Preformed Imide Groups

Aromatic copoly(amide—imide)s with Atriazine rings in the repeating unit of the backbone are also possible from a diacyl chloride reacting with preformed imide groups and diamines containing Atriazine rings (15). 

With the polyimides produced in situ, the imide group is simultaneously formed with the polymer. Synthesis and processing difficulties with polyimides formed in situ have led to the development of monomers and prepolymers with preformed imide groups. For example, maleic anhydride converts to what is known as bismaleimides with suitable diamines... 

Monomer and polymer syntheses of PAI were performed as reported previously (9). Diacids with preformed imide groups were reacted with diamines to yield the PAI in one step (9-11). The diphenol 2,2-bis(4-hydroxyphenyl)hexafluoropropane for the PEI synthesis was obtained from Aldrich. The analogous diol with 4 methyl groups ortho to the hydroxy moiety (2,2-bis(3,5-dimethyl-4-hydroxyphenyl)hexafluoropropane) was synthesized by condensing hexafluoroacetone hydrate with 2 moles of 2,6-dimethylphenol following a patent (12). PEFs were obtained from diacids and diols in dry N,N-dimethylformamide (DMF)/pyridine (1/1) and an excess (2.6 mole/mole diacid) of tosyl chloride (13). Reaction time was 3 to 5 h at 120 °C under a dry argon flux. Reduced viscosities (0.5% at 30°C in N-methylpyrrolidone (NMP)) of > 0.35 dUg were required for the preparation of free-standing, non-brittle, methanol stable films. 

Polybismaleimides utilize an approach to polyimide synthesis which is different from that used for the polyimides described above. In the latter cases, imidization takes place after polymerization has occurred. In polybismaleimides, preformed imide groups are present in low molecular weight intermediates which are subsequently polymerized. 

Diisocyanates containing an aliphatic sequence with phenylisocyanate end groups [111], and diisocyanates containing preformed imide rings [112], have been recently synthesized and used as monomers against aromatic dianhydrides. 

Our research group developed catalytic enantioselective protonations of preformed enolates of simple ketones with (S,S)-imide 23 or chiral imides 25 and 26 based on a similar concept [29]. For catalytic protonation of a lithium eno-late of 2-methylcyclohexanone, chiral imide 26, which possesses a chiral amide moiety, was superior to (S.S)-imide 23 as a chiral acid and the enolate was pro-tonated with up to 82% ee. 

Our research group independently found a catalytic enantioselective proto-nation of preformed enolate 47 with (S,S)-imide 30 founded on a similar concept (Scheme 5) [51]. The chiral imide 30, which has an asymmetric 2-oxazoline ring and is easily prepared from Kemp s triacid and optically active amino alcohol, is an efficient chiral proton source for asymmetric transformation of simple metal enolates into the corresponding optically active ketones [50]. When the lithium enolate 47 was treated with a stoichiometric amount of the imide 30, (K)-en-riched ketone 48 was produced with 87% ee. By a H-NMR experiment of a mixture of (S,S)-imide 30 and lithium bromide, the chiral imide 30 was found to form a complex rapidly with the lithium salt. We envisaged that a catalytic asym-... 

Yu and coworkers describe a technique to retain stability and maximize the electrooptic response. They preformed the imide structure with an aryl dihalide monomer and incorporated highly efficient chromophore groups before polymerization. This highly functionalized monomer was subjected to a Pd-catalyzed coupling reaction with 2,5-bis(tributyltin)thiophene to give the polymer... 

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