X. L. CHEN et al.: PREPARATION OF BIO-POLYMERIC MATERIALS, THEIR MICROSTRUCTURES ...
229–236
PREPARATION OF BIO-POLYMERIC MATERIALS, THEIR
MICROSTRUCTURES AND PHYSICAL FUNCTIONALITIES
PRIPRAVA BIOPOLIMERNIH MATERIALOV TER NJIHOVE
MIKROSTRUKTURE IN FIZI^NE FUNKCIONALNOSTI
Xiu-Li Chen, Ai-Juan Zhao, Hai-Jie Sun, Xian-Ru Pei
Zhengzhou Normal University, Institute of Environmental and Catalytic Engineering, College of Chemistry and Chenical Engineering,
Zhengzhou 450044, China
katiloudy@163.com, sunhaijie406@zznu.edu.cn
Prejem rokopisa – received: 2015-07-09; sprejem za objavo – accepted for publication: 2016-05-13
doi:10.17222/mit.2015.211
In this work, three kinds of bio-based aromatic triols were prepared based on vegetable oils. Furthermore, PUs were synthesized
using the three triols and 4,4’-methylenebis(phenyl isocyanate), 1,4-butanediol as a chain extender. The chemical structures,
molecular characteristics, and physical functionalities were studied and compared using nuclear magnetic resonance (NMR)
spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry
(DSC), and thermogravimetry-differential thermal analysis (TG-DTA). Results showed that the poly-(oxypropylene)-based
polyurethanes degrade in a single step, whereas the vegetable-oil-based polyurethane shows one-step decomposition. The
present study therefore suggests a feasible synthesis route for the use of the biomaterials for the production of polyurethanes.
Keywords: polymers, microstructures, functionalities
V delu so bili iz bioolj prvi~ pripravljeni trije bioaromati~ni trioli. Poleg tega so bili sintetizirani PU, z uporabo treh triol in
4,4’-metilenbis(fenil izocianata) ter 1,4-butandiola kot podalj{evalca verige. [tudirane so bile kemijske strukture, molekularne
zna~ilnosti in fizi~ne funkcionalnosti, ki so bile primerjane z uporabo spektroskopije jedrske magnetne resonance (NMR),
spektroskopijo Fourierjeve infrarde~e transformacije (NMR), rentgenske difrakcije (XRD), diferen~ne vrsti~ne kalorimetrije
(DSC) in termogravimetri~ne diferen~ne termi~ne analize (TG-DTA). Rezultati so pokazali, da poliuretan na osnovi
poli-oksipropilena razpade v enem koraku, medtem ko poliuretan na osnovi rastlinskih olj, ka`e enostopenjski razpad.
Predstavljena {tudija torej predlaga izvedljivo sintezo z uporabo biomaterialov za izdelavo poliuretanov.
Klju~ne besede: polimeri, mikrostrukture, funkcionalnosti
1 INTRODUCTION
In order to protect the environment and to reduce our
dependence on fossil fuels, a great deal of research effort
has been, and is still being, devoted to the development
of innovative technologies using renewable resources.1–7
Vegetable oils are abundant and cheap renewable re-
sources that represent a major potential alternative
source of chemicals suitable for developing safe, envi-
ronmentally products.8–10 The use of vegetable oils and
natural fatty acids as starting raw materials offers nume-
rous advantages: for example, inexpensive, abundant,
low toxicity, and inherent biodegradability, thus they are
considered to be one of the most important classes of
renewable resources for the production of bio-based
polymeric materials.11–17 Polyurethanes (PUs) form a
versatile class of polymers, which are used in a broad
range of applications, for example, as elastomers,
sealants, fibers, foams, coatings, adhesives, and bio-
medical materials. The industrial production of PUs is
normally accomplished through the polyaddition reac-
tion between organic isocyanates and compounds con-
taining active hydroxyl groups, such as polyols. Com-
paring with polyurethanes derived from petrochemical
polyols, the vegetable-oil-based polyols used to produce
polyurethanes have been the subject of many studies.9–12
Moreover, due to the hydrophobic nature of triglycerides,
vegetable oils produce PUs that have excellent chemical
and physical properties, such as enhanced hydrolytic,
high tensile strength and elongation, high tear strength,
and thermal stability.13–18
Vegetable oils are one of the most important sources
of renewable raw materials for the chemical industry and
provide versatile opportunities for a transformation to
meet specific applications. In the 1980s, H. Baumann et
al.10 mainly focused on the carboxyl group of fatty acids,
