Polydiene rubbers degradation

Thermoplastic elastomers (TPEs) with blocks of polydiene rubber are subject to degradation at the carbon-carbon double-bond sites and require proper stabilization. In SIS block copolymers, chain scission is the predominant degradation mechanism. In an SIS block copolymer, the addition of a more effective stabilizer, AO-3, alone or blended with a secondary antioxidant, PS-1, can provide a significantly superior performance over AO-1 alone or with PS-1. Resistance to discoloration after static oven aging at 80°C (176°F) is improved dramatically (Fig. 5). Viscosity stabilization (melt flow index stability) (Fig. 6) is also improved drastically using AO-3/PS-1. 

Polydiene rubber is a common low voltage electrical insulation material, used because of its low electrical conductivity and elasticity. But, it can degrade rapidly by peroxidation, even if there are antioxidant stabilisers in the system, which can lead to electrical shortages and fires. Polydiene rubbers are recently being replaced by saturated ethylene-propylene (EP) rubbers or plasticised PVC. 

Polydiene rubbers were used for many years in low voltage electrical insulation because of their low electrical conductivity and flexibility. However, the traditional rubbers degrade by peroxidation relatively rapidly even when stabilised with antioxidants. This frequently leads to fires due to electrical shortage and, in recent decades, they have been largely replaced with saturated elastomeric materials e.g. EP rubbers... 

Degradation by the Action of Ozone. The degradation of polydiene rubbers by the action of atmospheric ozone is characterized by the appearance of cracks on the surface of a finished rubber product. This degradation is caused by direct ozone attack and reaction with the double bond sites of unsaturation in a polydiene rubber. 

Due to their main chain double bond, polydiene rubbers are prone to oxidative degradation and can be cross-linked by reactive resins and sulfur compounds [227, pp. 233-261). Cross-linking can be achieved further by an electron beam (EB) and in presence of photoinitiators by UV radiation [228]. 

The simplest kinds of liquid diene rubbers are degradation products of normal polydienes and these are cross-linked via the remaining carbon-... 

Rubbers, often based on poly diene rubbers or else copolymers of dienes like 1,3-butadiene, were the first successful toughening additives, and they are effective partly because they have a low modulus, 100 to 500 times lower than that of most thermoplastic polymers. Unfortunately polydienes introduce chemical double bonds which are susceptible to UV, thermal and oxidative degradation. Hydrogenation removes some of them. Acrylic compounds and ethylene copolymers are also popular impact modifiers, and they do not necessarily introduce double bonds. 

The interest in the reaction of ozone with polydienes is due mainly to the problems of ozone degradation of rubber materials [1-4] and the application of this reaction to the elucidation of the structures of elastomers [5-8], It is also associated with the possibilities of preparing bifunctional oligomers by partial ozonolysis of some unsaturated polymers [9-12], Usually the interpretation of experimental results are based on a simplified scheme of Criegee s mechanism of C=C-double bond ozonolysis, explaining only the formation of the basic product - ozonides [13, 14],... 

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