Polyimides, additives

Polyimides for use in molded products and high temperature films can be produced by the reaction of pyromellitic dianliydiide [89-32-7] and 4,4 -diamino diphenyl ether [13174-32-8] in DAIAC to form a polyamide that can be converted into a polyimide (13). DAIAC can also be used as a spinning solvent for polyimides. Additionally, polymers containing over 50% vinylidene chloride are soluble up to 20% at elevated temperatures in DMAC. Such solutions are useful in preparing fibers (14). 

Polyimide (addition cure) Supported Areal wt. 0.5 kg/m Polyimide (condensation cure) Supported Areal wt. 0.5 kg/nf ... 

Another method used to improve the fracture energy of BMI resins consists in mixing the thermosetting material with linear thermoplastic polymers. This can be illusirated by the behavior of mixtures containing Compimide 796 and TM 123 BMI resins with SABIC Ultem 1000 , poly(ether-imide) 26 (Fig. 9.13). The critical stress intensity factor ATic of the Unear polymer is six times higher than that of the BMI matrix and does follow the mixture law for all BMI/Ultem combinations. The linear polyimide can also be added as 20—40 p.m spherical particles to the BMI resin before it is polymerized. In another example, particles of a soluble precyclized polyimide (Ciba Geigy XU 218 ) are dispersed in BMI monomer, which is subsequently melted at 177 °C and cured at 232 °C. The two-phase material obtained by this means exhibits a glass transition temperature of 348 °C compared with only 260 °C for the BMI resin without polyimide additive. 

The proposed chapter reviews the work done on 6FDA based fluorinated Pis with respect to its synthesis and various copolymers, polymerisation methods, poly(ether-imide), photosensitive polyimide, hyperbranched polyimide, addition polyimide, poly(amide-imide), poly(urethane-imide), poly(epoxy-imide), poly(ester-imide), poly(siloxane-imide), nanocomposites and non-linear optical polyimides. Finally, its application in electronics and use as a material for gas separation and corrosion protection are discussed. 

Polyimides (PI) were among the eadiest candidates in the field of thermally stable polymers. In addition to high temperature property retention, these materials also exhibit chemical resistance and relative ease of synthesis and use. This has led to numerous innovations in the chemistry of synthesis and cure mechanisms, stmcture variations, and ultimately products and appHcations. Polyimides (qv) are available as films, fibers, enamels or varnishes, adhesives, matrix resins for composites, and mol ding powders. They are used in numerous commercial and military aircraft as stmctural composites, eg, over a ton of polyimide film is presently used on the NASA shuttle orbiter. Work continues on these materials, including the more recent electronic apphcations. 

In addition to carbon and glass fibers ia composites, aramid and polyimide fibers are also used ia conjunction with epoxy resias. Safety requirements by the U.S. Federal Aeronautics Administration (FAA) have led to the development of flame- and heat-resistant seals and stmctural components ia civiUan aircraft cabias. Wool blend fabrics containing aramids, poly(phenylene sulfide), EDF, and other inherently flame-resistant fibers and fabrics containing only these highly heat- and flame-resistant fibers are the types most frequently used ia these appHcations. 

Printed circuit boards manufacture is aided by the use of KMnO. Alkaline permanganate solution is used to remove resin smeared on the interior hole wall of multilayered printed circuit boards. Additionally the hole wall is etched, resulting in a surface with excellent adhesion characteristics, for electrodeless copper (250). The alkaline permanganate etchback system containing >60 g/L KMnO and 40-80 g/L NaOH at 70—80°C, is effective for difunctional, tetrafiinctional, and polyimide resin substrates, where the level of etchback is direcdy proportional to the immersion time (10—20 min) (251). 

A variety of polyetherimides have been described in reviews on polyimides (qv) (88). Many more recent materials have additional heterocycHc units such as quinoxaline and ben2imida2ole units, besides the ether and imide functionahties (89). 

An interesting approach to thermosetting acetylene-terminated polyimides via the Michael addition reaction has appeared (38). Acetylene-terminated aspartimides are readily prepared ia high yield via two routes, shown ia Figure 7. 

Resins for advanced composites can be classified according to their chemistry typical resins are polyaryletherketones, polysulfides, polysulfones, and a very broad class of polyimides containing one or more additional functional groups (Table 2) (see also Engineering plastics). 

In addition they may contain ether, amide, carbonyl, sulfone, or other functional groups. References 28 and 29 provide excellent reviews of polyimide chemistry. 

In 1990 the majority of U.S. PCB production resulted from subtractive or print-and-etch processing additive processes were less than 6% of the total multilayer boards accounted for 55.8%. The ratio of rigid to flexible surface areas plated is about 15 1. High performance plastics including polyimide. Teflon, and modified epoxy comprised 6% of the market ( 324 million) flexible circuits were 6.6% ( 360 million) (42). 

To achieve low stress embedding material, low modulus material such as siUcones (elastomers or gels) and polyurethanes are usually used. Soft-domain elastomeric particles are usually incorporated into the hard (high modulus) materials such as epoxies and polyimides to reduce the stress of embedding materials. With the addition of the perfect particle size, distribution, and loading of soft domain particles, low stress epoxy mol ding compounds have been developed as excellent embedding materials for electronic appHcations. 

Additive Polyimides. Rhc ne-Poulenc s Kin el molding compound and Kerimid impregnating resin (115), Mitsubishi s BT Resins (116), and Toshiba s Imidaloy Resin (117) are based on bismaleimide (4) technology. Maleic anhydride reacts with a diamine to produce a diimide oligomer (7). Eurther reaction with additional diamine (Michael addition) yields polyaminohismaleimide prepolymer with terminal maleic anhydride double bonds. Cure is achieved by free-radical polymerization through the terminal double bonds. 

Tan et al. investigated polymers made from bis-benzocyclobutenes [13-15]. As the benzocyclobutane is analogous to tbe dien, tbe Diels-Alder addition takes place. This reaction is applied to the preparation of polyimides. The advantage of this system is that the resultant polymer is oxidized to form thermally stable aromatic polyimides (Fig. 7). 

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. 

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)... 

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