General Solution to the Band-Broadening Problem in Polymer Molecular Weight Distributions

Abstract

A method is developed for overcoming the problem of band broadening (where a sample which is monodisperse in molecular weight elutes over a range of elution volumes) in order to obtain accurate molecular weight distributions of polymers using size exclusion chromatography (SEC). It is proved that the SEC signal from an exponential number distribution (as obtained from free-radical polymerization under certain conditions) has the same functional form at the maximum, irrespective of band broadening. This leads to a method for quantifying the band broadening from any SEC trace, and hence for deconvoluting the trace to obtain the true distribution—by free-radical polymerization one should synthesize ‘standards’ which have exponential distributions and then carry out least-squares fitting to find the corresponding broadening function. The new method opens the way for mechanistic understanding and rate parameters to be obtained from the full detail that has hitherto been inaccessible in molecular weight distributions.