Reactive blending of polymeric systems via metal-ligand coordination chemistr

This research has investigated the application of metal-ligand coordination chemistry for generating functionalized polymeric systems. Transition metals have specific reactivity toward organic functional groups. However, only a limited number of reactions exist for the ligands attached to macromolecules in comparison to their monomeric analogs. The polymer-effect stems from the specific steric environment created by the polymeric ligand around the metal center in question. Consequently, macromolecular-metal complexes yield species with unforseeable catalytic properties. The direct application of the metal-polymer interactions focuses on blending two incompatible polymers. The concept of reactive blending is novel, because it has endless possibilities of creating metal-polymer blends. Reactive blending also has its implications in the preparation of tailor-made functionalized polymeric systems. The challenge is to find the proper combination of metal and polymer that works in synergy. A feasible approach of addressing this problem is to focus on a polymer with distinct functional groups either in the main-chain or in sidegroup, and to characterize the trends in reactivity with suitable transition metals. The primary objective of this research investigation was to modify diene polymers containing carbon-carbon double bonds in (i) the sidegroup and (ii) the main chain via coordination chemical concepts. The second objective is more important since most commercial diene polymers contain unsaturation in the backbone. Transition-metal compatibilization of two dissimilar diene polymers due to microstructural differences was also investigated.;The following polymers successfully coordinate to transition metals in this research: atactic 1,2 polybutadiene, 3,4-polyisoprene, cis-polybutadiene, styrene-butadiene-styrene triblock copolymers, poly(diphenoxy)phosphazene, nylon-6, and epoxy-based oligomers. Solid-state characterization of binary and ternary mixtures has been addressed by asking certain "intelligent" questions to generate a generic investigative strategy for characterizing the polymer-metal hybrid networks. The resulting polymeric complexes are unique because their macroscopic physical properties do not follow the simple rule of additivity that is characteristics of weakly interacting blends. For example, weak rubbery diene polymers and blends are transformed into (i) mechanically reinforced ductile materials, or (ii) glassy materials when the concentration of palladium chloride is $approx$4 mol%, in the absence of high temperature annealing. Macroscopic changes detected via (i) thermo-mechanical property measurements, (ii) sol-gel behavior, (iii) acid-base solution chemistry, and (iv) polarized light optical property measurements are supported by molecular-level observations via infrared spectroscopy and nonlinear stress relaxation measurements. This research has identified and characterized new combinations of polymeric ligands and transition-metal salts that exhibit attractive physical properties based on molecular engineering design principles.