Polyimide formation

The polyimide is formed by the thermal polycyclocondensation of the poly(amide acid). For this purpose, 5 ml of poly(amide acid) solution are placed on a watch glass (diameter 10 cm) and kept in a vacuum oven at 50 °C for 24 h.The solvent evaporates and at the same time cyclization to the polyimide takes place the resulting film is insoluble in dimethylformamide.The formation of the polyimide can be followed by IR spectroscopy the NH-band at 3250 cm disappears while imide bands appear at 1775 and 720 cm" Once the initial drying process has raised the solid content to 65-75%, the polyimide formation can be accelerated by heating the poly(amide acid) film to 300 °C in a vacuum oven for about 45 min.The polyimide made from pyromellitic dianhydride and 4,4 -oxydianiline exhibits long-term stability in air above 200 °C. 

The synthesis of the poly-(o-chlorophenyl)-imides was accomplished in two steps involving low-temperature reaction between the diamines and bis(phthalic anhydrides) in NMP followed by catalytic imidisation of the PCA directly in the reaction solutions using the catalytic complex pyridine acetic anhydride. The synthesis of polyimides from l,l-dichloro-2,2-di-(3-amino-4-aminophenyl)-ethylene proceeded homogeneously throughout the course of the reaction, as did reactions of 3,3 -diamino-4,4 -dichlorobenzophenone with the dianhydride of diphenyloxide-3,3, 4,4 -tetracarboxylic acid. As to reactions of 3,3 -diamino-4,4 -dichlorobenzophenone with the dianhydrides of pyromellitic and diphenylsulfone-3,3, 4,4 -tetracarboxylic acids, these were homogeneous at the PCA formation step but heterogeneous at the polyimide formation step. Some properties of these polyimides are given in Tables 3.3 and 3.4. 

Under certain conditions, aroyl chlorides are converted to arylsilanes by the reaction with disilanes. The oxidative addition of aroyl chloride and decarbonylation are followed by transmetallation and reductive elimination to give aryl silanes. Neat trimellitic anhydride acid chloride (377) reacts with dichlorotetramethyldisilane (376) at 145 °C to generate 378, which affords 4-chlorodimethylsilylphthalic anhydride (379) by reductive elimination. Finally it was converted to 380 and used for polyimide formation [185], Biphenyltetracarboxylic anhydride 381 is obtained at a higher... 

Stresses in solvent based coatings arise from the differential shrinkage between the thin film coatings and the corresponding substrates. These stresses are due to volume changes associated with solvent evaporation, chemical reaction (i.e. cyclization in polyimide formation) and differences in thermal expansion coefficients of the coating and substrate (4>5). The level of residual stress depends on the material properties such as modulus, residual solvent content and crosslinking (5) and its thermal-mechanical history. 

Figure 5.21. Reaction schemes for the most common types of step-growth polymerization. Shown are (a/c) polyester formation, (b/d) polyamide formation, (e) polyamide formation through reaction of an acid chloride with a diamine, (f) transesterification involving a carboxylic acid ester and an alcohol, (g) polybenzimidazole formation through condensation of a dicarboxyhc add and aromatic tetramines, and (h) polyimide formation from the reaction of dianhydrides and diamines.

PANI has been doped with poly(amic acid) in order to obtain an all-polymer conducting material, by Angelo-poulos el a . [337]. Its structure has not been investigated, but the authors present x-ray diffraction results for cured specimens, in which polyimide formation has taken place at the expense of the carboxylic acid groups. The diffraction is structureless there is no indication that the elimination of the ionic interaction leads to phase separation of the polymers. 

Ellenville, N.Y., 2nd-4th Nov. 1994, p.25.43C4 FTIR AND FLUORESCENCE MONITORING OF POLYIMIDE FORMATION... 

J.C. Johnston, M.A.B. Meador, W.B. Alston, A mechanistic study of polyimide formation from diester-diacids, J. Polym. Sci., Part A Polym. Chem. 25 (8) (1987) 2175-2183. 

Syntheses.—The principal use to which polyimides are put is in the production of high-temperature-resistant materials. This is still a comparatively new field and the balance of papers on this topic has been towards the synthesis and properties of the polyimides, while notably little work has appeared on the mechanism of the polymerization process or on the morphology of the polymer. Nevertheless an attempt has been made to describe polyimide formation in terms of an equilibrium process. ... 

Polyimides with aliphatic units in their main chain are generally obtained by thermal polycondensation by heating salts of aromatic tetracarboxylic acids and aliphatic diamines. Edwards and Robinson were the first to describe the preparation of an aliphatic polyimide by the fusion of a diamine with a diester of a tetracarboxylic acid. The reaction for the polyimide formation may be represented as follows [2] ... 

