A chemiluminescence study on thermal and photostability of ethylene/alpha-olefin copolymers synthesized with rac-Et(Ind)(2)ZrCl2/MAO catalyst system

摘要

Copolymers of ethylene and alpha-hexene or alpha-octadecene were synthesised, and the relationship between their degradation and the type and content of comonomer was investigated by chemiluminescence, FTIR and thermogravimetric analysis. A clear effect of the length of branches on the thermal behaviour of copolymers was found. The insertion of octadecene caused the formation of a higher content of oxidised species in those copolymers. It may be related to the increase of length of branching which favoured the scission of the carbon-carbon bonds to form alkyl radicals in the earlier stages. It was observed that thermal stability decreased as the comonomer was incorporated. The isothermal CL curves under oxygen exhibited double stage, oxygen independent and oxygen diffusion controlled reactions. The intensity of CL of second stage, decreased and shifted to longer time as the comonomer content increased. This effect was attributed to crosslinking processes which are favoured with the increase of branching degree. Otherwise, for copolymers with high comonomer content, the chemiluminescence intensity enhanced and shifted to shorter time. It was associated to the decrease of the molecular weight, and as consequence, more reactive terminal groups which drives to the promotion of the initiation of thermal oxidation. Copolymers were UV-exposured and CL measured at different irradiation period of times. From the beginning, CL intensity slightly increased with time, followed by a drastically enhancement of emission intensity, and enhancement of chemiluminescence decay rate values, as result of degradation of samples and the higher mobility of peroxides to recombine. The results were supported by FTIR and TGA analysis, which revealed the higher degree of degradation for the copolymers as the comonomer content increased.