DEFORMATION OF MATRIX MACROMOLECULES IN A UNIAXIALLY EXTENDED STYRENE-ISOPRENE-STYRENE LINEAR TRIBLOCK COPOLYMER

The results of small angle neutron scattering experiments on a linear styrene-isoprene-styrene triblock copolymer, polystyrene weight fracti on = 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 th e resultant small angle neutron scattering data leaving only the contr ibution from the molecular scattering of the labelled polyisoprene blo cks. Radii of gyration parallel and perpendicular to the stretching di rection have been obtained for bulk extension ratios between 1.0 and 2 .2. The radii of gyration have been compared with the predictions of v arious theories of the configuration of polymer molecules in stretched , crosslinked elastomers. Parallel to the direction of stretch, the mo lecular deformation is greater than affine whilst perpendicular to the stretch direction the values of the radii of gyration suggest a great ly reduced molecular deformation. These results are tentatively attrib uted to enhanced stress fields set up by the motion of the relatively massive spherical polystyrene domains in the microphase separated bloc k copolymer.