Lipidic polyols using thiol-ene/yne strategy for crosslinked polyurethanes

Article abstract of DOI:10.1002/pola.27159

Oleic acid and α,ω-diacid were converted into propargylic esters followed by thiol-ene/yne coupling (TEC/TYC) functionalization in presence of mercaptoethanol. The multiradical addition on fatty esters leads to the formation of lipidic polyols (OH1 and OH2), as judged by ¹H NMR and mass spectroscopies as well as by size exclusion chromatography. The crosslinking reaction between TEC/TYC-based polyols and 4,4′-methylene bis(phenylisocyanate) isocyanate reactant was monitored by FTIR experiment and reaction parameters were optimized. By differential scanning calorimetry, relatively high glass transitions are measured corresponding to structure with little or without dangling chain. Moreover, the thermal stability of the resulting plant oil-based polyurethane materials (PU1 and PU2) were found to be fully consistent with that of other lipidic PUs respecting a three-step process. Thanks to TYC methodology, fatty α,ω-diacid produces lipidic polyol without dangling chain and lipidic thermoset PU with relatively high T _g.

Full text of DOI:10.1002/pola.27159

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Lipidic Polyols Using Thiol-ene/yne Strategy for Crosslinked
Polyurethanes
Phuoc Dien Pham,1 Vincent Lapinte,1 Yann Raoul,2 Jean-Jacques Robin1
1
ꢀ
Institut Charles Gerhardt Montpellier UMR5253 CNRS-UM2-ENSCM-UM1 - Equipe Ingenierie et Architectures
ꢀ
ꢀ
Macromoleculaires, Universite Montpellier II – Bat 17 – cc1702, Place Euge`ne Bataillon 34095 Montpellier Cedex 5
2
ꢀ ꢀ
ꢀ
ꢀ
Societe Interoleagineuse d’Assistance et de developpement (S.I.A.), 11, rue de Monceau CS 60003 75378 Paris cedex 08, France
Correspondence to: V. Lapinte (E-mail: Vincent.Lapinte@univ-montp2.fr)
Received 29 January 2014; accepted 26 February 2014; published online 24 March 2014
DOI: 10.1002/pola.27159
ABSTRACT: Oleic acid and a,x-diacid were converted into prop-
argylic esters followed by thiol-ene/yne coupling (TEC/TYC)
functionalization in presence of mercaptoethanol. The multirad-
ical addition on fatty esters leads to the formation of lipidic
polyols (OH1 and OH2), as judged by 1H NMR and mass spec-
troscopies as well as by size exclusion chromatography. The
crosslinking reaction between TEC/TYC-based polyols and 4,40-
methylene bis(phenylisocyanate) isocyanate reactant was
monitored by FTIR experiment and reaction parameters were
optimized. By differential scanning calorimetry, relatively high
glass transitions are measured corresponding to structure with
little or without dangling chain. Moreover, the thermal stability
of the resulting plant oil-based polyurethane materials (PU1
and PU2) were found to be fully consistent with that of other
lipidic PUs respecting a three-step process. Thanks to TYC
methodology, fatty a,x-diacid produces lipidic polyol without
dangling chain and lipidic thermoset PU with relatively high
C
V
Tg. 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym.
Chem. 2014, 52, 1597–1606
KEYWORDS: fatty acid; polyol; polyurethanes; renewable resour-
ces; thiol-yne coupling; thermosets
acid16 was described. An alternative approach consists in the
oligomerization of fatty ester by ring-opening of epoxy
groups in presence of catalyst based on aluminum.17 Ozonol-
ysis of oils and further reduction of terminal acid groups
also lead to lipidic polyols.18 Cadiz et al. explored another
strategy by hydrosilylation of methyl 10-undecenoate with
phenyl tris(dimethylsiloxy) silane (PTDS).19 Additionally, pol-
yols were prepared by radical pathway: thiol-ene coupling
(TEC) using mercaptoethanol in presence of raw oil20 or
fatty esters.21,22 One drawback of plant oil-based PU is the
low Tg value (<40 ꢀC) due to both the low functionality of
polyols and the presence of dangling chains which act as
plasticizers.
