CHEMICAL MODIFICATION OF POLYOLEFINS BY FREE-RADICAL MECHANISMS - A MODELING AND EXPERIMENTAL-STUDY OF SIMULTANEOUS RANDOM SCISSION, BRANCHING AND CROSS-LINKING

The chemical modification of polyolefins in the melt, using free radical mechanisms suitable for reactive extrusion, was studied. An algorithm to approximate the solution to an equation for simultaneous random scission and crosslinking1 is presented. This solution is compared to the classical two-step solutions of Saito2-5, Flory6 and Charlesby-Pinner7, showing significant deviations for the simultaneous random scission and crosslinking case. Suggestions to improve further the scission term of this equation are presented. Experiments were performed using high density polyethylene and peroxides in a minitruder and in small ampoule reactors. Gel fractions, thermal properties and molecular weights were measured. The heats of transition and melting temperatures as measured by differential scanning calorimetry were found to decrease with increasing peroxide level but were independent of reaction temperature. A pure random crosslinking model was found to fit adequately the gel fraction data.