Styrene-butadiene rubber crosslink types

Sometimes the term reversion is applied to other types of nonoxidative degradation, especially with respect to rubbers not based on isoprene. For example, thermal aging of SBR (styrene-butadiene rubber), which can cause increased crosslink density and hardening, has been called reversion, since it can be the result of overcure and can also degrade a product s usefulness. 

For a long time elastomer materials were limited to thermoset type materials with permanent crosslinks, such as polyisoprene (natural rubber). However one major drawback with these materials was that they could not be recycled, which led to the development of thermoplastic elastomers (TPEs). One common example is styrene-butadiene-styrene (SBS). Since styrene and butadiene do not mix, the styrene breaks up when the SBS is heated allowing the material to be re-melted. TPEs offer considerable advantages over thermoset type elastomers ... 

A very special type of ABA block copolymer where A is a thermoplastic (e.g., styrene) and B an elastomer (e.g., butadiene) can have properties at ambient temperatures, such as a crosslinked rubber. Domain formations (which serves as a physical crosslinking and reinforcement sites) impart valuable features to block copolymers. They are thermoplastic, can be eaisly molded, and are soluble in common solvents. A domain structure can be shown as in Fig. 2. 

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