Synthesis and Evaluation of Novel Thermoplastic Elastomers via Anionic Polymerization of Bio‐Based α‐Methyl‐ <i>p</i> ‐Methylstyrene

ABSTRACT In this study, we examined novel thermoplastic elastomers employing α ‐methyl‐ p ‐methylstyrene (AMMS) as the monomer for the hard segment, which is an aromatic vinyl monomer derived from bio‐based limonene. Combining with isoprene (I) as the soft segment, PAMMS‐PI‐PAMMS triblock copolymers were synthesized via sequential anionic polymerization and coupling reactions. The resulting bio‐based block copolymers were evaluated in terms of thermomechanical property and microphase‐separated morphology by varying molecular weight, AMMS content, and vinyl content in I units. The triblock copolymers did not show well‐organized microphase separation by dynamic mechanical analysis and AFM/SAXS measurements, although the materials exhibited high elongation at break and low viscosity in melt. Upon the hydrogenation of the isoprene units, however, the microphase‐separated structure became more distinct, and the α‐relaxation temperature of the copolymers by dynamic mechanical analysis exceeded that of conventional styrenic elastomers.