these include the hydrolysis of fats to make soaps, and
synthesis of fatty amines from fatty acids. Recently,
increasing interest in industrial and academic research
has been focused on reactions on the hydrocarbon chains
of fatty acids, especially on the double bonds of un-
saturated fatty acids. Guo et al. applied the epoxidation
of the double bonds of fatty acids, followed by
nucleophilic ring opening of the epoxide to make polyols
for producing polyurethanes.19–23
To further expand applications of the bio-based
polymeric materials, previous studies were focusing on
converting vegetable oils into useful PUs. Based on these
studies, now it has become a main research field to func-
tionalize vegetable oils by the introduction of aromatic
Materiali in tehnologije / Materials and technology 51 (2017) 2, 229–236 229
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
UDK 66.017:543.442.3:534.44 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(2)229(2017)
co-monomers into the polymer structure, which could be
suitable in the search for new viable polymeric mate-
rials.12 The transition-metal-catalyzed trimerization of
alkyne fatty acid compounds provides an alternative
method for the preparation of highly functionalized
aromatic polyols.10,11
In the present study, we have synthesized three kinds
of bio-based aromatic triols prepared by oleic acid,
10-undecenoic acid, and erucic acid, which could be
obtained from sunflower oil, castor oil, and rapeseed oil,
respectively. PUs were synthesized by these aromatic
triols and 4,4’-methylenebis(phenyl isocyanate), 1,4-bu-
tanediol as a chain extender. The chemical structures,
molecular characteristics, physical properties, and ther-
mal properties were studied and compared using nuclear
magnetic resonance (NMR) spectroscopy, Fourier-trans-
form infrared (FTIR) spectroscopy, X-ray diffraction
(XRD), differential scanning calorimetry (DSC), and
thermogravimetry-differential thermal analysis (TG-
DTA).
2 EXPERIMENTAL PART
2.1 Materials
The following chemicals were obtained from the
sources indicated: Oleic acid (AR, from Sinopharm)
10-undecenoic acid (from Sinopharm), erucic acid (from
Aldrich), copper (II) chloride, CuCl2 (99 %, from Sino-
pharm), palladium (II) chloride, PaCl2 (AR, from
Sinopharm), palladium on carbon, Pa/C (10 % of mass
fractions, from Aldrich), potassium hydroxide, KOH
(AR, from Kermel), n-propanol (AR, from Kermel),
dimethyl sulfoxide, DMSO (AR, from Kermel), bromine
(AR, from Xilong), chlorotrimethylsilane, TMSCl (CP,
from Sinopharm), lithium aluminum hydride, LiAlH4
(97 %, from Aldrich), 1,4-butandiol, BD (AR, from
Bodi) and 4,4’-methylenebis(phenyl isocyanate), MDI
(98 %, from Aldrich) were used as received.
2.2 Synthesis of aromatic triol 4 from oleic acid
2.2.1 Dibromide carboxylic acid
To a solution of oleic acid (10.6 g, 33.6 m/mol) in
diethyl ether (150 mL) that was cooled to 0 °C in an
ice-water bath, bromine (2.7 mL, 52.3 m/mol) was added
dropwise over 30 min. Then the ice-water bath was
removed and the solution was stirred for another 2 h at
room temperature. A saturated sodium sulfite (Na2S2O3)
solution (20 mL) was added to reduce the excess bro-
mine. The resulting organic phase was separated, washed
with brine (20 mL) and dried over anhydrous magnesium
sulfate (MgSO4). The solvent was evaporated by reduced
pressure to give a pale yellow powder 1 (yield 73 %).
IR (thin film): 3440 (OH), 1703 (C=O) cm–1.
1H NMR (CDCl3/TMS, , 0.0001 %): 11.34 (s, 1H,
COOH), 4.23-4.14 (m, 2H, CH-Br), 2.38-2.33 (t, 2H,
CH2-COOH), 2.06-1.99 (m, 2H, CH-CHBr), 1.88-1.80
(m, 2H, CHBr), 1.64-1.56 (m, 6H), 1.35-1.25 (m, 16H),
0.88 (t, 3H, CH3).
2.2.2 Stearolic acid
The dibromide compound 1 (5.5 g, 15 m/mol) was
dissolved in DMSO (18 mL, 250 mmol). KOH (20 g,
360 m/mol) and 1-propanol (150 mL) were added. The
mixture was heated at 110 °C under reflux for 4 h. Then
the solution was poured into 2N hydrochloric acid (HCl)
(150 mL) at room temperature. The resulting organic
layer was separated, washed with brine (20 mL) and
dried over MgSO4. The solvent was evaporated under
reduced pressure to give a pale-yellow powder 2 (yield
76%).
IR (thin film): 3446 (OH), 2356 (CC), 1712 (C=O)
cm–1.
