Supertough Thermoplastic Elastomers of Polystyrene and Polyisoprene via the Pom-Pom Topology

High-performance polystyrene (PS)–polyisoprene (PI) low-disperse thermoplastic elastomers with a well-defined pom-pom topology are synthesized via anionic polymerization techniques, where two stars with each about 13 PS-b-PI arms are connected by a linear PS chain, with PI forming the inner core of the star. Samples with 70, 50, 30, and 10 vol % total PS content were prepared. First, a PI-b-PS-b-PI triblock copolymer (short PI block, M w,PI = 5 kg mol–1, M w,PS = 100 kg mol–1) was synthesized via anionic polymerization; second, the PI blocks were functionalized via epoxidation; and third, PS-b-PI anions were grafted onto the outer PI parts of the backbone, forming the pom-pom topology. Mechanical tensile testing at room temperature found extreme strain hardening, resulting in very high true strain at break and stress at break (ultimate tensile stress, UTS). For the pom-pom with 30 vol % PS σUTS = 30 MPa and εb = 1200% and with 10 vol % PS σUTS = 20 MPa and εb = 1500% could be reached. The synthesized model pom-poms match the mechanical performance of the best PS–PI model systems reported in the literature, e.g., UTS of ca. σUTS = 20 MPa for linear and branched PS–PI model systems, and the pom-pom with 30 vol % PS outperforms the UTS reported in the literature by nearly 50%.