Handbook of Size Exclusion Chromatography and Related ...

3.3 Factors Influencing the MW Determination
3.3.1 MWand Chemical Structure of Standards
Table 4 shows the average molecular weights and polydispersities of four
80/20 w/wAM/DMDAAChighMWcopolymers.Itappearsthattheuseofpoly
(DMDAAC)asastandardresultsinthereportingofahighermolecularweightand
polydisperity of the copolymer. It is also important to note that the chain
microstructure(stereostrucrure,endgroups,ormonomersequencedistribution)of
apolymer may affect the molecular size when in solution. Every effort should be
made to use apolymer with asimilar chain microstructure for standardization
when determining MW.Otherwise, erroneous values may be obtained because
eventhoughapolymermayhavethesamechemistry,itmayhaveadifferentchain
microstructure and behave differently in solution. When comparing relative MW,
the same MW standards must be used for all determinations.
3.3.2 MWand Calibration Technique
Table 5shows the given M w(determined by LALLS) and intrinsic viscosities
determined from an on-line viscometer (Viscotek Model 110) and the measured
M wdeterminedbydifferentcalibrationtechniquesforsixsamples.Thedeviations
{[(measured M w given M w)/(given M w)] 100} between the measured M w
and those given M wfor PAM are 210 to þ15% by universal calibration and 28
to þ4% by peak position calibration. The universal calibration technique gives
relativelyhigherdeviations,probablyduetothefactthattheintrinsicviscositywas
determined from asingle point (58) or the universal calibration curves included
two different types of polymers (five PAM and one low MW polyacrylic acid) as
shown in Fig. 5, or the polydispersity of PAM is not narrow (59). Bose and
co-workers (60) found that the universal calibrations of polystyrene sulfonate and
dextrans do not coincide. For a 25% hydrolyzed PAM, its absolute M w
Table 4 Molecular Weight of 80/20 w/w Acrylamide/DMDAAC Copolymers
Relative to poly(DMDAAC)
standards
Relative to polyacrylamide
standards
Sample M w M n M w=M n M w M n M w=M n
Copolymer 1 6.13 10 6
Copolymer 2 7.59 10 4
Copolymer 3 2.66 10 5
Copolymer 4 1.85 10 6
© 2004 by Marcel Dekker, Inc.
1.57 10 6
1.18 10 4
3.13 10 4
8.38 10 4
3.90 3.06 10 6
6.43 7.16 10 4
8.50 1.58 10 5
22.1 8.47 10 5
8.45 10 5
3.48 10 4
6.76 10 4
1.48 10 5
3.62
2.06
2.34
5.72