MOLECULAR-WEIGHT PARAMETERS OF ELASTOMERIC FLUOROCARBON MATERIALS

The key molecular-weight parameters of four different types of commerc ial fluorocarbon elastomers have been determined by size exclusion chr omatography (SEC) for use in automotive alternative fuel applications. The number-, weight-, and z-average molecular weights (M(n)BAR, M(w)B AR, and M(z)BAR) obtained for the soluble fraction (98.5-100%) of each fluoroelastomer were compared with the Mooney viscosity provided by t he suppliers. Correlations between the viscosity and any average molec ular weight were generally poor. The best correlation coefficient foun d was naturally the value obtained between the viscosity and M(w)BAR. This paper also evaluates the molecular-weight degradation of some flu oroelastomeric materials during the compound processing. Even at relat ively low shearing an accelerated rate of M(w)BAR degradation was obse rved in the early milling stages for a fluoroelastomer with longer-cha in molecules (M(r) greater-than-or-equal-to 10(6)). The molecular-weig ht data provides in part a helpful insight in understanding the morpho logy of fluoroelastomer prototype parts which have been exposed to fle xible fuel service conditions.