Osmometric study of the degradation of fluorine-containing polymers

Abstract

IN STUDIES of the influence of various chemical, physicochemica], and mechanical processes on the properties of polymers, it is frequently necessary to obtain information on the degradation of the polymer and the change in its polydispersity. The most widely used method [1] of determining the change in the molecular weight and polydispersity of a polymer due to degradation is the measurement of its intrinsic viscosity in dilute solutions. This method, however, only permits an estimation of the over-all change in the molecular weight of the polymer and does not enable the amount of low-molecular-weight fraction (molecular weights from 25,000 to 20,000) in the polymer formed by degradation to be determined or to be separated from the bulk of the polymer. These problems can be solved by using the osmometric method, which is widely employed at the present time to determine the molecular weights of polymers. In determining the molecular weight of a polymer having a high degree of polydispersity, the low-molecularweight fraction of the polymer may pass through the membrane; of course, this fact is reflected in the value of the number-average molecular weight and is negative. However, the diffusion of the low-molecular-weight fraction through the membrane may be used to obtain information on the increase in the content of low-molecular-weight fractions as a result of various influences on the polymer. We have used this circumstance in an investigation of the thermal-oxidative degradation of the fluorine-containing polymer Ftorlon.