The reactive modification of polyethylene. I: The effect of low initiator concentrations on molecular properties

Abstract Commercial samples of high density, linear low density, and low density polyethylene were modified by injection of low concentrations of free radical initiator during extrusion. Molecular properties monitored included molecular weight distribution, degree of unsaturation, and branching. When the polyethylene teed to this reactive extrusion process had similar values of Mw, but varying polydispersity, degree of branching and degree of unsaturation, the magnitude of the change in molecular weight distribution was found to be in the following order: HDPE 1 > LDPE2 > LLDPE. In general, terminal vinyls enhanced molecular weight increase, and branching promoted degradation. However, for a second high density polyethylene sample with Mw = 154,000 (rather than the previous sample's Mw of 85,600), the change in molecular weight distribution was small and located at the lower molecular weight end. This work provided data for the kinetic model development detailed in Part II.