CHARACTERIZATION OF THE MOLECULAR-WEIGHT DISTRIBUTION OF POLYPROPYLENE AND POLYETHYLENE BY TURBIDITY AT THE LOWER CRITICAL SOLUTION TEMPERATURE

The characterization in butane of noncrystalline atactic polypropylene (ncPP) (1) with a narrow molecular weight distribution (MWD) is prese nted. It uses a new technique based on a thermogram, consisting of tur bidity peaks developed in a solution at a Lower Critical Solution Temp erature (LCST) during a step-by-step temperature increase. Several ref inements concerning the analysis of data have been added to the expres sions used in earlier work on polyethylene. The relation between the v olume of the concentrated phase and the attenuation of light has been developed from an expression of the scattered light by a biphasic syst em. The thermograms gave a good agreement in Mw and Mw/Mn for four wel l-characterized ncPP samples. Wide MWD isotactic PP samples (2) were a lso analyzed in a mixture of butane and 2-methylbutane. Solution behav ior at the LCST of 1 and 2 was compared.