Amine and phenolic antioxidants have active hydrogen atoms in their molecules , this kindHAtoms are higher than those of molecular chainsHOriginally lively, it can be compared with the decomposed large Molecular chain free radicalR•orROO• Bind, thereby disrupting chain growth and acting as an antioxidant.
For example, antioxidantAwithROO,After effect, destroy的ROO，.
Reaction to generate new antioxidantAFree radicals. Whether this new free radical can initiate a chain reaction again is the key to determining whether a compound promotes oxidation or acts as an antioxidant. New free radicals are highly active and can cause new chain reactions; free radicals with low activity can only interact withanotherradical phase Combine to terminate the chain reaction and generate a relatively stable compound.
Such an antioxidant molecule terminates two Chain radical reaction.
Phenolic antioxidants are also easy to interact with chain free radicals It removes the ammonia atom and terminates the chain reaction of free radicals, and at the same time produces phenol
Phenolic oxygen free radicals are also in the same conjugate system as the benzene ring, so they are relatively stable and have low activity. They cannot initiate chain reactions, but can terminate another chain free radical.
Based on the above discussion, it can be summarized that effective antioxidants should haveHas the followingstructure.
LivelyHatoms, and the denier is higher than that on the main chain of the moleculeH Atoms must be active, and amines and phenols contain such HAtom. Introduce an electron-donating group (such as alkyl, alkoxybase, etc.), amine and phenolic antioxidants can be madeN—H , C—HThe polarity of the bond is weakened and it is easier to releaseHatoms, thereby improving the ability of the chain to terminate the reaction.
AntioxidantsThe activity of free radicals should be low to reduce the impact on polymer chains The possibility of triggering, but may also participate in the chain termination reaction•
As the crude system of antioxidant molecules increases , the effect of antioxidants is improved. Because the co-elimination system increases, the greater the degree of delocalization of the free radical’s single electron, the more stable the free radical becomes and avoids becoming an initiating free radical.
The antioxidant itself should be difficult to oxidize, otherwise it It is destroyed by oxidation. Cannot play its due role.
For phenolic antioxidants, due to the By increasing the number of substituents and their branches, and increasing the steric hindrance effect, phenolic oxygen free radicals can be protected by adjacent large groups, reducing the rate of reactions caused by gas attacks, that is, increasing the number of phenolic oxygen free radicals. stability, thereby improving its antioxidant properties.
In addition, polymer materials often During processing and molding, the antioxidant is too volatile and the consumption is high. Therefore, it is commonly used to increase the amount of antioxidants to increase the boiling point and reduce the temperature at high temperatures. lower volatility. To increase the weight, one is to increase the substituent, and the other is. is to increase the aromatic ring number. Therefore, common antioxidants are compounds with large molecular weight and complex structures. Antioxidants must have good compatibility with polymer compounds and good dispersion in polymer materials.
In recent years, the development trend of antioxidants is to develop High molecular weight antioxidants that have the dual functions of chain terminator and hydrogen peroxide decomposer. At the same time, attention should be paid to non-pollution and good compatibility with polymers.
