LIQUID-LIQUID PHASE-SEPARATION IN TERNARY BLENDS OF LINEAR POLYETHYLENE WITH 2 ETHYLENE-BUTENE COPOLYMERS

A commercial ethylene-butene linear low density polyethylene has been fractionated by preparative temperature rising elution fractionation. Each fraction was characterized by Fourier transform infra-red spectro metry to determine the branch content and by gel permeation chromatogr aphy to determine the molecular weight. Two fractions were then blende d, in various proportions, with each other and with a linear polyethyl ene. Using differential scanning calorimetry and transmission electron microscopy to examine quenched blends, the phase behaviour of this te rnary system was investigated at temperatures above the melting point. The phase behaviour is very similar to that previously found for a te rnary system of a linear polyethylene with two ethylene-octene copolym ers with branch contents close to those of the ethylene-butene copolym ers used in the present work. We deduce that the phase behaviour of bl ends containing ethylene-butene copolymers is essentially the same as that of blends containing ethylene-octene copolymers. We further deduc e that the length of the branches must be of secondary importance in d etermining phase behaviour. (Previously we have shown that the variati on of molecular weight has a secondary effect on phase behaviour). Thu s we conclude that in blends of linear polyethylene with lightly branc hed ethylene copolymers it is the number of branches that is the most important factor influencing the extent of phase separation in the mel t. (C) 1997 Elsevier Science Ltd.