MEASUREMENT OF THERMODYNAMIC INTERACTIONS IN TERNARY POLYMER BLENDS BY SMALL-ANGLE NEUTRON-SCATTERING

The feasibility of evaluating thermodynamic interactions between polym er species by small-angle neutron scattering (SANS) measurements on te rnary blends was investigated. Results were analysed for two ternary s ystems of saturated hydrocarbon polymers by means of the multicomponen t random phase approximation (RPA) as applied to the Flory-Huggins (FH ) model. In one ternary blend-head-to-tail polypropylene, head-to-head polypropylene, and a saturated polyisoprene with 50% 3,4 content-the interaction coefficient X(T) had been determined independently by SANS measurements on binary blends for all three component pair combinatio ns, permitting a direct test of internal consistency for the ternary R PA. The ternary blend data were found to agree well with RPA predictio ns despite some highly unusual behavior among its binaries, including negative values of X(T) for saturated hydrocarbon pairs. In the other ternary blend-three statistical copolymers of ethylene (E) and 1-buten e (B) with different E-B compositions-values of X(T) were available fo r only two of the binaries, the third pair being immiscible over the r ange of available temperatures. The SANS data for the ternary blend we re used to evaluate the interaction coefficient for the third pair. Th e interaction coefficients obtained were smaller than values calculate d from previously assigned solubility parameters, a result that is dis appointing although nonetheless still consistent with results obtained for other strongly interacting pairs.