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Thermal Field-Flow Fractionation of Acrylic Copolymers

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					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.

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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).


				
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