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the synthesis was performed using a multistep procedure
involving precipitation and modification steps.
to the sodium hydride suspension over 1 h, and the mixture
was stirred for 1 h. Subsequently, carbon disulfide (4 g, 52
mmol) was added dropwise to the mixture over a 10 min
period and stirred overnight at 0 ꢀC. The mixture was then
concentrated to remove the unreacted carbon disulfide and
resuspended in 100 mL of THF in a 250 mL round-bottomed
In this study, PVP-b-poly(L-lactide) (PVP-b-PLLA) block poly-
mers were synthesized using a hydroxyl-functionalized N,N-
diphenyldithiocarbamate RAFT agent, 2-hydroxyethyl 2-(N,N-
diphenylcarbamothioylthio)propanoate (HDPCP), as a dual
initiator for RAFT polymerization and ROP in a one-step pro-
cedure. 4-Dimethylamino pyridine (DMAP) was used as the
ROP catalyst of L-lactide (LLA). This one-step process is
believed to be the most convenient method for synthesizing
PVP-b-PLLA block copolymers.
flask.
A
solution of 2-hydoxyethyl 2-bromopropionate
(5.25 g, 26 mmol) in THF (20 mL) was then added dropwise
to the suspension over a 30 min period, and the resulting
mixture was stirred for 12 h. The product was filtered,
washed with diethyl ether, and purified by column chroma-
tography using hexane/ethyl acetate (7/3 v/v) as the eluent.
The final product was a slight incarnadine solid. 1H NMR
(400 MHz, CDCl3, d): 7.2–7.6 (m, 10H), 4.6 (m, 1H), 4.2–4.4
(m, 2H), 3.8 (t, 2H), 1.5 (d, 3H). 13C NMR (100 MHz, CDCl3,
d): 220.22, 172.60, 129.94, 128.76, 128.05, 67.33, 61.23,
49.78, 16.70. GC-MS (EI) m/z 5 361.3 (M1).
EXPERIMENTAL
Materials
VP (Aldrich, ꢁ99%) was passed through a neutral alumina
column, dried over calcium hydride, distilled under reduced
pressure, and degassed by three freeze-pump-thaw cycles. N-
Vinylcarbazole (VK, Aldrich, 98%) and LLA (Aldrich) were
recrystallized twice from ethyl acetate. Anisole (Junsei,
98.0%) was dried over calcium hydride, distilled under
reduced pressure, and degassed via three freeze-pump-thaw
cycles. 2,20-Azoisobutyronitrile (AIBN, Junsei, 96%) was
recrystallized twice from methanol. Diphenylamine (Aldrich,
98%), sodium hydride (Aldrich, 60% dispersion in mineral
oil), carbon disulfide (Aldrich, 99.9%), tetrahydrofuran (THF,
TCI, anhydrous, 98%), diethyl ether (Duksan, 99.0%), ethyl-
ene glycol (Aldrich, anhydrous, 99.8%), 2-bromopropionyl
bromide (Aldrich, 97%), triethylamine (Acros, 99%), pyridine
(Duksan 99.5%), N,N-dimethylformamide (DMF, Aldrich,
anhydrous, 99.8%), and DMAP (Aldrich, 99%) were used as
received.
RAFT Polymerization of VP Using HDPCP for a Kinetic
Investigation
The RAFT polymerization of VP was carried out at different
[VP]0/[LLA]0/[HDPCP]0/[AIBN]0 feed ratios at 60 ꢀC. For
example, the RAFT polymerization of VP at a feed ratio of
[VP]0/[LLA]0/[HDPCP]0/[AIBN]0 5 100/100/1/0.2 was per-
formed as follows. VP (2.0 mL, 18.8 mmol), LLA (2.7 g, 18.8
mmol), HDPCP (0.068 g, 0.188 mmol), and AIBN (0.0062 g,
0.0376 mmol) were dissolved in 4.7 mL of anisole. The mix-
ture was purged with nitrogen for 30 min and stirred at 60
ꢀC. During polymerization, 1 mL of the reaction mixture was
withdrawn periodically to monitor the level of monomer
conversion and the MW. The resulting PVP was precipitated
in an excess of cold diethyl ether, filtered, and dried under
vacuum for 24 h.
Characterization
ROP of LA Using HDPCP for a Kinetic Investigation
The ROP of LLA was performed at different [VP]0/[LLA]0/
[HDPCP]0/[DMAP]0 feed ratios at 60 ꢀC. For example, the
ROP of LLA at a feed ratio of [VP]0/[LLA]0/[HDPCP]0/
[DMAP]0 5 100/100/1/8 was performed as follows: VP (2.0
mL, 18.8 mmol), LLA (2.7 g, 18.8 mmol), HDPCP (0.068 g,
0.188 mmol), and DMAP (0.183 g, 1.50 mmol) were dis-
solved in 4.7 mL of anisole. The mixture was stirred at 60
ꢀC. During polymerization, 1 mL of the reaction mixture was
withdrawn periodically to monitor the level of monomer
conversion and the MW. The resulting PLLA was precipitated
in an excess of cold diethyl ether, filtered, and dried under
vacuum for 24 h.
The MWs and MW distributions of the polymers produced
were determined by gel permeation chromatography (GPC,
Young Lin SP930D solvent delivery pump) coupled with an
RI detector (RI 750F) and two columns (GPC KD-806 M 3 2,
Shodex). The eluent used was 0.01 M LiCl/DMF at 40 ꢀC
with a flow rate of 1.0 mL min21. PMMA standards were
used for calibration. The level of monomer conversion was
determined using a gravimetric method and the block poly-
mer composition was determined by 1H nuclear magnetic
resonance (1H NMR, Varian VXR-Unity NMR 400 MHz) spec-
troscopy in CDCl3. Gas chromatography-mass spectroscopy
(GC-MS) was performed using a Varian 1200 Single Quadru-
pole GC/MS System. Thermogravimetric analysis (TGA) was
performed using a thermogravimetric analyzer (Pyris 1 TGA,
21
ꢀ
One-Step Synthesis of PVP-b-PLLA Block Copolymers
Using HDPCP for a Kinetic Investigation
The one-step synthesis of PVP-b-PLLA block copolymers was
PerkinElmer) at a heating rate of 10 C min under a nitro-
gen atmosphere.
Synthesis of HDPCP
performed at
a
feed ratio of [VP]0/[LLA]0/[HDPCP]0/
ꢀ
2-Hydroxyethyl 2-bromopropionate was first synthesized by
the esterification of 2-bromopropionyl bromide with ethyl-
ene glycol in THF. Sodium hydride (1.24 g, 52 mmol) was
suspended in 20 mL of THF and cooled to 0 C. A diphenyl-
amine (2.93 g, 40 mmol) solution in a mixed solvent contain-
ing 36 mL of DMF and 18 mL of THF was added dropwise
[AIBN]0/[DMAP]0 5 100/100/1/0.2/8 at 60 C. VP (2.0 mL,
18.8 mmol), LLA (2.7 g, 18.8 mmol), HDPCP (0.068 g, 0.188
mmol), AIBN (0.0062 g, 0.0376 mmol), and DMAP (0.183 g,
1.50 mmol) were dissolved in 4.7 mL of anisole. The mixture
was purged with nitrogen for 30 min and stirred at 60 ꢀC.
During polymerization, 1 mL of the reaction mixture was
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JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 1607–1613
Shin, Sang Jin
