained.
This product is widely used as a synthesis intermediate for fragrance and aroma
industry. However, the use of this C7 cut of castor oil as an intermediate in
polymer chemistry is practically non existent.
The aim of this work was developing a more environmentally friendly synthetic strategy
for PUs by using heptanal as biobased starting material and by avoiding isocyanates.
The strategy relies on the preparation of a new five-membered disubstituted
cyclocarbonate methyl ester precursor through the carbonation of a renewable
heptanal derivative. The polymerization through carbonate ring opening and methyl
ester amidation afforded a poly(amide hydroxyurethane) PAHU containing pendant
aliphatic chains. The self-assembling of this amphiphilic structure into polymeric
nanoparticles was investigated.
Experimental Section
Materials
The following chemicals were used as received: heptanal (Arkema, 96%),
trimethyl phosphonoacetate (Aldrich, 98%), 1,8-diazabicyclo-[5.4.0]undec-7-ene
(DBU, Aldrich, ≥99%), n-decane (Merck, 99%, m-chloroperbenzoic acid
(MCPBA, Aldrich, 70%), 3-tert-butyl-4-hydroxy-5-methylphenyl sulphide
(Santonox®) (Aldrich), tetrabutylammonium bromide (TBAB, Aldrich, ≥99%),
Ytterbium (III) trifluoromethane sulfonate hydrate (Aldrich), hexylamine (Aldrich,
99%), 1,6-diaminohexane (HDA, Aldrich, 98%). Carbon dioxide (SCF Grade,
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99.999%, Air Products) was used introducing an oxygen/moisture trap in the line
(Agilent). Sugar cane bagasse (SCB) was obtained from the region of Loukos
(Morocco) after sugar extraction, washing with water and air dried. The inner part
was then milled and dewaxed in a Soxhlet extractor with toluene ethanol (2:1,
v/v) for 12 h and then dried under vacuum at 60 °C. Aluminum complex
[Al(salabza)Cl]11 and 2-bis(aminopyridinium) tetrachlorozincate14 were obtained
following reported procedures. All solvents were purified by standard
procedures.
Instrumentation
The IR analyses were performed on a FTIR- 680PLUS spectrophotometer with a
resolution of 4 cm-1 in the transmittance mode. NMR spectra were recorded on a
1
Varian VNMRS400. The samples were dissolved in CDCl3 or DMSO-d6, and H
and 13C NMR spectra were recorded at room temperature with tetramethylsilane
as an internal standard. ESI MS were run on a chromatographic system Agilent
1200 liquid chromatography coupled to 6210 Time of Flight (TOF) mass
spectrometer from Agilent Technologies with an ESI interface.
Size exclusion chromatography (SEC) analysis was carried out with an Agilent
1200 series system equipped with an Agilent 1100 series refractive-index
detector. DMF was used as eluents at a flow rate of 1.0 mL/min. The calibration
curves for SEC analysis were obtained with polystyrene standards. Differential
scanning calorimetry (DSC) measurements were carried out with a Mettler
DSC822e thermal analyser with N2 as the purge gas. Samples, 6-12 mg, were
used for DSC analysis. Thermal stability studies were carried out with a Mettler
TGA/SDTA851e/LF/1100 with N2 as the purge gas at a scanning rate of 10
°C/min.
Transmission electron microscopy (TEM) was performed using a JEOL JEM-
1011 TEM microscope. Before the measurement, a drop of solution was placed
on a copper grid which was allowed to dry at room temperature.
Fluorescence spectra were recorded using a Shimadzu RF-5301PC
fluorescence spectrometer at room temperature. The samples were excited at
335 nm, and the emission spectra were recorded from 350 to 500 nm.
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Dynamic light scattering (DLS) measurements were carried out at room
temperature using Zetasizer Nano ZS (Model ZEN3500) from Malvern
Instruments equipped with a He-Ne laser.
