PHASE BEHAVIOR AND INTERFACIAL MIXING IN BINARY POLYMER MIXTURES NEAR THE CONSOLUTE POINT.

Recently, we have discovered that mixtures of deuterated and protonated polymers, otherwise of identical chemical structure, do not form ideal solutions as generally assumed. Such isotopic polymer mixtures are actually characterized by a finite positive Flory-Huggins segment-segment interaction parameter 10** minus **4 less than multiplied by less than 10** minus **3. We have taken advantage of this effect in order to examine the interfacial profile in phase separated binary polymer mixtures near the consolute point. It is found that all four isotopic mixtures presently considered were found to phase separate at room temperature, as evidenced by the scattering of visible light. Samples PHI //D equals 0. 38, 0. 29 and 0. 20 are below the stability temperature, and exhibit a peak in the small-angle scattering of light which is indicative of phase separation via a spinodal decomposition mechanism. Sample PHI //D equals 0. 05 lies above the spinodal temperature but below the equilibrium phase boundary temperature, within the metastable gap. These mixtures have been located in the phase diagram obtained from the Flory-Huggins theory.