New high-temperature polyimides based on [5]helicene dianhydride

Abstract

The new anhydride, [5]helicene-5,6,9, 10-tetracarboxylic 5,6:9,10-dianhydride (HLDA) was thermally imidized with four diamrnines: methylenedianiline (AAFIII), xylylenedianifine (AAFIV). 3,3'-hexafluoroisopropylidene)dianiline (AAFV) and 4",4"'-(hexafluoroisopropylidene)bis(4-phenoxyaniline)(AAFVI). In thecase of AAFIII and AAFIV, a nadic endcap was added and the n value formulated for 2.087; for AAFV and AAFVI no endcap was used, Moulding powders were prepared either by imidizing these diamines in refluxing methanolic solutions of esterified HLDA followed by compression moulding at about 315 °C, or alternatively, in the case of AAFV and AAFVL, by imidizing in cold or refluxing NMP followed by compression moulding at about 365 °C. While the weight loss. results for AAFIII and AAFIV at 343 °C prove to be poorer than PMR-15, AAFV and AAFVI moulding powders prepared in cold or hot NMP result in resins which substantially outperform PMR-15. Indeed. the lowest rates of weight loss (mg cm ^-2)from AAFV (cold NMP) and AAFVI (hot NMP). respectively, were 1/5 and 1/2 that of PMR-15 at either 343 °C or 371 °C. The outstanding performance of AAFV approaches that of PMR-II-50, now considered one of the high-temperature polymer weight-loss standards.

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