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.