SPATIAL-DISTRIBUTION OF A MIDBLOCK-ASSOCIATING HOMOPOLYMER BLENDED INTO A TRIBLOCK COPOLYMER

The spatial distribution of a midblock associating homopolymer confine d within the lamellar microdomain structure of a triblock copolymer is probed with small angle neutron scattering experiments. The materials examined are poly(stryrene-b-[saturated 1,2-butadiene]-b-styrene) tri block copolymers to which a low molecular weight poly(saturated 1,2-bu tadiene) homopolymer has been added. The butadienes are saturated with either hydrogen, deuterium, or mixtures of the two gases in order to vary their neutron scattering contrast with respect to polystyrene. Th e results of contrast matching experiments demonstrate that there is a strong tendency for the homopolymer to localize at the center of the midblock microdomain. Experimental scattering profiles are modeled usi ng one-dimensional scattering density profiles in order to obtain a qu antitative description of the blend morphologies. This modeling indica tes that two distinct scenarios exist for homopolymer localization in a triblock copolymer: one wherein the microdomain structure contracts and a second wherein there is an expansion of the microdomain. Possibl e origins of this behavior are proposed on the basis of the considerat ion of the configurations available to the midblock sequence, that is, tie chains that traverse the midblock domain, or loops that enter and exit the midblock microdomain through the same interface.