The free radical scavenging ability of dopamine on the properties of peroxide vulcanized silicone rubber

EPR spectra and DFT calculations was used to reveal the hindering mechanism of polydopamine on vulcanization, the results showed that the bond dissociation energy of polydopamine was lower than rubber matrix, so it prioritizes reacting with benzoyl peroxide, resulting in the conversion of active free radicals into stable free radicals, thus hindering the vulcanization of rubber. • Dopamine affects the curing of silicone rubber by trapping free radicals when benzoyl peroxide is used as curing agent. • Electron paramagnetic resonance and reaction products showed that dopamine converted active free radicals into stable free radicals. • DFT calculations showed that benzoyl peroxide was more inclined to snatch hydrogen atoms from dopamine than from the rubber matrix, which led to the depletion of benzoyl peroxide and inadequate curing. Antioxidants are usually used to improve the anti-aging properties of rubber, however, which will hinder the vulcanization of rubber. It is great significance to reveal the hindrance mechanism for the preparation of high performance composites. There, a series of silica and dopamine modified silica filled silicone rubber compound were prepared, with benzoyl peroxide (BPO) as vulcanizator. The results show that, dopamine would inhibit the crosslinking of BPO, resulting in the decrease of the crosslinking density and the mechanical properties. Based on the vulcanization mechanism of BPO, it is speculated that dopamine hinders vulcanization by providing H atoms to consume BPO. The reaction product benzoic acid (BA) was detected on the surface, which was confirmed by mass spectrometry, 1 H NMR, FT-IR, and XPS, which confirms the conjecture. EPR and DFT analysis further explained the hindrance mechanism of polydopamine (PDA) on vulcanization, which indicates that BPO preferentially abstract hydrogen from PDA rather than rubber, due to the low bond dissociation energy of PDA. This leads to the consumption of BPO, and reduces the concentration of free radicals used for vulcanization, resulting in insufficient crosslinking. Understanding the reaction mechanism of dopamine and BPO is of great significance for screening antioxidants for peroxide crosslinking system.