Association of nucleobase-containing ammonium ionenes

Adenine- and thymine-functionalized ammonium ionenes with variation in spacer lengths are successfully synthesized using the Michael addition post-polymerization functionalization. This report describes the influence of pendant spacer length on homo-association and heteroassociation of complementary nucleobase-containing ionenes. The ionene homopolymers and complementary blends with various spacer lengths show a single glass transition temperature. Higher glass transition temperatures are observed for the shorter-spacer ionene homopolymers and their blends. The hydrogen bonding interactions in both blends of adenine-containing ionenes (ionene-A) and thymine-containing ionenes (ionene-T) with both spacer lengths are studied using differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). DSC analyses do not reveal hydrogen bonding interactions in the ionene blends with the shorter spacer length. In contrast, the longer spacer length ionene blends show the presence of hydrogen bonding interactions and demonstrate that homoassociation is stronger than heteroassociation. FTIR spectroscopy and AFM confirm hydrogen bonding interactions for the longer spacer ionene blends.