Thermoplastic elastomers (TPEs—sometimes called thermoplastic rubbers) are a chemically-bonded combination of multiple polymers ("copolymer")—typically a plastic and a rubber—that have both thermoplastic and elastomeric properties. The thermoplastic property is useful in injection molding, while the elastomeric property gives the object the ability to stretch and return to nearly its original shape. These materials are ubiquitous, for example, in the interiors and exteriors of vehicles. The best-known TPEs include "styrenic block polymers", which contain molecular blocks of polystyrene, which is hard, and polydiene, which is rubbery. Two important examples are polystyrene-b-polyisoprene-b-polystyrene (SIS) and polystyrene-b-polybutadiene-b- polystyrene (SBS). Styrenic block polymers were developed by the Shell Chemical Company in the 1960s and have since been further developed by many researchers in both academia and industry. While the annual global market for styrenic block polymer-based TPEs is worth several billion dollars, elastomers with enhanced mechanical properties, especially toughness, also remain in great demand.