SMALL-ANGLE X-RAY AND NEUTRON-SCATTERING FROM BULK AND ORIENTED TRIBLOCK COPOLYMER GELS

Gels of polystyrene-block-rubber-block-polystyrene were investigated b y small-angle X-ray (SAXS) and neutron (SANS) scattering. The rubber m idblock was either poly(ethylene/propylene) (PS-PEP-PS) or poly(ethyle ne/butylene) (PS-PEB-PS). The gels of these thermoplasts have similar superstructures consisting of domains of associated polystyrene (PS) b locks, connected by the midblocks which are dissolved in an extender o il. The microphase separation is more pronounced in the PS-PEP-PS gels and results in clear interdomain scattering maxima and form factor os cillations. The ordering of the PS domains is a function of block copo lymer concentration, molar mass, end block/midblock ratio, deformation , and temperature. Deformations up to 150% extension are reversible at room temperature. The scattering patterns of the unstretched samples were fitted with two different models: a hard-sphere liquid model and a model of a disordered solid with local coordination.