LIQUID-LIQUID PHASE-SEPARATION IN BINARY BLENDS OF A BRANCHED POLYETHYLENE WITH LINEAR POLYETHYLENES OF DIFFERING MOLECULAR-WEIGHT

Four binary blends were studied, each containing the same lightly branched polyethylene with one of a series of linear polyethylenes (LPEs) of varying molecular weight. Liquid-liquid phase separation was observed in all blend systems but one. The liquid-liquid phase separated regions were in the form of closed loops, asymmetrically placed at low linear polyethylene content. The liquid-liquid phase separated regions were found to decrease in size as the molecular weight of the LPE decreased, very slowly where the molecular weight of the LPE was high but more rapidly by the time that the molecular weight of the LPE fell to 2 x 10(4). In the fourth system, where the molecular weight of the LPE was 2500, no liquid-liquid phase separation was seen. This system fills a logical position in the sequence: the liquid-liquid phase separated region has reduced to zero in size at this very low LPE molecular weight. This communication contains additional data on systems previously studied in part - the liquid-liquid phase separated regions had been recorded only for temperatures just above the melting point of the LPE. Now, as a result of improved experimental techniques, the full liquid-liquid phase separated loops, including upper critical temperatures, are reported.