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Z. Beyazkilic et al. / Polymer 68 (2015) 101e110
completely renewable and biodegradable toughening agent that
enhances PLA properties. However, most tougheners derived
from renewable resources are less effective than those derived
from petroleum resources in improving the PLA toughness.
Consequently, the obtention of block copolymers is a better
approach to develop biocompatible, highly toughened PLA which
retains both completely renewable origins and the ultimate de-
gradability [10].
Multiblock polymers attract interest because they are expected
to have distinct microstructures, offering alluring opportunities to
generate exquisitely tailored materials with unparalleled control
over nanoscale-domain geometry, packing symmetry, and chemical
composition, thus exhibiting different mechanical behaviour
compared to conventional polymers with simple structures [27].
Moreover, advances in synthetic polymer chemistry methods allow
access to numerous structures of multiblock copolymers and a
considerable number of different strategies have been used. As
concerns PLA-based block copolymers, one can distinguish be-
tween those synthesized by sequential ring opening polymeriza-
tion (ROP) when comonomers are cyclic esters or carbonates, and
block copolymers synthesized by distinct polymerization methods.
In the latter case, most of the time, a macroinitiator is first syn-
thesized by another polymerization method than ROP and then
ROP of lactide is initiated by the reactive functions of the
macroinitiator.
2.2. Dihydroxyl-terminated prepolymers (HO-PTEHA-OH)
Hydroxyacid TEHA (2.000 g, 7.630 mmol), 1,4-butanediol
(0.034 g, 0.380 mmol in 1:0.05 M ratio or 0.068 g, 0.763 mmol in
1:0.1 M ratio) and Sn(Oct)2 (0.030 g, 0.076 mmol) in 1% TEHA/catalyt
molar ratio) were stirred at 140 ꢁC under argon atmosphere. After
1 h, dynamic vacuum was applied during 6 h. The resulted polyester
was obtained as a white solid and was dissolved in dichloro-
methane, precipitated into methanol, filtered and dried under
reduced pressure. (yield % 93). Molar mass are collected in Table 1.
1H NMR (CDCl3,
d, ppm): 4.21 (t, 2H, eCH2eOe), 4.09 (t, 2H,
eCH2eOCOe), 3.72 (m, 2H, eCH2eOH terminal unit), 2.73 (t, 2H,
eCH2eSe), 2.54 (t, 2H, eCH2eSe), 2.30 (t, 2H, eCH2eCOe), 1.70 (t,
2H, eCH2eCH2eOCOe), 1.63e1.25 (m, 16H, eCH2e)
13C NMR (CDCl3,
d, ppm): 173.8 (s), 63.5 (t), 34.4 (t), 32.6 (t), 30.7
(t), 29.9e29.0 (t), 25.1 (t)
2.3. Synthesis of triblock copolyesters (P(LA-b-TEHA-b-LA))
The desired amounts of dihydroxyl-terminated prepolymer
(HO-PTEHA-OH) and LA (Table 1) were refluxed in dry toluene at
120 ꢁC under argon atmosphere for 4 h with addition of Sn(Oct)2
(1% LA/catalyst molar ratio). After completion of the reaction,
toluene was removed under reduced pressure, the copolymer was
dissolved in dichloromethane followed by precipitation into
methanol and dried under reduced pressure. (yield % 85). Molar
masses are collected in Table 1.
This article describes the synthesis and characterization of fully
biobased triblock copolyesters from PLA and castor oil derivatives.
The synthetic strategy selected was to design a dihydroxy telechelic
polyester, from 10-undecenoic acid derivative, as a macroinitiator
1H NMR (CDCl3,
d, ppm): 5.17 (q, H, eCHeCH3), 4.35 (q, H,
eCHeCH3 terminal unit), 4.21 (t, 2H, eCH2eOe), 4.09 (t, 2H,
eCH2eOCOe), 2.73 (t, 2H, eCH2eSe), 2.55 (t, 2H, eCH2eSe), 2.31
(t, 2H, eCH2eCOe), 1.70 (t, 2H, eCH2eCH2eOCOe), 1.58 (d, 3H,
CH3eCHe), 1.50e1.25 (m, 16H, eCH2e)
for ROP of L-lactide (LA). This approach consisted of the use of a
sulfur-containing hydroxyacid, which self-polycondensation initi-
ated with low amounts of biobased 1,4-butanediol [28], enables the
obtention of a dihydroxy terminated prepolymer, which initiates
the ROP of LA to reach the targeted triblock copolymer. The intro-
duction of polar sulfur-containing groups by oxidation of the main
chain sulfide moiety to sulfone is expected to increase polarity and
thus, changes in the thermal behaviour and crystallinity of the
polymers are expected.
