The influence of molecular structure and molecular weight on antioxidants

There are many types of antioxidants, common antioxidants 1010, 168, 1076, 1024, 098, etc. Different types of antioxidants have different molecular structures and molecular weights, which leads to a great difference in the properties of different types of antioxidants.

Influence of molecular structure on antioxidants

1, the neighboring groups RI, 112 impact (1) If R1, R2 volume is large, the benzene ring and hydroxyl is not easy to be in the same plane, preventing the oxygen atom P orbital electrons and benzene ring on the electron co-choke, so that the substitution of phenol molecules lost due to resonance effect of the stabilization of the effect of the result is to make it easy for hydroxyl H detachment. (2) When R1, R2 volume is too large, but also because of the spatial obstruction makes the free radical is not easy to approach with the hydroxyl group, so it is not easy to play a role in capturing the free radical. Therefore, R2 should not be too large. In recent years, studies have shown that R1, R2 for t-Bu, its antioxidant efficiency is higher, because of the larger volume of t-Bu on the phenolic hydroxyl stereo-protection, so most of the hindered phenolic antioxidants are 2,6 position for the tert-butyl substituent. Recently, however, it has been found that semi-hindered phenolic structures with a methyl group and a tert-butyl group in the neighboring position of the phenolic hydroxyl group have better antioxidant effects. On the one hand, the spatial resistance of the tert-butyl group is sufficient to protect the phenolic hydroxyl group, and on the other hand, the antioxidant reaction rate of the methyl group in the neighboring position is faster, thus increasing the antioxidant activity. And it is more advantageous in NOx coloring resistance and co-stabilization with thioester auxiliary antioxidants.

2, the influence of para group R3 The difficulty of H detachment on the hydroxyl group is largely influenced by R3. (1) When R3 is an electron-withdrawing group, such as NO2, COOH, the detachment of hydroxyl H is easier than when there is no substituent. (2) When R3 is an electron-donating group, such as Me, t-Bu, the detachment of hydroxyl H is easier than when there is no substituent. (3) When R3 is a long-chain alkyl group, it is favorable to improve the compatibility and thus the efficiency of the antioxidant.

3, Molecular structure and compatibility When Rl, R2, R3 are alkyl groups or groups similar to the structure of the polymer, it increases the compatibility of the antioxidant with the polymer.

The effect of molecular weight on antioxidants

When polymer materials are thermally processed in air at 220-350t, antioxidants must be used to prevent oxidation during processing. Therefore, the thermal stability of the antioxidant used is very important. In recent years, studies have shown that increasing the molecular weight is an important means of improving the thermal stability and efficiency of antioxidants. However, it is not the case that the higher the molecular weight, the better, but there is an ideal molecular weight. Antioxidants with ideal molecular weight have higher efficiency. After years of research, it is shown that the ideal molecular weight for general antioxidants is between 500-1000, while for polymer antioxidants, it is between 1000-3000.