SYNERGISTIC MECHANICAL RESPONSE IN BLENDS OF DIENE POLYMERS AND THEIRCOMPLEXES WITH PALLADIUM-CHLORIDE

The mechanical properties of atactic 1,2-polybutadiene and 3,4-polyiso prene can be modified significantly with the addition of bis(acetonitr ile)dichloropalladium(II). These weak rubbery polymers are transformed into glassy materials when the salt concentration is approximate to 4 mol %, in the absence of high-temperature annealing. Stress-strain me asurements and Fourier transform infrared (FTIR) spectra for blends of cis-polybutadiene and PdCl2, without high-temperature annealing, sugg est that pi-complexes form between palladium and the olefinic groups w ithin the backbone of the polymer. These solid complexes cannot be dis solved in the original solvent (tetrahydrofuran), nor can they be disr upted by triphenylphosphine. Young's modulus of the cis-polymer is enh anced by a factor of 50 when the salt concentration is 4 mol %, and th e fracture strain is approximately 300%. An exothermic process centere d at approximate to 250 degrees C accompanied by minimal weight loss s uggests that PdCl2 could trigger high-temperature dimerization reactio ns of the carbon-carbon double bonds in the backbone of the cia-polyme r. High-temperature annealing effects on the stress-strain response of cis-polybutadiene with 4 mol % PdCl2 are consistent with the data fro m calorimetry, suggesting that catalytically induced chemical crosslin king is operative at high temperatures. This latter claim is verified by infrared spectroscopy at ambient and elevated temperatures. Hence, bis(acetonitrile)dichloropalladium(II) coordinates to and catalyzes di merization reactions of olefinic groups when they are present in the m ain chain or the sidegroup. This square-planar transition-metal salt a lso enhances the high-strain mechanical response of commercial styrene -butadiene-styrene triblock copolymers (Kraton(TM) D series). Reactive blending and compatibilization with transition-metal salts are attrac tive strategies to modify the mechanical properties of commercially im portant diene-based polymers that contain unsaturation in the main cha in or the sidegroup. (C) 1996 John Wiley & Sons, Inc.