ARTICLE
polymers with a cross-linked core without catalyst conta-
mination. Moreover, we investigate the influence of the
step-wise addition of initiator and cross-linker (multibatch
process) on the star polymer synthesis. Finally, after removal
of the benzyl group of the PBLG stars, we studied the pH
responsiveness of the polymers in water.
the NCA was fully dissolved, a solution of 4-vinylbenzylamine
(43 mg, 0.32 mmol, for MM1, MM2, MM3 and 51 mg,
0.38 mmol, for MM4) in 2 mL of dry DMF was added. The
ꢀ
reaction was maintained for 4 days at 0 C under inert
atmosphere. The reaction mixture was then precipitated in
an excess of diethyl ether, filtered, and dried under vacuum.
A white polymer solid was collected (Yield: 75%).
EXPERIMENTAL
Star Polymer Synthesis by FRP
A total ratio of reagents [PBLG MM] /[DVB] /[initiator]
0
Materials
¼
0
0
All chemicals were purchased from Sigma-Aldrich and used as
received unless otherwise noted. c-Benzyl-L-glutamate was sup-
plied by Bachem, diethyl ether was purchased from VWR, and
S-(2-cyanoprop-2-yl)-S-dodecyltrithiocarbonate was supplied by
Strem Chemicals. Anhydrous DMF was used directly from the
bottle under an inert and dry atmosphere. c-Benzyl-L-glutamate
1
/6/0.3 was used in all polymerizations. A clean and dry
Schlenk flask was charged with PBLG MM (150 mg,
.023 mmol), DVB (17.5 mg, 0.13 mmol), 1,1 -azobis(cyclohex-
ane carbonitrile) (ACHCN) initiator (1.9 mg, 0.0078 mmol),
and DMF (0.4 mL). The flask was sealed with a glass stopper
and was degassed by nitrogen bubbling for 30 min before it
0
0
27
NCA was synthesized following a literature procedure.
ꢀ
was immersed in an oil bath at 90 C. At timed intervals, sam-
ples were withdrawn via a syringe fitted with stainless steel
needle, dried under vacuum at 40 C and analyzed by size
exclusion chromatography (SEC). In the multibatch reactions,
ACHCN or ACHCN/DVB were added at time intervals.
Synthesis of 4-Vinylbenzylphthalimide
ꢀ
4-vinylbenzylchloride (10 g, 60 mmol) and potassium phtha-
limide (13.5 g, 72 mmol) were suspended in 30-mL dry THF.
