LIVING FREE-RADICAL DISPERSION POLYMERIZATION OF STYRENE

Polystyrene latexes were synthesized via living free-radical chemistry with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) in both alcoholic a nd aqueous alcoholic media using poly(N-vinylpyrrolidone) (PVP) as a s teric stabilizer at 112-130 degrees C. Genuine dispersion polymerizati on was only achieved in ethylene glycol or ethylene glycol-water mixtu res. In the absence of TEMPO, near-quantitative monomer conversions, h igh molecular weights, broad molecular weight distributions, and submi crometer-sized latexes were obtained. The addition of TEMPO had a prof ound effect on the polymerization chemistry: only moderate monomer con versions las low as 20%, with a maximum conversion of 60% obtained aft er 71 h) and larger, typically micrometer-sized, latexes were obtained with TEMPO-mediated syntheses. Polydispersities (M-w/M-n's) as low as 1.11 were achieved in the presence of TEMPO, but only relatively low molecular weight polystyrene chains were obtained. All TEMPO-synthesiz ed latexes had spherical particle morphologies and very broad size dis tributions, as evidenced by scanning electron microscopy (SEM) and dis k centrifuge photosedimentometry (DCP), respectively. Surprisingly, hi gh Gamma values were calculated for the adsorbed PVP stabilizer, which suggests that it is not located exclusively on the outside of the pol ystyrene latex particles.