ANALYSIS OF MICROGEL-CONTAINING POLYMERS USING
MONOLITHIC COLUMNS AND THERMAL FFF WITH MALS-dRI
DETECTION
Kim R. Williams, Dean Lee
Chemistry and Geochemistry Department, Colorado School of Mines, Golden, CO 80401,
USA. krwillia@mines.edu
The analysis of polymer samples that potentially contain microgels usually includes a filtration step prior to
injection into a GPC column. This sample preparation procedure helps prolong column life but comes at a
price as will be discussed below. The microgel components can be subsequently gravimetrically measured
to obtain information about their relative weight percent. However, this can be a tedious process and no
additional information such as size or molecular weight can be obtained.
We have investigated the use of polymeric and silica monolithic columns and thermal field-flow
fractionation (ThFFF) as methods for analyzing unfiltered polymer samples known to contain soluble
polymers and insoluble microgels. The polymeric (Isco) and the silica (Chromolith) columns had
macropore sizes of 5.1 μm and 2 μm, respectively. The ThFFF channel (similar to PostNova T100) had a
thickness of 127 μm. In all cases, detection was accomplished using a Wyatt Technologies multiangle light
scattering-differential refractometer (MALS-dRI) detector combination. Polyvinylacetate (PVAc) samples
were provided by National Starch & Chemical Company.
Results obtained using the monolithic columns showed sample recoveries in the range of 63-69% (Isco
polymeric) and 21-24% (Chromolith silica). The lower sample recovery for the silica monolith was
attributed to its smaller macropores. Interestingly, the mesopores on the silica monoliths contributed to a
second separation mechanism (size exclusion effect) with a distinctly different selectivity from the region
of separation where the hydrodynamic effect predominates.
Thermal FFF results showed that 98% of the sample was recovered. The MALS-dRI signals for the
unfiltered and filtered PVAc samples clearly demonstrated significant loss of high and ultrahigh MW
components (>107 Da) upon filtering. In addition, soluble polymer between 105 and 106 Da were also
removed in the sample filtration step. The consequence is that a lower average MW is measured and
reported for the soluble polymer component than that actually present in the original PVAc sample.
This combination of ThFFF and MALS-dRI allows characterization of both the soluble polymer and the
microgels. We have observed MWs in the region of 109 Da and root mean square radii of the order of 400
nm. Additional interesting aspects that will be discussed in this presentation are developing a working
definition for microgels and error analysis of MALS results at these ultrahigh MWs and large sizes.