Cationization effect on the molecular weight distribution of an ethoxylated polymer: A combined theoretical and time-of-flight secondary ion mass spectroscopic study

The effect of metal cationization on the molecular weight distribution (MWD ) of an ethoxylated polymer, Surfynol 465 (S465), is investigated by time-o f-flight secondary ion mass spectrometry (ToF-SIMS) and a hybrid theoretica l method combining ab initio density functional theory and molecular mechan ics. The MWDs generated from sodium and from silver-cationized oligomers of S465 were measured by ToF-SIMS. The structure and bonding of the cationize d complexes were calculated. The results suggest that upon cationization, t he metal atoms are chelated by oxygen atoms and, in the case of Ag+, by the pi-orbitals of the C-C triple bond. Although the binding energy of both Na + and Ag+ with the Surfynol molecules is very high for sufficiently long et hoxylate side chains, strong bonding preference is given to Ag+ over Na+ du e to the orbital interaction between Ag+ and the Surfynol oligomer via 4d-p i*: and 5s-pi overlap and the ion-dipole interaction between the cations an d the oxygen atoms in the ethoxylate chains with Na+ being of more ionic ch aracter. The theoretical results suggest that a minimum ethoxylate chain le ngth is required for Na+ chelation and that in the high molecular weight re gion both cations will bind with the Surfynol oligomers strongly, consisten t with our experimental observations. We demonstrate that ToF-SIMS is an ef fective technique for measuring the molecular weight distribution of a low molecular weight oligomer series.