A tetraphenylethylene-functionalized benzoxazine and copper(II) acetylacetonate form a high-performance polybenzoxazine

In this study, we synthesized TPE-BZ, a new tetraphenylethylene (TPE)-functionalized benzoxazine (BZ) monomer (1,1,2,2-tetrakis(3-phenyl-3,4-dihydro-2H-benzo[e] [1,3]oxazin-6-yl)ethane), through reduction of the Schiff base formed from TPE-4OH–CHO (1,1,2,2-tetra(3-formyl-4-hydroxyphenyl)ethylene) and aniline and subsequent reaction with paraformaldehyde. Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance spectroscopy, and mass spectrometry confirmed the structure of the TPE-BZ monomer. We used differential scanning calorimetry (DSC), FTIR spectroscopy, and thermogravimetric analysis (TGA) to investigate the thermal ring opening polymerization (ROP) and thermal stability of the TPE-BZ monomer after thermal treatment at various temperatures (from room temperature to 250 °C). The TGA profiles revealed that thermal treatment at 250 °C under a N2 atmosphere gave a poly(TPE-BZ) that possessed excellent thermal stability and a high char yield (435 °C, 64.3 wt%). Furthermore, water contact angle measurements of the poly(TPE-BZ) obtained at 210 °C for 2 h indicated a relatively low surface free energy (18.6 mJ m−2), presumably because of strong intramolecular hydrogen bonding between the phenolic OH groups and the N-Mannich bridge in the polybenzoxazine matrix. We also employed DSC, FTIR spectroscopy, and TGA to examine the specific interactions in TPE-BZ/Cu(acac)2 complexes. DSC analysis revealed that blending the TPE-BZ monomer with various weight ratios of Cu(acac)2 lowered the thermal curing temperature of TPE-BZ from 250 to 239 °C, accompanied by a lower curing temperature at 189 °C. Using the Kissinger method, the activation energy of the TPE-BZ/Cu(acac)2 complex (127 kJ mol−1) was lower than that of the TPE-BZ monomer (141 kJ mol−1), suggesting that Cu(acac)2 functioned as a catalyst that initiated ROP of the oxazine units, while providing a product that retained high thermal stability.