Effect of calixarenes on thermal stability of polyethylenes

The thermal degradation of some polyethylenes (one type of high density PE and two of low-density) was studied by isothermal chemiluminescence. Each polymer was stabilized by one of four phenolic additives: p-t-butylphenol (considered as reference), 2,4,6-tri-t-butylphenol, p-t-butylcalix[4]arene, and p-t-butylcalix[6]arene. Six kinetic parameters of thermal oxidation (induction period, maximum oxidation rate, half-period of ageing, maximum CL intensity, maximum degradation time, and activation energy) along with relative activity and stability were calculated. Protection efficiency of additives was evaluated by relative activity and relative stability indexes. Considerations of a stabilization mechanism involving calixarenes are presented. (C) 2003 Elsevier Science Ltd. All rights reserved.