Characterization of the molecular weight distribution of polypropylene and polyethylene by turbidity at the lower critical solution temperature

Abstract

The characterization in butane of noncrystalline atactic polypropylene (ncPP) (1) with a narrow molecular weight distribution (MWD) is presented. It uses a new technique based on a thermogram, consisting of turbidity peaks developed in a solution at a Lower Critical Solution Temperature (LCST) during a step-by-step temperature increase. Several refinements concerning the analysis of data have been added to the expressions used in earlier work on polyethylene. The relation between the volume of the concentrated phase and the attenuation of light has been developed from an expression of the scattered light by a biphasic system. The thermograms gave a good agreement in Mw and Mw/Mn for four well-characterized ncPP samples. Wide MWD isotactic PP samples (2) were also analyzed in a mixture of butane and 2-methylbutane. Solution behavior at the LCST of 1 and 2 was compared.