PHASE AND SUPERMOLECULAR STRUCTURE OF BINARY-MIXTURES OF LINEAR POLYETHYLENE FRACTIONS

The level of crystallinity, the interfacial content, and the supermolecular structure of binary mixtures of linear polyethylenes have been studied. The molecular weights of the parent fractions ranged from 1.3 x 10(4) to 8 x 10(6). For isothermally crystallized samples, the level of core crystallinity of the mixtures was found to be the same as that of the fractions when compared on the basis of weight-average molecular weight. However, for quenched samples, agreement between the mixtures and fractions is obtained when compared on a number-average basis. Starting with a series of high molecular weight fractions, which display randomly arranged Jamellae after rapid crystallization, spherulites begin to form in the mixtures when the number-average molecular weight is in the range (5-8) x 10(4). More regular spherulites develop with a further decrease in the molecular weight. An explanation is offered for the common observation of spherulites in unfractionated systems.