Radiation‐induced polymerization of ethylene in pilot plant. V. Molecular weight distribution of polyethylene

The molecular weight distribution of the polyethylene produced by radiation in a large‐scale pilot plant at pressures of 105–395 kg/cm 2 and temperatures of 30–80°C was determined by gel permeation chromatography and discussed in connection with the polymerization conditions. The bimodal molecular weight distribution was observed in most of polymers. The number‐average molecular weight at two peaks are 10 4 , and 10 5 , respectively. The fraction of the peak at higher molecular weight increased with pressure and mean residence time, and with decreasing dose rate and temperature. The distribution was unimodal in the early stage of the operation and became bimodal, remaining unchanged in the later stage. The distribution also changed from bimodal to unimodal with rising temperature. These results were consistent with those in static batch experiments and well explained by the polymerization scheme assuming two physical states to be different in polymer mobility.