13C (CDCl3,
d, ppm): 173.6 (s), 169.8 (s), 69.2 (d), 63.5 (t), 34.4 (t),
32.6 (t), 30.7 (t), 29.9e29.0 (t), 25.1 (t), 16.8 (q)
2.4. Oxidation of thioether-containing triblock copolyesters to
polysulfone (PSO(LA-b-TEHA-b-LA))
a) Thioether-containing triblock copolyesters (0.3 g, 1.14 mmol)
were dissolved in dicloromethane, 3-chloroperbenzoic acid
(mCPBA) (0.5 g, 2.28 mmol) was added and the mixture was
stirred at room temperature. After 1 h of reaction, the formed
polymer was washed with 5% Na2S2O3 and 5% NaHCO3 prior to
drying under reduced pressure.
2. Materials
The following chemicals were used as received: 10-undecenoic
acid (Fluka),
L-lactide (98%, Aldrich) 2-mercaptoethanol (99%,
Aldrich), 2,2-dimethoxy-2-phenylacetophenone (DMPA) (99%,
Aldrich), tin(II) 2-ethylhexanoate (Sn(Oct)2) (95%, Aldrich), dibutyl
tin oxide (DBTO) (98% Aldrich) 1,4-butanediol (BD) (99%, Aldrich),
3-chloroperbenzoic acid (mCPBA) (ꢀ77%, Aldrich), hydrogen
peroxide (50% Aldrich). Solvents were purified by standard
procedures.
1H NMR (CDCl3,
d, ppm): 5.17 (q, H, eCHeCH3), 4.50 (t, 2H,
eCH2eOe), 4.35 (q, H, eCHeCH3 terminal unit), 4.09 (t, 2H,
eCH2eOCOe), 3.28 (t, 2H, eCH2eSe), 3.02 (t, 2H, eCH2eSe), 2.31
(t, 2H, eCH2eCOe), 1.84 (m, 2H, eCH2eCH2eS), 1.70e1.25 (m,
16H,eCH2e).
13C (CDCl3,
d, ppm): 173.1 (s), 169.8 (s), 69.2 (d), 57.7 (t), 54.4 (t),
2.1. Thioether-containing
u-hydroxyacid (TEHA)
51.8 (t), 34.3 (t), 29.9e22.0 (t), 16.8 (q).
An equimolar mixture of 10-undecenoic acid (1.0 g, 5.43 mmol)
and 2-mercaptoethanol (0.4 g, 5.43 mmol) was irradiated in
b) Thioether-containing triblock copolyester (0.2 g, 0.82 mmol)
were dissolved in chloroform and subsequently 50% hydrogen
peroxide solution (0.09 ml) was added to the reaction flask. The
mixture was stirred at room temperature. After 48 h of reaction,
the formed polymer was washed with 5% NaHCO3 and water
prior to drying under reduced pressure.
dichloromethane solution at
l
¼ 365 nm in the presence of DMPA
(2% mol respect to C]C) as photoinitiator. The completion of the
reaction was confirmed after 10 min by the completely disap-
pearance of C]C double bonds from 1H NMR. The thioether con-
taining
54 ꢁC, LC-(ESI) MS: m/z calcd: 262.16; found: 262.16).
1H NMR (CDCl3,
, ppm): 3.72 (t, 2H, eCH2eOH), 2.72 (t, 2H,
u-hydroxyacid was quickly obtained. (yield % 100, mp:
d
2.5. Instrumentation
eCH2eSe), 2.50 (t, 2H, eCH2eSe), 2.34 (t, 2H, eCH2eCO),
1.69e1.27 (m, 16H, eCH2e).
The IR analyses were performed on a FTIR- 680PLUS spectro-
photometer with a resolution of 4 cm-1 in the transmittance mode.
NMR spectra were recorded on a Varian VNMRS400. The samples
13C NMR (CDCl3,
d, ppm): 179.9 (s), 60.3 (t), 35.4 (t), 34.1 (t), 31.7
(t), 29.9e29.0 (t), 24.8 (t).