Formation of carbamates of amino groups of microbial poly(ε-L-lysine) (ε-PL)1) and poly(allyl amine) (PAA) with carbon dioxide (CO2) was studied by using 13C and 15N solid NMR. Reversibility of formation of carbamates was also examined. Aqueous solutions of poly(amine)s through which CO2 was bubbled for relevant time were cast on a petri dish and dried in vacuum for several days to make film samples. Carbon peak of carbamate appeared at 164 ppm in the CPMAS spectrum of ε-PL film, by bubbling CO2 through aqueous solution of ε-PL at room temperature2). By bubbling N2 at 333 K through this ε-PL solutions with CO2 bubbling, carbamate peak in the CPMAS spectrum disappeared3). Carbamate formation was also observed in the ε-PL film cast from methanol solution through which CO2 gas was bubbled. On the other hand, carbon peaks of bicarbonate and carbamate appeared at 161 ppm and 164 ppm, respectively, by bubbling CO2 through aqueous solution of PAA4). By bubbling N2 at room temperature through this PAA solutions with CO2 bubbling, only the former peak disappeared remaining the latter peak unchanged. By bubbling N2 through this solution at 90˚C, the carbamate peak also disappeared. The PAA aqueous solution desorbed the absorbed CO2 completely by N2 bubbling.
1) S. Maeda, C. Sasaki, K.-K. Kunimoto, In: H. N. Cheng, et al. Ed., "NMR Spectroscopy of Polymers: Innovative NMR Strategies for Complex Macromolecular Systems" ACS symposium series, vol. 1077, chapter 19, pp 317-335.
2) S. Maeda, S. Oumae, S. Kaneko, K.-K. Kunimoto, Polym. Bull., 68, 745-754 (2012).
3) S. Maeda, K. Kato, K. Takagi, M. Kobayashi, K.-K. Kunimoto, Int. J. Mod. Phys. B, 25(31), 4315-4318 (2011).
4) K. Takagi, S. Maeda, K.-K. Kunimoto, Polym. Preprint, Jpn, 62(1),1015 (2013).