INTRODUCTION With growing concerns over sustainable
development and environmental impact of petrochemical
polymer products, researchers are paying more attention to
biobased materials. The main biobased materials are vegeta-
ble oils, polysaccharides, sugars, and woods1 that are chemi-
cally modified for the development of chemicals, plasticizers,2
polymers,3 blends,4 composites, and coatings.5 In particular,
vegetable oils and their derivatives (fatty alcohols, esters, and
acids) have been extensively modified to generate biobased
materials6 such as polyamides,7 nonisocyanate polyur-
ethanes,8,9 surfactants,10 and epoxy resins.11–13
Polyurethanes (PU)s are very interesting polymeric materials
allowing a huge variety of industrial applications from
paints, coatings, adhesives, sealants and insulation foams.
They are synthesized from polyol and poly(isocyanate) reac-
tants producing carbamate (urethane) bonds. The conversion
of unsaturated oils into polyols has been widely investigated
to prepare PUs with different physical and chemical proper-
ties. There are several approaches to introduce the hydroxyl
group into the vegetable oils structure. To date, the synthesis
of lipidic polyols has been mainly accomplished from epoxy
vegetable oils or fatty esters intermediate (Table 1). The
ring-opening of oxirane by various nucleophiles like alcohol
(methanol14 and propylene glycol15 or carboxylic acid (lactic
Herein, we report a new synthetic approach for the facile syn-
thesis of lipidic polyols via thiol-ene/yne coupling (TEC/TYC)
using 2-mercaptoethanol (Scheme 1).23 The TYC splits in two
cycle mechanism.24 In the first cycle, the thiyl radicals gener-
ated from thiol groups were added on the ethynyl groups to
form a vinyl sulfide radical, which could attract a hydrogen
atom from a thiol group, producing the vinyl sulfide and gen-
erating another thiyl radical at the same time. In the second
cycle, a thiyl radical adds on the double bond of the vinyl sul-
fide, generating a dithioether radical, which attracts a hydro-
gen atom from a thiol groups and forms the disubstituted
C
V
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TABLE 1 Comparison of Polyols Synthesized in This Work and in the Literature
Reference
Lipidic Precursor
Structure
Strategy
Reactant
1
2
3
4
5
6
7
8
9
Various VO
Soybean
FA
ROEG and esterification
ROEG
Propylene glycol
Lactic acid
TAG
TAG
oligomer
TAG
TAG
TAG
FA
Various VO
Methyl oleate
Various VO
Methyl oleate
Rapeseed oil
Methyl oleate
Methyl oleate
Oleate acid
Oleate diacid
ROEG
Methanol
ROEG and reduction
Ozonolysis and reduction
Hydrosylilation and reduction
TEC
LiAlH4
O3 and NaBH4
PTDS and AlLiH4
HS-(CH2)2OH
HS-(CH2)2OH
HS-(CH2)2OH
HS-(CH2)2OH
HS-(CH2)2OH
Allylation 1 TEC
Dehydrobromation 1 TYC
Eesterification 1 TYC
Esterification 1 TYC
FA
OH1
OH2
FA
FA
FA: fatty acid; PTDS: phenyl tris(dimethylsiloxy)silane; ROEG: ring-opening epoxy group; TAG: triacyl glycerol; VO: vegetable oil.
product. This synthetic strategy leads to high-functional poly-
ols since one ethynyl group turns into two thioether groups.
By this methodology, propargylic fatty acid (PFE), and a,x-
diacid (PFD) were converted into lipidic polyols (OH1) and
(OH2), respectively. Cadiz et al. have already synthesized lipi-
dic polyols by thiol-yne coupling after bromination, dehydro-
bromination of 10-undecenoic and 9-octadecenoic acids.25,26
However, the ethynyl group is in internal position, along the
fatty chain whereas in our case it is in terminal position via
propargylic precursor. The advantage of our strategy is to
obtain, in the case of a,x-diacid, a polyol without dangling
chain and plant oil-based PUs with relatively high Tg value.
The polyols were carefully characterized by NMR and mass
spectroscopies as well as size exclusion chromatography
(SEC). Finally, crosslinked PUs from lipidic polyols (OH1 and
OH2) and 4,40-methylene bis(phenylisocyanate) (MDI) isocya-
nate reactant were investigated in terms of thermal properties
and stability by differential scanning calorimetry (DSC) and
thermogravimetric analyzer (TGA) techniques.
