Synthesis and Properties of ABA and ABC Triblock Copolymers with Glassy (A), Elastomeric (B), and Crystalline (C) Blocks

We describe the synthesis, characterization, and properties of 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. Morphological investigations using TEM, SEM, and 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, whereas the PS- b -PEP- b -PS triblock copolymer shows interconnected, distorted PS cylinders in the PEP matrix. Mechanical characterization of these triblock copolymers demonstrated that for small strains the PS- b -PEP- b -PE triblock copolymers exhibit the aimed smaller plastic deformations, i.e. better elastic properties, compared to the polystyrene-based ABA type thermoplastic elastomer. However, at high strains the PS- b -PEP- b -PS triblock copolymer shows a significantly better elastic recovery. The high plastic set at high elongations in PS- b -PEP- b -PE triblock copolymers is attributed to the weaker resistance of the PE crystallites compared to amorphous PS domains in the PS- b -PEP- b -PS triblock copolymer.