Gel permeation chromatography (GPC) is a type of size exclusion chromatography (SEC) that separates molecules according to their hydrodynamic volume which is related to their molecular weight. The separation is based strictly on the size of the sample in solution, and there should be no interaction with the stationary phase of the GPC column. Elution order in GPC is that of an “inverse-sieving” technique, large molecules access a smaller pore volume than smaller molecules resulting in larger molecules eluting from the GPC column prior to the smaller molecules.
GPC can determine several important parameters. These include number average molecular weight (Mn), weight average molecular weight (Mw), Z weight average molecular weight (Mz), and the most fundamental characteristic of a polymer, its molecular weight distribution. These parameters are important, since they affect many of the characteristic physical properties of a polymer. Differences in these parameters can cause significant differences in the end-use properties of a polymer.
To prepare a sample for GPC analysis the polymer is first dissolved in an appropriate solvent. Most often a bank of 2-4 GPC columns is used to achieve high resolution analysis of the polymer sample. Today, modern semi-micro GPC column technology helps to reduce analysis time without compromising the resolution and to reduce the consumption of solvent. The latter being a great environmental as well as economic advantage if you have to determine the molecular weight of polymers that dissolves only in expensive solvents.
GPC/SEC is usually carried out at room temperature, but some polymers such as high molecular weight polyolefins need high temperature for effective dissolution. Hence, GPC analysis of these polymers needs to be performed at higher temperature. This application book compiles various examples of ambient and high temperature GPC analysis for a broad range of polymers.
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