Handbook of Size Exclusion Chromatography and Related ...

where r(t) is now given by
2
6
r(t) ¼Nþkn06
4
1 N
n0
e at þ aN
kn0
k a
1 e kt
3
7
5
(23)
where r(t) ¼R(t)M.Since fp and aare known from the analysis of the side chain
stripping data, and k and n0 are known from the random mannose backbone
degradation data, the only unknown parameters in the expression involving the
two enzymes are N=M,the total number of cleavable sites per g/moles of initial
polymer mass, and a.
It is hoped that TDSLS methods will become frequently used for both
degradation and structural studies. Whereas TDSLS can aid in determining
biodegradability,stability against UV radiation, enzymatic resistance, rheological
processability,andsoon,itshouldproveusefulinitsownrightfor“deconstructing”
branched and crosslinked polymers to understand their architecture.
2.3 Aggregation
Oftentimes, polymer solutions are unstable, in that they can undergo ahost of
reversible and irreversible associative processes; aggregation, microcrystallization,coacervation,liquid–liquidphaseseparation,microgelformation,andsoon.
Sometimes these associations are desirable (for example, water purification,
bioimmunoassays, and others), whereas in other cases they can render aproduct
useless or harmful (for example, aggregation in apharmaceutical formulation).
Because TDSLS isexquisitelysensitivetoevensmallchanges inmolecular mass,
it provides apowerful tool for monitoring such instabilities.
There are many scenarios for such associative processes, and areview is
beyond the scope of this chapter. Many references exist (57,58). Each associative
model yields predictions about TDSLS. Figure 10 shows raw light scattering
intensity data for the aggregation of gold nanospheres that were coated with a
protein and the corresponding antibody (T Nguyen and WF Reed, unpublished
results). The aggregation process is immediately detectable, whereas with standard
techniques, such as turbidity, there is a long latent period before any change in
signal is measurable.
2.4 Dissolution
The rate at which dry polymer, in the form of pellets, powders, granules, and so on,
dissolves in solution is often of paramount importance for a particular application.
In many instances the most rapid dissolution possible is desired, whereas in others
© 2004 by Marcel Dekker, Inc.