Characterization of the molecular weight distribution of isotactic polypropylene by turbidity at the lower critical solution temperature (LCST)

The molecular weight distribution (MWD) of high-molecular-weight isotactic polypropylene is measured by a new method developed for polyethylene (PE) using the turbidity at the lower critical solution temperature (LCST). The attenuation of transmitted light h_i is measured at T_i as each fraction i is separated from the solution during a temperature increase ΔT_i. From the thermogram, the set of h_i (T_i), the MWD can be calculated through a relation M_i = f(T_i). The solvent chosen, a mixture of butane and 2-methylbutane, optimizes resolution and relatively rapid dissolution. Homogenization and absence of degradation are verified by different methods including calorimetry in solution. © 1992 John Wiley & Sons, Inc.