Experimental investigation on the reliability of routine SEC–MALLS for the determination of absolute molecular weights in the oligomeric range

Abstract

Absolute number-average molecular weights were carefully measured for very-low to low molecular-weight poly(diisopropyl trimethylene-1,1-dicarboxylate) polymers that had been obtained from diisopropyl cyclopropane-1,1-dicarboxylate using a living anionic ring-opening polymerization technique (degree of polymerization in the range of 11–45 and polydispersity indices <1.13). Results obtained from four different analytical techniques, including end-group analysis ( 1H NMR), vapor pressure osmometry (VPO), size-exclusion chromatography coupled to a multi-angle laser light-scattering detector (SEC–MALLS), and matrix-assisted laser desorption ionization–time-of-flight mass spectrometry (MALDI–ToF), were compared and discussed. Although only crude estimates could be obtained by end-group analysis using 1H NMR (experimental errors of up to 20%), M ̄ n values estimated by SEC–MALLS were in perfect agreement with results obtained by VPO and MALDI–ToF. As the overall experimental protocol had been designed to prevent bias arising from some initial knowledge upon the exact molecular weights by the operator during the SEC–MALLS experiments, these results confirm a previous claim that SEC–MALLS is effective in measuring molecular weights in the oligomeric range.