Catalytic Insertion Polymerization of Norbornene in Miniemulsion

The catalytic insertion polymerization of norbornene (NB) was implemented under miniemulsion conditions. Using sodium dodecyl sulfate (SDS) as surfactant and hexadecane as hydrophobe, the insertion polymerization was initiated by multicomponent catalysts generated in situ by reacting allylpalladium chloride dimer, [(η3-allyl)Pd(Cl)]2, with a desired phosphine ligand and then activating the resulting procatalyst with a salt of noncoordinating anion, typically the lithium salt of tetrakis(pentafluorophenyl)borate (Li[B(C6F5)4]·2.5Et2O). By choosing either an organo-soluble (tricyclohexylphosphine) or a water-soluble phosphine ligand (tris(3-sulfonatophenyl)phosphine sodium salt), two palladium procatalysts I and II exhibiting different solubilities in water were generated and then used to polymerize NB in miniemulsion. After activation, both I and II displayed high activity and led to stable PNB latexes with good particle size control throughout the course of the reaction. Stable polynorbornene latexes with a relatively broad particle size distribution were produced. The number-average particle diameter is often below 100 nm. The nature of the surfactant and the effect of changing the concentrations of activating agent, procatalyst, and hydrophobe on the polymerization kinetics, latex stability, and particle size were investigated.