Characterization of grafting properties of ABS latexes: ATR-FTIR vs NMR spectroscopy

Acrylonitrile–Butadiene–Styrene (ABS) polymers have a complex microstructure which is formed during the grafting reaction of a polybutadiene seed latex. During the reaction, some styrene-acrylonitrile (SAN) chains are grafted onto the polybutadiene (PB) backbone chains, and this grafting is critical to achieve effective dispersion and compatibility of both phases. Therefore, accurate characterization of grafting properties helps understanding the polymerization mechanism as well as the final properties of the ABS polymer and its applications properties. In this work, the grafting properties of ABS latexes were determined by separation of the soluble and insoluble phase of the polymer, followed by the characterization of these phases using analytical techniques. Phase separation was carried out dispersing the latex in acetone followed by ultracentrifugation. The soluble and insoluble polymer phases were for the first time analysed by NMR spectroscopy to obtain the corresponding fractions of SAN and PB in each phase. The soluble fraction was analysed by liquid-state 1H Nuclear Magnetic Resonance (NMR) spectroscopy, whereas the insoluble fraction was analysed by solid-state 13C NMR spectroscopy. Moreover, both phases were analysed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), and the results obtained are compared and discussed in this article. We found that the most accurate grafting properties are achieved by analysing the composition of the soluble and insoluble fraction by NMR spectroscopy.