Journal of Polymer Science Part A: Polymer Chemistry, Vol.55, No.18, 3110-3116, 2017
The Effects of Counter Anions on the Dynamic Mechanical Response in Polymer Networks Crosslinked by Metal-Ligand Coordination
Metal-ligand coordination has been proven to be an attractive strategy to tune a polymer network's dynamic mechanical properties, such as self-healing ability. Nonetheless, the role of counter anions is often overlooked. To address this, a series of polydimethylsiloxane (PDMS) films crosslinked through lanthanide metal cations (Eu3+, Tb3+)-bipyridine interactions have been prepared and studied. Neutral 2,2'-bipyridine ligands were embedded into the linear polydimethylsiloxane (PDMS) chain through polycondensation. With nitrate (NO3-) as the coordinating anions, metal salts Eu(NO3)(3) and Tb(NO3)(3) were found to be ineffective crosslinkers. With noncoordinating anions, such as triflate (OTf: CF3SO3-), metal salts Eu(OTf)(3) and Tb(OTf)(3) showed improved interaction strength with bipyridine ligands. Surprisingly, the addition of Eu(OTf)(3) and Tb(OTf)(3) salts also increased the d-spacing distances of the phase-segregated domains between metal-ligand complexes and the PDMS polymer backbone. For the Eu(OTf)(3)(-), Tb(OTf)(3)-PDMS films, the muchimproved self-healing abilities are attributed to the crosslinker dynamics and the enhanced chain mobility. This work underlines the importance of counter anions on the mechanical properties, and provides further guidance on the future design of self-healing metal-ligand crosslinked polymers.) (C) 2017 Wiley Periodicals, Inc.