Polyamic acid films

The thermal imidization of a polyamic acid film (PMDA-ODA or BPDA-ODA) obtained by casting an NMP solution leads to an amorphous polyimide. Two different teams have shown that a polyamic acid solutions in NMP heated at 200°C for a short time (20 min) gives polyimide particles fully cyclized and highly crystalline, as shown by X-ray diffraction and solid 13C NMR spectroscopy.151152 The chemical imidization of the same solution gives only amorphous particles. The difference between the cyclization of a solution and a casted film in the same solvent is intriguing. In the case of the solution, the temperature and the heating time are lower than in the case of the casted film as a consequence, a less organized structure would be expected for the particle. 

Poly (2,4-d if luoro-1,5, pheny lene t r ime 11 i t ic amide-imide) was prepared by a two-step procedure 12 At the first step, the polyamic acid was prepared by reacting 2,4-difluoro-1,5-phenylene diamine with trimellitic anhydride acid chloride (with the mole ratio of one to one) in anhydrous N,N-dimethylacetaraide at room temperature under nitrogen. After reaction, the polymer was poured into water and precipitated. After filtration, the white solid was washed with distilled water and dried in a vacuum oven. The poly(amide-imide) was obtained from heating the polyamic acid at 220°C for 3 hours. The polyamic acid was dissolved in N,N-dimethyl acetamide or N,N-dimethyl forraamide, cast on glass plates, and the solvent evaporated in a vacuum oven to form a polyamic acid film before heating at 220°C. 

Procedures Polyamic Acid films were cast by delivering 1.5 to 2.0 ml of resin to the center of a non-spinning j6 mm dia. wafer with a positive displacement bellows-type pump Spinning then progressed via IK rpm/sec ramp to the final spin speed for 20 seconds. Films were dried 30 minutes at 90° 10°C while held horizontally in a 25" mercury vacuum. B-stage cures were performed at 205°C for one to two hours in a forced air oven. Unless noted otherwise, all annealing was done at 350°C in Op for 30 minutes. 

Figure 6 Nls XPS spectra of a thick polyamic acid film a) before and b) after deposition of less than a monolayer gold...

The experimental procedures and x-ray photoemission results for the preparation of ultrathin (d = 1.1 nm) polyimide films on polycrystalline silver by co-condensation of PMDA and ODA are described elsewhere [5]. In that work our XPS results suggested that the polyimide chains bond to the silver surface via a carboxylate type bonding. This conclusion was derived from an analysis of the results obtained for the interaction of the monomers (PMDA and ODA) and of the resulting ultra-thin polyimide film. Due to the relatively larger thickness of the polyamic acid films as compared to the monomer adsorbate phases and the polyimide film, no conclusions were possible about the reaction of the polyamic acid with the silver substrate. 

In figure 7 we show Infrared-Reflection Absorption data for a thin polyamic acid film (a), a thin polyimide film (b) (after curing the PAA film of spectra a) and a thick (d > 10 nm) polyimide film (c) on a polycrystalline silver surface. Transmission and reflection infrared absorption spectra of thick (d > 1000 nm) spun-on polyamic acid and polyimide films have been reported previously [22-24], Salem et al. [2] presented in their pioneering paper the infrared transmission spectra for vapor deposited polyamic acid and polyimide. Except for the relative intensities between the individual absorption bands, our results for a thick polyimide film (Fig. 7c) are identical to those for spun-on and vapor deposited films, showing the unresolved symmetric and asymmetric (strong) vc Q stretches between 1700-1800 cm 1, the v (l,4-CgH4) ring... 

Will imidization occur if KOH treated polyamic acid films of PI5878 are subsequently subjected to standard cure-cycles ... 

For evaluations of the effect of KOH on PI5878 polyamic acid films, the as-applied resin film ( b) after the 120 C solvent... 

For all cured, non-modified polyimide films studied, the C Is spectra showed extremely weak satellite features centered about 292.8 0.3 eV. To date, we have not studied these shake up structures extensively. We have noted, however, that they frequently do not exist in the C Is spectra of the polyamic acid films. These low intensity features appear resolvable into two Gaussian components of unequal intensity. Their chemical shifts are consistent with assignments given to n ntransitions e.g., D.T. Clark et al, J. Electron. Spectrosc. Relat. Phenom., 51... 

These observations suggest that the polyamic acid film surfaces may not have appreciable unsaturated carbon environments. ... 

Since polyimides 5 are essentially infusible and insoluble in organic solvents, they are processed into films at the stage of polyamic acids 3 which are readily synthesized from tetracarboxylic dianhydrides 1 and diamines 2, Thermal treatment of polyamic acid films to 300 C affords polyimide films through cyclodehydration (Scheme 1). Alternatively, chemical treatment of polyamic acid films with a mixture of acetic anhydride and pyridine is also effective in obtaining polyimide films.(1)... 

Figure 1. Dynamic mechanical spectrum (left log E (Pa), right tan S vs temperature (°C)) of the thermal cure of PMDA-ODA polyamic acid film at a.) 5 °C/min. and b.) 0.5 °C/min.

Another group of thermally stable polymeric materials for electronic application includes poly(ether-imide-benzoxazolejs. Mercer and McKenzie [228] prepared the polymer by polycondensation of 2,2 -bis[2-(4-aminophenoxy)benzoxazole-6-yl] hexafluoropropane with pyromellitic, biphenyl, benzophenone etc., followed by thermal imidization of polyamic acid films. The polymers showed an onset temperature for polymer degradation in the range of 424°-456°C and glass transition temperatures in the range of 299 -337°C. 

Pig. 8. Bilayer process for patterning polyamic acid films. 

The chemical imidization method consists of a treatment of a polyamic acid film or powder with dehydrating agents. Acetic anhydride or other lower aliphatic acids, such as propionic, valeric acid or others, can be used for this purpose. Ketenes and dimethyl ketenes can also be used as dehydrating agents. Tertiary amines are used as catalysts for the chemical imidization. The chemical imidization may also be carried out in a solution of the polyamic acid in aprotic solvent") by adding acetic anhydride and tertiary amine. 

Another polypyrrole/polyamide composite film was obtained by the electrode coating method [84]. In this work the polyamide film was obtained in situ by coating a stainless steel electrode with a polyamic acid film followed by imidization with pyridine and acetic anhydride. The coated electrode was submitted to a constant current in a pyrrole/LiC104 solution in acetonitrile. The surface conductivity measured after detaching the composite film from the electrode showed a strong dependence on the charge density used in the synthesis, i.e. on the amount of pyrrole polymerized in the composite. The maximum value obtained was 2 S cm . Combination of polypyrrole with this polyamide was shown to increase markedly its thermal and environmental stability. 

The IR spectra of polyimide and polyamic acid films were recorded. The spectra of all polyamic acids showed wide absorption bands anound 3270 and 1650 cm The band around 32 70 cm is ascribed to the stretching of N-H linkages with relatively low Intensity due to the formation of hydrogen bonds. The absorption band at 1650 cm is peculiar to secondary amide groups. In polyimides the 3270 cm and 1650 cm absorption bands are absent and new absorption peaks appear at about 1775, 1080 and 710 cm. ... 

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