Living Ring-Opening Metathesis Polymerization in Aqueous Media Catalyzed by Well-Defined Ruthenium Carbene Complexes

Abstract

In aqueous media, two well-defined ruthenium carbene complexes [(Cy 3 P) 2 Cl 2 Ru CHCH CPh 2 ( 1 ) and (Cy 3 P) 2 Cl 2 Ru CHPh ( 2 ), Cy = cyclohexyl] catalyzed living ring-opening metathesis polymerization (ROMP) of functionalized norbornenes and 7-oxanorbornenes. Monomers were dispersed in water using a cationic surfactant, and polymerization was initiated by injection of a catalyst solution to yield a polymer latex. The polymerization of hydrophilic 7-oxanorbornene monomer and a hydrophobic norbornene monomer displayed similar behavior in aqueous media, with the resultant polymers having lower molecular weights relative to polymerization in anhydrous organic solution on a similar time scale. The polydispersity indices (PDIs) of polymers prepared from the hydrophilic monomer using catalyst 1 in the presence of water (PDI = 1.20) were narrower than those obtained by solution polymerization (PDI = 2.11), while PDIs for polymers prepared using catalyst 2 remained low in both the presence of water and in anhydrous solution (PDI ≈ 1.13). The linear relationship between molecular weight and monomer/catalyst ratios and the absence of chain transfer and termination processes indicated that these systems are indeed living. Furthermore, this new ROMP technique was shown to be an efficient method for the preparation of well-defined block copolymers.