Anomalous Thermostabilization of Polybenzimidazoles by Ethylene Incorporation for Biobased Flexible Insulators

High-performance renewable polymer materials are highly required in a sustainable society. Here, unique biobased derivatives of polybenzimidazoles are produced from aromatic monomers 3-amino-4-hydroxybenzoic acid (34AHBA) and 4-hydroxycinnamic acid (4HCA), which are chemically converted into 3,4-diaminobenzoic acid (34DABA) and hydro-3,4-diaminocinnamic acid (h34DACA), respectively. A base catalyzed reaction of o-diamines and carboxylic acid was adopted to form an imidazole ring to prepare poly(2,5-benzimidazole) PBIBA from 34DABA, poly(2-benzimidazole-5-ethylene) PBICA from h34DACA, and its copolymers PBIBA-co-PBICA. PBICA has an alternate structure of benzimidazole and ethylene, while PBIBA-co-PBICA has an alternate structure of oligobenzimidazole and ethylene, meaning that cutting π-resonance continuity of benzimidazole repeats. Thermogravimetric analyses revealed that 20% incorporation of ethylene in PBIBA increased the 10% mass loss to 726 °C. Density functional theory calculations demonstrate that ethylene incorporation increases the interchain interaction between the benzimidazole trimer model, presumably because cutting π-resonance can increase the abilities of N–H proton donation and of −N═ proton acceptance of imidazole too stabilized by extended aromaticity. The ultrahigh thermoresistant insulators with good mechanical and dielectric properties were prepared, which may contribute to a next-generation wireless nanonetwork.