Polyamic salt

Figure 5.11. (a) A polyamic salt which will spread at the air/water interface and form LB films. (b) A polyimide which can be produced as a multilayer by heating a multilayer of the polyamic salt and driving oif the long chains associated with the salt. 

Moleculady mixed composites of montmorillonite clay and polyimide which have a higher resistance to gas permeation and a lower coefficient of thermal expansion than ordinary polyimides have been produced (60). These polyimide hybrids were synthesized using montmorillonite intercalated with the ammonium salt of dodecylamine. When polymerized in the presence of dimethyl acetamide and polyamic acid, the resulting dispersion was cast onto glass plates and cured. The cured films were as transparent as polyimide. 

Table 1 lists some of the metal compounds employed and the results obtained when attempts were made to cast films of the resulting metal ion filled polyimide derived from BTDA + m,m -DABP. Brittle films were produced in most cases regardless of whether the added metal ion was hydrated or anhydrous. The relatively low viscosities of the resulting polyamic acid-metal ion solutions no doubt accounted for this. Addition of AlCl3 6H20 or any simple aluminium salt to the polyamic acid produced immediately a rubbery material that could not be cast into a film. 

Figure 5.8. Reaction diagram illustrating formation of polyamic acid salt.

Figure 5.14. Dynamic TGA scan of BPDA-PDA polyimide (initial starting material is polyamic acid salt) in air (-) and N2(----) atmospheres (from Davis and Zimmerman74).

Figure 5.16. Dynamic TGA scans of BPDA-PDA polyimides where initial starting materials are polyamic acid (-) and polyamic acid salt (.) (from Davis and Zimmerman " ).

The initial reaction attains 70% conversion to the polyamic acid salt in five seconds, 97% conversion after five minutes. The... 

Mono- and multilayer films of polyimides were successfully prepared using Langmuir-Blodgett technique. Monolayer films of polyamic acid long alkylamine salts were prepared at the air-water interface. The mono-layer films were deposited on appropriate plates to produce multilayer films of the precursor to polyimide films. Finaly, the polyimide multilayer films were obtained by treatment of the multilayer films of the polyamic acid amine salts with acetic anhydride and pyridine. The polyimide multilayer films had excellent coating ability giving a very smooth surface. They also exhibited insulating characteristics as reliable as polyimide thick films. 

The present method consists of three steps as illustrated in Scheme 1. In the first step, monolayer films of polyamic acid long chain alkyl-amine salts 4 at the air-water interface are prepared.(9) Unexpectedly, the polyamic acid 3 itself, which possess hydrophilic carboxyl functions in the polymer backbone, did not afford a stable monolayer at the air-water interface. Introduction of a hydrophobic long alkyl chain into 3 was performed by mixing polyamic acids and longchain alkylamines. Polyamic acid salts 4, thus obtained, afforded very stable monolayer films at the air-water interface. In the second step,(10) the polyamic acid salt monolayer films are successfully deposited on appropriate plates such as glass, quartz, or silicon wafer. Finally polyimide multilayer films are obtained by treatment of polyamic acid salt multilayer films on the plates with a mixture of acetic anhydride and pyridine. 

Figure 1 7T-A Curves of polyamic acid salts varying the ratio of N,N-dimethylhexadecylamine (DMC16) to polyamic acid 3a. A polyamic acid 3a, B 3a DMC16=2 1, C 3a DMC16=1 1>...

Table 1. Extrapolated Surface Area of Various Polyamic Acids Salts...

Preparation of Multilayer Films of Polyamic Acid Alkylamine Salts ... 

Deposition of polyamic acid salt was carried out at a surface pressure of 25 dyne/cm onto a appropriate plate by drawing down and up through the air-water interface at a rate of 3-5 mm/min at 20 C (vertical dipping method). 

In the IR spectrum of polyimide films of 5a, the absorption-due to hydrocarbon group of the film disappeared, and new characteristic absorptions corresponding to the imide carbonyl groups appeared at 1780 and 1720 cm. This suggested that the cyclization of the polyamic acid salt to polyimide 5a proceeded almost completely with the removal of the long chain alkylamine. 

The elemental analysis of multilayer films (50 layers) of polyamic acid salt and polyimide 5a was performed by ESCA (electron spectroscopy for chemical analysis), with the following results ... 

Aliphatic diamines react with a diester-diacid derived from a dianhydride to form an ammonium salt which can be polymerized, usually in the melt, to a polyamic acid. Further heat converts the polyamic acid to the polyimide... 

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