Thin-Layer Methods for Determining Molecular Weight Distribution

Abstract

Thin-layer chromatography (TLC) is a common laboratory technique for separating complex mixtures of solutes, usually by an adsorbtion mechanism. Several laboratories have applied the technique to the separation of polymer fractions and characterization of polymer molecular weight distribu tions. This work reviews the experimental results and theoretical approaches to the fractionation mechanisms.^phin-layer chromatography (TLC) is a well-known technique for the separation of mixed solutes by adsorption. Compared with related techniques in column chromatography, TLC offers several advantages. The use of adsorbents having large surface area ( particle size ~10 μ vs. 50 μ) results in excellent resolution. Separation and analysis time are reduced because many samples can be run simultaneously and material need not be eluted for quantitation. Several references provide a com prehensive background on TLC ( 1-3 ).TLC has been a widely accepted technique in biochemistry and or ganic chemistry for a number of years. With modern quantitation TLC is being used today in such diverse applications as air pollution analysis and clinical medicine.The initial applications of TLC to problems in polymer chemistry were directed to the separation of polymer blends, stereoisomers, and a variety of copolymers ( 4-8 ). From these investigations occasional molec ular weight effects were noted (8). Recently efforts in three separate laboratories have been successful in determining the molecular weight distribution of a polymer sample by TLC techniques (9-12). An explana tion of the facility and high resolving power observed has been sought through a number of continuing experiments (11)(12)(13)(14)(15)(16). The purpose of this report is to review the results of these studies and to comment on the fractionation mechanisms postulated. 55Downloaded by UCSF LIB CKM RSCS MGMT on December 2, 2014 |