Handbook of Size Exclusion Chromatography and Related ...

microcrystalline cellulose with a DS of 2.7 are completely soluble in THF whereas
no sample having a DS of 3 was soluble in THF. Because soluble and insoluble
fractions had similar DS it was concluded that the solubility depended not only on
the DS of the derivative. The insolubility was suggested to be due to some kind of
hydrophobic aggregation of high molecular mass cellulose samples. For SEC
purposes, it is thus important to control the DS. During the past few years,
systematic investigations of silylation conditions have been performed and some
SEC applications reported (Table 4). The chromatograms have been evaluated
using differential refractive index (DRI) detectors (98,100–102), dual detector
systems consisting of either differential viscometry (DV) detector/DRI (97), or
multi-angle laser light scattering (MALLS) detector/DRI (101), and also by using
an evaporative light-scattering detector (95).
Complete (100) and controlled partial DS silylations, depending on reaction
conditions and type of cellulose (98,103), have been reported. The derivatization was
performed with HMDS, using liquid ammonia as solvent and saccharine as catalyst.
The obvious advantage of the procedure, besides controlled substitution, is that no
purification of the derivative is needed. According to SEC results no degradation
takes place during derivatization. Another way to obtain cellulose samples with a
controlled DS is to desilylate trimethylcellulose in THF/liquid ammonia (102).
According to SEC characterizations, the molecular mass of microcellulose increases
with increasing DS and no degradation could be observed.
Using partially substituted trimethylsilylates (DS 2.1 + 0.2), Einfeldt and
Klemm (97) studied bacterial cellulose by SEC using THF as mobile phase. The
derivatives were synthesized in a homogeneous reaction in LiCl/DMAc with
hexamethyldisilazane (HMDS). Continuous polymer fractionation (CPF) of
cellulose has been investigated using silylated cotton linters (DP Cuoxam 850) (101).
Table 4 SEC of Trimethylsilylcellulose using THF (1 mL/min) as Mobile Phase a
Packing material
Exclusion limits of
each column (A ˚ ) b
Ultrastyragel 500, 10 4 , and linear c
Polystyrene 10 2 ,10 3 ,10 5 ,10 6
PS/DVB d
10 3 ,10 5 ,10 6
PS/DVB d
10 3 ,10 5 ,10 6
PS/DVB d
Linear c
DS of studied
samples References
2.1 + 0.2 97
2.5 98
3.00; 2.57 100
2.89 101
1.53; 1.78; 2.37 102
a No information about temperature during analysis.
b A ˚ ¼ 10 2 10 m, generally defined as the exclusion limit of polystyrene dissolved in THF.
c Exclusion limit not reported.
d Polystyrene/divinyl benzene.
© 2004 by Marcel Dekker, Inc.