Crown Ether-Functionalized Polybenzoxazine for Metal Ion Adsorption
Mohamed Gamal Mohamed, Shiao‐Wei Kuo
Abstract
In this study, we synthesized a new crown ether-functionalized benzoxazine monomer (crown-ether BZ) in high yield and purity through reduction of the Schiff base prepared from a dibenzo[18]crown-6 diamine derivative and salicylaldehyde and subsequent reaction of the resulting o-hydroxybenzylamine species with CH2O. We used differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis to examine the thermal ring opening polymerization and thermal stability of the crown-ether BZ monomer during various types of thermal treatment. DSC revealed that this crown-ether BZ monomer featured a relatively low curing temperature (210 °C; that of the typical Pa-type 3-phenyl-3,4-dihydro-2H-benzooxazine monomer: 263 °C) because the flexibility of the crown ether moiety on the main chain backbone structure catalyzed the ring opening polymerization. We also used DSC, FTIR spectroscopy, and ionic conductivity measurements to investigate the specific metal–crown ether interactions of crown-ether BZ/LiClO4 complexes. The presence of Li+ ions decreased the curing temperature significantly to 186 °C, suggesting that the metal ions functioned as an effective catalyst and promoter that accelerated the ring opening polymerization of the crown-ether BZ monomer. The ionic conductivity reached 8.3 × 10–5 S cm–1 for the crown-ether BZ/LiClO4 = 90/10 complex after thermal curing; this value is higher than those of typical polymer-based systems (e.g., PEO, PCL, PMMA, and PVP) while also providing a polymer electrolyte of higher thermal stability.