DETERMINING THE TEMPERATURE-DEPENDENT FLORY INTERACTION PARAMETER FORSTRONGLY IMMISCIBLE POLYMERS FROM BLOCK-COPOLYMER SEGREGATION MEASUREMENTS

We have determined the segregation of diblock copolymers of deuterated polystyrene (dPS) and poly(2-vinylpyridine) (PVP) to a planar interfa ce between the homopolymers using forward recoil spectrometry. The seg regation isotherms, namely the interfacial excess versus its volume fr action in the homopolymer phase far from the interface, for the dibloc k copolymers were measured at several temperatures. Using a self-consi stent mean field (SCMF) theory, one can fit the segregation data accur ately if the Flory interaction parameter chi is treated as a fitting p arameter. Using this scheme, the temperature-dependent Flory interacti on parameter chi between PS and PVP was determined to be -0.033+63/T(K ). In contrast to this evaluation of chi which depends heavily on a mo del, we have shown that the isosteric heat of segregation q(seg) can b e directly extracted from the experimental data. We demonstrate that t he enthalpic portion of the Flory interaction parameter chi(H) can be estimated directly from q(seg), without recourse to a model of the seg regation layer, and the chi(H) from this direct method is in good agre ement with that determined using the SCMF theory. These two methods pr ovide a new approach for determining chi for strongly immiscible polym ers.