728 Ben-Haida et al.
Macromolecules, Vol. 38, No. 3, 2005
°C. It had FT-IR 1656 cm-1; m/z (E/I) [100%, (M)+] 347; 1H
NMR (DMSO-d6 containing 0.5 % w/v of LiCl, 300 MHz) δ
10.15 (s, 2 H), 8.45 (s, 1 H), 8.08 (d, 2 H), 7.64 (t, 1 H), 7.15 (s,
2 H), 7.01 (t, 2 H), 6.90 (d, 2 H), 6.36 (d, 2 H) and 5.15 ppm (b,
4 H). Anal. Calcd for C20H18N4O2: C, 69.36; H, 5.20; N, 16.18.
Found: C, 69.10; H, 5.05; N, 16.15.
4.3. Synthesis and Methylation of Compound 9. 4.3.1.
Phenyl 3-Chloroformylbenzoate. This compound was pre-
pared as described by Rabilloud et al. in 35% yield.41 It had
mp 70 °C (lit.41 70-71 °C).
mixture of distilled water (300 mL) and concentrated hydro-
chloric acid (10 mL). The desired MCO’s precipitated out as a
white solid which was collected by vacuum filtration and
washed with water until the washings were neutral. The
product was resuspended in methanol (100 mL) and stirred
at 60 °C for 30 min, then filtered off and dried. This gave a
white solid (12.25 g, 95% yield). It had νmax 1656 cm-1; m/z
(MALDI, dithranol, LiCl, DMAc) 721, 959, 1197, 1435, 1674,
1913, and 2151 corresponding to a series of macrocyclo
oligomers from the trimer [(M × 3) + Li]+ up to the nonamer
[(M × 9) + Li]+. GPC analysis revealed a series of low MW
oligomers (see Figure 1b).
4.3.2. Synthesis of Compound 9. Phenyl 3-chloroformyl-
benzoate (5.00 g, 19.20 mmol) in toluene (30 mL) was added
slowly at 20 °C to a solution of m-phenylenediamine (1.03 g,
9.60 mmol) in DMAc (60 mL) under nitrogen. The mixture was
heated gradually to 90 °C over 4 h. After removing the solvent
was removed under reduced pressure, the solid residue was
resuspended in a mixture of ethanol (150 mL) and 2% aqueous
sodium hydroxide (20 mL). The mixture was heated under
reflux for 2 h then cooled to 20 °C. The mixture was then
added, with vigorous stirring, to 20% hydrochloric acid (200
mL). The white precipitate that formed was collected by
filtration, washed with water and then with methanol, and
finally dried. This gave compound 9 as a white powder (6.20
g, 80% yield). It had mp 349 °C (by DSC); νmax 1691 cm-1; m/z
4.6. Treatment of MCO’s 2 with Diazomethane. This
was carried out using the procedure described in section 4.3.3.
4.7. Isolation of a Mixture of Cyclic Trimer 3 and
Cyclic Tetramer 13. A portion of the crude cyclic product
(3.0 g) from the reaction summarized in Table 1 (entry 1) was
placed in a Soxhlet apparatus and extracted with THF for 24
h. Evaporation of the solvent left a residue (0.27 g, 9% of the
original mass), which decomposed at >400 °C and was shown
by GPC to be a mixture of two cyclic oligomers: see Figure 4.
Analysis by MALDI-TOF MS confirmed these were the cyclic
trimer 3 (m/z 722 [(M × 3) + Li]+) and the cyclic tetramer 13
(m/z 959 [(M × 4) + Li]+).
1
(ES) [100%, (M)+] 405; H NMR (DMSO-d6 with 0.5% w/v of
4.8. Preparation of Catalysts. 4.8.1. Benzanilide So-
dium Salt (15). Benzanilide (5.00 g, 0.025 mol) was dissolved
in dry THF (40 mL) under nitrogen. Sodium hydride (0.63 g,
0.026 mol) was quickly added, and the mixture was stirred
under reflux for 5 h. The reaction solvent was then removed
under reduced pressure. The residue (5.40 g) was dried in a
vacuum oven at 60 °C and then stored in a desiccator under
nitrogen.
LiCl, 300 MHz) δ 10.65 (s, 2 H,), 8.61 (s, 1 H), 8.48 (s, 2 H),
8.20 (d, 2 H), 8.10 (d, 2 H), 7.73 (m, 3 H) and 7.51 ppm (t, 2
H). Anal. Calcd for C22H16N2O6: C, 65.35; H, 3.96; N, 6.93.
Found: C, 65.19; H, 4.11; N, 6.78.
4.3.3. Methylation of Compound 9. An ethereal solution
of diazomethane containing between 0.030 and 0.035 g mL-1
was prepared as described in the literature.42 To a tube
containing a sample of the diacid 9 (50 mg) in of DMSO (2
mL) was added the ethereal diazomethane solution (10 mL).
The mixture was shaken every few minutes, and after 15 min,
glacial acetic acid (1 mL) was added to destroy the excess of
diazomethane. Methanol (3 mL) was then added and the white
precipitate was filtered off, washed with water and with
4.8.2. Preparation of N,N-Dibenzoylaniline (16). To a
cold solution (ca. - 50 °C) of benzanilide (6.00 g, 0.030 mol) in
dry THF (50 mL) under nitrogen was cautiously added a
solution of n-butyllithium (1.34 g, 0.021 mol) in hexane. The
resultant mixture was stirred at room temperature for 1 h.
