Handbook of Size Exclusion Chromatography and Related ...

molecular characteristics of macromolecules, namely their molar mass (MM),
physical (molecular) architecture (MA), and chemical structure (CS). As is known,
molar masses of macromolecular substances range from a few hundreds, through
a few thousands (oligomers), to a few millions [(high) polymers] and, eventually
up to tens of millions (ultra-high molar mass polymers). The term physical
(molecular) architecture of polymers represents differences between linear and
short- — or long- — chain branched macromolecules, as well as between species
of various stereoregularities, head-to-head and head-to-tail structures, and so
on. Chemical structure of polymers includes mainly their chemical composition
(CC) corresponding to relative concentration of building units in copolymers and
constituents of polymer blends, as well as functional groups, both type (FT) and
concentration (FC), in functional polymers.
The nonuniformity of molecular characteristics is expressed by differences
of various mean (average) values of molecular characteristics, that is, MMM,
MMA, and MCS, as well as with the distribution of molecular characteristics, that
is, MMD, MAD, and CSD (CCD, FTD, FCD).
Besides primary molecular characteristics, we can also define secondary
molecular characteristics of macromolecules. For example long-chain branches in
branched macromolecules including also comblike, grafted, or starlike structures
may simultaneously exhibit differences in their molar mass, architecture, or
chemical structure.
Polymeric substances that exhibit more than one distribution of their
molecular characteristics are called complex polymer systems.
Mean values of molecular characteristics can be determined by various bulk
methods while for assessment of distributions, macromolecules are usually
separated. Both bulk and separation procedures utilize differences in particular
physical and chemical properties of macromolecules. Information on distribution
of molecular characteristics is generally more conclusive than the mean values and
therefore separation methods are often preferred over bulk methods. Presently,
separations of macromolecules are dominated by chromatographic and mass
spectrometric procedures. Chromatographic separation is based on different
extents of retention for different macromolecules within chromatographic columns.
Separated macromolecules are transported along the chromatographic column by
the mobile phase (eluent), which is a liquid or supercritical fluid. Correspondingly,
we speak about liquid chromatography (LC) and about supercritical fluid
chromatography (SFC). In this chapter, we shall deal mainly with the former.
Chromatographic columns contain an array of porous or nonporous particles,
which form a packing or a rodlike monolith. Monoliths possess larger flowthrough
channels with usual sizes in the range of 1 or 2mm and smaller “separation
pores.” Particles of typical column packings have narrow size distribution with a
maximum in the range 3–20mm, depending on the separation task. The smaller the
packing particles, the more efficient is separation (narrower peaks), but also the
© 2004 by Marcel Dekker, Inc.