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.