Comprehensive NMR Studies of the Structures and Properties of PEI Polymers

In this research, a suite of multinuclear and multidimensional NMR experiments such as 1D H-1, C-13, and N-15 NMR and 2D homonuclear H-1-H-1 COSY, 2D heteronuclear H-1{C-13} HMQC, HMBC, HMQC-TOCSY, and 2D heteronuclear H-1{N-15} HMBC NMR were used to study a set of representative PEI polymers including hyperbranched polymers of high and low molecular weight and a low molecular weight linear oligomer. Furthermore, the protonation of the multiple unique basic sites of the low molecular weight hyperbranched PEI polymer was also studied through titration with 9.0 M aqueous hydrochloric acid solution and monitored in situ using C-13 NMR by tracking the change of C-13 chemical shifts as a function of pH during the titration. Such thorough NMR characterizations of PEI polymers can provide a comprehensive understanding of their structures and properties which may aid in more and better applications of these interesting polymers.