Imide oligomer, Nadic

To improve the processability of PI and to alleviate or eliminate volatiles, work began in the late 1960 s under NASA Lewis sponsorship (23), to end-cap oligomers with reactive groups. The first report involved the use of 3,6-endomethylene-l,2,3,6-tetrahy-drophthalic anhydride (5-norbornene-2,3-dicarbo ylic anhydride, nadic anhydride) and alkyl derivatives thereof (e.g. citraconic anhydride) and 1,2,3,4-tetrahydrophthalic anhydride (4-cyclohexene-1, 2-dicarboxylic anhydride) as the reactive end group on imide oligomers (23-25). This initial effort led to the development of P13N [with T for polyimide, 13 for Mn of 1300g/mole and N for nadic end cap] whose structure is shown below. 

Two types of reactive groups, ethynyl and nor-bomene (Nadic), have been placed on the ends of imide oligomers in an attempt to develop more processable high temperature PI adhesives. The thermal reaction of the ethynyl groups occurs without the evolution of volatiles, whereas the thermal reaction of the nor-bomene group may involve the release of a small amount of cyclopentadiene from the reverse Diels-Alder reaction (depending on con-... 

The structures and corresponding calculated MI values are given in Table 7 (nos. 1-5). Mesophases were observed for scores of MI=12 and 13 but not for the odd structures (MI range 9.5-11). In addition, a series of imide-amide oligomers were synthesised with molecular weights above 1000, in which the terminal groups were nadic anhydride. Mis ranged from 8.3 to 10.7 but no positive identification of mesophases were made in any of these (Table 7, nos. 6-9)... 

Nadicimide end-capped oligomers were usually prepared in two steps namely preparation of amine terminated nadicimide and chain extension with a dianhydride. Appropriate quantities of nadic or methyl nadic anhydride and diamine in glacial acetic acid were refluxed for several hours and the amine terminated nadicimide was recovered by precipitation. Then chain extension with 6FDA was carried out in acetone at 60 C. Chemical imidization of the amic acid to imide was carried out using sodium acetate and acetic anhydride [130,131]. Instead of diamines, triamines can also be used [132-134]. Chemical structure of nadicimide end-capped resins prepared from di and triamine (Figure 23) is given below. 

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