Green Chemistry
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1H NMR (400 MHz, CDCl3): δ 6.99–7.86 (m, 9H, aromatic),
4.25 (t, J = 5.90 Hz, 2H, –O–CH2–), 3.65 (t, J = 6.47 Hz, 2H, –
CH2–Br), δ 2.30–2.45 (m, 2H, –CH2–CH2–CH2–).
A-Si-A/B/C (7.80/11.02/15.62 g, 0.01 mol), HBP-Br (6.40 g,
0.02 mol) and 30 mL of acetonitrile were added into a 100 mL
four-necked round bottom flask, which was equipped with a
mechanical stirrer, a thermometer and a condenser. The reac-
tion was performed under stirring at 60 °C for 20 h. Then, the
solvent was removed by vacuum distillation. The crude
product was purified by silica gel (200–300 mesh) column
chromatography using ethyl acetate and petroleum ether
(1 : 25 v/v) as the eluents. The yield of the three photoinitiators
was 60.5%, 52.7% and 48.4%, respectively. Their molecular
weights measured by GPC were about 1063, 1682 and 2056 g
Scheme 4 Schematic representation of the preparation of gradient polymer
(PAM) by using W-Si-HBP2-A as the photoinitiator.
a Hamamatsu R928B detector. In the tests for transient
spectra, the concentrations of the W-Si-HBP2-A/B/C were opti-
cally matched (0.5 at 355 nm).
mol−1
Scheme 3.
W-Si-HBP2-A/B/C: 1H NMR (400 MHz, CDCl3): δ 6.99–7.86
, respectively. The synthesis process is shown in
(m, 18H, aromatic), 4.25 (t, J = 5.90 Hz, 4H, –O–CH2–), 3.28 (t,
J = 6.47 Hz, 4H, –CH2–Br), 3.10 (s, 4H, –Si–CH2–CH2–),
δ 2.50–2.60 (m, 4H, –CH2–CH2–CH2–), 1.94 (s, 4H, –NH2–), 0.65
(t, J = 7.14 Hz, 4H, –CH2–Si–), 0.08 (s, 54/84/120H, CH3–Si–).
Synthesis of gradient polymer cylinder initiated by W-Si-HBP2-
A/B/C in aqueous solution
Photoinitiators W-Si-HBP2-A/B/C with the same molarity (1.2 ×
10−3 mol L−1) were dissolved in a 40 wt% aqueous solution of
AM with TEOA (3.3 × 10−2 mol L−1), respectively, and then
added into a vertical glass tube with an inner diameter of
6 mm to form 4 cm fluid columns. Dissolved oxygen was
removed by purging the acrylamide aqueous solution with
nitrogen gas for 15 min.21,22 After standing for 60 min, each
fluid column was irradiated with a high-pressure mercury
lamp with an incident light intensity of 50 W m−2 for 1 h. The
light intensity was measured by a UV light radiometer (Photo-
electric Instrument Factory, Beijing Normal University, Beijing,
China). The synthesized gradient polyacrylamide rod was dried
under vacuum at 30 °C for 24 h. The basic concept for our
approach is schematically illustrated in Scheme 4. Similarly,
the gradient polymers (PAMs) initiated by W-Si-HBP2-A were
also prepared under different concentrations of AM. When the
concentration of AM was 10%, 20% and 30% respectively, the
amount of addition of W-Si-HBP2-A was 3 × 10−4 mol L−1, 6 ×
10−4 mol L−1 and 9 × 10−4 mol L−1, respectively. The molecular
weight, microstructure and photoinitiator content of different
vertical levels of the gradient polymers were measured by GPC,
X-ray photoelectron spectroscopy (XPS), SEM and an energy
dispersive spectrometer (EDS) respectively.
Water-solubility test of W-Si-HBP2-A/B/C
Water-solubility was measured according to the following
steps: different amounts of W-Si-HBP2-A/B/C (0.10 g, 0.24 g,
0.32 g, 0.50 g, 0.64 g and 0.84 g) were dissolved in deionized
water (20 mL) respectively at 30 °C. The aqueous solution was
stored and protected from light for 1 h after stirring for 5 min,
and the clarity of the aqueous solution was observed. If the
aqueous solution presented a clear and transparent appear-
ance, the photoinitiator was identified as completely solved;
accordingly, if the solution was turbid or with an appearance
of flocculent precipitate, the photoinitiator was identified as
partially solved or insoluble.
Transient properties
Transient properties were recorded in acetonitrile with an
Edinburgh LP920 laser flash photolysis system. A Nd:YAG laser
(Continuum Surelite I 10, 355 nm and 4–6 ns) was used as an
excitation source. The analyzing light was from a pulsed Xe920
xenon lamp. The samples with the concentration (1.0 × 103
mol L−1) in acetonitrile were contained in a quartz cell with an
optical path length of 1 cm. The signal was displayed
and recorded on a Tektronix TDS 3012B oscilloscope and
Preparation of gradient polymer film initiated by W-Si-HBP2-
A/B/C
The photoinitiator W-Si-HBP2-A/B/C was dissolved in 40 wt%
aqueous solution of AM with TEOA (3.3 × 10−2 mol L−1) at
various concentration levels of 1.0 × 10−3, 2.5 × 10−3, 4.5 × 10−3
and 6.0 × 10−3 mol L−1, respectively. A measured volume of the
UV-resin formulation was dispensed on a pre-cleaned glass
slide and allowed to spread to a diameter of 20 mm to obtain
liquid resin film, and then covered with a cover glass to ensure
the anaerobic conditions. After standing for either 10 or
60 min, the deposited liquid films were then exposed to a
Scheme 3 Synthesis route of W-Si-HBP2-A/B/C (n = 7–8/12–13/19–20).
high-pressure mercury lamp (incident light intensity = 50 W m−2
)
This journal is © The Royal Society of Chemistry 2013
Green Chem., 2013, 15, 2457–2465 | 2463
Wang, Jiansheng
