Introduction

Size exclusion chromatography (SEC), also known as gel permeation chromatography (GPC), is a particularly valuable tool in the measurement of the molecular weights and molecular weight distributions of polymers. There are a number of variations on the basic technique to accommodate the requirements of different polymer types and to elicit additional information. This article seeks to describe the basic technique with particular comment to the often under-appreciated limitations together with detailed comment on the main variations to the basic technique. The relationship between SEC and other techniques for polymer molecular weight techniques will be summarized.

As examples of the technique, Figure 1(A) is an overlay plot of the computed molecular weight distributions for a range of extrusion grades of polystyrene from various producers and Figure 1(B) illustrates the variation in molecular weight for a series of poly(methylmethacrylate) (PMMA) materials polymerized under different conditions. The descriptions in this article will normally relate to the general practice in the use of SEC with polymers soluble in the normal organic solvents. Some comments will also be made on the aqueous-based SEC of process-able polymers. Biopolymers, such as polypeptides and proteins are also examined using SEC, but the consideration of appropriate buffers and column packings has not been considered appropriate for separate comment.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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