Fractionation of Polymers

Fractionation is an important tool for obtaining structural information on polymers. It is also important for isolating relatively homogeneous samples of polymer to use in determining relationships between structure and properties. The most common structural information obtained from fractionation is molecular weight distribution (MWD). This is a very important factor in determining processing behavior. To a lesser extent MWD affects the properties of finished polymer products. It is quite important in helping to elucidate mechanisms of polymer formation. Development of gel permeation chromatography (GPC) over the past few years has provided a fast convenient tool for comparing molecular weight distributions. GPC is fast enough that it may even be considered as a potential means of controlling polymerization processes. The chemical composition of copolymers can be determined using fractionation techniques. For this the fractionations based on polymer solubility are particularly suitable. Thin layer chromatography also shows promise in this area. This information is of importance in respect to some physical properties such as solvent and oil resistance and crystallinity. It is also useful in elucidating mechanisms of polymerization. While the ultracentrifuge has not been used extensively in the investigation of industrial polymers, it does have the advantage of being capable of providing absolute moleclar weight information. When it is desired to establish relationships between the structure of polymers and their physical properties it is always desirable to work with polymers having a narrow molecular weight distribution and a homogeneous composition. This can frequently best be accomplished by using fractionated polymer samples. At the present time fractionations based on solubility are the principal ones used through preparative fractionations based on GPC are now possible and a limited amount of literature in this area is now appearing.