Synthesis and oxidative stability of hyperbranched macromolecule-bridged hindered phenols

Abstract

A series of hyperbranched macromolecule-bridged hindered phenols was successfully synthesized with 3-(3,5-di-tert-butyl-4-hydroxy-phenyl)-propionyl chloride and a series of 1.0 generation (1.0G) hyperbranched macromolecules. Their antioxidant ability was investigated by DPPH˙ scavenging assay and oxygen uptake test to establish the correlation between the alkyl-chain length of the core in the bridged group and antioxidant property of hyperbranched macromolecule-bridged hindered phenols. Effective concentration that scavenges 50% radical (EC₅₀), reaction rate that scavenges 50% radical (TC₅₀) and antiradical efficiency (AE) have been reported with DPPH˙ assay, and the results indicate that the antioxidant activity decreased with an increase in the alkyl-chain length of the bridged groups. The inhibition period (t_inh), the rate constant of inhibition (k_inh) and the stoichiometric factor (n) were used to evaluate the ability of inhibiting styrene against AIBN-induced oxidation for hyperbranched macromolecule-bridged hindered phenols. The results showed that the steric effect of the hyperbranched macromolecule-bridged hindered phenols increased with an increase in the alkyl-chain length of the bridged groups, which led to a decline in the reactivity between the hindered phenols and free radicals produced in the AIBN-induced oxidation process of styrene. For the simple free radical systems, the oxidative stabilities of the hyperbranched macromolecule-bridged hindered phenols decreased with an increase in the alkyl-chain length of the bridged groups.