Synthesis of methyl 2-nonenoate (1)
5.00 g (43.8 mol) of heptanal, 7.98 g (43.8 mmol) of trimethyl phosphonoacetate
and 0.62 g (4.4 mmol, 10 mol% to heptanal) of n-decane as internal standard
were added to a round-bottom flask. The flask was immersed into an ice bath
with magnetic stirring and 6.57 mL (43.8 mmol) of DBU was slowly added over
15 min. The temperature was maintained at 0°C. The conversion of heptanal,
determined by GC, was 97% after 3 hours. The crude of reaction was dissolved
in diethyl ether and washed with 10% HCl solution, 10% K2CO3 solution and
finally with brine. The organic phase was dried over anhydrous magnesium
sulfate, filtered, and the solvent was removed under reduced pressure. The
obtained oil was distilled under reduced pressure (7 mmHg) and the fraction at
85-90°C was collected. The product was obtained as a mixture of E:Z isomers
(ratio 98.5:1.5) in a 93% yield.
1H NMR [CDCl3, TMS, δ (ppm)] (Figure S1a): 6.96 (dt,
−CH=CH−CO−), 5.82 (dt,
−CH=CH−CO
−), 3.73 (s,
−O
−CH3), 2.21 (m,
−CH2
−
CH=CH ), 1.57-1.28 (m,
−
−
CH2 ), 0.88 (t,
−
−CH3).
13C NMR [CDCl3, TMS, δ (ppm)] (Figure S1b): 167.41 (
−
CO
−
), 150.06
32.42
CH2 ),
(−
CH=CH
CH2 CH=CH
CH3).
−
CO
−),
120.96
CH2
(−CH=CH
−CO−),
51.98
(−O
−
CH3),
(−
−
−
), 31.79 (
−
−), 29.00 (−CH2−), 28.17 (−CH2−), 22.75 (
−
−
14.26 (
−
Synthesis of 2,3-epoxynonanoic methyl ester (EE)
The epoxidation reaction was carried out by dissolving 14.8 g (60.1 mmol) of dry
MCPBA (70%), 5 g (29.4 mmol) of and 0.15 g (0.44 mmol) of 3-ter-butyl-4-
1
hydroxy-5-methylphenylsulphide into 50 mL of 1,2-dichloroethane. The mixture
was maintained at reflux temperature for 4 h. Then, 7.5 g (30.4 mmol) of dry
MCPBA was dissolved into 25 mL of 1,2-dichloroethane and this solution was
added to the reaction flask. The reaction was followed by 1H NMR and after 2h,
the crude of reaction was washed with 5% Na2S2O5 solution, 5% NaHCO3
solution, and brine. The organic phase was dried over anhydrous magnesium
sulfate, and 1,2-dichloroethane was evaporated off. The obtained oil was purified
5

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by column chromatography using hexane:ethyl acetate, 10:1, as eluent, to afford
the pure compound as an oil, in a 72 % yield .
1H NMR [CDCl3, TMS, δ (ppm)] (Figure S2a): 3.79 (s,
CH COO ), 3.16 (dt, CH CH2 ), 1.57-1.28 (m, CH2
13C NMR [CDCl3, TMS, δ (ppm)] (Figure S2b): 169.93 (
CH CH2 ), 53.05 ( CH COO ), 52.52 ( CH3), 31.76 (
31.57 ( CH2 ), 29.01 ( CH2 ), 25.79 ( CH2 ), 22.64 ( CH2 ), 14.16 (−
−
O
−
CH3), 3.23 (d,
), 0.89 (t, CH3).
CO ), 58.69
CH CH2 ),
CH3).
−
O
−
−
−
−
O
−
−
−
−
−
−
−
−
(−
O
−
−
−
−O
−
−
−
−O
−
−
−
−
−
−
−
−
−
−
−
−
HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C10H18O3 186.1252; found 186.1256.
