A Simple Method for Synthesizing Ultra-high-molecular-weight Polystyrene through Emulsion Polymerization Using Alkyl-9-BBN as an Initiator

Organoboron-mediated polymerizations

The scientific community has witnessed extensive developments and applications of organoboron compounds as synthetic elements and metal-free catalysts for the construction of small molecules, macromolecules, and functional materials over the last two decades. This review highlights the achievements of organoboron-mediated polymerizations in the past several decades alongside the mechanisms underlying these transformations from the standpoint of the polymerization mode. Emphasis is placed on free radical polymerization, Lewis pair polymerization, ionic (cationic and anionic) polymerization, and polyhomologation. Herein, alkylborane/O2 initiating systems mediate the radical polymerization under ambient conditions in a controlled/living manner by careful optimization of the alkylborane structure or additives; when combined with Lewis bases, the selected organoboron compounds can mediate the Lewis pair polymerization of polar monomers; the bicomponent organoboron-based Lewis pairs and bifunctional organoboron-onium catalysts catalyze ring opening (co)polymerization of cyclic monomers (with heteroallenes, such as epoxides, CO2, CO, COS, CS2, episulfides, anhydrides, and isocyanates) with well-defined structures and high reactivities; and organoboranes initiate the polyhomologation of sulfur ylides and arsonium ylides providing functional polyethylene with different topologies. The topological structures of the produced polymers via these organoboron-mediated polymerizations are also presented in this review mainly including linear polymers, block copolymers, cyclic polymers, and graft polymers. We hope the summary and understanding of how organoboron compounds mediate polymerizations can inspire chemists to apply these principles in the design of more advanced organoboron compounds, which may be beneficial for the polymer chemistry community and organometallics/organocatalysis community.

Anionic/nonionic surfactants for controlled synthesis of highly concentrated sub-50 nm polystyrene spheres

Polystyrene nanospheres are of great importance in 3D hard templating along with many other fields like pharmaceuticals and coatings. Therefore, it is important to be able to prepare polystyrene beads with different sphere sizes that suit each application. In this work, the emulsion polymerization method was used to prepare monodispersed polystyrene (PS) spheres with an average size of 50 nm, using styrene monomer, sodium dodecyl sulfate (SDS) and polyvinylpyrrolidone (PVP) as surfactants, and potassium persulfate (KPS) as the initiator. The average size and size distribution of the PS spheres were controlled by optimizing the synthesis parameters such as the concentration of the monomer, initiator, and surfactant, the type of surfactant, and the time and temperature of polymerization. The shape, size, and size distribution of the prepared PS spheres were characterized using dynamic light scattering (DLS) and scanning electron microscopy (SEM). The preparation of perfectly spherical PS spheres as small as 50 nm with a narrow size distribution is obtained using 8% styrene with (5% SDS and 2% KPS of the styrene amount) at 90 °C, with the monomer and surfactant molar ratio and concentration and the polymerization temperature being the dominating factors that affect the PS bead size.