1H NMR (CDCl3/TMS, , 0.0001 %): 11.34 (s, 1H,
COOH), 2.33 (t, 2H, CH2-COOH), 2.12 (m, 4H,
CH2-CC), 1.26-1.62 (m, 22H), 0.88 (t, 3H, CH3)
2.2.3 Stearoyl alcohol
Stearolic acid 2 (2.4 g, 8.6 m/mol) was dissolved in
50 mL diethyl ether and added dropwise to a dispersion
of LiAlH4 (0.4 g, 10.2 m/mol) in 100 mL of anhydrous
diethyl ether. The mixture was stirred for 2 h at room
temperature, and then the excess LiAlH4 was decom-
posed by adding 20 mL of water dropwise. A 2N HCl
(30 mL) aqueous solution was added until the pH was
neutral. The resulting organic layer was separated,
washed with brine (20 mL) and dried over MgSO4. The
solvent was evaporated under reduced pressure to give a
pale-yellow oil 3 (yield 82 %).
IR (thin film): 3392 (OH), 2360 (CC) cm–1.
1H NMR (CDCl3/TMS, , 0.0001 %): 3.65 (t, 2H,
CH2OH), 2.14 (t, 4H, CH2-CC), 1.58-1.48 (m, 6H),
1.41-1.23(m, 18H), 0.90 (t, 3H, CH3).
2.2.4 Aromatic triols
Stearoyl alcohol 3 (1.05 g, 4.0 m/mol) was dissolved
in tetrahydrofuran (THF) (50 mL). 0.25 g of Pd/C (10 %
of mass fractions) and TMSCl (0.75 mL, 6.0 m/mol)
were added. The reaction mixture was heated at 65 °C
refluxed for 8 h. The resulting mixture was cooled to
room temperature and filtered to remove the Pd/C. The
resulting organic layer was separated, washed with brine
(20 mL) and dried over MgSO4. The solvent was evapo-
rated under reduced pressure to give a dark-yellow oil 4a
and 4b (yield 58 %).
IR (thin film): 3438 (OH), 1652 (C=C of benzene)
cm–1.
1H NMR (CDCl3/TMS, , 0.0001 %): 3.56 (t, 6H,
CH2OH), 2.43 (m, 12H, CH2Ph), 1.49-1.20 (m, 72H),
0.83 (t, 9H).
13C NMR (CDCl3/TMS, , 10–4 %): 136.77 (Ph-CH2),
62.94 (CH2OH), 31.94, 31.86, 29.68, 29.64, 29.57,
29.33, 29.26, 25.72, 22.68, 22.66, 14.12 (CH3).
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2.3 Synthesis of aromatic triol 4’ from 10-undecenoic
acid
2.3.1 Dibromide carboxylic acid 1’
10-Undecylenic acid (9.2 g, 50 m/mol) in diethyl
ether (150 mL) was cooled to 0 °C in an ice-water bath.
Bromine (4.2 mL, 81 m/mol) was added dropwise over
30 min. Then the ice-water bath was removed and the
solution was stirred for another 2 h at room temperature.
A saturated Na2S2O3 solution (20 mL) was added to
reduce the excess bromine. The resulting organic phase
was separated, washed with brine (20 mL) and dried over
MgSO4. The solvent was evaporated under reduced pres-
sure to give a gray solid 1’ (yield 78 %).
IR (thin film): 3433 (OH), 1705 (C=O) cm–1.
1H NMR (CDCl3/TMS, , 0.0001 %): 11.58 (s, 1H,
COOH), 3.85-3.80 (q, 1H, CH-CHBr), 3.64-3.57 (t, 2H,
CH-Br), 2.35-2.30 (t, 2H, CH2-COOH), 2.17-2.05 (m,
3H), 1.84-1.50 (m, 3H), 1.30-1.23 (m, 8H).
2.3.2 10-Undecynic acid 2’
The dibromide compound 1’ (5.2 g, 15 m/mol) was
dissolved in DMSO (18 mL, 250 mmol). KOH (20 g,
360 m/mol) and 1-propanol (150 mL) were added. The
mixture was heated at 110 °C under reflux for 4 h. Then
the solution was poured into 2N HCl (150 mL) at room
temperature. The resulting organic layer was separated,
washed with brine (20 mL) and dried over MgSO4. The
solvent was evaporated under reduced pressure to give a
white solid 2’ (yield 63 %).
IR (thin film): 3440 (OH), 2360 (CC), 1710 (C=O)
cm–1.
1H NMR (CDCl3/TMS, , 0.0001 %): 11.54 (s, 1H,
COOH), 2.31 (t, 2H, CH2-COOH), 2.17-2.11 (m, 2H),
1.92 (t, 1H), 1.55-1.44 (m, 4H), 1.33-1.23 (m, 8H).
