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 (D w /D n ) at a high yield. For example, polymer microspheres with a number-average diameter (D n ) of 1.10 μm and D w /D n of 1.01 were obtained at a yield of 97%; these microspheres are composed of a polymer with a controlled molecular weight (M n = 11 700) and narrow molecular weight distribution (M w /M n = 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. NPG Asia Materials (2016) 8, e307; doi:10.1038/am.2016; published online 9 September 2016 INTRODUCTION Polymer microspheres are frequently applied in scientific and industrial fields such as coatings, electronics, biomedical engineering and organic synthesis. [1][2][3][4][5][6] Precision synthesis of polymer microspheres with a regulated size, a narrow size distribution and surface functionality is very important for the further development of polymer microspheres for advanced applications. The crosslinking of polymer microspheres is also likely to be very important for achieving sufficient reagent resistance, thermal stability and good mechanical properties. 7 Among the heterogeneous polymerization techniques, dispersion polymerization is an effective method for obtaining polymer microspheres with narrowly dispersed diameter distributions. 8,9 Dispersion polymerization is defined as a heterogeneous polymerization process that starts from a homogeneous solution of all the starting materials (i.e., the monomer, initiator and stabilizer), whereas the polymer microspheres precipitate out during the progress of the polymerization. 10 Accordingly, the polymerization should be carried out in good solvents for the monomers but poor solvents for the polymers being formed. To establish precision dispersion polymerization, the living anionic polymerization of styrene was studied in hydrocarbon solvents. [11][12][13] Although this technique successfully provides narrowly dispersed polym...