Acid, polyamic

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. 

The polyimide shown is a tme thermosetting resin, but the general reaction procedure, coupling the dianhydride with the diamine, is extremely important throughout polyimide chemistry. The intermediate polyamic acid polymers form the basis for many of the polyimide resins used in advanced composites. 

Fig. 32. High resolution C(ls) XPS spectra obtained from the bulk (A) polyamic acid and (B) polyimide of PMDA/4-BDAF. Reproduced by permission of the American Chemical Society from Ref. [39].

Tsai then applied thick films of the polyamic acid of PMDA and 4-BDAF to polished silver substrates and thermally imidized the films. The substrates were immersed into liquid nitrogen, causing the films to delaminate and XPS was used to examine the polyimide and silver fracture surfaces (see Fig. 33). The C(ls) spectra of the silver fracture surface were very similar to those of neat polyamic acid, indicating that imidization was inhibited by interaction of the polyamic acid with the silver substrate. This was evident from the observation of two peaks near... 

FIGURE 5.4 Analysis of polyamic acid, two columns AMGEL Linear 300 X 7.8 mm, eluant NMP, flow rate I ml/min, temperature 50 C, detector (DRI). 

From a mechanistic point of view, the polyimide synthesis via the polyamic acid is not a convenient method of preparing the block copolyimide for two main... 

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. 

The reactivity of T8[OSiMe2H]g is dominated by its capacity to undergo hydrosilylation reactions with a wide variety of vinyl and allyl derivatives (Figure 30) that have subsequently mainly been used as precursors to polymers and nanocomposites by the introduction of reactive terminating functions as shown in Table 19. For example, T8[OSiMe2H]g has been modified with allyglycidyl ether, epoxy-5-hexene, and 1,2-cyclohexene-epoxide to give epoxy-terminated FOSS. These have then been treated with m-phenylenediamine, with polyamic acids or... 

Polyamic acid also reacts with a more complicated POSS precursor containing both hexafluoroisopropyl and glycidyl termini (both introduced via hydrosilylation) to give low dielectric constant pol3nmides. ... 

Lewis et al. [22] presented experimental evidence for such an assumption after measurements of rate constants at different temperatures for the unimolecular imi-dization of a polyamic acid (Eq. (1), Fig. 3.2, and Tab. 3.2). 

The polyamic acid (Fig. 3.7) precursor was prepared by adding stoichiometric amounts of3,3,4,4-benzophenonetetracarboxylic acid dianhydride (BTDA) anddiami-nodiphenylsulfone (DDS). The solution in NMP was then submitted to either thermal or MW activation with accurate monitoring of the temperature (Scheme 3.14). 

The rates of certain reactions of polymers have been reported to be enhanced by MW under homogeneous conditions at atmospheric pressure. Lewis et al. [64] performed kinetic studies on the imidization of the polymer BDTA-DDS polyamic acid 46 in N-methylpyrrolidone (NMP) giving the polymer 47 (Scheme 4.24) and showed that the apparent activation energy was reduced from 105 kj mol-1 under conventional heating to 55 kj mol-1 under MW heating. Rate enhancements (kMw/kthermai)... 

Scheme4.24 Imidization of polymer BDTA-DDS polyamic acid.

In 1977, Parshall and co-workers published their work on the separation of various homogeneous catalysts from reaction mixtures.[46] Homemade polyimide membranes, formed from a solution of polyamic acid were used. After reaction the mixture was subjected to reverse osmosis. Depending on the metal complex and the applied pressure, the permeate contained 4-40% of the original amount of metal. This publication was the beginning of research on unmodified or non-dendritic catalysts separated by commercial and homemade membranes. 

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. 

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