EXPERIMENTAL
Materials
Triethylamine, 2-mercaptoethanol, p-toluenesulfonic acid, thi-
onyl chloride, propargylic alcohol, 2,2-dimethoxy-2-phenyla-
cetophenone (DMPA), oleic chloride (purity 85%), and MDI
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SCHEME 1 General mechanism of thiol-ene and thiol-yne couplings between alkene and alkyne and thiol - Application to PFE and
PFD and mercaptoethanol.
ꢀ
were purchased from Aldrich and were used as received.
N,N-dimethylformamide (DMF) and chloroform were dried
and distilled according to standard procedures. C18:1 a,x-
diacid [(9Z)-octadec-9-enedioic acid] (purity 95 %) was gen-
erously gifted by S.I.A.. Deuterated solvents were purchased
from SDS and were used without further purification. 2,20-
Azobisisobutyronitrile was purified twice by recrystallization
in methanol and dried under vacuum. Commercially available
reagents and solvents were purified and dried, when neces-
sary, by standard methods prior to use.
the dry temperature was set at 350 C and dry gas flow was
maintained at 13 mL min21. The mass acquisition range was
from m/z 50 to 1000. The thermo-oxidative stability of the
PU materials was examined using a Q50 TGA from TA
R
V
Instruments . The experiments consisted in registering the
weight loss of the sample under nitrogen flow (60 mL
min21) as a function of temperature from the ambient up to
21
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ꢀ
550 C. Different experiments were heated at 10 C min
.
Conversion of a,x-Diacid into Fatty a,x-Diacid Chloride
(DCl)
Analytical Techniques
In a 500 mL two-necked flask equipped with a reflux con-
denser and a dropping funnel, 53.5 g (171.2mmol) of a,x-
diacid were dissolved in 150 mL of dry chloroform. The chlo-
roform solution (200 mL) containing thionyl chloride was
added dropwise over a period of 1 h. The mixture was
heated gently on an oil bath held at 60ꢀC for 16 hours. The
mixture was evaporated under pressure in order to remove
any excess of thionyl chloride. The product was used without
any further purification in 97% yield.
1H and 13C NMR spectra were recorded using a Bruker AC
300 and 400 MHz with CDCl3 as solvent. Chemical shifts (1H
NMR) were referenced to the peak of residual CHCl3 at 7.26
ppm. Chemical shifts (13C NMR) were referenced to CDCl3 at
77 ppm. Fourier Transform Infrared (FTIR) spectra were
recorded with a Perkin–Elmer Spectrum 100 spectrometer
equipped with an attenuated total reflectance crystal made
of ZnSe. SEC analyses were performed in DMAc (0.1% LiCl)
as eluent. Two PL-gel mix C columns were used at 50 ꢀC
with a flow rate of 0.8 mL min21, calibrated using PS stand-
ards. DSC analyses of the samples were carried out on 5–10
mg samples in aluminum pans, using a Mettler Toledo appa-
ratus. The DSC heating and cooling schedules used were as
1H NMR (CDCl3, 300 MHz) d (ppm): 1.16–1.48 (16H, H4-7
12-15), 1.55–1.82 (4H, H3, H16), 1.86–2.12 (4H, H8, H11),
,
H
2.79–2.98 (4H, H2, H17), 5.25–5.41 (2H, H9, H10).
21
ꢀ
follows: the samples were heated at 10 C min and cooled
at the same rate to room temperature. LC/ESI-MS chromato-
grams were acquired in the positive ion mode with the capil-
lary voltage set at 3000 V and cone voltage at 30 V while
Synthesis of Propargylic Esters
Propargylic Fatty Ester (PFE)
Propargylic alcohol (4.04 g, 72 mmol) and triethylamine
(7.28 g, 72 mmol) were dissolved in dry dichloromethane
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(80 mL). The solution was cooled in an ice bath under N2 for
15 min. At 0 ꢀC, dichloromethane solution (80 mL) of oleoyl
chloride (18.05 g, 60 mmol) was added dropwise to the previ-
ous solution over 1 h. The stirring was continued for one
additional hour. Then, the mixture refluxed for 16 h. The solu-
tion was washed with water (33 150 mL) and brine (23100
mL), dried over anhydrous MgSO4, filtered, and concentrated
under reduced pressure to yield a brown oil (15.57 g, 81 %).
amount of DMF (5 mL) was added to dissolve the photoinitiator.
