CHARACTERIZATION OF NONHOMOGENEOUS POLYMERS WITH SIZE-EXCLUSION CHROMATOGRAPHY BY IMPLEMENTING AN ONLINE VISCOMETER

The 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 (w(i)[eta(i)] vs. M(i)[eta(i)]). The intrinsic viscosity ([eta]) and number-average molecular weight (M(n)BAR) can be obtained directly from a viscosity distribution. If the Mark-Houwink exponent a is known (or approximately known) for non-homogeneous polymer the M(w)BAR/M(n)BAR 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 M(w)BAR/M(n)BAR 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.