Synthesis of methyl 2,3-carbonyldioxynonanoate (CE)
The reactions were carried out in a 25 mL Parr reactor equipped with a magnetic
stirrer and automatic temperature control system. The reactor was charged with
epoxide (1.5 g, 8.1 mmol) and TBAB (5 or 3 mol %). When a binary catalyst
system was employed, cocatalyst was also added to the reactor. The reactor
was purged with vacuum and argon several times and after that heated to the
specific temperature (80, 100 or 120 °C depending on the experiment) and
finally was pressurized with CO2 to reach the desired pressure (300, 600 or 1275
Psi). After the desired reaction time (1, 3 or 6 hours), the reactor was cooled to
room temperature and gradually depressurized. The conversion of epoxide and
1
the yield were determined by H NMR of the crude reaction mixture using
mesitylene as internal standard. The reaction mixture was dissolved in diethyl
ether (10 mL) and washed with water (3 x 15 mL). The organic layer was dried
over anhydrous magnesium sulfate, filtered, and the solvent was removed under
reduced pressure. The product was purified by column chromatography using
hexane:ethyl acetate, 40:1 to 20:1, as eluent, to afford the carbonate cyclic as
viscous oil, in a 46 % yield.
1H NMR [CDCl3, TMS, δ (ppm)] (Figure S3a): 4.66, 3.87, 1.84, 1.55-1.25, 0.90.
13C NMR [CDCl3, TMS, δ (ppm)] (Figure S3b): 167.78, 153.38, 79.68, 76.98,
53.30, 34.34, 31.50, 28.65, 24.12, 22.47, 14.02.
HRMS (ESI-TOF) m/z: [M + H]+ Calcd for C11H18O5 230.1150; Found 230.1154.
Polymerization of CE and 1,6-diaminohexane
2,3-carbonyldioxynonanoate (CE) (4.2g, 1.8 mmol) and 1,6-diaminohexane
(2.2g, 1.8 mmol) and 1.5mL of anhydrous DMF were added to a dry 10 mL
round-bottom flask. The reaction mixture was stirred at room temperature for 30
6

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min under nitrogen purge. Then, the polymerization was continued under
reduced pressure (30 mBar). After 24h, the polymer was precipitated into diethyl
ether, centrifuged, filtered and dried in vacuum. The polymer was obtained as a
white solid in 84 % yield.
1H NMR [DMSO, δ (ppm)] (Figure S5a): 7.58, 6.80, 4.82, 3.87, 3.59, 3.51, 3.04,
2.91, 2.59, 1.80-1.15, 0.85.
13C NMR [DMSO, δ (ppm)] (Figure S5b): 172.52, 171.35, 169.01, 156.12, 73.82,
72.34, 51.59, 38.32, 31.36, 30.55, 29.59, 29.26, 28.77, 26.22, 24.97, 22.17,
14.05.
Results and Discussion
Synthesis of 2,3-epoxynonanoic methyl ester (EE)
The Horner-Wadsworth-Emmons (HWE) reaction is one of the most popular and
powerful method for the generation of C-C double bonds.15 This modification of
the Wittig reaction is widely used for the preparation of α,β-unsaturated esters. It
has several advantages over the Wittig reaction, which are a result of the strong
nucleophilic nature of the phosphonate carbanion created during the reaction.
This increase in nucleophilicity allows milder reaction conditions, tolerance of a
variety of functional groups and use of less electrophilic aldehydes and ketones.
The HWE reaction of triethyl phosphonoacetate with a variety of aldehydes using
17
stoichiometric amounts of DBU16 or catalyzed by DBU in presence of K2CO3
was described to give α,β-unsaturated esters with high yield and E-selectivity.
We evaluated the reactivity of heptanal and trimethyl phosphonoacetate in bulk
using 1 eq of DBU at room temperature (Table 1). The aldehyde consumption
was measured by GC using an internal standard. A conversion of 98% was
1
reached after 3h. The reaction was also monitored by H NMR spectroscopy
through the appearance of signals at 6.96 and 5.82 ppm corresponding to the
carbon double bond protons and signal at 3.73 ppm corresponding to the methyl
protons of the methyl 2-nonenoate (1). Isomers E and Z could be identified thus
allowing their quantification. Moreover, unexpected signals at 5.54 and 3.02 ppm
7

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could be observed, that can be ascribed to methyl 3-nonenoate (2) as the
isomerization product. Isomerization of 2-pentenoates to 3-pentenoates has
been described to occur in presence of catalytic amounts of cyclic tertiary
amines such as DBU at temperatures higher than 50°C.18 The extension of
isomerization was 18% as obtained by 1H NMR.