The reaction carried out under UV irradiation (365 nm) at room
temperature for 8 h. DMF was then removed under reduced
pressure. The mixture was dissolved in CHCl3 (200 mL), then
washed with water (3x200 mL), and brine (2x200 mL), dried
over anhydrous MgSO4, filtered, and evaporated under reduced
pressure to yield a dark yellow oil. The product was purified by
column chromatography using AcOEt/CH2Cl2 3/7, as eluent, to
afford a viscous light yellow product (11.78 g, 68%).
23.35 g, 81%; yield.1H NMR (300 MHz, CDCl3, d): 0.79–0.95
(3H, H1), 1.15–1.44 (20H, H2-7, H12-15), 1.52–1.72 (2H, H16),
1.87–2.11 (4H, H8, H11), 2.27–2.39 (2H, H17), 2.45–2.50 (2H,
H21), 4.60–4.72 (4H, H19), 5.26–5.41 (2H, H9, H10); 13C NMR
(100 MHz, CDCl3, d): 14.04 (C1), 22.64 (C2), 24.74 (C16),
27.10 and 27.16 (C8, C11), 28.99-29.72 (C4-7, C12-15), 31.87
(C3), 33.88 (C17), 51.63 (C19), 74.61 (C21), 77.74 (C20), 129.62
and 129.89 (C9, C10), 172.72 (C18); IR: m 5 3312 (O-H), 2923
and 2853 (C-Hstretching), 1744 cm21 (C5Oester stretching).
1H NMR (400 MHz, CDCl3, d): 0.81-1.02 (3H, H1), 1.15–1.76
(29H, H2-16), 2.27–2.44 (2H, H17), 2.53–3.23 (11H, H20, H21
H
,
22, H24), 3.63–3.91 (6H, H23, H25), 4.06–4.43 (2H, H19); 13C
NMR (100 MHz, CDCl3, d): 13.52 (C1), 22.05 (C2), 24.23
(C16), 26.02–29.01 (C4-8, C12-15), 31.25 (C3), 32.77 (C17),
33.56–35.27 (C9, C11, C21, C22), 44.43 (C10), 45.32 (C20),
60.54, 60.86 (C19, 2 3 C23), 64.77 (C25), 173.15 (C18); IR: m
5 3389 (O-H), 2930 and 2858 (C-Hstretching), 1736 cm21
(C5Oester stretching).
Propargylic Fatty Diester (PFD)
Dichloride route
Polyol Derivating from PFD (OH2)
Propargylic alcohol (7.71 g, 137.4 mmol) and triethylamine
(13.9 g, 137.4 mmol) were dissolved in dry dichloromethane
(100 mL). The solution was cooled in an ice bath under N2
for 15 min. At 0 ꢀC, dichloromethane solution (100 mL) of
DCl (20 g, 57.2 mmol) was added dropwise to the previous
solution over 1 h. The stirring was continued for one addi-
tional hour. Then, the mixture refluxed for 16 h. The solution
was washed with water (33 200 mL) and brine (23100
mL), dried over anhydrous MgSO4, filtered, and evaporated
under reduced pressure to yield a brown oil (19.2 g, 86 %).
In a 50 mL flask, PFD (5 g, 12.86 mmol) was reacted with 2-
mercaptoethanol (15.07 g, 193 mmol) in presence of the radi-
cal initiator DMPA (1.65 g, 6.43 mmol) under N2 atmosphere.
An amount of DMF (2.4 mL) was added to dissolve the photo-
initiator. The reaction carried out under UV irradiation (365
nm) at room temperature for 8 h. DMF was then removed
under reduced pressure. The mixture was dissolved in CHCl3
(200 mL), then washed with water (3x 200 mL), and brine
(2x 200 mL), dried over anhydrous MgSO4, filtered, and
evaporated under reduced pressure to yield a dark yellow oil.
The product was purified by column chromatography using
AcOEt/CH2Cl2 3/7, as eluent, to afford a viscous light yellow
product (6.59 g, 66%).
