| Abstract
| - An isotactic polypropylene (iPP) sample (100% by FTIR) has been thermooxidized in thetemperature range 80−170 °C and the kinetics of the degradation followed by measuring the chemiluminescence intensity along the induction and autoacceleration stages. From those curves, the parameterp0, related to the initial concentration of oxidizable sites, has been calculated and compared to previousresults on other PP of different tacticity. A relationship between the relaxations and/or phase transitionstaking place in the temperature range under study and the temperature dependence of parameter p0 inthe four samples of fully or predominantly i-PP has been found. It is proposed that the discontinuities inthe rate of release of interchain interactions caused by these phase transitions or relaxations areresponsible for the slope of the temperature dependence of log p0. Polymers bearing α-relaxation show astrong decrease in p0 at temperatures under 115 °C which is absent in polypropylene samples where theα-relaxation is not resolved. As the α-relaxation has been attributed to the diffusion of chains from theamorphous to the crystalline phase and through the interphase, it is proposed that the α-relaxation makesit possible for crystals to act as radical scavengers and thus contribute to stabilize iPP at temperaturesunder 115 °C.
|
