Reactive blending via metal‐ligand coordination

Abstract

Abstractd‐Block transition‐metal‐containing polymer blends which form coordination complexes are described in this treatise. The model compounds are zinc acetate dihydrate, copper acetate dihydrate, nickel acetate tetrahydrate, cobalt chloride hexahydrate, palladium chloride bis (acetonitrile), and the dimer of dichlorotricarbonylruthenium (II). Two classes of ligands are of interest. Poly (4‐vinylpyridine), P4VP, and copolymers that contain 4‐vinylpyridine repeat units form complexes with zinc, copper, nickel, cobalt, and ruthenium salts. Atactic 1,2‐polybutadiene contains olefinic sidegroups that displace weakly bound acetonitrile ligands and coordinate to palladium chloride. Thermal analysis via differential scanning calorimetry suggests that the glass transition temperature of the polymeric ligand is enhanced by these low‐molecular‐weight transition‐metal salts in binary and ternary blends. In some cases, d‐block salts function as transition‐metal compatibilizers for copolymers that would otherwise be immiscible. The isothermal ternary phase diagram for polybutadiene with palladium chloride highlights regions of gelation, precipitation, and transparent solutions during blend preparation in tetrahydrofuran. Fourier transform infrared spectroscopy provides molecular‐level data that support the concept of polymeric coordination complexes. High‐resolution carbon‐13 solid‐state NMR spectroscopy identifies (1) near‐neighbor interactions between polymeric pyridine ligands and the ruthenium salt, and (2) a considerable reduction in the molecular mobility of the polybutadiene chain backbone when it forms a coordination complex with palladium chloride. The elastic modulus of polybutadiene increases by three orders of magnitude when the palladium salt concentration is 4 mol % in a solid‐state glassy film. A thermodynamic interpretation of ligand field stabilization energies appropriate to tetrahedral cobalt and octahedral nickel complexes is employed to estimate the synergistic enhancement of the glass transition temperature, particularly when coordination crosslinks are present. ©1995 John Wiley & Sons, Inc.