from Wako Pure Chemical Industry or Tokyo Kasei Kogyo Co.,
Ltd. Anhydrous DMF (organic synthesis grade) was purchased
from Aldrich.
CH3), 3.76 (s, 6H, OCH3), 3.81–3.85, 3.94–3.97 (m, 2H, Cb-H),
4.77 (m, 1H, Ca-H), 5.22 (d, 1H, J = 3.2, Ca-OH), 6.72 (s, 2H,
C2-H, C6-H); 13C-NMR (DMSO-d6): d 55.9 (OCH3), 71.7 (a),
78.2 (b), 103.7 (2,6), 135.6 (1), 137.5 (4), 152.1 (3,5). Polymer 9:
1H-NMR (DMSO-d6): d 1.27 (d, J = 6.4, CH3), 3.95 (br. s, 2H,
Cb-H), 4.80 (br s, 1H, Ca-H), 5.51 (br s, Ca-OH), 6.92 (d, 2H,
J = 8.5, C3-H, C5-H), 7.32 (d, 2H, J = 8.5, C2-H, C6-H); 13C-
NMR (DMSO-d6): d 70.4 (a), 73.1 (b), 113.9 (3,5), 127.4 (2,6),
134.3 (1), 157.7 (4).
Measurements
1H- and 13C-NMR spectra were recorded with a JEOL JNM
EX-270 FT-NMR (270 MHz) or a Bruker AMX500 FT-NMR
(500 MHz) spectrometer. HMQC and HMBC NMR spectra
were recorded with a Bruker AMX500 FT-NMR (500 MHz)
spectrometer. Chemical shifts (d) and coupling constants are
given in d-values (ppm) and Hz, respectively. Average molecular
weights were analyzed by gel permeation chromatography
(GPC) in tetrahydrofuran. A HITACHI Liquid Chromatograph
L-6200 with a UV detector, L-4000 (Hitachi, 280 nm) and a RI
detector (JASCO RI-2031 Plus) were used. Shodex GPC packed
columns KF-803l and 802 (30 cm × 8.0 mm) were connected
in a series and molecular weight was calibrated with standard
polystyrene (tetrahydrofuran, flow-rate: 0.5 ml min−1, 40 ◦C).
Acetylation of polymer
Polymer 7 (30 mg) was acetylated by acetic anhydride–pyridine
(1 : 1, v/v, 4 ml) at room temperature for 12 h. After 12 h ethanol
(2 ml) was added and the mixture was evaporated to 2 ml. The
reaction mixture was poured into water (50 ml) to precipitate
a polymer. The polymer was filtered and dried in vacuo over
P2O5. Polymers 8 and 9 were acetylated according to the same
procedure used for polymer 7.
Polymer 7 (acetate): 1H-NMR (CDCl3): d 2.09 (s, 3H,
OCOCH3), 3.84 (s, 3H, OCH3), 4.14–4.31 (m, 2H, Cb-H),
6.07 (m, 1H, Ca-H), 6.76–7.02 (m, 3H, aromatics); 13C-NMR
(CDCl3): d 21.3 (OCOCH3), 56.1 (OCH3), 72.1, 73.8, 111.4,
114.8, 119.3, 130.9, 148.1, 149.9, 169.9 (OCOCH3). Polymer
Preparation of monomers 1–3
To a stirred solution of acetovanillone (26 g) in anhydrous 1,4-
dioxane–diethyl ether (3 : 4, v/v) (700 ml), bromine (25 g) was
◦
1
added dropwise under nitrogen over 2 h at 0 C. The reaction
8 (acetate): H-NMR (CDCl3): d 2.08 (s, 3H, OCOCH3), 3.81
mixture was kept at 0 ◦C for 1 h. The reaction mixture was diluted
with ether and washed with iced water and brine. The solution
was dried over anhydrous Na2SO4 and concentrated to dryness in
(s, 6H, OCH3), 4.10–4.36 (m, 2H, Cb-H), 5.99 (m, 1H, Ca-H),
6.57 (s, 2H, C2-H, C6-H); 13C-NMR (CDCl3):
d 21.2
(OCOCH3), 56.2 (OCH3), 74.9, 104.0, 133.1, 136.5, 152.9, 170.0
(OCOCH3). Polymer 9 (acetate): 1H-NMR (CDCl3): d 2.08
(s, 3H, OCOCH3), 4.07–4.32 (m, 2H, Cb-H), 6.07 (m, 1H, Ca-
H), 6.88 (d, 2H, J = 8.4, C3-H, C5-H), 7.32 (d, 2H, J = 8.4,
C2-H, C6-H); 13C-NMR (CDCl3): d 21.2 (OCOCH3), 70.3, 73.4,
114.7, 128.1, 129.5, 158.4, 169.9 (OCOCH3).