2.3.3 10-Undecyn-1-ol 3’
10-Undecynic acid 2’ (1.6 g, 8.8 m/mol) was dis-
solved in 50 mL diethyl ether and added dropwise to a
dispersion of LiAlH4 (0.4 g, 10.2 m/mol) in 100 mL of
anhydrous diethyl ether. The mixture was stirred for 2 h
at room temperature, and then the excess LiAlH4 was
decomposed by adding 20 mL of water dropwise. A 2N
HCl (30 mL) aqueous solution was added until the pH
was neutral. The resulting organic layer was separated,
washed with brine (20 mL) and dried over MgSO4. The
solvent was evaporated under reduced pressure to give a
pale-yellow solid 3’ (yield 72 %).
IR (thin film): 3335 (OH), 2358 (CC) cm–1.
1H NMR (CDCl3/TMS, , 0.0001 %): 3.59 (t, 2H,
CH2OH), 2.20-2.14 (m, 4H), 1.76 (t, 1H, CH-C),
1.56-1.50 (m, 4H), 1.35-1.26 (m, 8H).
2.3.4 Aromatic triols 4’a and 4’b
10-Undecyn-1-ol 3’ (0.68 g, 4.0 m/mol) was dis-
solved in n-butyl alcohol (9 mL) and benzene (150 mL).
PdCl2 (0.15 g, 0.85 m/mol) and CuCl2 (2.05 g, 12 mmol)
were added. The reaction mixture was heated at 40 °C
and refluxed for 8 h. The resulting mixture was cooled to
room temperature and filtered to remove the PdCl2 and
CuCl2. The resulting organic layer was separated,
washed with brine (20 mL) and dried over MgSO4. The
solvent was evaporated by reduced pressure to give a
dark-yellow oil 4’a and 4’b (yield 68 %).
IR (thin film): 3456 (OH), 1639 (C=C of benzene)
cm–1.
1H NMR (CDCl3/TMS, , 0.0001 %): 6.40 (s, 3H,
Ph), 3.64 (t, 6H, CH2Ph), 2.29 (t, 6H), 1.61-1.24 (m,
42H).
13C NMR (CDCl3/TMS, , ppm): 138.22 (Ph-CH2),
120.35 (Ph-H), 64.11 (CH2OH), 39.86, 34.35, 30.68,
29.70, 29.08, 28.54, 27.46, 24.96.
2.4 Synthesis of aromatic triol 4’’ from erucic acid
2.4.1 Dibromide carboxylic acid 1’’
Erucic acid (15.88 g, 33.6 mmol) in diethyl ether
(150 mL) was cooled to 0 °C in an ice-water bath.
Bromine (2.7 mL, 52.3 mmol) was added dropwise over
30 min. Then the ice-water bath was removed and the
solution was stirred for another 2 h at room temperature.
A saturated Na2S2O3 solution (20 mL) was added to
reduce the excess bromine. The resulting organic phase
was separated, washed with brine (20 mL) and dried over
MgSO4. The solvent was evaporated under reduced
pressure to give a gray solid 1’’ (yield 78 %).
IR (thin film): 3425 (OH), 1706 (C=O) cm–1.
1H NMR (CDCl3/TMS, , 0.0001 %): 11.89 (s, 1H,
COOH), 4.27-4.18 (m, 2H, CH-Br), 2.35 (t, 2H,
CH2-COOH), 2.10-1.95 (m, 2H, CH-CHBr), 1.65-1.54
(m, 2H), 1.47-1.26 (m, 30H), 0.89 (t, 3H, CH3).
2.4.2 Behenolic acid 2’’
The dibromide compound 1’’ (7.5 g, 15 mmol) was
dissolved in DMSO (18 mL, 250 mmol). KOH (20 g,
360 mmol) and 1-propanol (150 mL) were added. The
mixture was heated at 110 °C under reflux for 4 h. Then
the solution was poured into 2N hydrochloric acid (HCl)
(150 mL) at room temperature. The resulting organic
layer was separated, washed with brine (20 mL) and
dried over MgSO4. The solvent was evaporated under
reduced pressure to give a pale-yellow powder 2’’ (yield
72 %).
IR (thin film): 3454 (OH), 2361 (CC), 1705 (C=O)
cm–1.
1H NMR (CDCl3/TMS, , 0.0001 %): 11.62 (s, 1H,
COOH), 2.37 (t, 2H, CH2-COOH), 2.15 (m, 4H,
CH2-CC), 1.69-1.23 (m, 30H), 0.90 (t, 3H, CH3).
2.4.3 Behenolic ester 3’’
To a solution of behenolic acid 2’’ (4.5 g, 12.9 mmol)
in methanol (100 mL) was added about 5 mL concen-
trated sulphuric acid. The reaction mixture was heated at
95 °C and refluxed for 3 h. The resulting organic
layer was separated, washed with brine (20 mL) and
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MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
dried over MgSO4. The solvent was evaporated under
reduced pressure to give pale-yellow oil 3’’ (yield 62 %).
