Macromolecules, Vol. 38, No. 23, 2005
Synthesis of PVAc and PVOH 9489
) 2 s, 30 000 scans, 5 wt % polymer). Infrared spectra (IR)
were recorded with a Perkin-Elmer FT-IR instrument (KBr).
Differential scanning calorimetry (DSC) was performed under
a nitrogen flow (50 cm3/min) at a heating rate of 10 °C/min
with a DSC Q100 from TA Instruments. Certified indium wire
encapsulated in an aluminum crucible was used for temper-
ature and heat flow calibration. Peak temperature, onset
temperature, and enthalpy of melting were determined for all
the samples (using the software of the apparatus). Thermo-
gravimetric analysis (TGA) was carried out under a nitrogen
flow (60 cm3/min) using a high-resolution mode (resolution 5,
sensitivity 1, initial heating rate of 50 °C/min), from room
temperature to 700 °C, with a Hi-Res TGA Q500 from TA
Instruments. Transmission electron microscopy (TEM) was
carried out with a Philips CM 100 operating at a voltage of
100 kV, equipped with a Gatan 673 CCD camera and a
computer loaded with the Kontron KS 100 software. Samples
were prepared by depositing a droplet of an aqueous copolymer
solution on a Formvar-coated copper TEM grid. Water was let
to evaporate under ambient atmosphere for 1 h. Dynamic light
scattering (DLS) was performed with a Brookhaven Instru-
ments Corp. DLS apparatus, which consisted of a BI-200
goniometer, a BI-2030 digital correlator, and an Ar ion laser
(LEXEL lasers, wavelength ) 488 nm, power ) 10 mW),
scattering angle ) 90°. A refractive index matching bath of
filtered decalin surrounded the scattering cell, and the tem-
perature was controlled at 25 °C. Elementary analyses (EA)
were carried out with a Carlo-Erba elemental analyzer CHNS-O
EA1108.
Synthesis of 1-Oxyl-(2,2,6,6-tetramethylpiperidine)-4-
yl 2-Bromo-2-methyl-propanoate (2). Dry triethylamine
(2.61 g, 25.8 mmol) followed by bromoisobutyryl bromide (4.84
g, 21.0 mmol) was added dropwise to a solution of 4-hydroxy-
2,2,6,6-tetramethylpiperidine 1-oxyl (1) (3.03 g, 17.6 mmol) in
tetrahydrofuran (50 mL), under argon. The red solution was
stirred at room temperature for 18 h, and a white precipitate
was formed. After dilution with diethyl ether, the solution was
filtered, washed two times with aqueous NaHCO3, and dried
over Na2SO3 before being evaporated under reduced pressure.
The residual red-orange powder, corresponding to the product
2 (4.6 g, 14.3 mmol), was stored under an inert atmosphere at
-20 °C. Yield ) 81%; mp ) 83.8 °C. IR (KBr) νmax: 1729.0
(vs, CdO stretch of R-bromoester), 1371.3 (s, N-O•), 684.8 and
652.3 cm-1 (m, C-Br stretch). Anal. Calcd for C13H23O3NBr:
C, 48.63%; H, 7.22%; N, 4.36%. Found: C, 49.88%; H, 7.89%;
N, 4.54%.
Synthesis of 1-Hydroxy-4-oxo-2,2,6,6-tetramethylpip-
eridine Hydrochloride (4). Concentrated hydrochloric acid
(37 wt %, 3.2 mL) was added dropwise, at 5 °C while stirring,
to a solution of 4-oxo-2,2,6,6-tetramethylpiperidine 1-oxyl (3)
(5.00 g, 29.4 mmol) in ethanol (3.6 mL). The solution was
stirred at 24 °C for 1 h, before the solvent was evaporated
(rotating evaporator) at 50 °C. The yellow residue was crystal-
lized twice in 2-propanol, and the colorless crystals of 1-hy-
droxy-4-oxo-2,2,6,6-tetramethylpiperidine hydrochloride (3.80
g, 18.4 mmol) were filtered and dried under reduced pressure.
Yield ) 63%; mp ) 164 °C. RMN 1H (400 MHz, D2O): 2.71
ppm (4 H, s, -CH2-); 1.31 ppm (12 H, s, -CH3). IR (KBr)
νmax: 1725.4 cm-1 (s, CdO stretch).
Synthesis of 3-Bromo-4-oxo-2,2,6,6-tetramethylpiperi-
dine 1-Oxyl (5). At room temperature, a bromine solution
(2.56 g, 16 mmol) in chloroform (30 mL) was added dropwise
to a stirred solution of 1-hydroxy-4-oxo-2,2,6,6-tetramethyl-
piperidine hydrochloride (4) (3.1 g, 15 mmol) in chloroform
(analytical purity, 4 mL). After discoloration, the reaction
medium was added with an aqueous solution of sodium nitrite
(3.0 g in 40 mL) with vigorous stirring and kept at 24 °C for
30 min. The organic phase was separated, washed with water,
and dried over anhydrous magnesium sulfate, before the
solvent was evaporated (rotating evaporator) at 40 °C. The
residue was recrystallized twice from n-hexane (at -20 °C),
and the collected orange crystals were dried under reduced
pressure (0.75 g, 3.0 mmol; yield ) 20%). Purity was checked
by thin-layer chromatography in chloroform and showed
contamination by a small amount of the product 3; mp ) 66
°C. IR (KBr) νmax: 1731.4 (vs, CdO stretch of R-bromoester),
1367.7 cm-1 (s, N-O•).
