Controlled degradation of polypropylene

A discussion is presented of the two general categories of the degradative process: thermal degradation and peroxide-promoted degradation. The properties of controlled-rheology polypropylenes are examined. It is shown that as a result of the changes in the MWD, the polymers produced exhibit reduced viscosities and higher melt index values. The narrowing of the MWD and the elimination of the high-molecular-weight species result in a more Newtonian melt as shown by the flattening of the viscosity curve. The changes in the MWD also affect the extensional viscosity of the polymer. Even at low peroxide levels the extensional viscosity changes dramatically.