Deformation of matrix macromolecules in a uniaxially extended styrene-isoprene-styrene linear triblock copolymer

Abstract

The results of small angle neutron scattering experiments on a linear styrene-isoprene-styrene triblock copolymer, polystyrene weight fraction = 0.16, under uniaxial extensions are reported. A proportion of the triblock copolymer had perdeuterated isoprene blocks, this proportion of a quantity such that the Bragg scattering would be cancelled in the resultant small angle neutron scattering data leaving only the contribution from the molecular scattering of the labelled polyisoprene blocks. Radii of gyration parallel and perpendicular to the stretching direction have been obtained for bulk extension ratios between 1.0 and 2.2. The radii of gyration have been compared with the predictions of various theories of the configuration of polymer molecules in stretched, crosslinked elastomers. Parallel to the direction of stretch, the molecular deformation is greater than affine whilst perpendicular to the stretch direction the values of the radii of gyration suggest a greatly reduced molecular deformation. These results are tentatively attributed to enhanced stress fields set up by the motion of the relatively massive spherical polystyrene domains in the microphase separated block copolymer.