Dispersion polymerization of styrene using a polystyrene/poly(l-glutamic acid) block copolymer as a stabilizer

A block copolymer (PS-b-poly(l-Glu)) composed of polystyrene and poly(l-glutamic acid) was used as a stabilizer for dispersion polymerization of styrene. When dispersion polymerization of styrene was conducted at 70 °C in 80% dimethylformamide–water with 0.5 wt% PS-b-poly(l-Glu), spherical polystyrene particles with Dn = 0.72 μm and narrow size distribution were obtained. Whereas AIBN concentration did not have any effects on particle size, molecular weight of the polystyrene particles was strongly dependent on the initiator concentration. As concentration of the PS-b-poly(l-Glu) increased from 0.2 to 1.0 wt%, particle size decreased from Dn = 0.91 to 0.69 μm with keeping surface area occupied by one poly(l-glutamic acid) chain about S = 50 nm2. On the other hand, an increase in initial concentration of styrene from 2 to 20 wt% caused an increase in particle size from Dn = 0.48 to 1.36 μm and a decrease in surface area per poly(l-glutamic acid) block from S = 91 to 45 nm2. Colloidal stability of the polystyrene particles in aqueous solution was responsive to pH due to the surface-grafted poly(l-glutamic acid). For dispersion polymerization of styrene, the PS-b-poly(l-Glu) functions as both a stabilizer and a surface modifier.

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► One-step preparation of well-defined and surface-functionalized polystyrene particles.
► α-Helical poly(l-glutamic acid) block copolymer was effective as a steric stabilizer.
► The poly(l-glutamic acid) segments were grafted on the particles.
► Size and surface property of the polystyrene particles were controllable.
► Resulting particles showed pH-responsive behavior.