Diacid route
In a 500-mL flask, 13.55 g of a,x-diacid (43.38 mmol) and 25
mL of propargylic alcohol (433.8 mmol, 10 equiv) were dis-
solved in 200 mL of toluene. The mixture is vigorously stirred
and 0.77 g of p-toluenesulfonic acid monohydrate (4.338
mmol, 0.1 equiv) was added. In a Dean–Stark apparatus the
resulting suspension refluxed for 16 h. The organic solution
was washed successively with saturated aqueous sodium
bicarbonate (3 3 50 mL) and brine (2 3 50 mL) then dried
over anhydrous MgSO4, filtered, and finally concentrated
under reduced pressure to yield an oil (15.35 g, 91 %).
1H NMR (400 MHz, CDCl3, d): 1.14-1.65 (27H, H2-16), 2.21-
2.36 (4H, H2, H17), 2.64–2.93 (18H, H21, H22, H24), 2.99–3.16
(2H, H20), 3.43 (OH), 3.61–3.80 (10H, H23, H25), 4.13–4.39
(4H, H19); 13C NMR (100 MHz, CDCl3, d): 24.27 (C3, C16),
26.06–28.88 (C4-8, C12-15), 32.86 (C2, C17), 33.61, 34.36, 35.41,
32.77 (C9, C11, C21, C22), 44.51 (C10), 45.33 (C20), 60.50, 60.84
(C19, 4 3 C23), 64.84 (C25), 173.20 (C1, C18); IR m 5 3375
(OH), 2931 and 2856 (C-Hstretching), 1731 cm21 (C5Oester
stretching); ESI-MS (m/z): calcd for M1H1 779.33; found:
779.40, calcd for M-(C7H15O3S2)1 567.30; found: 567.3.
1H NMR (300 MHz, CDCl3, d): 1.17–1.41 (16H, H4-7, H12-15),
1.61–1.71 (4H, H3, H16), 1.88–2.08 (4H, H8, H11), 2.24–2.40
(4H, H2, H17), 2.45–2.49 (2H, H21), 4.60–4.70 (4H, H19),
5.26–5.38 (2H, H9, H10); 13C NMR (100 MHz, CDCl3, d):
General Procedure for Crosslinked Polyurethanes (PU1
and PU2)
24.27 (C3, C16), 26.10 (C8, C11), 27.97, 28.01, 28.08 (C4-7
,
The PU materials were prepared by mixing OH1 or OH2
with MDI at 60 ꢀC in an aluminum mold. The [NCO]/[OH]
ratio ranged from 1/1 to 1.1/1. The vacuum was applied to
remove bubbles. The mixture was cured at 60 ꢀC for 24h
C12-15), 32.80 (C2, C17), 50.61 (C19), 73.86 (C21), 76.85 (C20),
128.73 (C9, C10), 171.51 (C1, C18); IR: m 5 3294 (O-H), 2926
and 2854 (C-Hstretching), 1739 cm21 (C5Oester stretching).
ꢀ
and post-cured at 110 C for 24h. The resulting PU materials
TEC/TYC Between Mercaptoethanol and Propargylic
Fatty Esters
were peeled off from the mold for characterization tests.
Polyol Derivating from PFE (OH1)
RESULTS AND DISCUSSION
In a 50 mL flask, PFE (10 g, 31.2 mmol) was reacted with
2-mercaptoethanol (21.9 g, 280.8 mmol) in presence of the radi-
cal initiator DMPA (2.4 g, 9.36 mmol) under N2 atmosphere. An
The various approaches described in the literature to synthe-
size lipidic polyols are summarized in Table 1. Herein, we
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SCHEME 2 Synthesis of propargylic fatty ester: PFE and PFD.
focus the discussion on the lipidic polyols used in thermoset
PUs in presence of MDI isocyanate. Three lipidic structures
are mentioned: i) the triacylglycerols (TAG) (2, 3, 5 and 7),
ii) the linear fatty acid derivatives (FA) (1, 8 and 9), and iii)
other structures like three-arm stars (6) and oligomers (4).
It is interesting to note that the presence of dangling chain
was observed in almost all structures, except for 5 and 6.
Otherwise, some structures carry primary alcohol groups (1,
5, 6, 7, 8 and 9) while others carry secondary ones (2, 3
and 4). This comparative study also highlights the presence
of ester group in polyol structures apart from 4, 6, 8 and 9.
Herein, we proposed two types of polyol based on oleic acid
and a,x-diacid. From the first one, a triol (OH1) bearing an
ester group and a dangling chain was elaborated whereas a
pentaol (OH2) bearing a diester structure without dangling
chain was synthesized using fatty a,x-diacid.
both cases the shift of CH2AC@O signal (H17) from 2.88 to
2.34 ppm as well as the appearance of the propargylic sig-
nals corresponding to H19 and H21 at 4.65 and 2.45 ppm.