Benzoyl chloride (17 g, 0.12 mol) was then added dropwise
under vigorous stirring and the mixture heated under reflux
for 4 h. The cooled solution was poured into acidified water
(150 mL) and the precipitate filtered off and washed with
water and then methanol. Recrystallization from ethanol/
chloroform gave white crystals (8.8 g, 85% yield). These showed
1
methanol, and then finally dried. The solid 12 had H NMR
(DMSO-d6, 300 MHz)1H NMR (DMSO-d6, plus 0.5 % w/v of
LiCl, 300 MHz) δ 10.60 (s, 2 H), 8.59 (s, 1 H), 8.40 (s, 2 H),
8.24 (d, 2 H), 8.20 (d, 2 H), 7.78 (t, 2 H), 7.60 (d, 2 H), 7.40 (t,
2 H) and 3.38 ppm (s, 3 H from -CO2CH3).
4.4. Synthesis of Linear Oligomers 10. To a flask (50
mL) equipped with a magnetic stirrer, nitrogen inlet, ther-
mometer, and condenser were added m-phenylenediamine
(2.16 g, 20 mmol), isophthaloyl chloride (2.03 g, 10 mmol),
anhydrous lithium chloride (0.42 g, 10 mmol), DMAc (30 mL),
and toluene (6 mL). The mixture was stirred magnetically and
heated under reflux for 10 h. The reaction mixture was then
cooled and precipitated into methanol. The beige product was
filtered off and washed several times with hot methanol. The
dried product 10 (1.47 g, 80% yield) had νmax 1656 cm-1; the
MALDI-TOF mass spectrum is shown in Figure 1a; GPC
showed Mn ) 1000 and Mw ) 1500; 1H NMR (DMSO-d6 + 0.5%
w/v LiCl), 300 MHz) δ 11.10-10.58 (s, 2 H), 9.00-8.80 (s,1
H), 8.64-8.50 (s,1 H), 8.28-8.02 (d, 2 H), 7.80-7.59 (m, 3 H)
and 7.42-7.19 ppm (t, 1 H), with end group signals appearing
at δ 6.58 ppm.
4.5. Synthesis of Cyclic Oligomers 2 under Pseudo-
High-Dilution Conditions.35 The reactions carried out are
summarized in Table 1. The following procedure is typical.
4.5.1. Synthesis Summarized in Table 1, Entry 1. A
solution of isophthaloyl chloride (11.00 g, 54.18 mmol) in
toluene (70 mL) was drawn into a 100 mL syringe. A solution
of m-phenylenediamine (5.85 g, 54.18 mmol) in DMAc (70 mL)
was drawn into a second syringe. A dual syringe pump was
then used to add these solutions simultaneously at a rate of
10 mL/h each to a three-necked, 500 mL flask containing a
solution of calcium chloride (6.01 g, 54.18 mmol) in DMAc (200
mL) at reflux temperature (165-168 °C) under nitrogen. A
clear brown solution was formed and, after addition was
complete, the reaction mixture was stirred at 150 °C for a
further 10 h, reduced in volume to ca. 80 mL using a rotary
evaporator, and then added slowly to a vigorously stirred
mp 180 °C (lit.,43 179-180 °C); νmax 1694 cm-1
.
4.9. Cyclodepolymerization. The various reactions car-
ried out are summarized in Table 2. The procedure below
(4.10.1) is typical. From a similar preliminary experiment
samples were removed every 10 h, precipitated into water,
collected, dried and analyzed by GPC. This showed that the
optimum reaction time for CDP was 70 h.
4.9.1. Reaction Summarized in Table 2, Entry 6. To a
warm solution containing poly(m-phenylene isophthalamide)
(Nomex) (1), (Mn 22500, Mw 53000, ηinh ) 1.8 dL g-1 in 98%
H2SO4) (2.00 g, 8.40 mmol) and lithium chloride (0.350 g, 8.40
mmol) in dry DMSO (200 mL) was added the sodium salt of
benzanilide (15) (74 mg, 4 mol %). The reaction mixture was
heated at 150 °C under nitrogen for 70 h and then cooled and
carefully added to dilute hydrochloric acid (500 mL, 1 M). The
precipitate was collected, washed with water and methanol,
and then dried to afford a white solid (1.85 g, 93% yield). It
had mp 400-440 °C; ηinh ) 0.15 dL g-1; m/z (MALDI-TOF
mass spectrum, dithranol, LiCl, DMAc) 721, 960, 1198, 1436,
1675, 1913, and 2151, corresponding to a series of cyclic
oligomers from the trimer [(M × 3) + Li]+ up to the nonamer
(M × 9 + Li)+. The results of the GPC analysis are summarized
in Table 2.
4.10. ED-ROP of Cyclic Oligomers (2) in Solution. The
various ED-ROP’s carried out are summarized in Table 3. The
following procedure is typical.
4.10.1. Experiment Summarized in Entry 1. Cyclic
oligomers (2) (1.00 g, 4.2 mmol), lithium chloride (0.32 g, 4.2
mmol), and DMSO (4 mL) were placed in a tube (10 mL)
equipped with a Claisen adapter, mechanical stirrer and gas
inlet. After purging the vessel with nitrogen, the solution was
heated gradually to 100 °C in an oil bath until it become clear