Reactions of Hindered Phenols with Unsaturated Hydrocarbons in the Presence of Free Radicals

Abstract

The reaction of hindered phenolic antioxidants , notably 2 ,6-
-ditert-butyl-4-methyl-phenol (TBC) and 3,5-ditert-butyl-4-hydroxy-benzyl
mercaptan (BHEM) with rubber has been investigated and the percentage
of antioxidant bound under optimum conditions has been determined. The
byproducts formed during the adduct formation and their effect on the
binding reaction was also studied.
The reaction mechanism involved in both cases has been studied.
It has been found that the BHBM adduct was formed by the addition of
thiol to the rubber double bond and that of TEC by the attachment of
the benzylic carbon atom to the allylic carbon atom of natural rubber,
Tensile measurements, oxygen absorption tests and stress relaxation
measurements have been used to evaluate the antioxidant activity of the
bound antioxidants. Comparison of their performances with commercial
antioxidants have shown that the latter are completely removed under
severe environmental conditions, whereas rubber-bound antioxidants
exhibit exceptional stability. A major advantage of the rubber-bound
systems, which has emerged during the evaluation was their suitability
for the preparation of bound antioxidant concentrates and the superior
performances of rubbers prepared using concentrated masterbatches
have been demonstrated under severe testing conditions.
Similar studies were carried out with nitrile-butadiene (NER)
latices and it has been found that NER containing bound antioxidants,
particularly, the BHEM adducts exhibit superior stability to conventionally
added antioxidants, when used in applications where loss of antioxidants
by volatilisation or leaching or by extraction may occur.

Date of Award	1977
Original language	English
Awarding Institution	Aston University