Liquid-Liquid Phase Separation in Multicomponent Polymer Systems: Influence of Molar-Mass Distribution on Shadow Curve and Phase-Volume Ratio

Abstract

The effect of the molar-mass distribution (MMD), in particular the effect of a few higher molar-mass averages, on liquid-liquid phase behaviour is studied with the aid of data based on the Flory-Huggis-Staverman model. The critical concentration and the critical slopes of the cloud-point curve and the shadow curve appear to be quite sensitive to mz and mz+1, and, theoretically, they could serve as a unique data source for estimating these averages. In practice, however, experimental difficulties and errors encountered, especially with the shadow-curve slope determination, are probably too great for these data to be of any use. Next, the entire cloud-point and shadow-curves, and phase-volume ratios are examined with respect to the possible use to supply information on the MMD. At constant weight- and number-average molar mass, the cloud-point curve does not appear to be overly sensitive to Mz-average in the studied range. As to the other curves, no simple relationship evolves either, higher averages and details of the MMD both determining shape and location of shadow and phase-volume curves. An alternative procedure is suggested which consists of fitting a set of delta functions to a series of data points.