Abstract
The dependence of Flory-Huggins interaction parameter χ on temperature, composition, and chain length was investigated for binary blends of amorphous model polyolefins, materials which are structurally analogous to copolymers of ethylene and butene-1. The components were prepared by saturating the double bonds of nearly monodisperse polybutadienes (78 %, 88 %, and 97 % vinyl content) with H2 and D2, the latter to provide contrast for small-angle neutron scattering (SANS) experiments. Values of χ were extracted from SANS data in the single-phase region for two series of blends, H97/D88 and H88/D78, using the randomphase approximation and the Flory-Huggins expression for free energy of mixing. These values were found to be insensitive to chain length (one test only) and to the component volume fractions for ϕ= 0.25, 0.50, and 0.75. Their temperature dependence (27-170 °C) obeys the form χ(T) =A/T + B with coefficients that connote upper critical solution behavior, yielding Tc ∼ 40 °C for one blend series (H97A/D88) and Tc ∼ 60 °C for the other (H88/D78). These estimates are consistent with SANS pattern changes and supplemental light scattering results that indicate two-phase morphologies at lower temperatures. The χ(T) coefficients for the two series are also consistent with the random copolymer equation, although the interaction parameter obtained for branch C4‑linear C4 chain units is much larger than that found by Crist and co-workers for saturated polybutadienes with lower ethyl branch contents. © 1992, American Chemical Society. All rights reserved.