Handbook of Size Exclusion Chromatography and Related ...

Table 3 Antioxidants Used for SEC Analysis of Rubbers
Antioxidant Concentration (%) References
4,4-Thiobis-3-methyl-6-tert-
0.1wt/vol
butylphenol (Santonox)
40,61
2,4-Di-tert-butylphenyl phosfite
0.1wt/vol 61
(D-13 168)
2,6-Di-tert-butyl-4-methylphenol 0.03 30
(Ionol) 1 for polymer 44
0.05wt/wt 43
or aggregates that cannot pass through the filter are removed from the SEC
columns.
3.3 SEC Calibration
As is well known, an SEC system should be calibrated by plotting the elution
volume Ve of the peak maxima of aseries of calibrants with narrow molecular
weight distribution against the log molecular weight Mbefore SEC analysis is
made. Commonly,standard polystyrenes are used for the calibrants. The calibrationcurvelogMvs.Ve
forthepolystyrenecalibrantsisvalidonlyforSECanalysis
of linear polystyrene samples. For rubbers, rubber standards of the same type of
rubber in question should be used. The difference in the calibration curves
between polystyrene and polyisoprene standards is depicted in Fig. 2(6). However,
only alimited number of commercial rubber standards are available, as
shown in Table 4.
An alternative approach to calibrating an SEC system has been to use a
single broad molecular weight distribution calibrant. However, this method is not
common.
Amethod to overcome this is Benoit’suniversal calibration plot (63) of
log½hŠM against Ve, where ½hŠ is intrinsic viscosity.However, this method needs
theconstants from theMark–Houwink ½hŠM relationships for therubber samples
tobe analyzed intheSECsolventsbefore theSECanalyses. However, aliterature
survey showed that few constants for rubbers are available, as shown in Table 5.
Another method is to use the Qfactor (64), which is defined as the ratio of the
extended chain length between polystyrene and rubber samples. This method is
valid only for vinyl polymers and is empirically crude (6).
A much more satisfactory calibration method is to use LALLS coupling
with the usual refractive index (RI) detector in the SEC system so that the
molecular weight corresponding to each elution volume can be obtained directly
(30,38). The molecular weight distributions of the polyorganophosphazenes have
© 2004 by Marcel Dekker, Inc.