Macromolecules
Article
an RI Shodex refractive index detector with two mixed packed
columns (Polar Gel L 300*7.5 mm). The eluent used is
dimethylacetamide (DMAc) at a flow rate of 0.8 mL/min at 50 °C
and poly(methyl methacrylate) standards were used for calibration.
Fourier transform infrared (FTIR) spectra were recorded on a
PerkinElmer spectrum 2000 FTIR, equipped with a diamond ATR
(Attenuated Total Reflection) device (16 scans were performed). DLS
measurements were recorded on a Malvern Zetasizer. MALDI−TOF-
MS analyses were performed on a MALDI−TOF/TOF Bruker
Ultraflex III mass spectrometer using a nitrogen laser for MALDI (λ
337 nm) operating at an acceleration voltage of 25KV and reflectron
lens potentials at 26.3 kV. Mixture of peptides was used for external
calibration. The polymer sample was dissolved at 10 mg/mL in a
mixture of acetonitrile and water (50/50 v/v). The matrixes used were
HCCA (α-cyano-4-hydroxycinnamic acid) and DHB (2,5-dihydrox-
ybenzoic acid). Each matrix was dissolved at 10 mg/mL in a
trifluoroacetic acid/acetonitrile solution (0.1% TFA/CH3CN: 70/30).
Solutions of matrix and polymer were mixed in a volume ratio of 10:4
respectively. The mixed solution was hand-spotted on a MALDI target
and left to dry. The theoretical mass was expressed as followed:
Synthesis of Amphiphilic Copolymer Using LTs. Lipid-b-p(MeOx),
3, [MeOx]0:[MeOTs]0 = 26:1, 20 min of polymerization; lipid-b-
p(EtOx), 5, [EtOx]0:[LTs]0 = 26:1, 30 min of polymerization; lipid-b-
p(iPrOx), 7, [iPrOx]0:[LTs]0 = 26:1, 30 min of polymerization; lipid-
b-p((EtOx)-co-(iPrOx)), 9−11: iPrOx79% = 17 equiv, iPrOx58% = 13
equiv, iPrOx25% = 5 equiv and EtOx21% = 2 equiv, EtOx42% = 6 equiv,
and EtOx75% = 12 equiv.
All the purified polymers are beige powders.
1H NMR (CDCl3, 300 MHz): δ (ppm): 5.34 (m, 2H, − HC
CH−), 3.7−3.1 (m, 4H, N−CH2−CH2), 2.80 (m, 2H, − HCCH−
CH2−HCCH−), 3−2.5 (m, 1H, -CH-(CH3)2), 2.4−2.1 (m, 2H,
-CH2-CH3), 1.85 (m, 2H, − HCCH−CH2−CH2), 1.25 (m, 2H,
alkyl CH2), 1.15 (m, 9H, CH3 isopropyl and ethyl group), 0.97 (t, 3H,
CH3 linolenic chain), 0.88 (m, 3H, CH3 other alkyl chain).
Preparation of Micelles. Lipid-b-poly(2-alkyl-2-oxazoline) was
first solubilized in methanol (2 mL) and then dropped into deionized
water containing 0.1 M of NaCl. The solution was stirred overnight to
evaporate the methanol. The solution was completed by deionized
water (containing 0.1 M of NaCl) to achieve a copolymer
concentration of 2 g/L and stirred a minimum of 3 h before analyses.
Lipid-b-p(EtOx) and lipid-b-p(iPrOx) solution prepared as
described above were mixed together in order to form mixed micelles.
Different solutions were prepared in order to obtain a range in EtOx
concentration. All solutions were stirred a minimum of 3 h before
analyses.
Mth = n × MEtOx,th + m × MiPrOx,th + RMth
Here Mth is the calculated mass of the (co)polymer, MEtOx,th and
MiPrOx,th are the mass of the ethyl and isopropyl repetitive units (99
and 113 g/mol, respectively), and RMth represents the calculated
residual mass (C18H33− and −OH terminal groups).
Cloud Point Temperature Measurements. Cloud points were
determined by spectrophotometric measurements of the absorbance of
micellar solutions at λ = 500 nm and heated at a constant rate of 0.5
°C/min. The cloud points temperatures were reached when the
absorbance increased by 10%.
DLS Measurements. Copolymer solutions at 2 g/L were prepared
in deionized water containing 0.1 M of NaCl and filtered on a 0.45 μm
cellulose filter prior to introduction in the Zetasizer device.
Temperature is controlled with a Peltier. Eight measurements were
performed by analysis.
Fluorescence Measurements. Sample solutions for fluorescence
measurements were prepared as described previously.24 The sample
solutions were prepared by first adding known amounts of pyrene
predissolved in acetone to a series of 10 mL volumetric flasks (to
obtain a final pyrene concentration of 4.10−7 mol L−1 after dilution).