IR (thin film): 2360 (CC), 1745 (C=O), 1170 (C-O)
cm–1.
1H NMR (CDCl3/TMS, , 0.0001 %): 3.66 (s, 3H,
CH3-O), 2.30 (t, 2H, CH2-COOCH3), 2.13 (m, 4H,
CH2-CC), 1.68-1.20 (m, 30H), 0.88 (t, 3H, CH3).
2.4.4 Aromatic triester 4’’a and 4’’b.
Behenolic ester 3’’ (2.8 g, 8.0 mmol) were dissolved
in n-butyl alcohol (9 mL) and benzene (150 mL). PdCl2
(0.15 g, 0.85 mmol) and CuCl2 (2.05 g, 12 mmol) were
added. The reaction mixture was heated at 40 °C and
refluxed for 12 h. The resulting mixture was cooled to
room temperature and filtered to remove the PdCl2 and
CuCl2. The resulting organic layer was separated,
washed with brine (20 mL) and dried over MgSO4. The
solvent was evaporated under reduced pressure to give a
yellow oil 4’’a and 4’’b (yield 68 %).
IR (thin film): 1745 (C=O), 1641 (C=C of benzene),
1174 (C-O) cm–1.
1H NMR (CDCl3/TMS, , 0.0001 %): 3.68 (s, 9H,
CH3-O), 2.54-2.43 (m, 12H, CH2Ph), 2.32 (t, 6H,
CH2-COOCH3), 1.70-1.26 (m, 90H), 0.90 (t, 9H, CH3)
13C NMR (CDCl3/TMS, , 0.0001 %): 174.41 (C=O),
136.71 (Ph-CH2), 51.48 (CH3-O), 34.13, 33.76, 31.96,
31.46, 30.69, 30.17, 29.71, 29.52, 29.42, 29.36, 29.31,
29.10, 24.97, 22.72, 14.16 (CH3).
2.4.5 Aromatic triols 5’’a and 5’’b.
Aromatic triester 5’’ (2.1g, 2.0 mmol) were dissolved
in 50 mL diethyl ether and added dropwise to a
dispersion of LiAlH4 (0.4 g, 10.2 mmol) in 100 mL of
anhydrous diethyl ether. The mixture was stirred for 2 h
at room temperature, and then the excess LiAlH4 was
decomposed by adding 20 mL of water dropwise. A 2N
HCl (30 mL) aqueous solution was added until the pH
was neutral. The resulting organic layer was separated,
washed with brine (20 mL) and dried over MgSO4. The
solvent was evaporated under reduced pressure to give a
pale-yellow oil 5’’a and 5’’b (yield 88 %).
IR (thin film): 3430 (OH), 1465 (C=C of benzene)
cm–1.
1H NMR (CDCl3/TMS, , 0.0001 %): 3.63 (t, 6H,
CH2OH), 2.56-2.40 (m, 12H), 1.64-1.26 (m, 96H), 0.89
(t, 9H, CH3).
13C NMR (CDCl3/TMS, , 0.0001 %): 136.71
(PhCH2), 63.06 (CH2OH), 34.12, 32.81, 32.61, 31.96,
31.49, 30.68, 29.70, 29.51, 29.42, 29.26, 25.75, 24.97,
22.70, 22.70, 19.15, 14.13(CH3).
2.5 Synthesis of polyurethanes
Polyurethane powders were prepared by reacting
aromatic triol with diisocyanate at different molar ratios
of the OH group to the NCO group. The desired
OH/NCO molar ratio satisfies Equation (1):
M
W EW
W W EWratio
polyol polyol
PU polyol diisocyanat
=
−
/
( ) /
e
(1)
where Wpolyol is the weight of the polyol, EWpolyol is the
equivalent weights of polyol, WPU is the total weight of
polyurethane, and EWdiisocyanate is the equivalent weight
of the diisocyanate.
The equivalent weight for the diisocyanate was cal-
culated based on the molar mass and was EWdiisocyanate =
250 g/mol. The equivalent weights of aromatic triol were
determined using Equation (2):
EWpolyol
molecular weight of KOH 1000
OH Number
=
×
= (2)
=
56110
OH Number
g per mole of hydroxyl group
The weights of the polyol and diisocyanate were
calculated using the above-calculated equivalent weight.
Polyurethane elastomers are block copolymers and
their domain structure can be controlled through the
selection of the materials and their relative proportions.
The polyurethanes were prepared using a single-stage
process. In our investigation the hard-segment compo-
sition was controlled by the molar ratios of poly-
ol/diisocyanate/diol and aromatic triol used in the
synthesis.18 The molar ratios of the OH group to the
diisocyanate (NCO) group chosen for the formulations
were 0.9. The OHdiol/OHaromatic triol molar ratio used was
1.0/2.0 in each of the synthesized polyurethane samples.
