A THEORY ON PHASE BEHAVIORS OF DIBLOCK COPOLYMER HOMOPOLYMER BLENDS

The local structural and thermodynamical properties of blends A-B/H of a diblock copolymer A-B and a homopolymer H are studied using the pol ymer reference interaction site model (RISM) integral equation theory with the mean-spherical approximation closure. The random phase approx imation (RPA)-like static scattering function is derived and the inter action parameter is obtained to investigate the phase transition behav iors in A-B/H blends effectively. The dependences of the microscopic i nteraction parameter and the macrophase-microphase separation on tempe rature, molecular weight, block composition and segment size ratio of the diblock copolymer, density, and concentration of the added homopol ymer, are investigated numerically within the framework of Gaussian ch ain statistics. The numerical calculations of site-site interchain pai r correlation functions are performed to see the local structures for the model blends. The calculated phase diagrams for A-B/H blends from the polymer RISM theory are compared with results by the RPA model and transmission electron microscopy (TEM). Our extended formal version s hows the different feature from RPA in the microscopic phase separatio n behavior, but shows the consistency with TEM qualitatively. Scaling relationships of scattering peak, interaction parameter, and temperatu re at the microphase separation are obtained for the molecular weight of diblock copolymer. They are compared with the recent data by small- angle neutron scattering measurements.