Table 1. HWE reaction in bulk and using equimolar amounts of aldehyde and
phosphonate
O
P
O
O
O
O
O
O
O
+
O
H
O
1
2
Entry
T
DBU
(eq)
Conv
(%)[a]
E1:Z1[b]
1:2[c]
Yield
(%)
(ºC)
25
0
1
2
3
4
1.00
1.00
0.75
0.50
98
98
97
94
98.8:1.2
98.5:1.5
98.5:1.5
98.5:1.5
82:18
97:3
98:2
99:1
81
98
94
90
0
0
[a] Heptanal conversion from GC. [b] E1:Z1 isomers ratio from 1H NMR [c] 1:2 isomers
ratio from 1H NMR
To avoid the isomerization process, the reaction was carried out at 0°C, reaching
similar aldehyde conversion and E1
Attempts to diminish the DBU amount were carried out. A slight conversion
decrease with no significant variations in -unsaturated ester selectivity were
observed. However, a yield decrease was observed, thus 1 eq. was used for
synthesis. After purification by distillation under reduced pressure, was
epoxidized using m-chloroperbenzoic acid to obtain methyl 2,3-epoxynonanoate
EE) in a 72% yield (Scheme 1). Both compounds were characterized by 1H and
:Z1 ratio, and higher 1:2 ratio and yield.
α,β
1
1
(
13C NMR spectroscopy (Figures S1 and S2)
Scheme 1. Epoxidation of methyl 2,3-nonenoate and cycloaddition of
CO2 to methyl 2,3-epoxynonanoate
8

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Cycloaddition of CO2 to methyl 2,3-epoxynonanoate
The cycloaddition of CO2 to EE producing the corresponding cyclic carbonate,
methyl 2,3-carbonyldioxynonanoate CE (Scheme 1) was first attempted using
tetrabutylammonium bromide (TBAB), which is a common low cost and easy to
handle catalyst for this reaction.19
The reaction of the substrate EE with CO2 at 600 psi and 80°C using 5 mol % of
1
catalyst provided an oily mixture. The H NMR spectra of the crude reaction
(Figure 1) showed a multiplet signal at 4.66 ppm, attributed to the cyclic
carbonate (44% yield) (entry 1, Table 2). Signals observed at 4.01-4.41 ppm
were attributed to the presence of the diol from the hydrolysis of the substrate.
Other signals at 3.54 and 2.84 ppm seems to indicate the presence of 1,2 and
1,3-dicarbonylic compounds as a result of the diol elimination.
1
Figure 1. H NMR spectra (CDCl3) of the crude reaction of EE
and CO2 (entry 1, table 2)
9

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Optimization of the catalytic reaction conditions was then undertaken. At 600 psi,
increasing the temperature to 100°C and 120°C, an increase of conversion up to
near completion was observed (entries 1-3, Table 2). In fact, at 120°C the
epoxide was not detected but the selectivity to the cyclic carbonated decreased
due to secondary reactions. To determinate if the presence of the catalyst
promoted the opening of the epoxide an experiment was run with less amount of
catalyst (3 mol%) and during a longer period of time (6 h) but similar selectivity
was obtained (entry 4, Table 2). Regarding the influence of the CO2 pressure,
conversion and selectivity were inferior when the pressure decreased to 300 psi,
but increasing the pressure to 1275 psi, the conversion and selectivity did not
improve either (entries 5 and 6, Table 2). Finally, the reduction of time to 1 h did
not decrease the formation of by-products (entry 7, Table 2).
