Condensation-type polyimides

Some of the problems associated with condensation-type polyimides were alleviated with the introduction of... 

Autoclave molding usually involves heat (up to 260°C), pressure (35-50 psi) and vacuum. This method is particularly attractive for processing condensation-type polyimides and some processable polyimides. ... 

The historically-firet condensation polyimides have recently been complanented by a second class of resins - addition-type polyimides. KINEL conqpounds and KERIMID 601 laminating resin are menbers of this new family of polyimides. Ch ically they eure designated polyaminobismaleimides (PABMs) ... 

Condensation type—such as linear thermoplastic polyimides (NR150)... 

Polyimides are the highest-temperature polymer in general advanced composite use, with a long-term upper temperature limit of 232°C (450°F) or 316°C (600°F). Two general types are condensation polyimides, which release water during the curing reaction, and addition type polyimides, with somewhat easier process requirements. 

The dianhydride of 1,4,5,8-naphthalene tetracarboxyhc acid [81-30-1] has been of research interest for the preparation of high temperature polymers, ie, polyimides. The condensation of the dianhydride with o-phenylenediamines gives vat dyes and pigments of the benzimidazole type. 

Condensation polyimides or SP-polyimides from the solvent-phase reaction of an aromatic tetra-acid with a diamine. Despite the thermoplastic form they are infusible and generally insoluble. Consequently, the producer can only mould this type. It is particularly convenient for the manufacture of thin parts and films, coatings... 

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. 

Polyimides for microelectronics use are of two basic types. The most commonly used commercial materials (for example, from Dupont and Hitachi) are condensation polyimides, formed from imidization of a spin-cast film of soluble polyamic acid precursor to create an intractable solid film. Fully imidized thermoplastic polyimides are also available for use as adhesives (for example, the LARC-TPI material), and when thermally or photo-crosslink able, also as passivants and interlevel insulators, and as matrix resins for fiber-reinforced-composites, such as in circuit boards. Flexible circuits are made from Kapton polyimide film laminated with copper. The diversity of materials is very large readers seeking additional information are referred to the cited review articles [1-3,6] and to the proceedings of the two International Conferences on Polyimides [4,5]. 

Cyclotrimerization of polyfunctional aryl acetylenes offers a unique route to a class of highly aromatic polymers of potential value to the micro-electronics industry. These polymers have high thermal stability and improved melt planarization as well as decreased water absorption and dielectric constant, relative to polyimides. Copolymerization of two or more monomers is often necessary to achieve the proper combination of polymer properties. Use of this type of condensation polymerization reaction with monomers of different reactivity can lead to a heterogeneous polymer. Accordingly, the relative rates of cyclotrimerization of six para-substituted aryl acetylenes were determined. These relative rates were found to closely follow both the Hammett values and the spectroscopic constants A h and AfiCp for the para substituents. With this information, production of such heterogeneous materials can be either avoided or controlled. 

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.

If trimellitic anhydride is used instead of pyromellitic dianhydride in the reaction shown in Figure 4.19a, then polyamide-imide is formed (see Figure 4.20a). Other possible routes to this type of product involve the reaction of trimellitic anhydride with diisocyanates, (Figure 4.20b) or diurethanes (Figure 4.20c). Closely related is the Upjohn process for polyimide by self-condensation of the isocyanate of trimellitic acid, as illustrated in Figure 4.19b, although the product in this case is a true polyimide rather than a polyamide-imide. 

Polyimides can be prepared as either thermoplastic or thermoset resins. There are two types of polyimides, condensation, and addition resins. Condensation polyimides are available as either thermosets or thermoplastics. The additional polyimides are available only as thermosets. 

Hyperbranched polyimides can result due to the self-polycondensation reactions of AB2-, A2- and Bs-types. The preparation of hyperbranched polyimides involves chemical imidization of polyamic acid ester synthesized from AB2-monomers, which are carboxylic dianhydrides containing an ether bond and a diamine [6,19,76]. Polyamic acid in combination with a condensation agent is used because it is difficult to separate the synthesized polymer from AB2-type monomers. 

Studies into the first of these types, the norbomene imides, have resulted in a high-temperature adhesive system known as LARC-13, which demonstrated improved process-ability over condensation polyimides. Some typical results obtained from this adhesive are shown in Table 4, demonstrating its high-temperature capabilities. 

There are two basic types of polyimides condensation and addition resins. The condensation polyimides are based on a reaction of an aromatic diamine with an aromatic dianhydride. A tractable (fusible) polyamic acid intermediate produced by their reaction is converted by heat to an insoluble and infusible polyimide, with water being given off during the cure. Generally, the condensation polyimides result in products having high void contents that detract from optimal mechanical properties and result in some loss of long-term heat resistance. 

This methodology is quite general and can be utilized to prepare several types of polymers such as polyamides, polyimides, polyurethanes, polyethers etc. The polymer properties depend on the type of functional groups that link the polymer building blocks. Further modulation is achievable by varying the nature of the difimctional monomer within each class of polymers. It is not always necessary to condense two difunctional monomers. Some polymers such as polyethers are prepared by the oxidative coupling of the corresponding phenols. A few examples of polymers that can be prepared by the condensation reactions are shown in Fig. 1.2. 

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