REACTIVE BLENDING VIA COORDINATION CHEMISTRY - EXTRAORDINARY MECHANICAL RESPONSE FOR ATACTIC 1,2-POLYBUTADIENE COMPLEXED WITH PALLADIUM-CHLORIDE

Experimental evidence in solution and in the solid state suggests that atactic 1,2-polybutadiene and palladium chloride form coordination co mplexes with unusual mechanical properties. Ternary phase diagrams wit h tetrahydrofuran as the solvent highlight regions where gelation is f avored relative to precipitation. The strongest evidence for a network structure is based on the facts that (i) solid films swell in heptane , and (ii) infrared spectroscopy identifies a new absorption character istic of three-membered rings and dihapto coordination of the olefinic sidegroup in 1,2-polybutadiene to the metal center in palladium chlor ide-bis(acetonitrile). Carbon-13 solid state NMR spectroscopy suggests that the polymeric palladium complex is a glass when the salt concent ration is 4 mol%. NMR linewidth data together with the pulse sequence parameters suggest that the chain backbone of the polymeric palladium complex experiences a significant reduction in molecular mobility whic h is consistent with diamagnetic glassy materials. Most importantly, t he elastic modulus of polybutadiene increases by three orders of magni tude during the transition from rubbery to glassy behavior. This type of mechanical response cannot be explained by a filler effect, crystal lite reinforcement, or antiplasticization. Transition-metal coordinati on concepts applied to polymeric materials suggest that the enhancemen t in mechanical properties is a direct consequence of 'coordination cr osslinks' where the palladium salt bridges different polymer chains. H owever, palladium-catalyzed reactions of the olefinic sidegroup, gener ating a chemically crosslinked network, represent a second explanation of the significantly enhanced macroscopic physical properties of 1,2- polybutadiene in the presence of the transition-metal salt. Reactive b lending via metal-ligand coordination represents a new mechanism to co mpatibilize polymeric mixtures that would otherwise exhibit phase sepa ration.