Macromolecules, Vol. 36, No. 20, 2003
PET-Based Liquid Crystalline Copolyesters 7545
for 18 h. Excess oxalyl chloride and CH2Cl2 were removed by
distillation under reduced pressure. CS2 (200 mL) was added
to the residue, and the resulting mixture was added to a stirred
mixture of AlCl3 (14.74 g, 110.5 mmol) and CS2 (200 mL) at 0
°C over 75 min under N2. When the addition was complete,
the stirred mixture was allowed to warm to room temperature
over 4 h. Water (140 mL) was carefully added to quench the
reaction. After mixing thoroughly, the reaction mixture was
filtered and the solid was combined with the CS2 layer of the
filtrate. The solvent was removed by distillation, and the
residue was dried under reduced pressure to yield 9 as a yellow
solid which was used without further purification (9.421 g,
73%); mp 325 °C (dec). In DMSO solution, 9 is in equilibrium
with its tautomer, 10-hydroxy-6-methoxy-2-anthracenoic acid,
9a . 3-Carboxy-7-methoxy-9(10H)-anthracenone, 9: 1H NMR
(300 MHz, DMSO-d6): δ 8.26 (d, J ortho ) 8 Hz, 1H, Ar-H4),
8.13 (s, 1H, Ar-H1), 7.99 (d, J ortho ) 8 Hz, 1H, Ar-H3), 7.62
(d, J meta ) 3 Hz, 1H, Ar-H5), 7.53 (d, J ortho ) 8 Hz, 1H, Ar-
H8), 7.31 (dd, J ortho ) 8 Hz, J meta ) 3 Hz, 1H, Ar-H7), 4.43 (s,
2H, CH2), 3.94 (s, 3H, -OCH3). 10-Hydroxy-6-methoxy-2-
anthracenoic acid, 9a : 1H NMR (300 MHz, DMSO-d6): δ 8.62
(s, 1H, Ar-H9), 8.41 (d, J ortho ) 9 Hz, 1H, Ar-H4), 8.19 (s, 1H,
Ar-H1), 7.94 (d, J ortho ) 9 Hz, 1H, Ar-H8), 7.80 (d, J ortho ) 9
Hz, 1H, Ar-H3), 7.73 (d, J meta ) 2 Hz, 1H, Ar-H5), 7.19 (dd,
J ortho ) 9 Hz, J meta ) 2 Hz, 1H, Ar-H7), 3.93 (s, 3H, -OCH3).
IR (KBr): 3450-2850 (O-H str), 1705 (CdO str, COOH), 1657
(CdO str, ketone), 1405 (C-O-H bend), 1302 (C-O str), 1223
cm-1 (C-O-C asym str). HRMS (EI) calcd for C16H12O4:
268.07356. Found: 268.07231.
6-Meth oxy-2-a n th r a cen oic Acid , 5. A mixture of 3-car-
boxy-7-methoxy-9(10H)-anthracenone (9) (10.00 g, 37.28 mmol)
and zinc dust (14.79 g, 226.3 mmol) in 200 mL of 5% aqueous
NaOH was stirred and heated at reflux for 4 h. The mixture
was cooled and filtered. The solid was placed in a Soxhlet
extraction thimble, and the filtrate was used to extract product
from the solid for 48 h. 10% HCl was added to the cooled
extract until the pH was below 7. The precipitate was collected
by filtration and dried under reduced pressure to yield 5 as a
yellow solid (6.629 g, 70%); mp 305-307 °C (lit.27 288-289 °C).
1H NMR (300 MHz, DMSO-d6): δ 8.72 (s, 1H, Ar-H9), 8.70
(s, 1H. Ar-H1), 8.44 (s, 1H, Ar-H10), 8.05 (d, J ortho ) 8 Hz,
1H, Ar-H4), 8.02 (d, J ortho ) 9 Hz, 1H, Ar-H8), 7.88 (dd, J ortho
) 8 Hz, J meta ) 2 Hz, 1H, Ar-H3), 7.41 (d, J meta ) 2 Hz, 1H,
Ar-H5), 7.22 (dd, J ortho ) 9 Hz, J meta ) 2 Hz, 1H, Ar-H7), 3.92
(s, 3H, -OCH3). IR (KBr): 3300-2850 (O-H str), 1703 (CdO
str), 1420 (C-O-H bend), 1295 (C-O str), 1223 cm-1 (C-O-C
asym str). HRMS (EI) calcd for C16H12O3: 252.07864. Found:
252.07873.
J ortho ) 9 Hz, 1H, Ar-H8), 8.13 (d, J ortho ) 9 Hz, 1H, Ar-H4),
7.93 (dd, J ortho ) 9 Hz, J meta ) 2 Hz, 1H, Ar-H3), 7.84 (d, J meta
) 2 Hz, 1H, Ar-H5), 7.37 (dd, J ortho ) 9 Hz, J meta ) 2 Hz, 1H,
Ar-H7), 2.34 (s, 3H, CH3). IR (KBr): 3200-2500 (O-H str),
2644-2552 (aliph C-H str), 1769 (CdO str, ester), 1690 (Cd
O str, COOH), 1433 (C-O-H bend), 1210 cm-1 (acetate C(d
O)-O str). HRMS (EI) calcd for C17H12O4: 280.07356. Found:
280.07357.
