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 D(n)=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 D(n)=0.91 to 0.69 µm with keeping surface area occupied by one poly(L-glutamic acid) chain about S=50 nm(2). On the other hand, an increase in initial concentration of styrene from 2 to 20 wt% caused an increase in particle size from D(n)=0.48 to 1.36 µm and a decrease in surface area per poly(L-glutamic acid) block from S=91 to 45 nm(2). 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.

Effects of polystyrene-b-poly(aminomethyl styrene)s as stabilizers on dispersion polymerization of styrene in alcoholic media.

The effects of polystyrene-b-poly(aminomethyl styrene) (PS(n)-b-PAMS(m)) stabilizers on the particle size (D(n)) and size distribution (PSD) in dispersion polymerization of styrene were investigated. The block copolymers, PS(n)-b-PAMS(m), were prepared as follows: (i) atom transfer radical polymerization (ATRP) of styrene (PS-Br), (ii) ATRP of vinylbenzylphthalimide with the PS-Br (PS-b-PVBP), and (iii) treatment of the PS-b-PVBP with hydrazine. When the dispersion polymerization of styrene proceeded at 60 degrees C in ethanol with PS(19)-b-PAMS(130) stabilizer, spherical polystyrene particles with D(n)=0.91 microm (PSD=1.01) were obtained. The particle size was strongly affected by the copolymer composition. With an increase in PAMS block length from m=54 to 100 in PS(17)-b-PAMS(m), particle diameter became smaller from 1.55 to 0.91 microm. On the other hand, an increase in the length from m=20 to 82 in PS(34)-b-PAMS(m)s caused an increase in particle size from 0.35 to 0.70 microm. Titration of the particles suggests that 14-81% of stabilizers used in the polymerization system were attached on the polystyrene particle surfaces, depending on the composition of the block copolymers. Thus, for the dispersion polymerization of styrene, PS(n)-b-PAMS(m) block copolymers have both functions as a stabilizer during polymerization and surface-modification sites of polystyrene particles.