从分子设计出发,用不同的二胺单体和相同的二酐单体合成聚酰胺酸并制备聚合物膜. 采用热重﹑热重-质谱﹑红外和X射线光电子能谱分析聚酰胺酸在热解过程中的结构变化及机理. 结果表明,在热解过程中,聚酰胺酸的热解包括4个阶段,经吸附水和吸附氧的脱除及溶剂挥发,亚胺化,交联,以及高温阶段的主链断裂﹑脱氧﹑脱氢﹑芳构化等热解过程转化为无定形炭结构. 前驱体的结构不同导致热解过程存在差异. PPD-PMDA和TMPPD-PMDA热解时所需的温度较高. 其它聚酰亚胺析出CH4﹑CO2﹑C6 H6的温度顺序为ODA-PMDA>BDAF-PMDA>BAPP-PMDA. 在700 ℃热解后,BDAF-PMDA所含的氟元素基本消失. 这表明聚酰亚胺的化学结构对炭膜的微结构有较大影响.
Polyimide membranes were synthesized by the polymerization of five diamines, p-phenylenediamine (PPD), 2,3,5,6-tetramethyl-1,4-phenylenediamine (TMPPD), 4,4′-oxydianiline (ODA), 4,4′-(4,4′-isopropylidenediphenyl-1,1′-diyldioxy)dian-iline (BAPP) and 4,4′-(hexafluoroisopropylidene)bis(p-phenyleneoxy) dianiline (BDAF), and the same dianhydride monomer, 1,2,4,5-benzenetetracarboxylic anhydride (PMDA). The chemical structures of the membranes pyrolyzed at different temperatures were investigated by TGA, TG-MS, FT-IR and XPS. Results indicate that there are five stages during pyrolysis:( a) the removal of the solvents, adsorbed oxygen and water, ( b) imidization, ( c) cross-linking and carbonization, which are accompanied by main chain breaking, ( d) deoxygenation and dehydrogenation, ( e) aromatization and turbostratic carbon formation. The chemical struc-ture of the precursor is the main factor that causes the great differences in chemical structures during pyrolysis. Imidization in the py-rolysis of the PPD-PMDA and TMPPD-PMDA occurs at higher temperatures than those for ODA-PMDA, BDAF-PMDA and BAPP-PMDA. The order of temperatures for the release of CH4 , CO2 and C6 H6 during the pyrolysis is ODA-PMDA>BDAF-PMDA>BAPP-PMDA. Elemental F in the BDAF-PMDA disappears after pyrolysis at 700 ℃. The chemical structures of the polyimides have a great influence on the microstructures of the carbon membranes obtained.
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