High temperature GPC of polypropylene

The highest temperature at which molecular weight distributions can be characterized by current techniques is 145°C. Supermolecular aggregates may exist at this temperature in polypropylene solutions in trichlorobenzene and other solvents. Dissolution procedures at higher temperatures are ineffective in this case because of the limited thermal stability of polypropylene. Aggregate‐free solutions can be prepared, however, by controlling storage times at 145°C in mixtures with added stabilizers. Low angle laser light scattering measurements can be used to determine when true solutions have been produced. This occurs when measured second virial coefficients agree with values predicted for the Mw measured in the light scattering experiment. GPC–LALLS measurements of Mw and Mz provide similar information about the effects of storage time on dissolution of aggregates and polymer degradation.