Polyimides containing phthalimides

An alternative order of introducing acylating reagents onto the bis[3-amino-4-(p-aminophenoxy)]-benzophenone, that is, the addition of first bis(phthalic anhydride) and then phthalic anhydride to the tetramine, yields polyimides containing predominantly N-phthalimide o-substituents (Scheme 3.7). These polyimides are characterised by higher viscosities and softening temperatures (Table 3.8) but poorer solubilities as compared to those polymerised according to Scheme 3.6. 

Structural modifications to attain soluble aromatic polyimides have also been carried out by introducing bulky substituents, aryl or heterocyclic rings. One of the first references to this approach was made by Korschak and Rusanov, who synthesized soluble aromatic polyimides containing side phthalimide groups [85 ]. More recent work by Rusanov et al. has enriched this topic with new soluble polyimides containing pendent imide groups [86,87]. 

Thermal dimerization of perfluoroalkcnes is also a good approach for obtaining interesting dimeric fluoro-substituted compounds. A -[4-Phenoxy-3-(trifluorovinyl)phenyl]phthalimide (3), which is a model for polyimides containing trifluorovinyl groups, undergoes thermal dimerization at 140-160"C to give predominantly the trtf .s-1,2,3,3,4,4-hexafluoro-l,2-bis(2-phenoxy-5-phthalimidophenyl)cyclobutane (4).6 See Section 2.1.1.6.2. for a more detailed discussion of this [2 + 2]-cycloaddition process. 

All LC-polyimides discussed in this review possess at least one phthalimide unit in the mesogenic unit and most of them contain an AT-phenyl phthalimide moiety. For a better understanding of the potential mesogenic character of aromatic imide groups it is useful to discuss briefly their stereochemical and conformational properties. 

In general, poly(naphthylimides) containing six-membered imide rings in backbones are characterised by significantly improved chemical resistance compared to analogous poly(phthalimides) [144-147]. A similar conclusion was made comparing the chemical resistance of sulfonated polyimides and poly(naphthylimides) [124,125]. 

Thianthrene-di-, tri-, and tetracarboxylic acids, and a variety of their derivatives, were prepared and polymerized with co-monomers to obtain thianthiene-containing polyimides, aramids and polybenzoxazoles. The multiply substituted thianthrene derivatives were prepared starting with dichloro-substituted benzamide or phthalimide via chlorine displacement by sulfur nucleophiles. The protected carboxyl groups enhanced the displacement reaction to give thianthrene bisamides and imides in good yields. Deprotection with base gave carboxylic acid derivatives. 

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