Intcractions of Macroradicals in Polyethylene‐Polypropylene Blends

Abstract

AbstractTransfer reactions of primary radicals formed by decomposition of dicumyl peroxide in atactic polypropylene–polyethylene blends give rise to the corresponding macroradicals. A mutual recombination of polypropylene and of polyethylene macroradicals leads to the formation of hybrid copolymer. From the values obtained experimentally it follows that the total crosslinking efficiencyE of the blend (defined as a number of total crosslinks formed per mole of dicumyl peroxide decomposed) depends on the concentration of atactic polypropylene in the blend and not on the concentration of dicumyl peroxide. The decrease in the total crosslinking efficiency of the blend is attributed to scission reactions of polypropylene macroradicals. On the basis of kinetic analysis of the crosslinking process, relations expressing the dependence of the total and interpolymer crosslinking efficiencies of the blend (the latter defined as the number of crosslinks between polypropylene and polyethylene macromolecules per mole of dicumyl peroxide decomposed) on the concentration of polypropylene and polyethylene monomer units in the blend were derived. The calculated course of interpolymer crosslinking efficiency of blend is in good agreement with the values of the interpolymer crosslinking efficiency E' for the blends determined from the concentration of polypropylene bound in the crosslinked blends. For the ratio of the rate constants of transfer to polypropylene and polyethylene we obtained a value k3/k2 = 2.3. The influence of the microheterogeneity of blends on the relations derived is discussed briefly.