General Recipe for the Synthesis of Poly(vinyl ac-
etate) Macroinitiators End-Capped by Either an R-Bro-
moester or an R-Bromoketone. V-70 and Co(acac)2 were
added into a glass tube capped by a three-way stopcock and
purged by three vacuum-argon cycles. After addition of
degassed vinyl acetate, the reaction mixture was heated at 30
°C under stirring. After a few hours, the color changed from
purple to dark green-brown, and a substantial increase in
viscosity was noted. To determine the monomer conversion
gravimetrically, a sample was picked out from the reaction
medium to which was then added the appropriate nitroxide
(2 or 5) dissolved in degassed toluene. After reaction for a few
hours, the solution was diluted by acetone and eluted through
alumina in order to eliminate the cobalt complex. The polymer
was precipitated in heptane and dried in vacuo at 40 °C. A
colorless poly(vinyl acetate) was collected and stored at -20
°C under an inert atmosphere.
PVAc Macroinitiator I. Conditions: V-70 (0.200 g, 6.5 ×
10-4 mol), Co(acac)2 (52 mg, 2.0 × 10-4 mol), VAc (5.0 mL, 4.7
g, 54 × 10-3 mol), 40 h at 30 °C, conversion ) 38%, R-bro-
moester containing nitroxide 2 (0.128 g, 4.0 × 10-4 mol) in
toluene (1.5 mL). Characteristics: Mn,NMR ) 86.09 × (3 ×
(-CH-OCOCH3, PVAc)/(-OCH3, V-70)) ) 8800 g/mol; Mn,theor
) 8900 g/mol; Mw/Mn ) 1.10; DSC: Tg ) 40 °C.
PVAc Macroinitiator II. Conditions: V-70 (4.00 g, 13.0 ×
10-3 mol), Co(acac)2 (1.03 g, 4.0 × 10-3 mol), VAc (50.0 mL,
46.7 g, 542 × 10-3 mol), 88 h at 30 °C, conversion ) 56%,
R-bromoester containing nitroxide 2 (1.84 g, 5.7 × 10-3 mol)
in toluene (5.0 mL). Characteristics: Mn,NMR ) 86.09 × (3 ×
(-CH-OCOCH3, PVAc)/(-OCH3, V-70)) ) 6700 g/mol; Mn,theor
) 6500 g/mol; Mw/Mn ) 1.20.
PVAc Macroinitiator III. Conditions: V-70 (750 mg, 24.4
× 10-4 mol), Co(acac)2 (0.19 g, 7.5 × 10-4 mol), VAc (16.0 mL,
14.9 g, 173 × 10-2 mol), 46 h at 30 °C, conversion ) 37%,
3-bromo-4-oxo-2,2,6,6-tetramethylpiperidinyl-1-oxy (5) (0.373
g, 15 × 10-4 mol) in toluene (3.0 mL). Characteristics: Mn,NMR
) 86.09 × (3 × (-CH-OCOCH3, PVAc)/(-OCH3, V-70)) ) 6900
g/mol; Mn,theor ) 7400 g/mol; Mw/Mn ) 1.15.
General Recipe for the Synthesis of PVAc Containing
Block Copolymers by ATRP Initiated by a Poly(vinyl
acetate) Macroinitiator. A solution of poly(vinyl acetate)
macroinitiator in degassed toluene was added under argon to
a glass tube capped by a three-way stopcock. It was heated at
70 °C for 30 min to decompose any residual V-70, followed by
toluene evaporation under reduced pressure. The copper
complex was then added to the macroinitiator, and the reactor
was purged by three vacuum-argon cycles. Degassed toluene,
vinyl monomer, and HMTETA solution (0.35 M in toluene)
were then added with a syringe. The flask was thermostated
at the desired temperature, under stirring. The monomer
conversion was determined by weighing the polymer collected
upon removing the unreacted monomer from a picked-out
sample, in vacuo at 80 °C. The residual monomer was similarly
removed from the reaction medium under reduced pressure,
and the polymer was diluted by THF, eluted through alumina,
and poured in a copolymer nonsolvent. The colorless copolymer
was filtered and dried under reduced pressure at 50 °C.
PVAc-b-PS1. Conditions: PVAc macroinitiator II (430 mg,
0.64 × 10-4 mol), CuBr (7 mg, 0.5 × 10-4 mol), toluene (1.0
mL), styrene (1.5 mL, 1.4 g, 13 × 10-3 mol), HMTETA (0.15
mL, 0.35 M, 0.5 × 10-4 mol), 5 h 30 at 110 °C, conversion )
24%, precipitation in heptane. Characteristics: Mw/Mn ) 1.15;
Mn,NMR PVAc ) 6700 g/mol; Mn,theor PS ) 5100 g/mol; Mn,NMR PS
104 × (3/5) × ((aromatic protons of PS)/(-OCH3, V-70)) ) 6000
g/mol; Mn,theor PS/Mn,NMR PS ) 0.85. DSC: Tg,PVAc ) 36°C, Tg,PS
)
)
94 °C. TGA: -38% (292 °C), -41% (399 °C), -10% (426 °C).
PVAc-b-PEA. Conditions: PVAc macroinitiator II (430 mg,
0.64 × 10-4 mol), CuBr (7 mg, 0.5 × 10-4 mol), toluene (1 mL),
ethyl acrylate (1.5 mL, 1.4 g, 14 × 10-3 mol), HMTETA (0.15
mL, 0.35 M, 0.52 × 10-4 mol), 1 h 30 at 90 °C, conversion )
55%, precipitation in heptane. Characteristics: Mw/Mn ) 1.50;
Mn,NMR PVAc ) 6700 g/mol; Mn, theor PEA ) 11 900 g/mol; Mn,NM
PEA
-
R
) 101.1 × (3/2) × ((CH2-CH-COOCH2CH3 of PEA)/