M. Zigon, T. Malavasic, Kemijski institut,
Ljubljana
Z izkljucitveno kromatografijo in odvisnostjo reducirane
viskoznosti od koncentracije smo studirali vpliv polarnosti
topila in deleza ionskih skupin na lastnosti razredcenih raztopin
karboksiliranih poliuretanov (PU) in PU ionomerov. Ugotovili smo,
da v manj polarnem tetrahidrofuranu (THF) povpre~ja molskih mas
padajo z delezem karboksilnih skupin in z nevtralizacijo. V
polarnem N,N-dimetilformamidu (DMF) so molske mase vecje zaradi
polielektrolitskega ucinka, porazdelitev molske mase pa je
multimodalna zaradi razlicne porazdelitve -COOH oz. ionskih
skupin v makromolekulah. Po dodatku litijevega bromida (0,05 M
ali vec) dobijo kromatogrami simetricno obliko, molske mase pa se
zmanjsajo. Tudi meritve viskoznosti so pokazale, da dodatek LiBr
prepreci polielektrolitski ucinek.
Kljucne besede: poliuretani (PU), ionomeri, izkljucitvena
kromatografija po velikosti (SEC), viskoznost
Dilute solution properties of carboxylated PU and PU ionomers,
which are strongly influenced by the polarity of the solvents and
by the content of ionic groups, were investigated by SEC and
viscosity. It was found out that the molar mass averages measured
in THF decrease with the degree of carboxylation and ionization.
Anomalous SEC behavior in DMF (higher molar weight and multimodal
peak distribution) is ascribed to the polyelectrolyte effect and
to different charge distribution in the polymer chains. With the
addition of LiBr to DMF in concentration 0.05 M or more, the
shape of chromatograms of ionomers and carboxylated PU become
symmetrical and much smoller molar weights are obtained. The
measurements of reduced viscosity as a function of concentration
confirmed that the polyelectrolyte effect is suppressed by the
addition of LiBr.
Key words: polyurethanes (PU), ionomers, size exclusion
chromatography (SEC), viscosity