Gel permeation chromatography (GPC)/ Size exclusion chromatography (SEC) is a widely used technique for measuring the molecular weight and molecular weight distribution of natural and synthetic polymers. It is based on liquid chromatographic techniques that separate individual polymer chains on the basis of their size in solution and not on their chemical properties. The separation mechanism is shown in Figure 1:
Figure 1. GPC mechanism
Diluted polymer solution passes through GPC column which is filled with porous beads. During the elution process, molecules with small hydrodynamic volume could enter into the pores of beads, thus taking relatively long time to pass through the column. By contrast, polymers with high molecular weight usually have large hydrodynamic volume. So they could get eluted from the column faster than those small molecules. Each GPC column could only separate a specific molecular weight range of polymers, usually from several KDa to several hundreds KDa.
After the separation of polymers, there’re different kinds of detectors to record the retention time of polymers. The most common detector is the differential refractometer, which could detect the changes in refraction index of eluted solution. The resulting chromatogram is therefore a weight distribution of the polymer as a function of retention time (See Figure 2 from ref).
Figure 2. GPC Chromatogram
In all, GPC is a convenient methodology to determine polymer molecular weight distribution and molecular weight. It requires only several milligrams of polymer samples for each test. Furthermore, all the samples will be eluted out in less than an hour without interaction with column or detector. Hence, polymer samples could be fully recycled after test. Compared with traditional methods for determining the molecular weights of polymers, GPC is quick, relatively easy and labour-saving.
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