Analysis of cyclic polymer purity by size exclusion chromatography: a model system

Because cyclic polymers have intriguing physical properties, considerable synthetic strategies have been developed to create a wide variety of cyclic architectures. One of the most utilized cyclization procedures is via ring-closure of a difunctional linear polymer using the copper catalyzed azide–alkyne cycloaddition (CuAAC) ‘click’ reaction. However, quantifying the percentage of mono-cyclic species (i.e. formed directly from the starting α,ω-linear polymer) still remains a challenge even with access to a variety of characterization techniques, including NMR, MALDI-ToF, size exclusion chromatography (SEC) and liquid chromatography at the critical condition (LCCC). Here, we demonstrated that SEC in combination with the log-normal distribution (LND) method and minimization of the sum of squares of the weighted residuals to fit the distribution provided an analytical method for the accurate analysis of cyclic purity. The key to the SEC analysis method relies on quantification of the hydrodynamic shift from linear to mono-cyclic. The technique developed in this work has wide applicability for the characterization of complex polymer architectures and compositions (and can be easily applied to sequence controlled polymers).