Role of Metal–Ligand Bond Strength and Phase Separation on the Mechanical Properties of Metallopolymer Films

This work studies the properties of poly­(<i>n</i>-butyl acrylate) functionalized with 2,6-bis­(1′-methylbenzimidazolyl)­pyridine ligand and cross-linked with either copper­(II), zinc­(II), or cobalt­(II) metal ions. Because of phase separation between the metal–ligand complex and the polymer matrix, these polymers have a rubbery plateau modulus that is 10 times higher than expected based on the theory of rubber elasticity. Differences in the metal–ligand bond strength influence the mechanical behavior at high temperature and strains. Because of the particularly weak bond strength associated with the copper–ligand bond, the metallopolymer containing copper degrades at a lower temperature and has lower yield strength, ultimate tensile strength, and creep resistance than polymers containing cobalt and zinc. To tune the properties of the polymer further, a polymer is made with both copper and cobalt ions. The hybrid polymer combines the properties of the stiffer cobalt-containing polymer with the more compliant copper-containing polymer