Catalytic Emulsion Polymerization of Olefins:  Ab Initio Polymerization of Norbornene

It has recently been shown that it is possible to polymerize homo- and copolymers of olefins in aqueous media by using late transition metal catalysts. This has opened a new set of opportunities to produce simple and composite latex particles based on ethylene and its olefinic derivatives. Here we report some of our experience in creating water-based latices from the strained cyclic olefin, norbornene. This has been done as ab initio batch emulsion polymerizations using two different allylpalladium catalysts and a lithium-based activator as substitutes for the free radical initiator in standard emulsion polymerization. Such experiments produce small latex particles (ca. 50 nm) and can be burdened with large amounts of coagulum. In studying the effects of catalyst levels, ionic strength, and temperature on the reaction rates, conversion levels, and particle size, we have determined that the coagulum is produced by the migration of the catalyst and activator to the emulsified monomer droplets, producing large agglomerates of ∼10 μm polymer particles. After separating out the coagulum, the latices are stable for over a year. It has also become clear that in the aqueous environment the lithium activator is not necessary to promote emulsion polymerization and that without it we eliminate the coagulum. Apparently, the surfactant (in our case SDS) works as a weakly coordinating anion with the Pd catalyst. This work has shown that Pd catalysts can tolerate direct injection into the water.