Matrix Assisted Laser Desorption Ionization Time-of-Flight mass spectrometry has been applied to obtain the molecular weight distribution of two polyether copolymers containing ethylene oxide and propylene oxide units. The measured molecular weights and their distributions were surprisingly different from the expected. Based upon the natural isotopic abundance, it was possible to provide a quantitative description of the number of ethylene oxide and propylene oxide units as a function of molecular weight. Important information on composition drift and heterogeneity can be obtained from the 3-D bivariate deconvolution of the mass spectra. As the molecular weight of a random copolymer increased, the ethylene oxide content also increased. A copolymer system with a narrow molecular weight distribution did not necessarily have a narrow composition distribution. These results provide information at the molecular level regarding the hydrophilicity of these copolymers used in polyurethane formulations.
Modeling of Molecular Weight Distribution in Ring-Opening Polymerization of l,l-Lactide
