Styrene-Diene Thermoplastic Elastomers. Milestones and Recent Developments

One of the unique synthetic aspects of living polymerizations,in general, and living alkyllithium-initiated poymerizations specifically is the ability to prepare block copolymers by sequential monomer additions.  The development of styrene-diene-styrene thermoplastic, elastomeric block copolymers was based on several important discoveries, i.e. living anionic polymerization, block copolymer syntheses and the unique role of lithium as counterion for anionic diene polymerizations.  These discoveries will be briefly reviewed as well as general methods for the synthesis of these block copolymers.  The following recent advances will be described; sulfonated pentablock copolymers; high T_g end blocks; all (meth)acrylate TPEs; chain-extension of hydroxyl-functionalized TPEs with polyurethane blocks; TPEs with random styrene-butadiene elastomeric blocks; TPEs with asymmetric end blocks; dilithium initiators.