Ionene segmented block copolymers containing imidazolium cations: Structure–property relationships as a function of hard segment content

Imidazolium ionene segmented block copolymers were synthesized from 1,1′-(1,4-butanediyl)bis(imidazole) and 1,12-dibromododecane hard segments and 2000 g/mol PTMO dibromide soft segments. The polymeric structures were confirmed using 1H NMR spectroscopy, and resonances associated with methylene spacers from 1,12-dibromododecane became more apparent as the hard segment content increased. TGA revealed thermal stabilities ≥250 °C for all imidazolium ionene segmented block copolymers. These ionene segmented block copolymers containing imidazolium cations showed evidence of microphase separation when the hard segment was 6–38 wt%. The thermal transitions found by DSC and DMA analysis found that the Tg and Tm of the PTMO segments were comparable to PTMO polymers, namely approximately −80 °C and 22 °C, respectively. In the absence of PTMO soft segments the Tg increased to 27 °C The crystallinity of the PTMO segments was further evidence of microphase separation and was particularly evident at 6, 9 and 20 wt% hard segment, as indicated in X-ray scattering. The periodicity of the microphase separation was well-defined at 20 and 38 wt% hard segment and found to be approximately 10.5 and 13.0 nm, respectively, for these ionenes wherein the PTMO soft segment is 2000 g/mol. Finally, the 38 and 100 wt% hard segment ionenes exhibited scattering from correlations within the hard segment on a length scale of approximately 2–2.3 nm. These new materials present structure on a variety of length scales and thereby provide various routes to controlling mechanical and transport properties.