Thermodynamic properties and unperturbed chain dimensions of ethylene-propylene copolymers

Abstract An ethylene-propylene copolymer (EPR) of remarkable homogeneity of composition and molecular structure was separated into many fractions, showing very sharp molecular weight distributions ( MWD ), using a recently described method. Phase equilibrium studies were performed on some of these fractions in order to determine, according to Flory's theory, the θ conditions of the copolymer (solvent and temperature). In these conditions, a relationship between limiting viscosity number [η] and molecular weight was used in order to ascertain agreement with the 0.5 exponent proposed by theory. The K θ coefficient, related to the unperturbed dimensions ( r 2 0 M ) 1 2 and their dependence on temperature, i.e. (d ln r 2 0 d T ), of the macromolecular chain, were also determined. Furthermore, the very sharp composition and MWD of the fractions allowed us to ascertain good agreement between experimental data and Scholte's assumption for the evaluation of molecular weights of EPR and linear low density polyethylene copolymers using size exclusion chromatography.