REACTIVE BLENDING VIA METAL-OLEFIN COORDINATION IN DIENE POLYMERS - SOLID-STATE PROPERTIES THAT SUPPORT THE CONCEPT OF A NETWORK STRUCTURE

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 (M(c)) 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 (PdCl2) content, as well as annealing at 80 degrees C, enhances the thermal stability of solid films. The glass transition temperatures (T-g) of solid films determined by differential scanning calorimetry increase with PdCl2 content until the thermal plateau is achieved between 1 and 3 mol % palladium salt, where the increase in T-g (i.e., Delta T-g) is approximately 100 degrees C relative to the undiluted polymer.