Phenolic antioxidants based on calixarene: Synthesis, structural characterization, and antioxidative properties in natural rubber

C-methylcalix[4] resorcinarene (CMCR) was first synthesized by condensation reaction between resorcinol and acetaldehyde, and then used as functional monomer to prepare two CMCR derivatives including CMCR-1 and CMCR-2 with four ethoxymethyl chains and four hexylthiolmethyl chains, respectively. The structures of CMCR and its derivatives were confirmed by Fourier transform infrared spectroscopy and high-resolution mass spectrometry. Thermogravimetric analysis revealed CMCR, CMCR-1, and CMCR-2 had superior thermal stability than commercial antioxidant 2,6-di-tert-butyl-4-methylphenol. Oxidation induction time and accelerated thermal aging tests indicated that CMCR-2 exhibited excellent antioxidative property in natural rubber, which was due to multiphenol groups, big steric hindrance, and synergistic effect between thiother and hindered phenol. Importantly, CMCR-2 also possessed outstanding extraction resistance. (C) 2017 Wiley Periodicals, Inc.