Substantial reduction of benzoxazine curing temperature using a chloroaluminate ionic liquid catalyst

Abstract

This study investigates the use of an aluminum-based ionic liquid (Al-N-IL) as a highly efficient catalyst to mitigate the high curing temperatures of benzoxazines. The Al-N-IL catalyst was synthesized in a 1:1 molar ratio of Et₃NHCl-AlCl₃ and then incorporated at various loadings into three structurally distinct benzoxazine monomers. Differential Scanning Calorimetry (DSC) demonstrated a drastic reduction in the cationic Ring-Opening Polymerization (ROP) temperature for all monomers. Most notably, the peak polymerization temperature (T_max) for bisphenol A, aniline based monomer was lowered from 238 °C to an exceptionally low 133 °C. NMR tracking at room temperature showed catalytic latency for a certain time that the Al-N-IL complex is stable and does not liberate free AlCl₃ to trigger premature ring opening. Thermogravimetric Analysis (TGA) revealed that while the catalyst significantly lowers the cure temperature, it also exhibits a degradation/evaporation at high temperatures.