Thermal Field-Flow Fractionation of Acrylic Copolymers
J. Ray Runyon, S. K. R. Williams
Colorado School of Mines, Department of Chemistry and Geochemistry, 1400 Illinois St.,
Golden, CO 80401. jrunyon@mines.edu, krwillia@mines.edu.
A new thermal field-flow fractionation (ThFFF) method has been developed for
the separation and analysis of polyacrylates and acrylic-styrene copolymers. This
important class of polymers is commonly used as pressure sensitive adhesives, in
coatings and paintings, and as the basis for polyelectrolyte materials. The structure and
chemical composition of these polymers play a vital role in the end use of these materials.
It is important to accurately analyze and characterize these materials to better understand
their structure-property relationships. These polymers have not previously been
investigated by ThFFF.
Size exclusion chromatography is commonly used to separate these materials.
However, SEC is a size based separation and will not differentiate between copolymers
of different chemical composition, or between polymers of different architectures if they
are the same size. Thermal FFF, on the other hand, separates analytes according to
differences in their thermal diffusion (DT) and normal diffusion (D) as expressed in the
retention parameter (λ) equation below.

D
DT T
The difference in temperature between the hot and cold walls is denoted as T.
The thermal diffusion process, which is observed in the presence of a temperature
gradient, provides ThFFF with the capability to separate polymers on the basis of
differences in chemical composition.
The challenge in developing a new analytical method using ThFFF is the
identification of a solvent that will retain the polymers of interest. This process is usually
done empirically and can be very time consuming. The approach we have taken involves
examination of theoretical models proposed by Schimpf and Semenov (1) and Mes et al.
(2) and solvent viscosity studies by Kassalainen and Williams (3) to determine the major
parameters that affect polymer retention. An additional consideration in this study is the
dn/dc value of the polymer-solvent system as a multiangle light scattering-differential
refractive index detector combination is used.
This presentation will focus on the selection of an appropriate solvent for ThFFF
of PS and PBA, ThFFF analysis of PS-PBA copolymers, and measured DT values and
trends for PS-PBA copolymers and their corresponding homopolymers.
1.) M.E. Schimpf, S.N. Semenov, Phil. Magazine, 83, 2185-2198 (2003).
2.) E.P.C. Mes, W. Th. Kok, R. Tijssen, Int. J. Polym. Anal. Charact., 8, 133-153
(2003).
3.) G.E. Kassalainen and S.K.R.Williams, J. Chromatogr. A, 988, 285-295 (2003).