Renewable Benzofuran Polymerization Initiated by Lewis Acid Al(C6F5)3 and Mechanism

The polymerization of a nature resourced aromatic compound benzofuran (BF) encounters the problems of low activity and molecular weight. Herein we report BF polymerization initiated by Lewis acids, which showed significant dependence on the type of Lewis acids, reaction solvents, and temperature. When a strong Lewis acid Al­(C6F5)3 was used, PBFs with high molecular weights (Mn = 17.9 × 104) and narrow molecular weight distributions (Mw/Mn = 1.56) were achieved for the first time. In addition, these PBFs are amorphous polymer possessing high glass-transition temperature (Tg = 210 °C), good thermal stability (Td,5% loss = 344 °C) as well as high transparency (transmittance >89%). The active species was isolated and characterized through NMR and X-ray diffraction analyses; meanwhile, the polymer chain ends were identified by MALDI–TOF MS and NMR studies, which allowed us to elucidate the mechanism for benzofuran polymerization.