After 10 min of mixing the appropriate amount of aro-
matic triols and chain extender (BD) at 75 °C,
diisocyanate at the OH/NCO ratio of 0.9 was added. The
mixture was cured for 2 h at 75 °C and then post-cured at
110 °C for 16 h.
2.6 Measurements and analysis
The X-ray diffraction (XRD) patterns obtained on an
X-ray diffractometer (type Bruker AXS D8) using
Cu-K1 radiation at a scan rate (2) of 0.02° s–1 were
used to determine the identity of any phase present and
the crystallite size. The accelerating voltage and the
applied current were 15 kV and 20 mA, respectively.
The Fourier-transform infrared spectroscopy (FTIR)
spectra were recorded on a Bruker Tensor 27 spec-
trometer in the range 400-4000 cm–1 using KBr disks. 1H
NMR and 13C NMR were recorded on Bruker Advance
III 300MHz spectrometers with CDCl3 as a solvent.
DSC measurements were carried out on a Diamond
DSC instrument (TA instruments, DE, USA), equipped
with a refrigerated cooling system. The samples were
heated at a rate of 10 °C/min from 25 °C to 200 °C to
erase the thermal history and cooled down to -65 °C at
cooling rate of 5 °C/min. The DSC experiments were
carried out with a liquid-nitrogen cooler under a dry-
nitrogen atmosphere.
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232 Materiali in tehnologije / Materials and technology 51 (2017) 2, 229–236
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
For thermal stability analysis, 10 mg of the dried
polyurethanes powders were used in TG-DTA thermal
analyzer (type PerkinElmer Diamond TG/DTA,
America) at a heating rate of 10 °C/min from 20 °C to
800 °C in an inert-gas atmosphere.
3 RESULTS AND DISCUSSION
3.1 Synthesis of bio-based aromatic triols
The synthesis of triol monomers from oleic acid,
erucic acid and 10-undecenoic through a cyclotrimeri-
zation reaction yielded a mixture of asymmertrical and
symmetrical molecules (Chart 1). Bio-based aromatic
triols oleic acid-based aromatic triols (O-BAT), erucic
acid-based aromatic triols (E-BAT) and 10-undecenoic-
based aromatic triols (U-BAT) were synthesized by two
different methods. Alkyne alcohol derivatives were
obtained in moderate yields from the corresponding fatty
acids by bromation, dehydrobromination, and reduction
of carboxylic acid using well-established procedures
(Scheme1). Alkyne fatty derivatives were obtained in
moderate yields from the corresponding fatty acids by
bromation, dehydrobromination, and esterification using
well-established procedures (Scheme1).9,12 Cyclotrimeri-
zation of the 10-undecyn-1-ol 3’ and behenolic ester 3’’
were carried out using PdCl2 as a transition-metal
catalyst. However, when cyclotrimerization of stearoyl
alcohol 3 was carried out under the same conditions,
some side products were slowly generated or no indi-
cation of the trimer formation was obtained. The reaction
was then carried out using Pd/C as a transition-metal
catalyst, and the expected product was obtained in
moderate yields.10,11
Transition-metal-catalyzed cyclotrimerization of
alkynes can be considered as one of the most powerful
and general methodologies used to assemble arene rings,
and a large number of transition-metal catalysts have
been developed for alkyne cyclotrimerization in organic
media.12,24–25 A simple method utilizes a heterogeneous
Pa/C catalyst in a nitrogen atmosphere with refluxing
THF as the solvent and commercial grade chlorotri-
methylsilane.10,26 Cyclotrimerization of Stearoyl alcohol
3 was carried out following this procedure, and the
symmetric and asymmetric isomers, such as aromatic
triols 4a and 4b, have almost identical IR or 13C NMR
spectra in CDCl3. The formation of the aromatic
derivative was confirmed by the appearance of the signal
at 0.013677 % in the 13C NMR spectrum corresponding
to the aromatic core. The two compounds could not be
separated by flash chromatography due to their similar
polarities. Therefore, the presence of two compounds
could not be ruled out.
The preparation of benzene derivatives via the
palladium-chloride-catalyzed cyclotrimerization of
alkynes in the presence of CuCl2 has been described as a
smooth and regioselective method.12 When the cyclo-
trimerization of 10-undecyn-1-ol 3’ was carried out using
PdCl2 and CuCl2 as transition-metal catalysts, a
1,3,5-trisubstituted benzene derivative was obtained
regioselectively in a moderate yield. The appearance of
signals at 0.000639 % in the 1H NMR spectrum and
0.012035 % and 0.013763 ppm in the 13C NMR spec-
trum confirms the formation of the symmetric product.
