title: Small-molecule dynamics and mechanisms underlying the macroscopic mechanical properties of coordinatively cross-linked polymer networks.
abstract: Specific metal-ligand coordination between bis-Pd(II) and Pt(II) organometallic cross-linkers and poly(4-vinylpyridine) in DMSO defines a three-dimensional associative polymer network. Frequency-dependent dynamic mechanical moduli of a series of four different bulk materials, measured across several decades of oscillatory strain rates, are found to be quantitatively related through the pyridine exchange rates measured on model Pd(II) and Pt(II) complexes. Importantly, the mechanism of ligand exchange in the networks is found to be the same solvent-assisted pathway observed in the model complexes, and so the bulk mechanical properties are determined by relaxations that occur when the cross-links are dissociated from the polymer backbone. It is how often the cross-links dissociate, independently of how long they remain dissociated, that determines the bulk mechanical properties. The quantitative relationship between bulk materials properties and the kinetics and mechanisms observed in model compounds holds promise for the rational, molecular design of materials with tailored mechanical properties.
authors.affiliation: Department of Chemistry and Center for Biologically Inspired Materials and Material Systems, Duke University, Durham, NC 27708-0346, USA.
authors.forename: Wayne C
authors.initials: WC
authors.lastname: Yount
authors.forename: David M
authors.initials: DM
authors.lastname: Loveless
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Craig
mesh_terms: D003198:Computer Simulation; D003432:Cross-Linking Reagents / Q000138:chemical synthesis / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D008970:Molecular Weight; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D010984:Platinum / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D011145:Polyvinyls / Q000737:chemistry
chemical_list: D003432:Cross-Linking Reagents; D009942:Organometallic Compounds; D011108:Polymers; D011145:Polyvinyls; C019535:poly(4-vinylpyridine); D010984:Platinum; D010165:Palladium