Polyimides via Regioselective Friedel-Crafts Hydroxyalkylation Polycondensation with Reaction-Enhanced Reactivity of Intermediate Mechanism

Owing to their excellent comprehensive properties, polyimides have long been regarded as indispensable high-performance materials. They are mainly synthesized via complicated and energy-intensive conventional processes that rely on inefficient imidization reaction between dianhydrides and diamines. In this paper, we reported our findings on the facile, mild, nonstoichiometric, highly efficient, and atom-economical regioselective Friedel-Crafts hydroxyalkylation polycondensation for the synthesis of polyimides with novel triarylmethane backbone structure. In this revolutionary approach, imide groups are not formed during polycondensation but are already present in the monomer structure. Taking advantage of the high efficiency and reaction-enhanced reactivity of intermediate characteristics of the Friedel-Crafts hydroxyalkylation, high molecular weight linear polymers can be prepared with no need for stoichiometric feeding or harsh reaction conditions, and polyimide with diverse chain structures can be obtained through the design of functional monomers. The reaction system employed linear molecules containing a central imide group flanked by two p-methylanisole terminals as nucleophilic monomers and to react with benzaldehyde derivatives bearing para electron-withdrawing substituents functioning as electrophilic monomers, with triflic acid serving as the catalyst. The resulting polymers maintain the outstanding thermal stability characteristic of polyimides, with 5% weight loss temperature (Td,5%) up to 415°C. The introduction of this polycondensation for synthesizing polyimide could solve many problems faced by the conventional method and will offer new opportunities in the production and application of polyimide materials.