Table 2. Results of the cycloaddition of CO2 to EE using TBAB as catalyst. [a]
Entry
Catalyst
(mol%)[b]
T
(ºC)
P
(psi)
t
Conv
(%)[c]
Yield
(%)[d]
(h)
1
2
3
4
5
6
7
5
5
5
3
5
5
5
80
600
600
600
600
1275
300
600
3
3
3
6
3
3
1
62
92
>99
86
92
80
72
44
59
51
60
58
47
43
100
120
100
100
100
100
[a] Reaction conditions: catalysts: tetrabutylammonium bromide (TBAB) substrate: 1.5
g. [b] mol % in relation to the substrate. [c] Conversion determined by NMR using
mesitylene as internal standard. [d] Yield determined by NMR using mesitylene as
internal standard.
In the literature it has been proved that binary catalytic systems formed by one
component able to activate the epoxide (a hydrogen bonding donor or Lewis
acid) and a nucleophile for the ring open step increased the conversion of the
epoxides into cyclic carbonates.5c,20 The effect of adding a co-catalyst was
analysed at the reaction conditions 80°C, 600 psi and 5 mol%. Among the
possible co-catalysts reported in the literature, we selected a bio renewable
product such as sugarcane bagasse SCB (
tetrachlorozincate ( ) and an aluminum complex
),14 ytterbium triflate (
[Al(salabza)Cl]11 (
3
),21 2-bis(aminopyridinium)
4
5
6
) (salabza: N,N’-bis(salicylene)-2-aminobenzylamine). The –OH
10

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groups of the components of SCB (cellulose, hemicelluloses and lignin) have
been reported to act as hydrogen-bonding donors to accelerate the ring-opening
of the epoxide.21 The addition of SCB (2.5% w/w at 80°C, 600 psi and at 5 mol%
TBAB) produced an increase in conversion and selectivity (entry 1, Table 3).
When the reaction was run at the optimized temperature (100 ºC, entry 2, Table
3) a 94 % of conversion was obtained (54 % yield) in 1 h reaction time using
catalytic systems SCB/TBAB. Addition of
4 to TBAB produced also high
conversion and good selectivity (entry 3, Table 3). Co-catalysts such as
produced a decrease of selectivity (entries 4 and 5, Table 3).
5 and 6
Table 3. Results of the cycloaddition of CO2 to EE using 3-6/TBAB as
catalysts.[a]
Entry
Catalyst
T
(ºC)
P
(psi)
t
Conv
(%)[b]
Yield
(%)[c]
(h)
1
2
3
4
5
3/TBAB
3/TBAB
4/TBAB
5/TBAB
6/TBAB
80
600
600
600
600
600
3
1
1
1
1
79
94
93
91
72
60
54
48
30
26
100
100
100
100
[a] Reaction conditions: catalysts: 3 SCB 2.5 % w/w; 4 [pyNH2]2[ZnCl4] 1 mol %; 5
Yb(OTf)3 1 mol %; 6 [Al(salabza)Cl] 1 mol %; TBAB 5 mol %; substrate: 1.5 g. [b]
Conversion determined by NMR using mesitylene as internal standard. [c] Yield
determined by NMR using mesitylene as internal standard.
The advantage of using the insoluble SCB was that it could be separated by
filtration after the catalytic reaction and reused. Indeed, after the catalytic
reaction the SCB was separated, washed with ether and dried. After adding
fresh TBAB, it could be reused 5 more times without significant loss of activity
and selectivity (Figure 2). CE was purified by column chromatography and
characterized by NMR spectroscopy (Figure S3).
11

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Figure 2. Recycling experiments of catalytic system 3/TBAB
in the cycloaddition of CO2 to EE. Reaction conditions: 3:
2.5 % w/w, TBAB: 5 mol %, substrate: 5 g, 80°C, 600 psi, 3h.