P r ep a r a tion of Cop olym er s. The preparation of a PET-
co-OA10 is described here to illustrate the preparation of
copolymers. PET pellets (4.520 g, 90 mol %) and 11 (0.739 g,
10 mol %) were placed in a glass reaction vessel equipped with
a mechanical stirrer, nitrogen inlet, distillation head, and
condenser. The reaction vessel was purged with N2, and the
mixture was heated under N2 for 30 min at 300 °C, during
which time it formed a homogeneous melt. The N2 flow was
stopped, and the pressure was gradually reduced over 10 min
to <1 mmHg. The reaction temperature was lowered to 275
°C over 30 min and was held there for 3.5 h, during which
water was removed by distillation. The total reaction time was
4.5 h, with the reaction temperature above 275 °C for only
the first hour. Upon cooling, the polymer was removed from
the reactor by dissolving it in a ca. 1:1 (v/v) mixture of CHCl3
and trifluoroacetic acid (TFA). The polymer was reprecipitated
by pouring the solution into an excess of MeOH. The solid was
washed thoroughly with MeOH and dried in a vacuum oven.
Incorporation of 4-acetoxybenzoic acid and 6-acetoxy-2-
naphthoic acid into PET was performed in a similar fashion,
except that the reaction temperature was held at 275 °C
throughout the procedure. PET-co-OA30 and PET-co-OA40 did
not completely dissolve, but they were removed from the
reactor by forming slurries with CHCl3 and TFA which were
poured into MeOH.
Samples of the polymers were subjected to solid-state
polymerization (SSP) by placing the polymer in a flask at
reduced pressure (<0.2 mmHg). The flask was placed in a
heated oil bath (180-210 °C) for ca. 24 h. The temperature of
the SSP was chosen to be about 10 °C below the onset of
melting of the polymer.
Resu lts a n d Discu ssion
Mon om er Syn th esis. A 10-step synthesis of 6-meth-
oxy-2-anthracenoic acid, 5, from p-anisic acid has been
previously reported with a 13% overall yield.26,28 That
synthetic scheme involved preparation of 2-methoxy-6-
methylanthracene and the subsequent oxidation of the
methyl substituent to form the carboxylic acid. However,
this approach required steps to protect the 9- and 10-
positions of the anthracene core from oxidation, which
would give the corresponding anthraquinone. To avoid
the protection and deprotection steps, shorten the
synthesis, and improve the overall yield, we focused on
synthetic schemes in which the oxidation step takes
place prior to formation of the anthracene ring system.
6-Hydr oxy-2-an th r acen oic Acid, 10. A mixture of 6-meth-
oxy-2-anthracenoic acid (5) (3.12 g, 12.4 mmol) and 48% HBr
(11.0 mL, 97.2 mmol) in 60 mL of acetic acid was stirred and
heated at reflux for 3 h. The mixture was poured into 250 mL
of cold water. The precipitate was collected by filtration and
dried under reduced pressure to yield 10 as a green solid which
was used without further purification (1.77 g, 60%); mp 275-
278 °C. 1H NMR (300 MHz, DMSO-d6): δ 8.68 (s, 1H, Ar-
H9), 8.64 (s, 1H, Ar-H1), 8.30 (s, 1H, Ar-H10), 8.00 (d, J ortho
)
9 Hz, 1H, Ar-H4), 8.00 (d, J ortho ) 9 Hz, 1H, Ar-H8), 7.83 (d,
J ortho ) 9 Hz, 1H, Ar-H3), 7.24 (d, J meta ) 2 Hz, 1H, Ar-H5),
7.18 (dd, J ortho ) 9 Hz, J meta ) 2 Hz, 1H, Ar-H7). IR (KBr):
3500-2900 (O-H str), 1703 (CdO str), 1427 cm-1 (C-O-H
bend). HRMS (EI) calcd for C15H10O3: 238.06299. Found:
238.06209.
6-Acetoxy-2-a n th r a cen oic Acid , 11. A mixture of 6-hy-
droxy-2-anthracenoic acid (10) (9.663 g, 40.56 mmol), pyridine
(29.5 mL, 365 mmol), and acetic anhydride (123.0 mL, 1.221
mol) was stirred at room temperature for 19 h. The mixture
was poured into 600 mL of cold water, and the precipitate was
triturated with 270 mL of 1% HCl. The solid was added to
150 mL of acetone and 50 mL of water, and the mixture was
heated at reflux for 22 h. After cooling, the solid was collected
by filtration and recrystallized from an acetone/water mixture
(380 mL/38 mL) to yield 11 as a yellow solid (5.62 g, 49%); mp
289-291 °C. 1H NMR (300 MHz, DMSO-d6): δ 8.84 (s, 1H,
Ar-H9), 8.79 (s, 1H, Ar-H1), 8.61 (s, 1H, Ar-H10), 8.17 (d,
Our synthesis of 6-acetoxy-2-anthracenoic acid (11)
as a monomer for incorporation into copolyesters is
outlined in Schemes 1 and 2. The original strategy was
to prepare 11 by a synthetic route similar to that used
to make dimethyl 2,6-anthracenedicarboxylate in which
the fused ring system was prepared by a thermally
promoted Elbs reaction29 of an appropriately substituted
2-methylbenzophenone.21 The first step was a Friedel-
Crafts acylation of p-xylene with p-anisoyl chloride to
yield 2,5-dimethyl-4′-methoxybenzophenone, 1. How-
ever, attempts to ring-close 1 by the Elbs reaction gave
anthrone 2 and anthraquinone 3 (Scheme 1) in only 35%
yield. Oxidation of mixtures of 2 and 3 with CrO3
afforded very low yields (17%) of the anthraquinone
acid, 4, which could then be reduced to the correspond-
ing anthracene, 5. Although this reaction sequence