Dual detection, chemical composition

The reason for this discrepancy can be deduced from Fig. 30 all the constituents differing in chemical composition had approximately equal SEC distributions. Dual detection SEC can provide only information on the average composition of the eluted portions. The broad but symmetric CCD of the sample yield roughly constant values for the average at any point of the SEC curve for the whole sample. The investigation is a fine demonstration for the advantage of cross-fractionation over dual-detection... 

Besides the overall composition of blends and random copolymers, valuable information can be obtained in the case of block copolymers. If a block copolymer contains a homopolymer fraction, a shoulder or second maximum in the MMD curve can be obtained that should have a different chemical composition. Figure 9 shows the MMD of a block copolymer of methyl methacrylate and decyl methacrylate, in which a second lower molar mass maximum can be identified as poly(decyl methacrylate) (PDMA) by dual detection [37]. The increase in the PDMA content with molar mass in the main fraction is reasonable and corresponds well with what is expected from the synthesis. It is worth noticing that this type of information can only be obtained by the D-RI detector combination, because both PDMA and PMMA have a similar low response in UV. 

Determination of Chemical Composition Distribution by Dual Detection Based on detection with independent concentration detectors, this approach provides information on the chemical composition of copolymers or polymer blends and the variation with the molar mass [26]. An independent detector signal is required for each comonomer in the macromolecule. Many results have been published for chemically heterogeneous samples using two detectors. Obviously, there is a practical limit (four signals have been reported so far), as there are not many detectors to choose from. In addition, the approach is limited by the contribution of each detector to band broadening. 

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