Molecular Structure of High Pressure Polyethylene:VII. Cloud Temperature of Some Commercial High Pressure Polyethylene Fractions

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On the fractions of some typical commercial high pressure polyethylenes, cloud temperatures from dilute xylene solution were measured. In the region of [η] >0.3-0.4, cloud temperatures of high pressure polyethylenes decreased with increasing molecular weight and showed very particular molecular weight dependency as compared with that of linear polyethylene which scarcely varied with molecular weight.<BR>Moreover, the molecular weight dependency of cloud temperature characteristically differed between samples, i. e., vessel-type polyethylenes showed much lower cloud temperature than that of tubular-type polyethylenes at the same molecular weight.<BR>In the "cloud temperature difference", in which the influence of short-chain branchings on the cloud temperature was eliminated, the molecular weight dependency also appeared and the differences between samples were further remarkably observed.<BR>The cloud temperature difference at low molecular weight region which has some positive value could be explained as caused by the branching dispersion in the fraction. On the other hand, the cloud temperature difference at high molecular weight region which has substantially large negative value could not be attributed to the branching dispersion or the degree of long-chain branching. The influence of the complicated long-chain branching having many short-chain branchings was suggested on this respect.
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