Polyimide-imide

The addition to alkenes normally leads to unstable adducts that lose carbon dioxide under the reaction conditions. The intramolecular cycloaddition of the sydnone (30) takes place at room temperature, however (Equation (5)) and the cycloadduct (31) has been characterized <86HCA927>. The unstable species formed by the loss of carbon dioxide are also azomethine ylides. It is therefore possible for a second 1,3-dipolar addition to take place, as illustrated in Scheme 6 for the reaction of 3-phenylsydnone with Al-phenylmaleimide <86TL317,92JA8414>. This 2 1 addition has been used as the basis of a synthesis of polyimides. Imides of the type (32) were used as the dipolarophiles and their reaction with 3-phenylsydnone gave linear polymers <87MM726>. 

The values for polyimide groups and the corresponding mesogenic length were derived from work carried out by the author [43] on the synthesis and characterisation of liquid crystalline polyimides. Imide groups contribute +2 and have a mesogenic length of 2. 

Potyimide adhesives S J SHAW Condensation and thermoplastic polyimides, imide prepolymers high-temperature stability... 

The conversion of polyamic acids into polyimides - imidization or dehydrocyclization - consists of the intramolecular formation of water from the polyamic acid to form a cyclic polyimide. It can be carried out in two ways, thermally and chemically. 

Two basic types of polyimides are of commercial significance. In the first type, which are unmodified polyimides, imide is the principal functional group present. In the second type, which are modified polyimides, other functional groups are also present modified polyimides include poly(amide-imide)s, polyesterimides, polyetherimides and polybismaleimides. The development of this large variety of modified polyimides has been stimulated by the desire to find materials which are more readily processable than the unmodified polyimides whilst retaining the same superior properties. 

VDP Polyimides. Polyimide films have also been prepared by a kind of VDP (16). The poly(amic acid) layer is first formed by the coevaporation and condensation of two monomers, followed by copolymerization on the substrate. The imidization is carried out in a separate baking step (see POLYIMIDES). 

The reactions of primary amines and maleic anhydride yield amic acids that can be dehydrated to imides, polyimides (qv), or isoimides depending on the reaction conditions (35—37). However, these products require multistep processes. Pathways with favorable economics are difficult to achieve. Amines and pyridines decompose maleic anhydride, often ia a violent reaction. Carbon dioxide [124-38-9] is a typical end product for this exothermic reaction (38). 

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). 

Syntheses. The presence of the ether and imide functionahties provides two general approaches for synthesis. Polyetherimides can be prepared by a nucleophilic displacement polymerkation similar to the haUde displacement inpolysulfone synthesis or by a condensation of dianhydrides and diamines that is similar to normal polyimide synthesis (see POLYIMIDES). 

Polymerization by G—G Goupling. An aromatic carbon—carbon coupling reaction has been employed for the synthesis of rigid rod-like polyimides from imide-containing dibromo compounds and aromatic diboronic acids ia the presence of palladium catalyst, Pd[P(CgH )2]4 (79,80). 

Polyimides have been synthesized by Diels-Alder cycloaddition of bismaleimides and substituted biscydopentadienones (81,82). The iatermediate tricychc ketone stmcture spontaneously expeU carbon monoxide to form dihydrophthalimide rings, which are readily oxidized to imides ia the presence of nitrobenzene. 

The diene undergoes Diels-Alder cycloaddition with dienophiles. Polyimides have been synthesized from various imide-containing benzocyclobutenes and dienophiles (83—85). 

Other Polyimides. In 1979, Rohm Haas introduced Kamax resin, which was thought to be an /V-methylamine imidization product of poly(methyl methacrylate) (118). The product was then withdrawn, but was reintroduced in the late 1980s. The partly imidized resins are similar to poly(methyl methacrylate) but have a higher glass-transition temperature. 

Closely related to the polyamides are the polyimides and derivatives such as polyamide-imides and polyether-imides. These are discussed in Sections 18.13 and 18.14. 

The successful introduction of the polyimides stimulated attempts to produce somewhat more tractable materials without too serious a loss of heat resistance. This led to the availability of a polyamide-imides, polyester-imides and the polybismaleinimides, and in 1982 the polyether-imides. 

The polyester-imides form yet another class of modified polyimide. These are typified by the structure shown in Figure 18.43. 

Over the years polymers have been produced suitable for use at progressively higher temperatures. Where this is a requirement, it is usual first to decide whether a rubbery or a rigid material is required. If the former, this has been dealt with by the author elsewhere." If the latter, it is usually convenient to look in turn at polycarbonates, PPO-based materials, polyphenylene sulphides, polysul-phones, polyketones such as PEEK and PEK, polyamide-imides, poly-phthalamides, fluoropolymers, liquid crystal polymers and polyimides. 

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... 

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