1 Research Center of Soft Materials Technology, AECC Beijing Institute of Aeronautical Materials, Beijing 100095, China 2 National Key Laboratory of Advanced Composites, Beijing 100095, China 3 Laboratory of Advanced Polymer Materials, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
With precursor modification by regulating dianhydride hydrolysis degree, the viscosity of polyimide precursor solution, derived from 3, 3', 4, 4'-biphenyl tetracarboxylic dianhydride (BPDA) and para-phenylenediamine (PDA), was facilely manipulated. The chemical structure of the precursor was characterized by infrared (IR) spectrometry and proton nuclear magnetic resonance (1H-NMR) spectrometry. The effects of dianhydride hydrolysis on the viscosity, imidization process and properties were investigated. The results show that the precursor can be formed from hydrolytic BPDA and PDA, with amide acid and carboxylic ammonium salt groups in the molecular structure. The viscosity of the precursor can be reduced by the introduction of carboxylic ammonium salt group, achieving the effective regulation of viscosity in the 10-105cP range. Importantly, the existence of carboxylic ammonium salt shows no influence on the complete imidization of the precursor, which guarantees the maintenance of mechanical property. Interestingly, the coefficient of thermal expansion (CTE) of this BPDA-PDA polyimide films can be reduced by this viscosity manipulation method.
Unsymmetrical stretching vibration of imide C=O bond
1715
PI
Stretching vibration of imide C=O bond
1713
PAS
Stretching vibration of C=O bond in COOH
1656
PAS
Stretching vibration of C=O bond in amide group (amide band Ⅰ)
1605
PAS
Bending vibration of NH bond in amide group (amide band Ⅱ)
1406
PI
Stretching vibration of C—N bond in imide group
1316
PAS
Stretching vibration of COO-N+ bond
732
PI
Bending vibration of imide C—N bond
Table 2 PAS(A)和PI(A)的红外吸收峰归属
Fig.3 PAS(A)的1H-NMR谱图(水酐摩尔比：20%)
Sample (charging sequence)
Water content of solvent/%
Molar ration of H2O to anhydride/%
Rotary viscosity/cP
PAS(A) (dianhydride added first)
0
0
Gel
0.32
20
37000
0.55
35
12800
0.79
50
3200
1.58
100
72
PAS(B) (diamine added first)
0
0
Gel
5
316
183000
8
506
61650
10
633
45000
Table 3 PAS前驱体溶液的旋转黏度(25℃)
Fig.4 PAS(A)溶液旋转黏度(ηRot)随水/酐摩尔比的
Fig.5 不同水/酐摩尔比PAS(A)的TGA曲线
Fig.6 PAS的亚胺化反应过程
Sample
Molar ratio of H2O to anhydride/%
σt/MPa
E/GPa
CTE/(10-6·K-1)
PI(A)
20
245
6.0
15.9
35
279
6.0
10
50
243
6.2
6.2
100
Unable to be processed
PI(B)
316
166
5.3
-
Table 4 PI薄膜的力学性能和CTE
Fig.7 PI薄膜的CTE曲线
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2019, Vol. 47 
), 邢宇1,2, 戴霄翔1,2, 李军1,2, 张代军1,2, 杨士勇3, 陈祥宝1,2
