Determination of Chemical Composition Distributions, Functionality Type Distribution
Since ideal GPC/SEC separates by molecular size, irrespective of polymer structure, it does not allow to distinguish molecules which are of identical size but differing in chemical structure.
Todays polymeric materials are often composed of more than one type of monomer unit resulting in polymer blends or copolymers. The properties of such materials will be influenced by their molar masses as well as by the distribution of the different chemical entities within the different chains. Similar to molar mass, the composition of a sample can in principle determined by spectroscopic techniques like NMR. However, the composition determined in that way provides only an average value, similar to the molar mass determination by batch measurements. It provides, however, no information on how the monomer units are distributed among the chains.
The following different samples have identical average compositions but different chemical composition distributions
Similarly to SEC/GPC the separation step in IPC occurs in columns filled with porous particles (stationary phase). However, while in SEC/GPC any interaction between the molecules and the stationary phase is avoided, such interactions form the basis of the IPC separations. Depending on whether interactions or size exclusion effects prevail or whether an exact compensation of both is achieved, different modes of interaction chromatography can be realized, allowing separating by different structural features.
In two-dimensional liquid chromatography (2D-LC), polymer sample are separated by at least two different structural features, with size (molar mass) being typical one of them. Thus, in order to separate by a different structural feature, a separation different from SEC/GPC is required. Consequently, typically IPC is applied as the other separation dimension in 2D-LC.