硅倍半氧烷改性聚酰亚胺(PI/Si)复合膜性能

通过在聚酰亚胺(PI)中分别添加笼型八氨基苯基硅倍半氧烷(OAPS)、 笼型八苯基硅倍半氧烷(OPS)、 梯形聚苯基硅倍半氧烷(PPSQ)和无机纳米SiO₂, 制备了4种含硅聚酰亚胺(PI/Si)复合膜. 对PI/Si复合膜的相容性、 力学性能、 热性能和阻燃性能进行了研究. 结果表明, OAPS与PI间展现出较好的相容性, PPSQ次之, 而OPS, SiO₂与PI的相容性较差; 但相容性与复合膜的力学和热性能无明显的对应关系. SiO₂可提高PI的力学性能; PI/OAPS复合膜的T_g最高; OAPS, PPSQ或SiO₂的加入使PI复合膜的热稳定性稍有提高, 而少量OPS的加入大大降低PI膜的热稳定性. 这类PI/Si复合膜的显著特点是能够大幅提高PI膜的极限氧指数, 含硅化合物能够增加PI燃烧后残炭量, 使残炭的形貌得到显著改善. PI/Si复合膜在燃烧过程中在表面形成一层白色含硅包裹层, 起到隔热隔氧及保护内层有机物不被燃烧的作用. 硅倍半氧烷对炭层形貌的改善显著, 展现出比SiO₂更好的阻燃性能.

Polyimide Membranes Modified by Polyhedral Oligomeric Silsesquioxane

Four kinds of polyimide(PI)/Si membranes were prepared using PI with octaphenylsilsesquioxane(OPS), octa(aminophenyl)silsesquioxane(OAPS), polyphenylsilsesquioxane(PPSQ) of ladder structure, and nano-silica(SiO₂), respectively. Their morphologies were studied by scan electron miscroscope(SEM) and the mechanical properties were measured by tensile testing and the thermal properties were studied by differential scanning calorimetry(DSC), thermogravimetric analysis(TGA) and limited oxygen index(LOI). The SEM and XRD results of the PI/Si composites proved that there were good compatibility between PI and OAPS because the aminophenyl groups in OAPS could participate in the polymerization process of PI. The mechanical properties of PI/OAPS membrane were nearly the same with that of PI. And the addition of OPS or PPSQ decreased the PI mechanical properties sharply. DSC analysis implied that the additives could increase the glass-transition temperature(T_g) a little and the T_g of PI/OAPS was the highest because the Si—O caged structures existed in the PI main chain. The addition of OAPS, PPSQ or SiO₂ would improve the thermal stability a little according to the TGA results. One interesting result is that the LOI of PI/Si membranes significantly increased compared with pure PI membrane. The LOI for PI/OPS membrane was 57%, while that for PI was 46.5% only. The improvement was caused by the formation of a well covered silicate char structures after burning. And the LOI of the membranes of PI with polyhedral oligomeric silsesquioxanes are higher than PI/SiO₂.