DISPERSION POLYMERIZATION OF STYRENE IN POLAR-SOLVENTS .6. INFLUENCE OF REACTION PARAMETERS ON PARTICLE-SIZE AND MOLECULAR-WEIGHT IN POLY(N-VINYLPYRROLIDONE)-STABILIZED REACTIONS

Polymerization of styrene in alcoholic media in the presence of poly(N-vinylpyrrolidone) (PVP) produces monodisperse latex particles from 1 to 18 μm in size. The results are rationalized in the context of a mechanism involving grafting of polystyrene chains to PVP steric stabilizer. Increasing the initial styrene concentration from 5 to 40% by volume increases the particle size obtained. Comparison of this effect to that of added toluene suggests that the primary effect of monomer concentration is a solvent effect: the more soluble the polystyrene is in the reaction medium, the larger the particles. The influence of PVP concentration and molecular weight was found to obey the approximate relationship d50 = 90.4[PVP]-0.31MW-0.18. The power law dependence of diameter on initiator concentration was found to be 0.39, in good agreement with prior work. The addition of a chain-transfer agent produced polydisperse particles with molecular weight dispersities (Mw/Mn) of ca. 100, modifying the power law dependence of size on initiator concentration to a slope of 0.19. A maximum in particle size was found in a series of solvents varying from 80% ethanol/water to ethanol and from methanol to decanol, with 4-μm particles obtained in butanol and pentanol, 1.2-μm particles in 80% ethanol/water, and 1.6-μm particles in decanol. The molecular weights correlated inversely with particle size and could be semiquantitatively rationalized on the basis of the locus of polymerization shifting from particle capture of growing oligomers from the continuous phase in the case of smaller particles to particle capture of dead polymer in the case of large particles. © 1990, American Chemical Society. All rights reserved.