Polyimides linear aromatic

Synthesis and Properties. In 1972, Du Pont marketed a series of linear aromatic polyimides called NR-150 (105) based on... 

Figure 10.6 Tentative representation of the CRU of a polynadimide. A is a linear aromatic polyimide chain of molar mass 1500 g mol1. The male and female complementary junctions are distinguished.

Fig. 14. Synthesis of linear aromatic polyimide by Diels-Alder reaction between a BMI and a biscyclopentadienone...

It is interesting that formation of a linear aromatic polyimide was observed as early as 1908 when a polyimide was formed by heating 4-aminophthalic anhydride ... 

On the one hand, linear aromatic polyimides have been generally used as electronic and aerospace materials because of their excellent mechanical strength, thermal, chemical and electronic/optic properties compared with other common amorphous polymers. Polyimides are also excellent membrane materials for gas separation due to their rigid chemical structures, allowing the production of larger functional free volume. Over the... 

In 1965, workers from DuPont first prepared a linear thermoplastic polyimide. When aromatic diamines are reacted with aromatic dianhydrides, aromatic tetracarboxylic acids, or dialkyl esters of aromatic tetracarboxylic acids, in a solvent such as DMF (Table 13.7), they were converted to a polyamic acid, which when heated, cured by cyclization (imide ring closure, or imidization). This ring closure is a condensation process, releasing either water, or an alkyl alcohol, or both [36]. 

It is well known that polymers based on linear aromatic and other cyclic structures promote char formation on degradation in nitrogen (Bair 1997). In Fig. 3,9 the polyimide retains nearly half of its original mass when heated above 800 °C, while at this high temperature the degradation of PVC yields a stable char of about 8 mass%.The remaining polymers completely decompose into volatile products above 600 °C. 

Synthesis and Properties. Several methods have been suggested to synthesize polyimides. The predominant one involves a two-step condensation reaction between aromatic diamines and aromatic dianhydrides in polar aprotic solvents (2,3). In the first step, a soluble, linear poly(amic acid) results, which in the second step undergoes cyclodehydration, leading to an insoluble and infusible PL Overall yields are generally only 70—80%. 

Nonthermoprocessible Condensation Polyimides. These are obtained from condensation of aromatic dianhydrides with aromatic diamines. They are linear noncross-linked resins but their rigid chain stmcture and strongly hydrogen-bonded character leads to systems which do not melt or soften before decomposition. 

The most important application for bismaleimide resin is multilayer boards. The development in this area requires resins with low dielectric constants. It is well documented in the literature that fluorine containing linear polyimides show lower dielectric constants vis a vis their non-fluorinated counterparts. Recently, Hitachi Research Laboratory, Japan, reported the thermal and dielectric behaviour of fluorine-containing bismaleimides (29). The chemical structures of the fluorinated BMIs investigated are provided in Fig. 6. The non-fluorinated four aromatic rings containing BMI, 4,4 -bis(p-maleimidophenoxyphenyl) propane, was tested in comparison. 

Considerable research effort has been devoted in recent years to the use of chloral derivatives for the synthesis of linear heterocyclic polymers. Of these, the most common are aromatic polyimides [1-12], Many of these polymers have been synthesised from compounds like 4,4 -diaminobenzophenone, and other diamines, which, as demonstrated in the previous chapter, can be obtained from chloral. Polyimides prepared from these diamines were largely synthesised by the conventional two-step procedure [11, 12] involving mild reaction of the diamines with the bis(phthalic)anhydrides, isolation of poly(o-carboxy)amide (PCA) prepolymers, and then processing into products followed by thermal or chemical imidisation [13—16] (Scheme 3.1). Some properties of polyimides prepared from 4,4 -diaminobenzophenone are provided in Table 3.1. 

The double bond of maleimides in very reactive towards electron-rich dienes, to give a normal Diels-Alder cycloaddition. Thus BMIs were used to obtain linear polyimides by reaction with several kind of dienes [46-51]. However the dienes are often difficult to prepare [51] and functionalized dienes have been used. Furan terminated oligomers react with BMIs at 70 °C leading to an oxygen-containing cycloadduct [52-57] which can react with acetic anhydride to give an aromatic imide (Fig. 13) [58-59]. 

Because of their toughness, flexibility and remarkable thermal stability, linear all-aromatic polyimides are excellent candidate film and coating materials for advanced electronic circuitry and wire coating applications. In past years, however, the inherent insolubility (1-2) of these polymers has somewhat limited their usefulness for electronic applications. 

An example of how ab initio calculations may be applied to the study of fragments of polymer chains is given by Jaffe, Yoon, and McLean, who studied a series of mono- and diphenyl molecules containing up to 35 atoms. These compounds are models for a variety of important polymers such as polycarbonates (see Figure 1), polyimides, aromatic polyamides, aromatic polyesters, and polyether sulfone. A variety of basis sets, representing linear combination of Gaussian functions to approximate Slater-type orbitals (STOs) as compiled in Table 1, were employed. 

SCHEME 27. Synthesis of linear polyimides, where R = alkene, aromatic moiety etc. 

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