Efficient transformation of renewable vanillin into reprocessable, acid-degradable and flame retardant polyimide vitrimers

Efficient transformation of renewable resources and the production of high performance polymers through a simple and environmentally friendly method remains a great challenge. In this study, a reactive, bio-based, flame-retardant, hexasubstituted cyclotriphosphazene (HVP) was synthesized from lignin-derived monomer vanillin and hexachlorocyclotriphosphazene by nucleophilic aromatic substitution. Seven different diamines were used to cure the resulting HVP to prepare high performance polyimide vitrimers with dynamic imine covalent bond. The prepared HVP-diamine polyimide vitrimers could be hydrolyzed in acidic solution to recover 95 wt% of the HVP monomers. The polyimide vitrimers cured with alkyl containing diamines had higher limiting oxygen index (LOI) value (around 28 vol/%), and exhibited the V-0 rating in the UL-94 vertical burning test. The novel bio-based polyimide vitrimers demonstrate a number of advantages, including excellent mechanical performance, acid-degradability and flame retardancy and facilitate a more environmentally friendly and economical process than conventional thermosetting polymers.