Poly(amide-hydroxyurethane) synthesis
The aminolysis of cyclic carbonates has been widely investigated. Not only the
size but also the nature of the substituents attached to the cyclic carbonate
influence the reactivity, as well as the structure of the amines and other
parameters like the catalyst or the solvent. 5-membered cyclic carbonates are
the least reactive cyclic carbonates. 6- and 7-membered cyclic carbonates are
more reactive, but aminolysis of these compounds still requires the use of high
temperatures.22 N-substituted 8-membered cyclic carbonates appeared to be
much more reactive than the smaller cyclic carbonates.23 Even being the less
reactive, the 5-membered cyclic carbonates are still the most used ones and the
influence of the substituent on the reactivity has been studied and attributed to
electronic effects. Electron-withdrawing substituents increase the electrophilicity
of carbonyl and activate nucleophilic attack of the amine.13 Moreover, the steric
hindrance of the substituents and the effect of hydrogen bonds have also been
considered.22 The remarkable reactivity of α-alkylidene substituted 5-membered
cyclic carbonates has been recently described.24
We investigated the aminolysis of the five membered carbonate CE. Primary
aliphatic amines are the most reactive for the aminolysis of cyclic carbonates,
thus n-hexylamine was used as a model compound. The reaction was carried
1
out with a molar ratio CE/amine 1:1 at 70°C in bulk and monitored by H NMR
spectroscopy. The appearance of urethane methylene signals at 3.13 ppm (f1
and
hydroxyurethane formation (Figure 3b, Figure S4). Moreover, intense signals at
3.26 ppm (e1 and 2) can be seen that can be attributed to amide formation, as
f2) and methyne signals at 4.00-5.20 ppm (b1, b2, c1 and c2) confirmed the
e
well as at 3.49 ppm, due to the presence of methanol obtained as a by-product.
The reaction of the primary amine with the ester function has been previously
described as a side reaction at high temperatures and could be avoided by
working at 25°C.12,13 Other side reactions25 that can take place during the
aminolysis of cyclic carbonates such as the formation of ureas, oxazolidinones
and dehydration products seems not to take place.
12

ACCEPTED MANUSCRIPT
To further elucidate the relative reactivity of the carbonate and the ester
functions in front of primary amines, we carried out the reaction using a
CE/amine molar ratio 1:0.5 at 25°C in bulk. Hydroxyurethane and amide signals
can be observed, thus indicating that both carbonate aminolysis and amide
formation are taking place. After 40 min of reaction, a conversion of 20% for
carbonate and 24% for ester moieties can be obtained by 1H NMR spectroscopy
(Figure 3c). This seems to indicate that the reactivity of both moieties does not
differ significantly. When the reaction is carried out at 25°C using a molar ratio
CE/amine 1:2, a mixture of amide-hydroxyurethanes AHU1 and AHU2 (81:19) is
obtained after 30 min (Figure 3d).
Figure 3. 1H NMR spectra (CDCl3) of a) CE and of the reaction
of CE and hexylamine in bulk b) molar ratio 1:1 at 70ºC, c)
molar ratio 1:0.5 at 25°C, d) molar ratio 1:2 at 25°C
As has been previously reported,22 the electron-withdrawing effect of the ester
moiety increases the electrophilicity of the carbonyl and activates the
nucleophilic attack of the amine and the opening of the carbonate ring.
According to the proposed reaction mechanism, the nucleophilic attack of the
13

ACCEPTED MANUSCRIPT
amine to the carbonyl takes place, followed by the carbonate ring opening and
the formation of secondary hydroxyurethanes. The rupture of the carbon-oxygen
bond α to the ester group position seems to be more favoured than the one in
the β position, according to a higher electron-withdrawing effect of the ester
group, thus leading to a higher amount of AHU1. Moreover, the amide formation
seems to be activated by the presence of the carbonate moiety, being the
carbonyl ester more reactive than the 5-membered cyclic carbonate derived from
methyl 9-decenoate, when the amidation takes place at 70-180°C using TBD as
catalyst.26
Taking into account the model reaction results, we carried out the one pot
polymerization using 1,6-diaminohexane (Scheme 2, Table 4). The mixture of
reactants was kept at the initial temperature for 30 min and vacuum was applied
in the next step to remove the methanol byproduct and reach high conversion.
