Characterization of non‐homogeneous polymers with size‐exclusion chromatography by implementing an on‐line viscometer

Abstract

AbstractThe viscosity distribution of a polymer sample can be obtained by using an on‐line viscometer as a detector in size‐exclusion chromatography. This newly defined viscosity distribution is closely related to the molecular weight distribution and expresses weight fraction times intrinsic viscosity of species i as a function of the corresponding molecular weight times intrinsic viscosity (wi[ηi] vs. Mi[ηi]). The intrinsic viscosity ([η]) and number‐average molecular weight (M̄n) can be obtained directly from a viscosity distribution. If the Mark‐Houwink exponent a is known (or approximately known) for non‐homogeneous polymer the M̄w/M̄n can be estimated from the viscosity distribution when the molecular weight distribution is approximated with a known distribution function. These estimates are independent of any other detector and are valid even for non‐homogeneous polymer samples. The relation between the moments of the viscosity distribution and the M̄w/M̄n is presented for two widely used distribution functions, the Log‐Normal and the Generalized Exponential Distributions. Polymer characterization based on the viscosity distribution is shown to be a robust technique. It is particularly attractive in characterizing non‐homogeneous polymers since it is solely obtained from on‐line viscometer.