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ABSTRACT:The growing number of heterogeneous polymeric species that are being synthesized places increasing demands on existing analytical techniques. Although sizeexclusion chromatography (SEC) has established itself as a powerful analytical tool, it has its limits when complex polymers, e.g., graft copolymers, must be analyzed. In this case, complementary techniques such as gradient HPLC and liquid chromatography at critical conditions (LCCC) are more favorable. The present study describes the synthesis and analysis of methyl methacrylate-and styrene-grafted epoxidized natural rubber by different chromatographic techniques. The grafting efficiency was evaluated by gradient HPLC under normal and reversed phase conditions. Methyl methacrylate-grafted ENR50 was further analyzed by LCCC, where separation of the rubber and grafted rubber occurred according to chemical composition but was independent of the molar mass of the methyl methacrylate homopolymers. This was followed by the combination of LCCC and SEC, where separation was achieved in two dimensions. Relevant deductions were made of both the chemical composition distribution and the molar mass distribution of the functional groups of methyl methacrylategrafted ENR50.

ABSTRACT:The evaluation of heterogeneous polymeric species by a selective, dual detector size-exclusion chromatography setup can provide accurate results on the incorporation of specific functional groups in copolymers as a function of the molar mass distribution. However, when non-UV-absorbing species are used in copolymerization reactions, the dual detector method becomes less reliable. By interfacing a Fourier transform infrared (FTIR) spectrometer with size-exclusion chromatography (SEC), the problem can be overcome, making it possible to map non-UV-absorbing species as a function of the molar mass distribution. Coupling takes place via a solvent-evaporation stage, which delivers the mobile phase as a dry, solvent-free polymeric film onto a germanium disk. In this article, styrene and methyl methacrylate were grafted onto epoxidized natural rubber (ENR50) and analyzed by SEC. The accuracy of FTIR as a suitable detector was evaluated by comparing results from a dual detector SEC setup and FTIR coupled to SEC. FTIR proved to be a successful detector for the analysis of non-UV-absorbing species. This was consequently followed by the characterization of methyl methacrylategrafted ENR50. From the relevant data, Gram-Schmidt and contour plots could be made to indicate the incorporation of methyl methacrylate into the grafted epoxidized natural rubber as a function of the molar mass distribution.

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