The results of small angle neutron scattering expertments on a linear styrene-isoprene-styrene triblock copolymer, polystyrene weight fraction = 0.16, under uniaxtal extensions are reported. A proportion of the triblock copolymer had perdeuterated rsoprene blocks, thus 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 scattermg of the labelled polyisoprene blocks. Radii of gyratton parallel and perpendtcular to the stretching directton have been obtained for bulk extension ratios between 1.0 and 2.2. The radii of gyration have been compared wtth 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 al&e whilst perpendicular to the stretch dnection 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.