Effect of planar extension on the structure and mechanical properties of polystyrene-poly(ethylene-co-butylene)-polystyrene triblock copolymers

Two thermoplastic poly(styrene)-poly(ethylene-co-butylene) -poly(styrene) t riblock copolymers containing either spherical or cylindrical poly(styrene) microdomains were pre-oriented through extensional flow. Small angle neutr on scattering (SANS) measurements revealed that the pre-oriented triblock w ith a spherical microstructure adopts a body-centred cubic (bcc) structure with a [111] orientation along the Row direction. For the pre-oriented trib lock with a cylindrical microstructure, the cylinder axis is aligned along the extensional Row direction. Investigation of the mechanical properties s howed that Young's moduli of the pre-oriented copolymers are highly anisotr opic. Specimens were then subject to uniaxial deformation along the extensi onal Row direction and at the same time microstructural changes induced by the deformation were investigated by SANS. It was found that the deformatio n of the bcc lattice is affine, and that the deformation of the microstruct ure is reversible. For the triblock copolymer with a cylindrical microdomai n structure the deformation of the lattice was found to be non-affine. In t his case, SANS patterns suggest a "micronecking" and a breaking of the cyli ndrical domains without any change in the domain spacing. (C) 2000 Elsevier Science Ltd. All rights reserved.