◦
vacuo below 30 C. The obtained crude crystalline was treated
with activated carbon powder and recrystallized from ether–
hexane to afford monomer 1 (76 mol%). Monomer 1 was further
recrystallized from the same solvents for polymerization in order
to remove impurities completely. Monomers 2 and 3 were synthe-
sized according ◦to the method used for monomer 1. Monomer
1: mp 82.3–82.8 C (lit. 81 ◦C)◦,6 monomer 2: m◦p 127.0–127.5 ◦C,
monomer 3: mp 130.3–130.9 C (lit. 129–130 C).6
Solubility test of polymer 7
A small amount of polymer 7 (25 mg) was shaken in various
solvents (0.5 ml) at room temperature and examined for the
presence of undissolved material. In some cases the amount of
solvent was increased to 1.0 ml.
Polymerization
Prior to polymerization, starting monomers and glassware were
dried under a vacuum over P2O5. To a stirred solution of
monomer 1 (500 mg, 2.0 mmol) in anhydrous DMF (2.5 ml)
was added finely powdered K2CO3 (422 mg, 3.0 mmol). The
reaction mixture was kept under nitrogen at 50 ◦C for 3 h.
The clear solution became clouded and gradually produced a
precipitate. After 3 h, the reaction mixture was poured into
iced water (100 ml) to precipitate a polymer. The polymer was
filtered and washed with water and methanol. The polymer was
dried over P2O5 under a vacuum to give polymer 4 (315 mg,
94 mol%). Polymers 5 and 6 were prepared from monomers 2 and
3, respectively, according to the procedure used for polymer 4.
Results and discussion
Preparation of monomers 1–3
Three brominated 4-hydroxy-acetophenone derivatives, 2-
bromo-1-(4-hydroxy-3-methoxyphenyl)ethanone (1), 2-bromo-
1-(4-hydroxy-3,5-dimethoxyphenyl)ethanone (2) and 2-bromo-
1-(4-hydroxyphenyl)ethanone (3), were selected as starting
monomers for preparation of lignin related polymers composed
of the b-O-4 structure using a solution polymerization method
(Fig. 3). The monomers correspond to three structural units of
lignin; guaiacyl, syringyl and p-hydroxyphenyl propane units,
respectively. Monomers 1–3 were prepared from commercially
available 4-hydroxy-3-methoxy-acetophenone, 4-hydroxy-3,5-
dimethoxy-acetophenone and 4-hydroxy-acetophenone, respec-
tively, using a procedure similar to the reported method.9 Special
attention was paid to the purity of the starting monomers
in order to obtain the polymer with high molecular weights,
because a conversion ratio of monomer very much affects
the molecular weight of polymer in polycondensation. The
obtained monomers were treated with activated carbon powder
and recrystallized twice from ether–hexane and the purity
was checked by thin layer chromatography. Melting points of
monomers 1 and 3 were higher than the reported data,6 which
suggests the higher purity of the monomers.
Reduction of polymers 4–6
To a stirred suspension of polymer 4 (200 mg) in dimethyl sulfox-
ide (DMSO) (10 ml) was added NaBH4 (230 mg). The reaction
mixture was kept at 50 ◦C for 24 h. The suspension gradually be-
came a clear solution. The reaction mixture was poured into iced
water (200 ml) and was acidified to pH 3.0 with 2 N HCl. The
obtained precipitate was filtered, washed with water and dried
in vacuo over P2O5. The precipitate was dissolved in 1,4-dioxane
(distilled over Na, 2 ml) and poured into diethyl ether (50 ml) to
remove low molecular weight compounds. The precipitate was
filtered and then dried in vacuo to give polymer 7 (180 mg). Poly-
mers 8 and 9 were prepared from polymers 5 and 6, respectively,
according to the same procedure used for polymer 7.
1
Polymer 7: H-NMR (DMSO-d6): d 1.28 (d, J = 6.4, CH3),
3.76 (s, 3H, OCH3), 3.90–3.98 (m, 2H, Cb-H), 4.84 (m, 1H, Ca-
H), 5.49 (d, 1H, J = 4.7, Ca-OH), 6.90 (s, 2H, C5-H, C6-H),
7.06 (s, 1H, C2-H); 13C-NMR (DMSO-d6): d 55.5 (OCH3), 70.7
(a), 74.1 (b), 110.7 (2), 113.1 (5), 118.3 (6), 135.2 (1), 147.1 (4),
148.5 (3). Polymer 8: 1H-NMR (DMSO-d6): d 1.31 (d, J = 6.4,
Polymerization of monomers 1–3 and characterization of polymers
Polymerization of monomer 1 was carried out with K2CO3 in
anhydrous DMF. Reaction conditions were similar to those
reported by Hirose et al.6 However, in our hands, the molecular
1 0 6 8
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 0 6 7 – 1 0 7 3