title: Molecular Motion of the Junction Points in Model Networks Prepared by Acyclic Triene Metathesis.
abstract: The junction dynamics in a selectively deuterated model polymer network containing junctions on every 21st chain carbon is studied by solid state (2) H echo NMR. Polymer networks are prepared via acyclic triene metathesis of deuteron-labeled symmetric trienes with deuteron probes precisely placed at the alpha carbon relative to the junction point. The effect of decreasing the cross-link density on the junction dynamics is studied by introduction of polybutadiene chains in-between junctions. The networks are characterized by swelling, gel content, and solid state (1) H MAS NMR. Line shape analysis of the (2) H quadrupolar echo spectra reveals that the degree of motion anisotropy and the distribution of motion correlation times depend on the cross-link density and structural heterogeneity of the polymer networks. A detailed model of the junction dynamics at different temperatures is proposed and explained in terms of the intermolecular cooperativity in densely-packed systems.
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, Florida, 32611-7200, USA.
authors.forename: Lucas Caire
authors.initials: LC
authors.lastname: da Silva
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, Florida, 32611-7200, USA.
authors.forename: Clifford R
authors.initials: CR
authors.lastname: Bowers
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz, 55128, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Graf
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, Florida, 32611-7200, USA.
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Wagener
mesh_terms: D016880:Anisotropy; D002070:Butadienes / Q000737:chemistry*; D003903:Deuterium / Q000737:chemistry*; D020724:Elastomers / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D015394:Molecular Structure; D009038:Motion; D013696:Temperature
chemical_list: D002070:Butadienes; D020724:Elastomers; C028834:polybutadiene; D003903:Deuterium
keywords: NMR; cross-linking; dynamics; metathesis