Dispersity in Polymer Science: (IUPAC Recommendations 2009) (International Union of Pure and Applied Chemistry: Polymer Division Subcommittee on Polymer Terminology) (Report‪)‬

INTRODUCTION A dimensionless ratio of two average values of a property is widely used in polymer science as a characteristic of the dispersion, or spread, of the distribution of values of that property in a sample of polymer. In particular, the ratios [[bar.M].sub.w]/[[bar.M].sub.n] and [[bar.X].sub.w][[bar.X].sub.n] are quantities commonly used to characterize the dispersions of distributions of molar masses and degrees of polymerization, respectively. However, they do not have satisfactory names and the present recommendation seeks to rectify this situation.