Polymer-reactive antioxidant reactions process

The above approach of mechanochemically initiated addition of reactive antioxidants on different polymers, such as rubbers and unsaturated thermoplastics such as ABS is illustrated here for thiol-containing antioxidants. For example, using thiol compounds (37) and (38) as the reactive antioxidants, Kharasch-type addition of the thiol function to the polymer double bond takes place during melt processing to give bound antioxidant adduct (see reaction 7) the polymer becomes much more substantive under aggressive environments. 

Al-Malaika, S. Suharty, N. Reactive processing of polymers mechanisms of grafting reaction of functional antioxidants on polyolefins in the presence of a coagent. Polym. Deg. Stab. 1995,49 (1), 77-89. 

Scavenging of R may explain retardation of autoxidation of polymers by QI, as a supporting antioxidant mechanism [75]. To explain the reactivity with alkyls, reactions of 1 -cyano-1 -methylethyl with PD llb,d, the derived BQDI 53 (R1 =isopropyl, R2=phenyl and R, R2 = phenyl) and BQMI 57 (R = H) were studied in the presence of catalytic amounts of organic acids [4], Four sites are available for a nucleophilic attack on the A, A -di substi tu ted BQDI positions 2 and 3 on the central ring and both nitrogens. The process is accompanied by PD regeneration. 

It is apparent that photo-oxidation of polymers is a complex and very important component of photodegradation of such materials. Detailed discussion of mechanism and the effects of these reactions is not part of this review. However, prevention of breakdown has a very obvious economic impact and a few generalizations on stabilization of polymers are relevant before the detailed discussion which follows in Volume 6, Chapter 19. Given that radiation produces free radicals, which become involved in a chain reaction, then any substance which preferentially absorbs the harmful radiation (a screen) or any substance which can efficiently remove radicals via non-reactive products (an antioxidant) will operate as a stabilizer. However, the planning and chemical design of stabilizers is not easy and Volume 6, Chapter 19 gives an excellent survey of just how complicated the process of stabilization can be. 

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