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Materiali in tehnologije / Materials and technology 51 (2017) 2, 229–236 233
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Scheme 1: Synthesis of aromatic triols from oleic acid, erucic acid
and 10-undecenoic acid, respectively
Shema 1: Sinteza aromati~nih triol iz oleinske kisline, eruka kisline in
10-undekenojske kisline
Chart 1: Chemical structures of aromatic triols monomers obtained
by oleic acid, erucic acid and 10-undecenoic, respectively
Grafikon 1: Kemijske strukture aromati~nih triol monomerov, doblje-
nih z oleinsko kislino, eruka kislino in 10-undekenojsko kislino
The attempt to cyclotrimerize behenolic ester 3’’ via
Pa/C catalyst in nitrogen atmosphere with refluxing THF
as the solvent and chlorotrimethylsilane, some side
products were slowly generated. The preparation of
benzene derivatives via the palladium-chloride-catalyzed
cyclotrimerization of alkynes in the presence of CuCl2
has been described as a smooth and regioselective
method.12,27–28 When we applied the reaction to behenolic
ester 3’’, the symmetric and asymmetric isomers, such as
aromatic triols 4’’a and 4’’b, have almost identical IR or
13C NMR spectra in CDCl3. The formation of the aro-
matic derivative was confirmed by the appearance of the
signal at 0.013671 % in the 13C NMR spectrum corres-
ponding to the aromatic core. The two compounds could
not be separated by flash chromatography due to their
similar polarities. Therefore, the presence of two com-
pounds could not be ruled out. The reaction can also pro-
ceed with behenolyl alcohol. However, when cyclotri-
merization of the behenolyl alcohol was carried out in
the same conditions, a lot of side products were slowly
generated and the yields of aromatic triester 4’’a and 4’’b
were lower. So, aromatic ester derivatives were used as a
starting material for the reduction of the carboxylate
groups to synthesize two triols with primary hydroxyl
groups.
3.2 Synthesis and characterization of polyurethanes
Vegetable-oil-based polyols have been widely used to
produce segmented and non-segmented polyuretha-
nes.19–22 Segmented polyurethanes are elastomeric block
copolymers that generally exhibit a phase-segregated
morphology made up of soft rubbery segments and hard
glassy or semi-crystalline segments.23,24 The soft segment
usually consists of polyether or polyester diols, whereas
the hard segment consists of the diisocyanate component
and a low molecular weight consists of the diisocyanate
component and a low-molecular-weight chain extender.
The advantage of segmented polyurethanes is that their
segmental and domain structure can be controlled over a
considerable range through the selection of the materials,
their relative proportions, and the processing condi-
tions.12
In the study, bio-based polyurethanes were prepared
using the one-shot technique from O-BAT, E-BAT or
U-BAT, BD as a chain extender, and MDI as a coupling
agent. The bio-based aromatic triols/MDI part is consi-
dered as the soft phase, even though its glass transition is
above room temperature (Table 1). These hard segments
are polar, crystallizable and likely to form a separate
phase if the hard-segment content is high enough. The
chemical composition and hard-segment content of the
synthesized polyurethanes are also shown in Table 1.
The OH/NCO molar ratio was kept at 1.5. Reactants
were mixed at 75 °C and cured at this temperature for
2 h and post-cured at 110 °C for 18 h to give the poly-
urethanes.
Table 1: Formulations and hardness of the polyurethanes obtained
Tabela 1: Formulacija in trdota dobljenega poliuretana
Sample code Ratio(OH:NCO)
Ratio
(Polyol/BD/M
DI)
% Hard
segment*
O-BAT-PU 0.9 1:3:3 56.9
E-BAT-PU 0.9 1:3:3 52.1
U-BAT-PU 0.9 1:3:3 67.6
*The hard-segment percentage is calculated as the w/% of BD and
MDI per total material weight
To investigate the molecular structure of polyure-
thanes WAXD and FTIR were employed. The amor-
phous character of both the asymmetric and symmetric
polyurethanes was verified by WAXD (Figure 1). All the
samples show similar WAXD curves with a broad peak
at about 2  22°. This broad peak is a typical charac-
teristic of amorphous polymers12,13,15–17, which confirms
that there are no crystals in O-BAT-PU, E-BAT-PU and
U-BAT-PU.
