Determination of a number criterion of polymer heterogeneity

Abstract

AbstractA critical survey of number criteria of heterogeneity of polymers based on differential distribution function and on measurements of different average molecular weights has been presented. Because of the difficulties connected with measurements of the number‐average molecular weight and the errors inherent in differentiation of the integral distribution function a number criterion of heterogeneity based on the latter is proposed. The area limited by the integral distribution curve and the straight line defining an absolutely homogenous polymer having the same weight‐average degree of polymerization as the polymer tested is defined as absolute heterogeneity. On the basis of the weight‐average degrees of polymerization calculated directly from the integral distribution curve it is proved that the value of proposed number criterion increases with the increase of the weight amount of fractions having different degree of polymerization from the average one of the tested polymer. This value also increases with the increase of the difference between the degree of polymerization of these fractions and the average degree of polymerization of the tested polymer. On the basis of Flory's equation the absolute heterogeneity of polymers having the most probable distribution has been determined. The ratio of absolute heterogeneity of the tested polymer to the absolute heterogeneity of polymer having the most probable distribution and the same average molecular weight as the tested polymer has been defined as relative heterogeneity. On the basis of Scott's theoretical fractionation data changes in heterogeneity occurring during the fraction have been revealed.