1
PAHU formation was followed by H NMR spectroscopy by the appearance of
new methyne signals at 4.82 ppm (b1
2.91 ppm (f1 2) attributed to the hydroxyurethane moiety and methylene signals
at 3.04 ppm (e1 2) linked to the amide group (Figure 4a, Figure S5a). Signals
, c2), 3.87 (c1, b2) and methylene signals at
,
f
,
e
labelled as * can be attributed to end groups. 13C NMR spectra showed the
disappearance of carbonate and ester signals and the appearance of
hydroxyurethane signals at 156.12 and 155.94 (h1
c1 2) ppm and amide signals at 172.57, 171.35 ppm (g1
S5b).
,
h
2), 73.82 and 72.34 (b1
, b2,
,
c
, g
2) (Figure 4b, Figure
Scheme 2. Synthesis of poly(amide-hydroxyurethane)
The PAHU formation was also confirmed by IR spectroscopy by the appearance
of bands at 1692cm-1 and 1637cm-1 attributed to the carbonyl of the urethane
and amide moieties respectively, a broad band between 3590cm-1 and 3150cm-1
14

ACCEPTED MANUSCRIPT
due to NH and OH groups and the disappearance of bands at 1810 and
1748cm-1 due to carbonate and ester groups (Figure S6)
When the reaction was carried out in bulk at 25°C for 3h and the obtained solid
showed a molar mass of 5800 gmol-1 from the SEC analysis in DMF (Table 4).
Higher reaction time and temperature and solvent conditions were examined
after this preliminary experiment. When DMF or higher reaction temperatures
were used, higher molar masses were obtained. However, increasing reaction
time seems not to have a significant effect on polymer molar masses (Figure
S7).
Table 4. PAHU synthesis
Entry
T
(ºC)
Solvent
t (h)[a]
Mn
Ð
(g mol-1)[b]
1
2
25
25
-
3
6
5800
7200
8200
1.7
1.6
1.6
DMF
24
48
7800
1.7
9700[c]
1.4[c]
3
4
60
60
-
3
3
8200
1.5
9700[c]
1.4[c]
DMF
7900
1.7
9800[c]
1.5[c]
[a] Vacuum was applied after 30 min at atmospheric pressure [b] Molar mass by SEC
in DMF prior to precipitation [c] Molar mass by SEC in DMF after precipitation
In spite of the high reactivity of CE, low molar masses were obtained. The
synthesis of polyhydroxyurethanes from bis(cyclic carbonate)s and polyamines
usually leads to low molar mass polymers. The presence of numerous side
reactions that disturbs the stoichiometric carbonate/amine ratio and creates non
reactive chain ends has been demonstrated when the reaction takes place at
80°C.25 Moreover, the formation of high amounts of hydrogen bonds between
urethane, hydroxyl and amine groups at room temperature can also limit the
diffusion of the reactants thus limiting molar masses.22 This effect can explain
the results in our case, in bulk as well in presence of an aprotic solvent.
The polymer was found to be soluble in DMF and DMSO and insoluble in water,
acetone, THF and CHCl3. It was purified by precipitating in diethyl ether from the
15

ACCEPTED MANUSCRIPT
crude of reaction in DMF and isolated as a white solid with high yield (76%). The
poly(amide-hydroxyurethane) was characterized using spectroscopic methods
and thermal analysis, showing a Tg at 47°C and a 5% of weight loss at 219°C
(Figure S8).
