G Model
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A.-Q. Ju et al. / Chinese Chemical Letters xxx (2014) xxx–xxx
reduced pressure to remove excess methanol and followed by
standing to get precipitation. The precipitation was recrystallized
from benzene-petroleum ether (v/v, 1:1).
32
24
16
8
White crystals, 84.52% yield. IR (KBr, cmꢀ1): ymax 3004, 2955
(C–H), 1726, 1691 (C55O), 1636 (C55C), 1237, 1170 (C–O). 1H NMR
(400 Hz, DMSO-d6, r.t., TMS):
d 12.616 (s, 1H, COOH), 6.149 (d, 1H,
PAN
J = 1.20 Hz, CH255), 5.763 (d, 1H, J = 1.20 Hz, CH255), 3.580 (s, 3H,
OCH3), 3.336 (s, 2H, CH2) (see Fig. S1 in Supporting information).
2.2. Synthesis of ABM
P(AN-AM-MA)
P(AN-co-ABM)
To a 150 mL three-necked flask, 1.44 g of MHI, 40.00 mL of
chloroform, 1.10 mL of thionyl chloride and 0.10 mL of N,N-
dimethylformamide were added and the mixture was refluxed at
70 8C for 0.5 h and then cooled to room temperature. The reaction
mixture was distilled under reduced pressure to remove excess
thionyl chloride. Chloroform (40 mL) was added to the remaining
residue. Then anhydrous ammonia was passed into the solution at
0 8C until no more precipitate formed. The precipitate was filtered
off and washed with chloroform (3 ꢁ 40 mL). The obtained
chloroform solution was distilled under reduced pressure to leave
crystalline residue.
0
150
200
250
300
350
Temperature (oC)
Fig. 1. DSC curves of PAN, P(AN-AM-MA) and P(AN-co-ABM) heated at 10 8C minꢀ1
.
thermogravimetry (TG) curves of powder samples were carried out
on TA instrument Modulated DSC 2910 and Netzsch TG 209 F1
thermal analyzer, respectively. The sample (3–4 mg) was scanned
under air atmosphere (40 mL minꢀ1) for TG analysis and under N2
(40 mL minꢀ1) for DSC analysis. The oxygen (O) contents of P(AN-
co-ABM) copolymer and P(AN-AM-MA) terpolymer were deter-
mined on an Elementar Vario EL III elemental analyzer. Rheological
measurements were recorded on a Haake RS150L Rotational
rheometer at 70 8C from 0 sꢀ1 to 1000 sꢀ1, and the concentration of
polymer solutions was 18 wt%.
Yellow crystals, 82.49% yield. IR (KBr, cmꢀ1): ymax 3409, 3174
(N–H), 3000, 2953 (C–H), 1736, 1670 (C55O), 1645 (N–H), 1605
(C55C), 1174 (C–O). 1H NMR (400 Hz, DMSO-d6, r.t., TMS):
d 7.594
(s, 1H, CONH2), 7.031 (s, 1H, CONH2), 5.893 (s, 1H, CH255), 5.531 (d,
1H, CH255), 3.587 (s, 3H, OCH3), 3.3329 (s, 2H, CH2) (see Fig. S2 in
Supporting information).
2.3. Preparation of acrylonitrile polymers
PAN homopolymer, P(AN-AM-MA) and P(AN-co-ABM) were
prepared by solution polymerization using DMSO as reaction
media under nitrogen atmosphere. A typical polymerization is
described as: 30,0000 g of AN, 1.6516 g of ABM, 0.2532 g of AIBN
and 94.9547 g of DMSO were added into a 250 mL three-necked
flask equipped with condenser tube and stirrer. The polymeriza-
tion was carried out at 60 8C and terminated by methanol after
24 h. Then, the reaction mixture was added to excessive methanol
with vigorous agitation to precipitate the polymer. The isolated
polymer was washed with methanol for several times and then
dried at 60 8C under vacuum to a constant mass. The details of PAN
polymers used in this study are given in Table 1.
3. Results and discussion
3.1. DSC studies of PAN, P(AN-AM-MA) and P(AN-co-ABM)
Fig. 1 shows the DSC curves of PAN homopolymer, P(AN-AM-
MA) and P(AN-co-ABM) heated at 10 8C minꢀ1 from ambient
temperature to 400 8C under N2 (40 mL minꢀ1). The parameters
obtained from the exotherms, including the initiation temperature
(Ti), the termination temperature (Tf) and their difference
(
D
T = Tf ꢀ Ti), the first peak temperature (Tp1, the peak at low
temperature), the second peak temperature (Tp2, the peak at high
temperature), the released heat ( H), and the velocity of releasing
heat ( H/ T), are listed in Table 2.
D
D
D
2.4. Characterization
The DSC curves of PAN polymers were obtained under N2
atmosphere, so there were no oxidative reactions occurred during
this process and the exothermic peaks were attributed to the
cyclization reactions. As shown in Fig. 1, there is one sharp
exothermic peak in PAN homopolymer and the cyclization
reactions can only be initiated through a free radical mechanism,
resulting in a large amount of heat to be released at the same time,
which breaks molecular chains and further results in defects in the
final carbon fiber. Although the initiation temperature of P(AN-
AM-MA) decreases from 244.16 8C to 205.25 8C compared with
PAN homopolymer, the heat release of P(AN-AM-MA) is still
concentrative and expeditious because there is only one exother-
mic peak in DSC curve of P(AN-AM-MA). Whereas in P(AN-co-
ABM) copolymer, there are two exothermic peaks and the
cyclization reactions can be initiated through both radical and
ionic mechanisms, which broadens the exothermic peak and
effectively avoids centralized heat release. The lower exothermic
peak (peak 1) is assigned to cyclization reactions initiated by the
comonomer ABM through an ionic mechanism. As shown in
Scheme 1, the nitrogen of the amide group (–CONH2) in ABM can
initiate a nucleophilic attack on the carbon atom of adjacent nitrile
groups and then induce molecules to cyclize. The DSC curve of
Proton nuclear magnetic resonance 1H NMR (400 MHz) spectra
and 13C NMR spectra were recorded on a Bruker DMX-400 NMR
spectrometer in dimethyl sulfoxide (DMSO-d6) as solvent at room
temperature. The differential scanning calorimetry (DSC) and
Table 1
Experimental and calculated parameters of polymer samples.
Polymer
samples
Comonomer/AN O content Comonomer
Molecular
weights of
in the feed
(mol/mol)
in the
content in
polymers the polymersa the polymersb
(mass%)
(mol%)
(g/mol)
PAN
0/100
0
0
8.82 ꢁ 104
8.78 ꢁ 104
8.79 ꢁ 104
P(AN-co-ABM) 2/98
2.79
1.56
2.40
P(AN-AM-MA) 2/2/98
0.95 (AM)
3.38 (MA)
a
The comonomer content in the copolymer was determined by elementary
analysis, and the comonomer content in the terpolymer was determined through
the combination of elementary analysis and estimation of the COOH group by
titration.
b
The viscosity average molecular weight of the resultant polymers was
measured by Ubbelolohde viscometer method.
Please cite this article in press as: A.-Q. Ju, et al., Poly(acrylonitrile-co-3-aminocarbonyl-3-butenoic acid methyl ester): A better