Determination of the polydispersity of poly(tetramethylene ether) glycol by means of high-performance liquid chromatography and curve fitting

A modified high-performance liquid chromatographic method for the analysis of the molecular weight distribution of poly(tetramethylene ether) glycol (PTMEG) is described. The weight percentage of the polymer homologues, up to a degree of polymerization X of 79, can be determined. This covers about 93 wt.-% of the material with number-average molecular weight (M) over bar(n) = 1000, but only 65 wt.-% of that with (M) over bar(n) = 2000. Direct calculation of the means (M) over bar(n), (M) over bar(w), and (M) over bar(z) from these percentages leads to erroneous results because of the neglect of the summands with X > 79. Therefore, a curve fit is performed and (M) over bar(n), (M) over bar(w), and (M) over bar(z) are calculated from the fitting parameters. From the known molecular weight distribution functions, Wesslau's and Kubin's function yielded the best fit. The results of this method are compared with those of gel permeation chromatography, viscosimetric measurements, supercritical fluid chromatography, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and evaporative light scattering detector methods. The scope and the limitations of this method are discussed.