ꢀ
The suspension was stirred at 40 C for 24 h. This reaction
mixture was allowed to cool down to room temperature, and
Star Polymer Synthesis by RAFT
8
0 mL water was added. The reaction mixture was extracted
The synthesis of star polymers by RAFT polymerization in
a multibatch process was started with the ratio of reagents
with 75 mL diethyl ether and subsequently twice with 30
mL diethyl ether. The combined organic layers were washed
with 25-mL 0.2 M NaOH and 25-mL brine and dried over
MgSO . After removal of the solvent, the product was recrys-
tallized twice from methanol. The pure product was obtained
[
PBLG MM4] /[DVB] /[AIBN] ¼1/3/0.0167 and [CTA]0/
0
0
0
[
AIBN] ¼ 2.5/1. A clean and dry Schlenk flask was charged
0
4
with PBLG MM (100 mg, 0.016 mmol), DVB (6.5 mg in 100 lL
of DMF, 0.05 mmol), AIBN (0.046 mg in 10 lL of DMF,
1
ꢁ
4
after filtration (Yield: 9.1 g, 56%). H NMR: (400 MHz,
CDCl
2
.78.10 mmol), chain transfer agent (CTA) (0.24 mg in 10
ꢁ
4
3
): 7.82–7.85 (m, 2H), 7.71–7.73 (m, 2H), 7.40–7.42 (m,
lL of DMF, 6.95.10 mmol), and DMF (0.2 mL). The flask
was sealed with a glass stopper and was degassed by nitrogen
bubbling for 30 min before it was immersed in an oil bath at
2
5
H), 6.62–6.69 (m, 1H), 5.68–5.72 (d, 1H), 5.26 (s, 2H),
.20–5.23 (d, 1H), 4.97–5.01 (d, 2H) ppm. C NMR (400
1
3
ꢀ
MHz, CDCl ): 168.0, 137.2, 136.3, 135.8, 134.0, 132.1, 128.8,
3
125 C. Every 24 h, 1 eq. DVB, 0.0167 eq. AIBN, and 0.05 eq.
1
26.5, 123.3, 114.1, 41.3 ppm.
CTA were injected into the reaction. At time intervals, samples
were withdrawn via a syringe fitted with stainless steel needle,
dried under vacuum at 40 C and analyzed by SEC.
Synthesis of 4-Vinylbenzylamine
To a solution of 4-vinylbenzyl phtalimide (5 g, 18 mmol) in 50
mL ethanol, hydrazine (1.3 g, 26 mmol) and terbutylcatechol
ꢀ
Poly(Glutamate Acid) Star Polymer (Deprotection
of Star Polymer)
(50 mg) were added. The resulting mixture was heated to
reflux for 3 h under vigorous stirring. The solution was
allowed to cool down and 1 M HCl was added until pH ¼ 1–2
was reached. The white suspension was filtered off, and the
residue was washed twice with 10 mL 1 M HCl. The combined
filtrates were made alkaline to pH 10–11 by addition of NaOH.
The turbid aqueous layer was extracted four times with
diethyl ether (30 mL). The combined organic layers were then
washed once with 0.2 M NaOH (10 mL) and once with brine.
After concentration under vacuum, a slightly yellow liquid was
obtained. After distillation under high vacuum, a colorless liq-
The PBLG star polymer (60 mg) was dissolved in 2 mL of
trifluoroacetic acid at room temperature. Then 0.6 mL of
hydrobromic acid was added. After 12 h, the solution was
added drop-wise into an excess of diethyl ether and filtered.
A slightly yellow solid was collected and dried under vac-
ꢀ
uum at 40 C overnight and reprecipitated from DMF in
diethyl ether, filtered, and dried.
Methods
H and
1
13
C-NMR analysis were performed on a Brucker
1
Avance 400 MHz in deuterated chloroform. SEC analysis using
DMF (0.1 M LiBr) as eluent was done using PSS GRAM analyti-
cal (300 and 100 Å, 10 l) columns on an Agilent 1100 series
equipped with a Wyatt Optilab rEX refractive index detector
uid was obtained (Yield: 1.11 g, 42%). H-NMR: (400 MHz,
CDCl ): 7.34–7.36 (d, 2H), 7.22–7.24 (d, 2H), 6.64–6.71 (m,
3
1
H), 5.68–5.72 (d, 1H), 5.18–5.20 (d, 1H), 3.81 (s, 2H), 1.65
13
(broad, 2H) ppm. C-NMR (400 MHz, CDCl ): 142.9, 136.5,
3
ꢀ
thermostated at 40 C and a Wyatt DAWN HELEOS-II multi
136.2, 127.2, 123.3 113.4, 46.2 ppm.
angle light scattering (MALS) detector. Molecular weights and
PDI were calculated from the MALS signal by the ASTRA soft-
ware (Wyatt) using a dn/dc value of 0.118 mL/g for PBLG in
Synthesis of Vinyl-Terminated PBLG
(
Macromonomer Synthesis)
28
c-Benzyl-L-glutamate NCA (2 g, 7.6 mmol) was dissolved in
DMF. Before SEC analysis was performed, the samples were
ꢀ
1
8 mL of dry DMF in a Schlenk tube at 0 C under N . After
filtered through a 0.4-lm PTFE filter (13 mm, PP housing,
2
CROSS-LINKING OF LINEAR PBLG MACROMONOMERS, AUDOUIN ET AL.
4603