邻苯二甲酸酐
聚酰亚胺
材料科学
电介质
玻璃化转变
高分子化学
热稳定性
聚合物
缩聚物
热分解
放松(心理学)
化学工程
复合材料
有机化学
化学
催化作用
心理学
工程类
社会心理学
光电子学
图层(电子)
作者
Ştefan Chişcă,Valentina-Elena Musteata,Ion Sava,Maria Brumǎ
标识
DOI:10.1016/j.eurpolymj.2011.01.008
摘要
Aromatic polyimides were prepared by polycondensation reaction of two aromatic diamines, such as 4,4′-diaminodiphenylmethane (DDM) and 3,3′-dimethyl-4,4′-diaminodiphenylmethane (MDDM), with aromatic dianhydrides, such as 4,4′-isopropylidene-diphenoxy-bis(phthalic anhydride) (6HDA), benzophenonetetracarboxylic dianhydride (BTDA) and hexafluoroisopropylidene-bis (phthalic anhydride) (6FDA). These polymers are soluble in polar aprotic solvents and can be cast into thin films from such solutions. The polyimides show high thermal stability, with decomposition temperature being above 430 °C in air, and high glass transition temperature being in the range of 200–287 °C. The free standing films, having the thickness of tens of micrometers, exhibited good mechanical and electrical insulating properties. The dielectric constant, molecular mobility and AC conductivity of thin films prepared from these polymers were investigated in detailed. The study of their dielectric behavior evidenced low dielectric constant values, in the range of 2.88–3.48 at 1 Hz at room temperature, and three relaxation processes (γ, β1 and β2) were observed at sub-glass temperatures for polyimides based on 6HDA and 6FDA and only two (γ and β) relaxations were detected for polyimides based on BTDA. The cooperativity of the molecular motions associated with the relaxation processes was discussed.
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