Methylated Tetrahydrophthalic Anhydrides as End Caps in Addition Polyimides

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• 作者：David E. Rajsfus ; Mary Ann B. Meador ; Aryeh A. Frimer
• 刊名：Macromolecules
• 出版年：2010
• 出版时间：July 27, 2010
• 年：2010
• 卷：43
• 期：14
• 页码：5971-5980
• 全文大小：1189K
• 年卷期：v.43,no.14(July 27, 2010)
• ISSN：1520-5835

文摘

Thermolysis of methylenedianiline (MDA) 1,2,3,6-tetrahydrophthalic (THP) bismides up to 371 °C, produces aromatic product, with a concomitant lowering in cross-linking. This aromatization is responsible for both the improved thermal oxidative stability of THP end-capped polyimides and their substantial frangibility. In the hope of inhibiting precuring aromatization, 2,3-dimethyl, 3,3-dimethyl, and 1,2,3-trimethyl THP analogues were synthesized and reacted with MDA in a 2:1 ratio, heating gradually from 204 to 371 °C. In the lower temperature range, monoimide transforms to bisimide. At temperatures above 320 °C, cross-linking predominates—generally reaching 30% at 371 °C, though it was as much as 69% for 3,3-dimethyl THP. The surprising facility of cross-linking in the latter was correlated to the double bond length of the trans imide formed via thermal enolization. The aromatization (2−25%) observed in these methylated systems at higher temperatures presumably results from oxidative decarboxylation of the pendant methyls, which is the preferred pathway for degradation after cross-linking.