Acetone was allowed to evaporate and accurate amounts of a
copolymer stock solution (2 g/L, 0.1 M NaCl) were added to each
of the volumetric flask to reach various concentrations ranging from 1
mg/L to 2 g/L after dilution with a 0.1 M NaCl solution. The
solutions were stirred at least 2 h prior the analysis. Excitation spectra
of pyrene were recorded between 330 and 360 nm (bandwidth = 1.5
nm) at a fixed emission wavelength (λEm = 374 nm, bandwidth = 1.5
nm).
Fatty Alcohols Synthesis. The linseed oil reduction into fatty
alcohols was realized following a previously reported method.10
Lipoinitiator (LTs) Synthesis. A mixture of p-TsCl (2 equiv, 7.05
g) in anhydrous chloroform (40 mL) was added dropwise to a mixture
of fatty alcohol (1 equiv, 5 g), TEA (3 equiv, 5.63 g) and DMAP (0.1
equiv, 0.22 g) in anhydrous chloroform (35 mL) under inert
atmosphere. The reaction media was stirred overnight at 30 °C,
then extracted with AcOEt (50 mL) and washed with NaHCO3 and
brine. The resulting solution was dried over anhydrous magnesium
sulfate, filtered and concentrated under vacuum. The crude product
was purified through a column chromatography over silica gel
(cyclohexane/ethyl acetate =91:9) leading to a yellowish liquid with
57% yield.
1H NMR (CDCl3, 300 MHz), δ (ppm): 7.80 and 7.35 (d, 4H
benzyl), 5.34 (m, 2H, −HCCH−), 4.01 (t, 2H, −CH2−OS), 2.80
(m, 2H, −HCCH−CH2−HCCH−), 2.44 (s, 1H, CH3), 2.05 (m,
2H, −HCCH−CH2−CH2), 1.63 (m, CH2−CH2−OS), 1.25 (m,
2H, alkyl CH2), 0.97 (t, 3H, CH3 linolenic acid), 0.88 (m, 3H, CH3
other acid). 13C NMR (CDCl3, 75 MHz), δ (ppm): 144.8 (benzyl),
139−127.3 (−HCCH−), 71 (−CH2−OS), 32.1−20.9 (alkyl CH2),
14.6 (alkyl chain). MS [M+ Na+]: m/z 441 (linolenic), m/z 443
(linoleic), m/z 445 (olenic). IR: νCC = 3009 cm−1, νCH ,CH = 2924
2
3
and 2853 cm−1, νSO = 1361 cm−1, νSO = 1180 cm−1.
RESULTS AND DISCUSSION
■
CROP Polymerization. The protocol for the thermal CROP is
Polymerization of 2-Methyl-2-oxazoline (MeOx) Using
Tosylated and Mesylated Initiators. Two methods can be
envisaged toward the preparation of lipid-b-poly(oxazoline)
copolymers by (1) the “initiator route”, where the lipidic block
(lipoinitiator) is introduced from the beginning of the
polymerization or (2) the “termination route”, adding the
fatty alcohol during the termination step of the CROP
polymerization. The first method permitting a quantitative
incorporation of the lipidic chain to the polyoxazoline block
was preferred.11
identical to the previously reported method.19
For all microwave-assisted polymerizations, the initiator (MeOTs or
LTs) (1 equiv) and dried acetonitrile are first introduced in a
microwave vial flushed with nitrogen. Then monomer(s) (4 M) is
added via a syringe. The polymerization mixture is stirred at 140 °C
during the appropriate reaction time and terminated with methanolic
KOH (1 M) to introduce a hydroxyl group at the chain end. The
polymer obtained is purified by dialysis (500 Da cutoff) against
distilled water for 2 days changing the water every 6 h. The final
polymer is recovered by lyophilization.
Synthesis of Hydrophilic (Co)polymers Using MeOTs. p(EtOx), 4,
[EtOx]0:[MeOTs]0 = 18:1; p(iPrOx), 6, [iPrOx]0:[MeOTs]0 = 26:1;
p((EtOx)-co-(iPrOx)), 8, [EtOx]0:[iPrOx]0:[MeOTs]0 = 2:17:1. The
polymerizations run for 30 min and the purified polymers are white
powders.
In our previous study, the CROP polymerization of 2-
isopropyl-2-oxazoline was initiated from a mesylated lip-
oinitiator (LMs), family of initiators very little studied. The
polymerization control was not entirely satisfying. Herein, the
study of the oxazoline polymerization was extended to more
conventional lipidic initiator: tosylated lipoinitiator (LTs) and
its efficiency was compared to that of LMs. Both initiators were
1H NMR (CDCl3, 300 MHz), δ (ppm): 3.7−3.1 (m, 4H, N−CH2−
CH2), 3 (s, 1H, −CH3), 3−2.5 (m, 1H, −CH−(CH3)2), 2.4−2.1 (m,
2H, −CH2−CH3), 1.15 (m, 9H, CH3 isopropyl and ethyl group).
C
Macromolecules XXXX, XXX, XXX−XXX