Tuning enthalpic and entropic interactions in blends of block copolymer and polymeric additives

Block copolymer thermoplastic elastomers (TPE) are used for a wide range of applications including adhesives, footwear and automobile parts. However, durability of these materials is challenged by creep and stress relaxation behavior. Blending TPEs with miscible polymeric additives is a simple potential strategy to tailor their mechanical properties. In this work, we conduct a systematic study on the effects of interaction-tuned additives on the structure and mechanics of poly(styrene-b-ethylene butadiene-b-styrene) (SEBS), a widely used TPE. The additive used are linear poly(methyl methacrylate-co-cyclohexyl methacrylate). The enthalpic interaction between the additive and the polystyrene blocks is controlled by the mole fraction of cyclohexyl methacrylate, and the entropic interactions are tuned by the relative molecular weights. Blend structures are analyzed using small angle X-ray scattering, which shows that short chain additives that are miscible with polystyrene are distributed throughout the domain. These blends showed increased modulus and creep resistance in proportion to the strength of the favorable interaction (as captured by χ). This study provides a framework to manipulate the nanoscale structure and bulk mechanical properties of TPEs.