Well-defined polymer microspheres formed by living dispersion polymerization: precisely functionalized crosslinked polymer microspheres from monomers possessing cumulated double bonds

The precise method for synthesizing well-defined polymer microspheres via π-allylnickel-catalyzed living coordination polymerization of allene derivatives under dispersion polymerization conditions is described. The π-allylnickel-catalyzed living coordination polymerization of allene derivatives such as phenoxyallene was carried out in protic solvents such as methanol in the presence of stabilizers such as polyvinylpyrrolidone to produce polymer microspheres with a narrowly dispersed diameter distribution (Dw/Dn) at a high yield. For example, polymer microspheres with a number-average diameter (Dn) of 1.10 μm and Dw/Dn of 1.01 were obtained at a yield of 97%; these microspheres are composed of a polymer with a controlled molecular weight (Mn=11 700) and narrow molecular weight distribution (Mw/Mn=1.06). The size of the resulting polymer microspheres proved to be affected by polymerization conditions such as the initial monomer concentrations, monomer structures, polymerization media and stabilizers. Unlike conventional dispersion polymerization systems, the use of a bifunctional monomer, 1,4-diallenoxybenzene, for this living dispersion polymerization successfully produced well-defined crosslinked living polymer microspheres that exhibited high solvent tolerance. The postpolymerization of functional allene monomers in the living dispersion polymerization was also successful, resulting in functionalized polymer microspheres that could be applied in solid-phase organic synthesis and solid-supported transition metal catalysis. A controllable process for producing uniform, robust microspheres can make mixed solid-liquid chemical reactions easier to perform. Tiny beads of polymers such as polystyrene are finding increasing use as supports for catalysts in organic synthesis. Now, Ikuyoshi Tomita from the Tokyo Institute of Technology and co-workers have used a ‘living’ coordination mechanism, which polymerizes molecules until directed to stop, to improve the size distribution and modification capabilities of microspheres. Nickel-based catalysts and unsaturated, bifunctional carbon reagents worked together to generate microspheres with cross-linked internal structures for additional strength and solvent tolerance. Furthermore, the microsphere surfaces contained living, growing ends that can attach to additional reagents. Synthetic trials revealed that decorating the microspheres with palladium produced a heterogeneous catalyst that could be recovered and reused multiple times with little loss of activity. The precision synthetic method of well-defined polymer microspheres by the π-allylnickel-catalyzed living coordination polymerization of allene derivatives under the dispersion polymerization conditions is described. Unlike the conventional dispersion polymerization systems, the use of a bifunctional monomer, 1,4-diallenoxybenzene, to this living dispersion polymerization successfully gave well-defined crosslinked living polymer microspheres that exhibit high solvent-tolerant properties. The postpolymerization of functional allene monomers in the living dispersion polymerization also proceeded smoothly to give functionalized polymer microspheres that enabled their applications to the solid-phase organic synthesis and the solid-supported transition metal catalysts.