Preparation of polyimides containing carborane moiety and the thermal resistance mechanism
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摘要: 聚酰亚胺是先进复合材料重要的基体材料之一。在聚酰亚胺主链中成功引入碳硼烷笼状单元，制备出一系列有机-无机杂化的聚酰亚胺材料。从单体设计入手，设计合成了含邻碳硼烷单元的二胺单体(DNCB)，再与4,4'-二氨基二苯醚(ODA)和3,3',4,4'-苯甲酮四羧酸二酐(BTDA)进行共聚反应，合成前驱体聚酰胺酸(PAA)溶液并制备PAA薄膜，再经高温热亚胺化处理得到含碳硼烷单元的聚酰亚胺。对制备的聚酰亚胺材料的耐热性能和耐热氧化稳定性进行了系统研究，结果表明，碳硼烷单元的引入使聚酰亚胺基体的热稳定性和热氧化稳定性得到显著提升。当二胺单体中DNCB摩尔分数为40%时，N2气氛下，5wt% 热失重温度T5%提升近13℃，T10%提升近43℃，质量残留率高达82.6wt%；空气氛围下，T5%提升近36℃，T10%提升近64℃，质量残留率高达83.1wt%。X-射线光电子能谱(XPS)及扫描电镜(SEM)结果表明在聚酰亚胺主链中引入碳硼烷笼状单元后在高温环境中易在材料表面形成氧化硼(B2O3)钝化层，从而显著提升材料的耐热氧化稳定性。Abstract: A series of polyimide materials were successfully prepared by embedding o-carborane cage structure into polyimide main chains. First, the diamine monomer (DNCB) containing o-carborane unit was designed and synthesized, and then copolymerized with 4,4'-diaminodiphenyl ether (ODA) and 3,3',4,4'-benzophenone tetracarboxylic anhydride (BTDA) to synthesize the polyamic acid (PAA) precursor solution. PAA films were prepared by solution casting method, and then polyimide films containing different contents of carborane unit were obtained after high-temperature thermal imidization. Thermogravimetric analysis (TGA) shows that the addition of DNCB significantly improves the thermal stability and thermal oxidation stability of polyimide materials. When the molar content of DNCB in all diamines reaches 40%, the temperature corresponding to 5wt% mass loss (T5%) increases by nearly 13℃, T10% increases by nearly 43℃ and the mass residual rate was as high as 82.6wt%. Under the air atmosphere, T5% increases by nearly 36℃, T10% increases by nearly 64℃, and the mass residual rate reaches as high as 83.1wt%. This is due to the oxidation of carborane cage and the formation of multi-layer passivation protective layer on the surface of the film, which prevents the degradation of internal polymer materials in contact with oxygen.
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图 1 新型含碳硼烷单元二胺单体DNCB的合成路线
Figure 1. Synthesis route of novel carborane-containing diamine DNCB
DPCB—Diphenyl o-carborane; DOCB—1,2-di(nitrobenzene) o-carborane; DNCB—1,2-bis(aminobenzene) o-carborane
图 2 新型含碳硼烷单元聚酰亚胺薄膜的制备
Figure 2. Synthesis route of polyimides containing DNCB
ODA—4,4'-diaminodiphenyl ether; BTDA—3,3',4,4'-benzophenone tetracarboxylic anhydride; RT—Room temperature; DMAc—N,N'-dimethyl acetamide
图 3 (a) 1,2-二(硝基苯)-邻碳硼烷(DOCB)的FTIR图谱；(b) DOCB的1H NMR图谱
Figure 3. (a) FTIR spectrum of DOCB; (b) 1H NMR spectrum of DOCB
DMSO—Dimethyl sulfoxide
图 4 (a) DNCB的FTIR图谱；(b) DNCB的1H-NMR图谱
Figure 4. (a) FTIR spectrum of DNCB; (b) 1H NMR spectrum of DNCB
图 5 含邻碳硼烷单元聚酰亚胺薄膜(xDNCB/PI)的FTIR图谱
Figure 5. FTIR spectra of polyimides containing DNCB (xDNCB/PI)
图 6 N2氛围 (a) 和空气氛围 (b) 下xDNCB/PI的TGA曲线
Figure 6. TGA curves of xDNCB/PI in N2 (a) and in air (b)
图 7 xDNCB/PI在500℃下热处理60 min的数码照片
Figure 7. Digital photos of xDNCB/PI treated at 500℃ for 60 min
图 10 xDNCB/PI的应力-应变曲线 (a) 和平均拉伸强度、杨氏模量 (b)
Figure 10. Stress-strain curves (a) and average tensile strength and young's modulus (b) of xDNCB/PI
图 11 20DNCB/PI在600℃恒温处理后的B1s图谱
Figure 11. B1s spectra of 20DNCB/PI isothermally treated at 600℃
图 12 20DNCB/PI在600℃处理不同时间的数码照片 (a) 及SEM表面图像 (b) 和SEM截面图像 (c)
Figure 12. Digital photos (a), SEM surface images (b) and SEM cross section images (c) of 20DNCB/PI treated at 600℃ for different time
表 1 聚酰亚胺的DNCB摩尔分数汇总
Table 1. Summary of DNCB mole percent of polyimides
Code BTDA∶ODA∶DNCB (Molar ratio) DNCB content
(Molar percentage)PI 100∶100∶0 — 10DNCB/PI 100∶90∶10 10.0 20DNCB/PI 100∶80∶20 20.0 30DNCB/PI 100∶70∶30 30.0 40DNCB/PI 100∶60∶40 40.0 
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表 2 20DNCB/PI中各元素的理论值和测试值
Table 2. Calculated and experimental values of different elements in the 20DNCB/PI
Elemental content C/at% N/at% O/at% B/at% Calculated value 69.01 5.48 18.14 4.23 XPS analysis 72.47 4.24 17.71 5.58
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表 3 xDNCB/PI的分子量
Table 3. Molecular weight data of xDNCB/PI
Code Mn/(g·mol−1) Mw/(g·mol−1) PDI PI 93815 193315 2.06 10DNCB/PI 74001 176173 2.38 20DNCB/PI 69068 105342 1.53 30DNCB/PI 65757 98810 1.50 40DNCB/PI 54147 78799 1.45 Notes: Mn—Number-average molecular weight; Mw—Weight-average molecular weight; PDI—Polymer dispersity index.
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表 4 N2氛围下xDNCB/PI的热重分析数据
Table 4. TGA data of xDNCB/PI in N2
Code T5%/℃ T10%/℃ Residue at
900℃/wt%PI 554.3 574.4 60.3 10DNCB/PI 562.0 589.4 65.8 20DNCB/PI 562.1 595.0 69.1 30DNCB/PI 562.6 601.9 78.1 40DNCB/PI 566.9 617.4 82.6 Notes: T5%—Temperature for 5wt% mass loss; T10%—Temperature for 10wt% mass loss.
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表 5 空气氛围下xDNCB/PI的热重分析数据
Table 5. TGA data of xDNCB/PI in air
Code T5%/℃ T10%/℃ Residue at 900℃/wt% PI 545.5 572.4 0.6 10DNCB/PI 556.4 579.7 13.6 20DNCB/PI 561.5 586.8 39.0 30DNCB/PI 564.8 589.3 67.3 40DNCB/PI 581.8 635.9 83.1
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