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Toward Strong Thermoplastic Elastomers with Asymmetric Miktoarm Block Copolymer Architectures
CALIFORNIA UNIV SANTA BARBARA
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Thermoplastic elastomers TPEs are designed by embedding discrete glassy or semicrystalline domains in an elastomeric matrix. Typical styrenic-based amorphous TPEs are made of linear ABA-type triblock copolymers, where the volume fraction f of the glassy domains A is typically less than 0.3. This limitation ultimately restricts the range of mechanical strength attainable with these materials. We had previously predicted using self-consistent field theory SCFT that ABA n miktoarm block copolymers with an approximately 81 ratio of the A to A block molecular weights and n 3 should exhibit discrete A domains at considerably larger f and offer potential for the combination of high modulus, high recoverable elasticity, and high strength and toughness. Using transmission electron microscopy and small-angle X-ray scattering on model polystyrene-b-polyisoprene PS-PI miktoarm copolymers, we show that such polymers indeed possess discrete PS domains for f values considerably higher than 0.3. The hexagonal morphology with PS cylinders was achieved for f 0.5 and n 3. Mechanical testing indicates that these miktoarm materials are strong, tough, and elastic and thus may be potential candidates for a new generation of thermoplastic elastomers.
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