Alternative route may be considered. For instance, PFD was
also prepared in presence of a,x-diacid using p-toluenesul-
fonic acid in good yield.
Photoinduced Thiol-ene/yne Reaction for an Efficient
Synthesis of Polyols
To access the highly functional fatty polyols, thiol-ene and
thiol-yne couplings could be both associated. In our case, the
key step is the functionalization of propargylic fatty (di)e-
sters (PFE and PFD) into fatty polyols (OH1 and OH2) by
photoinduced TEC/TYC (Scheme 1). Mercaptoethanol was
both added on internal double bond by thiol-ene coupling
and terminal propargylic unsaturation by thiol-yne coupling.
The photoinduced radical addition of thiol into unsaturation
carried out at room temperature in presence of DMPA photo-
initiator. Thanks to a simple work-up, the highly functional
moieties OH1 (triol) and OH2 (pentaol) were successfully
synthesized in good yields (66–68%). The 1H NMR spectra
confirmed the chemical structure of both polyols as illus-
trated in Figures 1 and 2. The total consumption of unsatu-
Synthesis of Propargylic Fatty Ester and Diester
The synthesis of PFE and diester (PFD) starts from activated
species of oleic (di)acids. The a,x-diacid chloride (OACl) is
marketed whereas the corresponding DCl is easily synthe-
sized in 97% yield (see experimental part). Thus, the treat-
ment of OACl and DCl with propargylic alcohol in presence
of triethylamine in CH2Cl2 afforded PFE and PFD in a good
yield (81 and 86%, respectively) (Scheme 2). The complete
reaction was monitored by 1H NMR experiment using in
rations: ethylenic (H9-10) and propargylic (H19 and H21
)
protons at 5.3, 4.7, and 2.4 ppm, respectively was observed
in both cases. Moreover, the appearance of signals assigned
FIGURE 1 1H NMR spectra of PFE and OH1 in CDCl3.
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FIGURE 2 1H NMR spectra of PFD and OH2 in CDCl3.
to CH2AOH at 3.6–3.8 ppm (H23 and H25) and thioether
groups (H20, 21, 22, 24) at 2.55–3.0 ppm attested the mercap-
toethanol addition on fatty structures. It is interesting to
notify that the both OH1 and OH2 polyols are soluble in
common solvents such as CHCl3, THF, and DMSO and insolu-
ble in water.
the utilization of gel permeation chromatography (GPC). By
this technique, Curtis et al. detected 17% of oligomers dur-
ing the epoxy ring-opening process by lactic acid followed by
esterification in the case of 2, described in Table 1.15 Addi-
ꢀ
tionally, Petrovic et al. estimated 18–25% of oligomers for 3
during oxirane ring-opening reaction of epoxidized vegetable
oil in presence of methanol.14 In our case, the synthesis of
OH1 polyol happened without oligomer formation since no
trace was observed at higher retention time whereas very
little oligomers likely dimers appeared for OH2 polyol. In
addition, the shift of the polyol traces related than those of
PFD and PFE precursors confirmed the addition of three and
five mercaptoethanol units into fatty structures. GPC analysis
of OH1 and OH2 show an increase in molecular weight from
400 and 500 g mol21 to 1400 and 2400 g mol21 (Fig. 3).
The large difference between targeted and experimental
molecular weights can be attributed to large difference in
hydrodynamic volume between the polyols and the polysty-
rene standards.
Numerous synthetic methodologies of polyols including ring-
opening epoxy group, ozonolysis, and hydrosylilation were
described in the literature. Unfortunately, in many cases the
side reactions accompany the polyol synthesis such as the
oligomerization of unsaturated compounds into dimers,
trimers, etc. The best way to observe this phenomenon is
FIGURE 3 GPC traces in DMAc of PFE and PFD precursors and
OH1 and OH2 polyols. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
FIGURE 4 LC ESI/MS spectrum of PFD.