Condensation polymers. A. Polyester/polyamide/polyimide formation by combining A2 and 82 monomers or from a single AB monomer. Several common polymers of this class are shown. B. The diisocyanate route to polyurethanes and polyureas. C. Bakelite synthesis. Note that the final product is heavily cross-linked because of the presence of bis and tris adducts in the initial reaction with formaldehyde. 

Hodkin, J. H., Reactivity Changes During Polyimide Formation, J. Polym. Sci., Polym. Chem. Ed., 14, 409-431, 1976. 

It condenses with resorcinol and amino-phenols to give phthalein and rhodamine dyestuffs respectively. Esters are used in the formation of polyimides. ... 

This polymerization is carried out in the two stages indicated above precisely because of the insolubility and infusibility of the final product. The first-stage polyamide, structure [IX], is prepared in polar solvents and at relatively low temperatures, say, 70°C or less. The intermediate is then introduced to the intended application-for example, a coating or lamination-then the second-stage cyclization is carried out at temperatures in the range 150-300°C. Note the formation of five-membered rings in the formation of the polyimide, structure [X], and also that the proportion of acid to amine groups is 2 1 for reaction (5.II). 

Carboxyhc acids react with aryl isocyanates, at elevated temperatures to yield anhydrides. The anhydrides subsequently evolve carbon dioxide to yield amines at elevated temperatures (70—72). The aromatic amines are further converted into amides by reaction with excess anhydride. Ortho diacids, such as phthahc acid [88-99-3J, react with aryl isocyanates to yield the corresponding A/-aryl phthalimides (73). Reactions with carboxyhc acids are irreversible and commercially used to prepare polyamides and polyimides, two classes of high performance polymers for high temperature appHcations where chemical resistance is important. Base catalysis is recommended to reduce the formation of substituted urea by-products (74). 

After deposition of 0.5 nm of copper onto plasma modified polyimide, the peaks due to carbon atoms C8 and C9 and the oxygen atoms 03 and 04 were reduced in intensity, indicating that new states formed by the plasma treatment were involved in formation of copper-polyimide bonds instead of the remaining intact carbonyl groups. Fig. 28 shows the proposed reaction mechanism between copper and polyimide after mild plasma treatment. 

Some diamines carrying very bulky substituents like cardo groups can give colorless polyimides. For example, the bis-9,9-(4-aminophenyl)fluorene (FDA) or brominated and acetylenic FDA derivatives react with 6FDA giving copolymer films62 with low birefringence (low difference between in-plane and out-of-plane refraction index) (Fig. 5.8). A new cardo diamine l,l-bis[4-(4-aminophenoxy)phenyl]cyclododecane (Fig. 5.8) reacts with different aromatic dianhydrides with formation of colorless polyimides.63... 

In addition to the research on fluorinated and cardo polyimides, an important work was devoted to the semiaromatic cycloaliphatic polyimides. Volk-sen points out the potential interest of these materials in electronic industry.64 He reports that the simplest procedure to prepare these materials is to use a cycloaliphatic dianhydride and an aromatic diamine (Fig. 5.9) instead of an aliphatic diamine and an aromatic dianhydride, which leads to formation of gels. 

The competition at 200°C between an aliphatic and an aromatic amine toward the formation of an imide is a very selective reaction (Fig. 5.1) for the formation of an aliphatic imide.141 This reaction suggests that the reactive processing in extruder, for example, could be used to transform a melt-processable polyimide with an oligomer end capped with an aliphatic amine. In order to get a perfecdy alternate block polyimide-block siloxane, Rogers et al. used low-temperature transimidization.142 An oligomeric aromatic imide was end capped... 

An unusual method has been used to prepare a hyperbranched polyimide starting from two monomers a difunctional A2 and a trifunctional B3. The gel formation can be avoided with careful control of the polycondensation conditions (molar ratio, order of the monomer addition, and low concentration). The A2 and B3 monomers were respectively 6FDA and tris(4-aminophenyl)... 

American Society for Testing and Materials (ASTM), 242 Amic acid ammonium salt, polyimide cyclization via, 305 Amic acid formation, 301 Amidation reaction scheme, 151 Amide-amide interchange reaction, 158 Amide concentration, in polyamides, 139-141... 

More recently, St. Clair and co-workers176) reported the use of aromatic amine terminated polydimethylsiloxane oligomers of varying molecular weights in an effort to optimize the properties of LARC-13 polyimides. They observed the formation of two phase morphologies with low (—119 to —113 °C) and high (293 to 318 °C) temperature Tg s due to siloxane and polyimide phases respectively. The copolymers were reported to have improved adhesive strengths and better thermal stabilities due to the incorporation of siloxanes. 

---