Influence of homopolymer on the correlation hole in a homogeneous diblock copolymer.

A homogeneous, symmetric 1,4-polybutadiene-1,2-polybutadiene diblock copolymer containing a perdeuterated 1,4-polybutadiene block has been mixed with equal molecular weight 1,2-polybutadiene homopolymer and examined by small-angle neutron scattering (SANS). The undiluted diblock copolymer exhibits a well defined peak as measured by SANS which derives from the correlation hole effect. Addition of homopolymer initially shifts this peak to smaller scattering wavevectors and subsequently eliminates the correlation hole scattering. These results are in close agreement with the theoretically predicted scattering from homogeneous diblock copolymer-homopolymer mixtures, thus providing a method for determining the Flory-Huggins interaction parameter chi. The value of chi measured from the mixtures is found to be equivalent to that previously determined from undiluted diblock copolymer containing the same monomers, and at a similar composition.