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SCHEME 3 Schematic network based on various architectures of lipidic polyols. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
The structure of OH2 polyol, alcohol highest functionality of
both synthesized, was also explored by LC-ESI/MS technique
(Fig. 4). As expected, the isomolecular peak [M 1 H]1was
detected at m/z of 779.40 in accordance with the m/z theoret-
ical value of 779.33. Another peak was observed at m/z of
567.3 and corresponds to [M-211]1, outcome of the breaking
of the CAO bond’s breaking of one of the two ester group.
of the thermosets are influenced by the lipidic polyol struc-
tures described in Table 1. It is widespread that the dangling
chains of the fatty polyols affect the physical properties of
the resulting materials and act as plasticizers decreasing the
their Tg values.18 Apart from 5 and 6, the polyols described
in the literature carry one (1, 8, and 9), three (2, 3, and 8)
or numerous (4) dangling chains as illustrated in Scheme 3.
The design of our vegetable oil based polyols considers this
aspect. Thus, thanks to fatty acid and a,x-diacid precursors
coming from oleic chain, OH1 and OH2 polyols were pro-
vided with three and five alcohol groups, respectively and
without or one dangling chain using a simple and versatile
TEC/TYC approach.
Preparation of PU Materials Based on Lipidic Polyols
The polyol structure obviously impacts the density of PU
network. Therefore, the Tg values and the thermal properties
TABLE 2 Comparison of PUs Synthesized in This Work and in
the Literature
The comparative study gathers the thermoset PUs coming
from MDI and various polyols as compiled in Table 2. The
relationship between the polyol structure and the Tg value of
Reference
[NCO]/[OH]
Tg (ꢀC)
T5% loss (ꢀC)
1
2
3
4
5
1.1/1
1.05/1
1.02/1
1.02/1
1.02/1
1.02/1
1.05/1
1/1
69 2 114a
96b
30 2 77b
23 2 57d
22 and 36
39
–
273e
–
337 2 352
330 and 337e
322f
6
7
25c
–
8
9
8 2 56
42 2 59
36
269 2 290
245
1/1
PU1
PU2
1/1
297
1.1/1
1/1
45
295
68
279
1.1/1
72
282
PU materials were curing at 110ꢀC apart from
a
100 ꢀC;
b
80 ꢀC;
c
65 ꢀC.
d
Tg value determined by DMA experiment.
Deduced from figure.
e
f
FIGURE 5 FTIR spectra of OH1, MDI and PU1 (NCO/OH 5 1.1).
Temperature of 10% of weight loss.
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FIGURE 6 DSC thermograms of thermoset PUs (right) and the OH1 and OH2 precursors (left).
the resulting material was discussed. The Tg values were
affected by the number of alcohol groups of each fatty chain.
This value is directly related to the number of double bonds
of precursors fatty chains. Note that the fatty chains are clas-
sified according to the number of carbon atoms (n) and of
double bonds (m) such as Cn:m. For 1, 3, and 5 polyols, sev-
eral types of vegetable oils are employed carrying various
contents in oleic (C 18:1), linoleic (C 18:2), and linolenic (C
18:3) chains.14,15,18 For instance, 3-based PU using canola oil
(iodine index of 114) or linseed oil (iodine index of 182)
alcohol group and the long distance between two reactive
alcohol functions producing a network with wide mesh.
As mentioned above, the presence of dangling chain in pol-
yol structure decreased the Tg value by plasticization the Tg
value. Besides the oligomer nature of 7, low Tg values were
measured (23 and 57 ꢀC) likely caused by the dangling
chain.27 By TEC functionalization, the same problem
occurred with modified TAG (7) and modified fatty acid
(8).20,21 The Tg values varied between 25 and 56 ꢀC. Sur-
prisingly, the structure 1 exhibited the highest Tg value
(114 ꢀC) with 3 alcohol groups (2 secondary and 1 pri-
mary) with one dangling chain.15 In order to enhance the
alcohol density in polyol structure without dangling chain,
Cadiz et al. reported the thiol-yne functionalization of 10-
undecynoic and 9-octadecynoic acids after bromation of
double bond, deshydrobromation into alkenic bond fol-
lowed by esterification of acid group.25 The resulting PU
thermosets have a Tg value up to 59 ꢀC. In our methodol-
ogy, even if we kept TYC approach, a shorter strategy was
used to incorporate an alkenyl group in fatty acid (PFE)
and a,x-diacid (PFD) structures. Unlike Cadiz, thiol-yne cou-
pling led the introduction of terminal alkenyl group by
esterification instead of bromation/deshydrobromation of
internal double bond.
