Separation of oligoolefins from industrial polyolefins

Very little work has been published dealing with the light products in high-pressure free radical polymerization of ethylene. Kohayashi [947] has examined the liquid fraction produced during high-pressure polymerization of ethylene in a stirred autoclave at pressures from 1200 to 1600 atm. He reported the liquid fraction to be a complex mixture and identified several individual compounds. 

Chromatographic analysis of the liquid residue extracted from a resin and of the oils condensed from the vapor phase again reveal a peak-for-peak correspondence showing the continuity of these materials. To determine how the low molecular weight fractions fit into the overall polymer MWD, a commercial low-density resin was analyzed by GPC (gel permeation chromatography). The gel chromatogram shown represents about 30 wt% of the total sample. A closer ex- 

The differences in the structures and quantities of oligoethylenes represent the differences in the reactions producing them. The first type of oligomers is considered to be due to the particular chain transfer agent used in the polymerization process, the second to monomer impurities, and the third to both these origins. 

The main consequence of these studies is that the formation of the oil in industrial high-pressure polyethylene is determined by the structure of the chain transfer agent used in the polymerization process and by the nature of the impurities of the monomer. 

A partial analysis of the low molecular weight oil fraction produced in the low-pressure polyethylene obtained with Ziegler catalysts is given by Turcu et al. [952], This study reveals that the impurities of the monomer improve the formation of the oligoethylenes and that the increase of the partial pressure of the monomer results in the decrease of the oligomer amount in the industrial polyethylene. 

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