Short Chain Branching Effect on the Cloud-Point Pressures of Ethylene Copolymers in Subcritical and Supercritical Propane

The cloud-point pressures of copolymers of ethylene with propylene, butene, hexene, and octene in propane were measured with a variable-volume optical batch cell to investigate the effects of the number and length of branches on the phase behavior in the temperature range from 25 to 200 °C and at pressures up to 700 bar. As the degree of branching increased in the ethylene−propylene copolymers, ethylene−butene copolymers, and ethylene−hexene copolymers, the cloud-point pressures decreased. At the same degree of branching, the cloud-point pressures decreased slightly upon increasing branch length. The copolymer SAFT (statistical association fluid theory) equation of state was found to correlate the experimental cloud-point data by adjusting the branch segment energy.