Liquid–liquid phase separation in linear low‐density polyethylene

Abstract

Abstract The issue of multiple equilibrium phases in compositionally heterogeneous random copolymers is studied with an ethylene‐butene copolymer representative of many linear low‐density polyethylenes (LLDPE). This material has a dispersed minority phase (volume fraction ƒ β ≈ 0.02) of highly branched, amorphous chains. A thermodynamic calculation of the equilibrium liquid state is done using the distribution of chain branching from temperature rising elution fractionation and the Flory‐Huggins interaction parameter χ AB for linear and ethyl branched C 4 H 8 repeat units. The calculation indicates that this copolymer is metastable, between the binodal and spinodal at a melt temperature of 150°C. The predicted volume fraction of the second phase, ƒ β = 0.016, is in good agreement with experiment. This work is the first to compare directly the observed and calculated two‐phase behaviors in a random copolymer. © 1994 John Wiley & Sons, Inc.