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This study focuses on the properties of solid films formed from tetrahydrofuran solutions containing diene polymers, polybutadiene or polyisoprene, and an inorganic salt, bis(acetonitrile)dichloropalladium(II). Upon mixing, effective cross-links are formed, because the acetonitrile ligands of the palladium salt are displaced by olefinic pendant groups of the polymers. Infrared data measured herein and previous studies of the chemistry of palladium compounds suggest that a Heck-like mechanism is operative to generate chemical cross-links via palladium-catalyzed reactions. The swelling behavior of polybutadiene and polyisoprene was studied in various solvents. In both cases, equilibrium swelling ratios decrease with an increase in salt content, indirectly supporting the concept of a network structure. Using the Flory-Rehner relation, the number-average molecular weight between cross-link junction points (Mc) was calculated from the swelling data. Relative to the undiluted polymers, the mechanical properties of polybutadiene and polyisoprene solid films show a dramatic increase of 3 orders of magnitude in Young's modulus of elasticity when the palladium salt content is 4 mol %. Thermogravimetric measurements show that an increase in the transition-metal salt (PdCh) content, as well as annealing at 80 °C, enhances the thermal stability of solid films. The glass transition temperatures (Tg) of solid films determined by differential scanning calorimetry increase with PdCh content until the thermal plateau is achieved between 1 and 3 mol % palladium salt, where the increase i: undiluted polymer.

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Experimental evidence in solution and in the solid state suggests that atactic 1,2‐polybutadiene and palladium chloride form coordination complexes with unusual mechanical properties. Ternary phase diagrams with tetrahydrofuran as the solvent highlight regions where gelation is favored 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 characteristics of three‐membered rings and dihapto coordination of the olefinic sidegroup in 1,2‐polybutadiene to the metal center in palladium chloride‐bis(acetonitrile). Carbon‐13 solid state NMR spectroscopy suggests that the polymeric palladium complex is a glass when the salt concentration 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 which is consistent with diamagnetic glassy materials. Most importantly, the elastic modulus of polybutadiene increases by three orders of magnitude during the transition from rubbery to glassy behavior. This type of mechanical response cannot be explained by a filler effect, crystallite reinforcement, or antiplasticization. Transition‐metal coordination concepts applied to polymeric materials suggest that the enhancement in mechanical properties is a direct consequence of ‘coordination crosslinks’ where the palladium salt bridges different polymer chains. However, palladium‐catalyzed rections of the olefinic sidegroup, generating 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 blending via metal‐ligand coordination represents a new mechanism to compatibilize polymeric mixtures that would otherwise exhibit phase separation.

Surface and interaction characteristics of styrene-4 vinyl pyridine (S-4VP) diblock copolymers have been investigated by the method of inverse gas chromatography. Both constituents of the diblock were found to be basic, the 4VP moiety being the stronger base. When adsorbed onto a standard chromatographic support (Chromosorb), a mildly acidic surface, the 4VP block is preferentially oriented to the substrate, leaving an air interphase which is enriched in polystyrene (PS). The surface enrichment by PS is furthered by the lower surface energy of the PS block. Thus, when adsorbed on acidic surfaces, the wettability and related surface properties of P(S-4VP) diblocks will resemble those of PS, in keeping with the observed compositional heterogeneities.