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234 Materiali in tehnologije / Materials and technology 51 (2017) 2, 229–236
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 2: FTIR spectra of: a) O-BAT-PU, b) E-BAT-PU, and c)
U-BAT-PU
Slika 2: FTIR-spektri: a) O-BAT-PU, b) E-BAT-PU in c) U-BAT-PU
Figure 1: Wide-angle X-ray diffraction patterns of: a) O-BAT, b)
E-BAT and c) U-BAT polyurethane
Slika 1: [irokokotna rentgenska difrakcija: a) O-BAT, b) E-BAT in c)
U-BAT poliuretana
The FTIR spectra for O-BAT-PU, E-BAT-PU, and
U-BAT-PU are shown in Figure 2. From Figure 2, it is
clear that the spectra are similar for the PUs prepared
from the same diisocyanate but different aromatic triols
sources. The unreacted diisocyanate (NCO group) is
clearly shown by a peak centered at 2362 cm–1. A strong
stretching band located at around 3317 cm–1 charac-
teristic of the N-H group and a stretching vibration band
centered around 1708 cm–1 characteristic of the C=O
group are present in the FTIR spectra.7,8,15 There are also
two stretching regions attributed to the C=O group. The
band centered at around 1768cm–1 corresponds to the
free carbonyl group. These results indicated that the
three kinds of PU materials undergo physical bond-
ing.16,18
3.3. Thermal stability of polyurethanes
Thermal analysis of the polyurethanes obtained was
performed to provide insights into the morphological
structure of the material. Figure 3 shows the DSC ther-
mogram for the polyurethanes. There were two
endothermic peaks at about 45–50 °C and 175–190 °C.
The glass-transition temperature of the samples
measured by DSC was 45–50 °C. The transition
appeared in the region from 45 °C to 50 °C and were
attributed to the soft-segment glass-transition tempe-
rature (Tg). The Tg value is a measure of relative purity of
the soft-segment regions; when there are hard segments
dispersed in the soft domains, the Tg is raised.12 The
addition of bifunctional components such as MDI/BD
reduces the cross-linking density, but increases the
phenyl ring content. In principle, a reduced cross-linking
density should decrease the Tg, but an increased aromatic
content should have the opposite.12 The peak in the
region from 175 °C to 190 °C was ascribed to the
melting point of hard-segment domains, which supports
the development of a phase-separated morphology and
indicates that the hard-segment content is high enough to
achieve phase separation.12
TGA is the most favored technique for the evaluation
of the thermal stability of polymers. Polyurethanes have
a relatively low thermal stability, mainly because the
presence of urethane bonds. From the DTG curves it can
be seen that in nitrogen only one process occurs during
thermal degradation. G. Lligadas et al.12 observed a
similar behavior in the case of vegetable-oil-based
polyurethanes. They showed that poly-(oxypropylene)-
based polyurethanes degrade in a single step, whereas
vegetable-oil-based polyurethane shows one-step decom-
position.4,7,15 Figure 4 shows the DTG curve and Fig-
ure 5 shows the TGA curves of different polyurethanes,
which reveals a degradation stage at temperatures bet-
ween 300 °C and 400 °C. The results are similar to the
three bio-based polyurethanes systems. That can be
associated with the decomposition of urethane bonds,
which takes place through the dissociation to diiso-
cyanate and alcohol, the formation of primary amines
and olefins, or the formation of secondary amines.16,18
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Materiali in tehnologije / Materials and technology 51 (2017) 2, 229–236 235
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 5: TGA curves of: a) O-BAT-PU, b) E-BAT-PU, and c)
U-BAT-PU
Slika 5: TGA-krivulje: a) O-BAT-PU, b) E-BAT-PU in c) U-BAT-PU
Figure 3: DSC thermograms (10 °C/min) of: a) O-BAT-PU, b)
E-BAT-PU, and c) U-BAT-PU
Slika 3: DSC-termogrami (10 °C/min): a) O-BAT-PU, b) E-BAT-PU
in c) U-BAT-PU
Figure 4: DTG curves of: a) O-BAT-PU, b) E-BAT-PU, and c)
U-BAT-PU
Slika 4: DTG-krivulje: a) O-BAT-PU, b) E-BAT-PU in c) U-BAT-PU
4 CONCLUSIONS
Bio-based aromatic triols, O-BAT, E-BAT and
U-BAT have been synthesized using two different
methods. It is demonstrated that alkyne alcohol deriva-
tives can be obtained in the moderate yields from the
corresponding fatty acids by bromation, dehydrobromi-
nation, and reduction of carboxylic acid, and alkyne fatty
derivatives can also be obtained in moderate yields from
the corresponding fatty acids by bromation, dehydro-
bromination, and esterification. Such a synthesis metho-
dology has indicated a practical feasibility of utilizing
the new bio-based aromatic triols for the production of
bio-based polyurethanes. The crystalline structure and
thermal stability of these polyurethanes have been com-
pared to their counterparts made from a similar O-BAT,
E-BAT, and U-BAT, respectively. The corresponding
polyurethane networks with hard-segment have been
further prepared by the reaction of the polyol, BD, and
MDI. The synthesized materials have been characterized
using the spectroscopic techniques, WAXD, DSC and
TG-DTA. The results have showed that it is possible to
exploit renewable resources to achieve environment-
friendly green materials.
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