Handbook of Size Exclusion Chromatography and Related ...

Figure 10 Differential refractometer (DRI) and viscometer outputs for a 1 : 1 mixture of
845,000 g/mol of polymethyl methacrylate and 170,000 g/mol of polystyrene. With this
method (for example, see Ref. 15), the determined Mn was 265,000 g/mol, compared with
an expected value of 283,000 g/mol. (From Ref. 20, with permission from John Wiley and
Sons, Inc.)
a smaller size than a linear molecule of the same molecular weight. This smaller
size also means a correspondingly smaller intrinsic viscosity. By comparing the
measured intrinsic viscosity of the branched molecule at each elution volume
increment to the intrinsic viscosity of the linear molecule with the same molecular
weight, a branching factor g 0 , defined as
g 0 ¼ [h] b
[h] l M
(27)
can be determined, where the subscripts b and l correspond to the branched and
linear polymers, respectively. For a linear polymer g 0 is unity. For a branched
polymer it decreases as the number of branch points per molecule increases.
Zimm and Stockmayer (67) determined the extent of the relative decrease in
the radius of gyration under u conditions for a given number and type (tri- or
© 2004 by Marcel Dekker, Inc.