Thermodynamic properties of polyolefin solutions at high temperature: 2. Lower critical solubility temperatures for polybutene-1, polypentene-1 and poly(4-methylpentene-1) in hydrocarbon solvents and determination of the polymer-solvent interaction parameter for PB1 and one ethylene-propylene copolymer

Abstract

Lower critical solubility temperature ( LCST) for 3 polyolefins, polybutene-1 (PB1), polypentene-1 (PP1) and poly(4-methylpentene-1) (P4MP1), and the x interaction parameter in concentrated solutions for PB1 and the 33% ethylene ethylene-propylene copolymer have been measured in linear, branched, cyclic alkanes and some other solvents. Effects on x of the equation of state term, of correlations of molecular orientations ( CMO) and of the solvent steric hindrance were investigated. The solvent density d s is found to be a good empirical parameter to characterize the equation of state term and to correlate the LCST. The parameter d s d p (where d p is the polymer density) affords an excellent correlation for the LCST of all polyolefins in normal and branched alkanes (polyethylene (PE) excepted). In dilute solution (at the LCST) the effect of CMO and solvent steric hindrance could not be distinguished from equation of state effects. However, values of x, found to be higher in branched than in linear alkanes in solutions of the linear polymer (PE) but not with the branched PB1 and the copolymer, are indicative of the importance in concentrated solutions of CMO even at high temperatures (100°–135°C). Furthermore, the lowering of x from linear PE to the branched PE and to the ethylene-propylene copolymers, following the expected diminution of CMO in the corresponding melts, is another indication of the persistance of CMO at high temperature. Solvent steric hindrance is seen to lower x (measured here by gas-liquid chromatography).