Successful synthesis of a 1: 1 salt monomer derived from bis(4-aminophenyl) ether and pyromellitic acid for direct polycondensation to an aromatic polyimide
✍ Scribed by Yoshio Imai; Takafumi Fueki; Tatsuo Inoue; Masa-Aki Kakimoto
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 253 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0887-624X
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✦ Synopsis
Introduction
During the course of these studies, we have found that bis(4-aminophenyl) ether, a weakly basic aromatic diamine, together with tetrafunctional pyromel-Aromatic polyimides have been well-known since the litic acid, could form readily the salt monomer with 1 : early 1960s as the most useful superengineering plas-1 composition regardless of their 2 : 4 functionality. tics because of their high thermal stability, good chemi-This article deals with a successful synthesis of the 1 : cal resistance, and excellent mechanical properties and 1 salt monomer derived from bis(4-aminophenyl) ether are used widely in aerospace, electronics, and other inand pyromellitic acid and the subsequent solid-state dustries. [1][2][3][4] Aromatic polyimides are generally prethermal polycondensation leading to the direct rapid pared in two steps by the ring-opening polyaddition of formation of the aromatic polyimide (Scheme 1). aromatic diamines to aromatic tetracarboxylic dianhydrides yielding soluble polyamic acids, followed by thermal cyclodehydration to insoluble polyimides. [1][2][3][4] Prior to the aromatic polyimide preparation, aliphatic-aro-EXPERIMENTAL matic polyimides were synthesized by the melt polycondensation of the nylon-salt type monomers composed of aliphatic diamines and pyromellitic acid diesters. 1,5,6 Preparation of the 1 : 1 Salt Monomer However, no one had recognized the utility of this type of salt monomers for polyimide synthesis until recently when we found that the salt monomers were Bis(4-aminophenyl) ether was purified by sublimation. Pyromellitic acid was prepared by dissolving pyromel-extremely reactive, producing directly aliphatic-aromatic polyimides by the polycondensation in a very litic dianhydride, which was previously purified by sublimation, in hot water, followed by cooling. This acid short reaction time at a temperature around 250ЊC. 7- 11 Bell also reported in 1967 only briefly that aromatic was further purified by recrystallization from water. 10 In a flask were placed 2.00 g (10.0 mmol) of bis(4-polyimides could be obtained by the thermal polycondensation of the salt monomer derived from bis(4-aminophenyl) ether, 2.62 g (10.3 mmol) of pyromellitic acid, and 100 mL of methanol. The mixture was stirred aminophenyl) ether and pyromellitic acid diisopropyl ester. 12 Recently we have also reported the solid-state under nitrogen atmosphere at room temperature for 24 h. During this period, the two reactants at once were thermal synthesis of the aromatic polyimide from the salt monomer composed of bis(4-aminophenyl) ether dissolved in methanol, and then the resulting salt began to precipitate. The white salt formed was collected and pyromellitic acid diethyl ester. 13 by filtration and dried at 100ЊC under vacuum overnight. The yield was 4.13 g (91%). The salt was used Correspondence to: Y. Imai (1-9-2-303, Nakamagome, for the subsequent polycondensation without further Ohta-ku, Tokyo 143, Japan) purification. The endothermic peak temperature of the