Exploring the Effects of Bulky Cations Tethered to Semicrystalline Polymers: The Case of Tetraaminophosphoniums with Ring-Opened Polynorbornenes

Herein, a simple synthetic method to functionalize norbornene at the S-position with a base-stable tetraaminophosphonium cation was developed. Upon confirmation that the cationic monomer could be polymerized in a living fashion, statistical and diblock copolymers were synthesized with norbornene as a comonomer. After hydrogenation, the statistical copolymers were effective anion-exchange materials, while the diblock did not produce a free-standing film. Differential scanning calorimetry and atomic force microscopy indicated that crystallinity was mostly suppressed by the bulky phosphonium cations in the statistical copolymers, with the impact somewhat dependent on the amino groups bound to the phosphorus atom. Small-angle X-ray scattering profiles revealed a two-phase morphology with 3 nm domains arising from ion clustering in the film. Altogether, the study revealed the large impact these novel phosphonium cations have on polymer organization and packing, which is a critical consideration when targeting larger delocalized cations in anion-transport materials.