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

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-2,2-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 (H-1 NMR), vapor pressure osmometry (WO), 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 H-1 NMR (experimental errors of up to 20%), (M) over bar (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. (C) 2002 Elsevier Science Ltd. All rights reserved.