Thermoplastic elastomers based on semicrystalline block copolymers

Thermoplastic elastomers are used in a wide range of applications due to easy processing by conventional methods like injection molding and extrusion. ABC triblock copolymers with two hard domain forming end blocks in a rubbery matrix of B are one way to approach thermoplastic elastomers. In this contribution we will compare polystyrene-block-poly(ethylene-alt-propylene)-block-polyethylene (PS-b-PEP-b-PE) and polystyrene-block-poly-(ethylene-alt-propylene)-block-polystyrene (PS-b-PEP-b-PS) triblock copolymers with similar middle block content with respect to their morphological and mechanical properties. Transmission electron microscopy (TEM) and scanning force microscopy (SFM) reveal for the PS-b-PEP-b-PE triblock copolymers a morphology consisting of PS cylinders and PE crystallites within a matrix of the PEP block. Mechanical characterization of these triblock copolymers demonstrated that for small strains the PS-b-PEP-bPE triblock copolymers exhibit the aimed smaller plastic deformations, i.e. better elastic properties, compared to the polystyrene based ABA type thermoplastic elastomers. However, at high strains the PS-b-PEP-b-PS triblock copolymers show a significantly better elastic recovery.