Mechanisms of antioxidant action: The catalytic rôle of iodine in the stabilisation of polypropylene

It is shown that I₂ is an effective melt stabiliser for polypropylene at 190°C in a closed mixer but that it is much less effective in an open mixer. The formation of HI and unsaturation in the polymer show that a catalytic antioxidant mechanism (CB-A/CB-D) is involved in the antioxidant activity of I₂ in a closed mixer similar to that occurring in the stabilisation of polyolefins with galvinoxyl and nitroxyl radicals.The processed polymer shows slightly greater uv stability than the control with no additive but is essentially similar to the control in thermal oxidative stability. The volatility of HI in an air oven probably accounts for the fact that it has no CB-D activity under these conditions.