ANNEALING EFFECTS ON THE SOLID-STATE PROPERTIES OF TRANSITION-METAL COORDINATION-COMPLEXES AND NETWORKS BASED ON DIENE POLYMERS WITH PALLADIUM-CHLORIDE

This study focuses on the thermal and mechanical properties of 1,2-pol ybutadiene and 3,4-polyisoprene with an inorganic salt, bis(acetonitri le)dichloropalladium (II). Upon mixing in THF, effective crosslinks ar e formed because the acetonitrile ligands of the palladium salt are di splaced by olefinic pendant groups of the polymers. Using a simple nth -order irreversible kinetic rate model, the palladium-catalyzed Heck-l ike exothermic reaction in solid films was characterized via isotherma l and nonisothermal DSC. Thermal energy and mass balances appropriate to a batch reactor are developed from first principles and applied to the isothermal DSC output curve to calculate the time dependence of re actant conversion. Relevant kinetic parameters, such as the order of t he reaction, the characteristic time constant for the chemical reactio n, and the activation energy, have been determined. The kinetic data s uggest that the palladium-catalyzed crosslinking reactions are diffusi on controlled in the solid state because the reaction order is very cl ose to unity. Higher glass transition temperatures (T-g) are measured by dynamic mechanical thermal analysis (DMTA) and differential scannin g calorimetry (DSC) when (i) palladium concentration, (ii) annealing ( heat treatment) time, and (iii) annealing temperature increase. After 2 h of annealing at 80 degrees C, which corresponds to a temperature b elow the first exothermic crosslinking reaction (approximate to 115 de grees C) during nonisothermal DSC kinetic studies, rubbery materials c ontaining very low concentrations of PdCl2 (i.e., 0.5 mol %) exhibit r einforced ductile stress-strain response. When annealing is performed at the peak temperature of the first exothermic event, the rubbery mat erials are transformed into glasses. Transition-metal compatibilizatio n of atactic 1,2-polybutadiene and 3,4-polyisoprene via PdCl2 is demon strated by monitoring the glass transition obtained from dynamic mecha nical tan delta profiles. The effect of annealing this ternary reactiv e ''blend'' produces a glassy material exhibiting an elevated T-g and synergistic mechanical properties. (C) 1996 John Wiley & Sons, Inc.