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A.Q. Ju et al. / Chinese Chemical Letters 23 (2012) 1307–1310
1
. Experimental
Synthesis of b-methylhydrogen itaconate: To a 100 mL round-bottomed flask was added itaconic acid (13.00 g,
00.00 mmol), methanol (14.20 mL, 350.00 mmol) and benzoyl chloride (0.50 mL, 4.30 mmol). The mixture was
1
refluxed at 65 8C for 0.5 h and then cooled to room temperature. The reaction mixture was distilled under reduced
pressure to remove excess methanol and then followed by standing to get precipitation. The precipitation was
recrystallized from benzene–petroleum ether (v/v = 1:1) to obtain pure b-methylhydrogen itaconate. White crystal,
ꢀ
1
1
8
4.52% yield. IR (KBr) ymax cm : 3004, 2955 (C–H), 1726, 1691 (C O), 1636 (C C), 1237, 1170 (C–O). H NMR
400 Hz, DMSO-d ): d 10.681 (s, 1 H), 6.481 (d, 1 H, J = 1.20 Hz), 5.847 (d, 1 H, J = 1.20 Hz), 3.716 (s, 3 H), 3.355 (s,
(
6
2
H) (see Fig. S1 in supporting information).
Synthesis of 3-ammoniumcarboxylate-3-butenoic acid methyl ester (ACBM): The synthesized b-methylhydrogen
itaconate (1.4413 g, 10.00 mmol) and tetrahydrofuran (40.00 mL, 0.49 mol) were added to a 150 mL three-necked
flask. Then anhydrous ammonia was passed into the solution until no more precipitate formed. The precipitate was
ꢀ
1
cm : 3432, 3143
filtered off and washed with tetrahydrofuran (3ꢁ 40 mL). White solid, 94.28% yield. IR (KBr) y
max
1
(
N–H), 3007, 2959 (C–H), 1730 (C O), 1635 (N–H), 1570 (C C), 1165 (C–O). H NMR (400 Hz, DMSO-d ): d
6
7.321 (s, 4 H), 5.916 (s, 1 H, J = 2.40 Hz), 5.394 (s, 1 H, J = 2.40 Hz), 3.544 (s, 3 H), 3.199 (s, 2 H) (see Fig. S2 in
supporting information).
Copolymerization of acrylonitrile (AN) and ACBM were carried out in a three-necked flask at 60 8C under nitrogen
atmosphere for 24 h. In the reaction system, dimethyl sulfoxide (DMSO) and azodiisobutyronitrile (AIBN) were used as
reactionmediumandinitiator, respectively. Thetotalmonomerconcentrationwas25 wt%,andtheconcentrationofAIBN
was 0.8 wt% based on total monomers. Two PAN homopolymer samples were also prepared in this article. One was used
for molecular weight and DSC studies, which was preparedbyusing the samereactionconditionsas the copolymerization
of AN and ACBM; the other was prepared for spinnability studies by changing the concentration of AIBN to 1.3 wt%.
Viscosity average molecular weights (Mh) of the resultant polymers were measured by Ubbelolohde viscometer
method at a constant temperature water bath of (50 ꢂ 0.5) 8C. The equation is depicted as follows:
hꢃ ¼ 2:83 ꢁ 10ꢀ Mh
4
0:759
(1)
½
where [h] is the intrinsic viscosity calculated by linear extrapolation. The required polymer weight is 0.50 g in 50 mL
DMSO [6].
Differential scanning calorimetry (DSC) curves were carried out on a TA instrument Modulated DSC 2910 under
N (40 mL/min). Rheological measurements were recorded on a Haake RS150L Rotational Rheometer at 70 8C, and
2
the concentration of PAN/DMSO and P(AN-co-ACBM)/DMSO solutions were 18 wt%.
2
. Results and discussion
The effect of monomer feed ratio on the polymerization conversion and molecular weight of P(AN-co-ACBM) are
shown in Fig. 1. Both the polymerization conversion and molecular weight of P(AN-co-ACBM) reduce with the
increasing amounts of ACBM in the feed. It may be attributed to large volume of ACBM, which counteract the growth of
polymer chains and reduce the polymerization conversion and molecular weight [7]. It is well known that the molecular
weight of PAN polymers plays an important role on the performance of carbon fiber, so the amounts of comonomer in the
feedshouldbewellcontrolledtogethighmolecular weightP(AN-co-ACBM). For thesynthesizedcomonomerACBMin
this article, the amounts of ACBM in the feed should be controlled less than 2.0 wt% based on total monomers.
Fig. 2 shows the DSC curves of PAN and P(AN-co-ACBM) heated from ambient temperature to 400 8C at 10 8C/
min under N (40 mL/min). The parameters obtained from the exotherms, including the temperature of initiation (T ),
2
i
the temperature of termination (T ), their difference (DT = T ꢀ T ), the first peak temperature (T , the peak at lower
f
f
i
p1
temperature), the second peak temperature (T , the peak at higher temperature), the released heat (DH), and the rate of
p2
heat release (DH/DT), are listed in Table 1.
The DSC curves of PAN polymers were measured under N atmosphere and no oxidative reactions occurred during
2
this process, so the exothermic peaks in DSC curves were attributed to the cyclization reactions. As shown in Fig. 2,
there is one exothermic peak in PAN and the cyclization reactions of PAN can only be initiated through free radical
mechanism. Whereas in P(AN-co-ACBM), there are two exothermic peaks and the cyclization reactions can be