Toughening benzoxazines with hyperbranched polymeric ionic liquids: Effect of cations and anions

In the present work, we developed a type of novel hyperbranched polymeric ionic liquid (HBPIL) that was derived from 1-allyl-3-methylimidazolium (AMIM), 1-allyl-3-methylpyridinium (AMPy), or 1-allyl-1-methylpiperidinium (AMPIP) cation with different anions, tetrafluoroborate (BF4), bis (trifluoromethylsulfonyl) amide (NTF2), and hexafluorophosphate (PF6), to elucidate the role of cations and anions on the reactivity and mechanical properties. The blending of HBPILs with bisphenol-F-based benzoxazines decreased the temperature required for opening the rings of the benzoxazines and improved the mechanical performances and thermal behaviors of the formed polybenzoxazoles. Moreover, differential scanning calorimetry, TGA, and Fourier transform infrared data exhibited the following differences: (i) the curing process was correlated to the structural differences of the anions, and the onset temperature was lower for the HBPIL with the PF6 anion in comparison to those with the NTF2 and BF4 anions; (ii) the type of cation had a significant influence on the curing reactivity of the benzoxazines, with the highest catalytic activity observed for the HBPIL containing AMIM, compared to those with (AMPy) and (AMPIP). Furthermore, the higher catalytic activity of the HBPILs for the benzoxazines suggested a higher crosslink density of the cured resin, which enabled the glass transition temperature to shift to a higher value and enhanced the mechanical strength and thermal stability of the obtained polybenzoxazoles.