14
ꢀ
have got a Tg value of 32 and 77 C, respectively. In short,
as expected, the high level of unsaturations (iodine index
closed to 220) favors the high Tg value in relation to the
crosslinking density. The Tg values also depend on the strat-
egy of incorporation of alcohol groups on fatty chains (TEC,
ring-opening (RO) of oxirane). For instance, even if in all
cases, fatty precursors are vegetable oils (TAG structure), PU
based on 2 (RO), 3 (RO), and 7 (TEC) offered a large panel
of Tg values ranging from 25 ꢀC for 7 until 96 ꢀC for
2.14,16,20 Thus, the nature of the functional alcohol unit (lac-
tic acid for 2 and methanol for 3) added on epoxidized vege-
table oil influenced the Tg value. Interestingly, the three-arm
star structure (5 and 6) having a terminal alcohol group exhib-
18,19
ꢀ
ited low Tg values ranging from 22 and 39 C.
This result
can be explained by the flexibility of the alkyl chain bearing
FIGURE 7 TGA chromatograms of PU1 (left) and PU2 (right) under nitrogen. [Color figure can be viewed in the online issue, which
is available at wileyonlinelibrary.com.]
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CONCLUSIONS
The thermoset PU materials were prepared by mixing OH1
or OH2 with MDI at 60 ꢀC in aluminum mold. The mixture
In this contribution, propargylic fatty ester of oleic acid and
a,x-diacid were synthesized in good yields. It has been
showed that TEC/TYC is an effective approach to synthesize
lipidic polyols without oligomers. For a,x-diacid, polyol with-
out dangling chain was prepared and produced PU materials
ꢀ
ꢀ
was cured at 60 C for 24 h and postcured at 110 C for 24
h. The [NCO]/[OH] ratio ranged from 1/1 to 1.1/1 being
careful to keep the NCO amount superior than OH amount to
compensate the consumption of NCO species by side reac-
tions. The PU crosslinking was confirmed by FTIR analysis
as illustrated by the overlapping of OH1, MDI, and PU1 spec-
tra in Figure 5. The total disappearance of AN@C@O stretch-
ing of the isocyanate moiety at 2240 cm21 in PU1 means
that the network was complete. Furthermore, the stretching
vibration of C@O urethane appeared at 1708 cm21 and over-
lapped with the C@O ester band at 1736 cm21. The NAH
deformation as well as CAN stretching vibration occurred at
1520 and 1215 cm21, respectively. In addition, the broad
band at 3500 cm21 corresponding to OAH stretching, shifted
to lower frequencies at 3350 cm21, characteristic of NAH
stretching.
ꢀ
with Tg value of 72 C after optimization of the crosslinking
parameters (temperature and [NCO]/[OH]). Comparing our
results to those reported in the overview regarding to plant
oil-based crosslinked PUs, it has been showed a typical ther-
mal stability in a three-step process of plant oil-based ther-
moset PUs. Thus, through the synthesis of these lipidic
polyols, we illustrated the opportunity of TYC/TEC function-
alization in the synthesis of high functional monomers and
branched polymers using biobased building blocks.
ACKNOWLEDGMENTS
The authors gratefully acknowledge S.I.A. for their financial
support.
The thermal behaviors of PU1 and PU2 coming from OH1
and OH2 were investigated by DSC technique as shown in
Figure 6. First, the glass transition temperatures of lipidic
polyols (before crosslinking) were estimated. The ꢀTg of OH1
and OH2 polyols were found to be 270 and 258 C, respec-
tively (Fig. 6, left). The larger number of alcohol groups
reduced the mobility of fatty chain and increased the Tg
value. Secondly, the same experiments were conducted on
resulting thermoset PUs (Fig. 6, right). The influence of
[NCO]/[OH] ratio on the crosslinking density and the Tg
value was also investigated and reported in Table 2. For
both polyols, the best results were observed for slight excess
in isocyanate: 1.1/1 related than 1/1 as widely described in
the literature. It is noteworthy that higher Tg value was
measured for PU2 in comparison to PU1 (72 and 45 ꢀC,
respectively). This difference could be explained by the pres-
ence of dangling chain in the structure of OH1 in opposition
to OH2 as well as the densification of the network resulting
in higher functionality in alcohol groups in the latter case.
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