a)
a2
a1
c1
HO
Ha
a1
c1
O
O
O
O
O
Hu
N
e1
b1
O
b1
O
b2
e1
N
N
N
O
N
Ha
c2
f1
Ha
Hu
OH
x
e2
OH
O
y
e1,e2
f1,f2
c1,b2
DMSO-d6
b1,c2
*
NHa
NHu
*
*
b)
DMSO-d6
e1, e2
f1, f2
a2
a1
HO
a1
O
O
Hu
N
O
O
O
e1
b1
O
Ha
N
c1
b1
b2
e1
c1
g2
N
g
1 Ha
h1
O
h1
N
O
c2
N
g
1 Ha
f1
OH
h2 Hu
y
x
e2
OH
O
h1, h2
g1, g2
b1, b2
c1, c2
*
*
*
**
Figure 4. a) 1H NMR and b) 13C NMR spectra of PAHU (DMSO-d6)
The obtained polymer contains an aliphatic amide-hydroxyurethane amphiphilic
backbone and aliphatic hydrophobic pendant chains. Thus, it can self-assemble into
nanoparticles in aqueous solution and be used in catalysis or drug delivery among
other applications. It has been described that the presence of pendant aliphatic chains
plays an important role in creating nanocavities when solvent diffusion method is used
to obtain polymer nanoparticles.27 We investigated the ability of the poly(amide-
hydroxyurethane) to form nanoparticles with hydrophobic cavities using a water-based
solvent diffusion method. The polymer was dissolved in DMF and added dropwise to
stirring water and dynamic light scattering experiments confirmed the formation of
stable and monodisperse nanoparticles with an average diameter of 106 nm (PI=0.1)
(Figure 5a) that could be observed by TEM (Figure 5b) . To determine the critical
micelle concentration (CMC), pyrene was encapsulated as a fluorescent probe. The
intensity variation of fluorescence emission peaks at 384 and 374 nm confirmed the
effective encapsulation of the hydrophobic probe and the self-assembling bringing the
hydrophobic moieties into the cavities (Figure 5c). A CMC value of 0.75 mg/L was
16

ACCEPTED MANUSCRIPT
obtained (Figure 5d). This low value ensures high stability of the nanoparticles and less
disruption with dilution, which can be very important in medical applications that involve
intravenous injection.
100
80
60
40
20
0
0,90
0,85
0,80
0,75
0,70
0,65
0,60
Increasing PAHU
concentration
CMC = 0,75 mg/L
360
380
400
420
440
460
480
500
-6
-5
-4
-3
-2
-1
Wavelength (nm)
Log C
Figure 5. a) DLS size distribution by intensity of PAHU (0.8
mg/mL). b) TEM image of nanoparticles of PAHU (0.8
mg/mL). c) Fluorescence spectra of an aqueous solution of
pyrene (6.0 x10-7 M) and different concentrations of PAHU
(1.7 x10-6 to 0.12 mg/mL). d) Fluorescence intensity ratio
I384/I374 as a function of PAHU concentration.
Conclusions
In conclusion, heptanal, the by-product of thermal craking of ricinoleic acid, has
been functionalized by a HWE reaction and the obtained has been epoxidized
1
to obtain EE in good yield. To obtain CE, the catalytic cycloaddition of CO2 to the
epoxide has been investigated and good results have been obtained using
renewable SCB in combination with TBAB catalytic system, which has been
shown to be recyclable.
The reactivity of CE in front of amines has been investigated and the results
show that not only the ester activated five-membered cyclic carbonate displayed
a high reactivity, but also the ester moiety turn out to be very reactive. This
allowed to carry out the bulk polymerization of CE and 1,6-diaminohexane at low
temperature and in absence of catalyst, leading to NIPUs of molar mass similar
17

ACCEPTED MANUSCRIPT
to the ones previously described. The obtained polymer forms stable and
monodisperse nanoparticles in water, showing potential application in catalysis
or drug delivery among other applications.
Acknowledgements
Financial support from the MINECO (Ministerio de Economia y Competitividad)
(MAT2014-53652-R, CTQ2016-75016-R) is gratefully acknowledged. G.L.
Acknoledges the Serra Húnter Programme (Generalitat de Catalunya).
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-
-
-
An activated cyclic carbonate is obtained from castor oil derived heptanal and
CO2
Renewable sugar cane bagasse/TBAB system is an efficient and recyclable
catalyst
Non isocyanate PAHU are prepared in bulk at low temperature in absence of
catalyst