Cationization effect on the molecular weight distribution of an ethoxylated polymer: A combined theoretical and time-of-flight secondary ion mass spectroscopic study
Hs. Cheng et al., Cationization effect on the molecular weight distribution of an ethoxylated polymer: A combined theoretical and time-of-flight secondary ion mass spectroscopic study, J PHYS CH A, 104(12), 2000, pp. 2641-2647
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.