Polydispersity Ratio and Its Application for the Characterization of Poloxamers

The
data processing and visualization methods are of paramount
importance in the mass spectrometry of copolymers. To determine the
copolymer composition, in this article, a robust algorithm is proposed
for the compositional assignment and for the estimation of the relative
abundance of each species present in copolymer mass spectra. Our homemade
software enables the accurate calculation of the compositional drift,
i.e., the variation of copolymer composition with the polymer chain
lengths. Furthermore, we introduce a novel copolymer quantity, namely,
the polydispersity (also called as dispersity) ratio (PDR) of the
comonomers, and establish a characteristic relationship between the
shape of the composition drift curves and the PDR values. This relation
allows, for instance, a quick visual recognition of the presence of
diblocks in a triblock copolymer by means of mass spectrometry. Our
approach is demonstrated by the analysis of various poloxamers, i.e.,
polyethylene oxide (PEO)–polypropylene oxide (PPO) block copolymers
up to the average molecular weight of approximately 4000 g/mol. The
determined number-average molecular weights and the ethylene oxide
contents were also confirmed by nuclear magnetic resonance spectroscopy.
Dynamic light scattering experiments revealed that small variations
in the copolymer composition significantly affect the properties of
the copolymer.