Kinetics studies of the sulfate radical-initiated polymerization of vinyl acetate and 4-vinylpyridine in the presence of silica nanoparticles.

PAULA CAREGNATO; GALO CARRILLO LE ROUX; DANIEL O. MÁRTIRE; MÓNICA C. GONZALEZ

LANGMUIR

American Chemical Society

Lugar: Washington D.C. , US.; Año: 2005 vol. 21 p. 8001 - 8009

0743-7463

The photolysis of silica suspensions of pH ~ 8 containing peroxodisulfate ions leads to the generation of two “surface transients” with a distinct spectrum and reactivity. Time-resolved and continuous irradiation experiments of similar dispersions also containing variable concentrations of vinyl acetate (VA) or 4-vinyl pyridine (4-VP) allowed the evaluation of the contribution of silica/water interfacial reactions to the kinetics and structural pattern of polymers synthesized using sulfate radicals as initiators. The rate constants measured for the reactions of the surface transients with 4-VP are 1 order of magnitude higher than those of VA, despite the fact that both species show similar reactivity in homogeneous solution toward sulfate radicals. It is suggested that both the sorption capacity and the different specific interactions with the silica surface of 4-VP and VA contribute to the observed reaction rates. Micrometer-sized latex particles of 4-VP and VP showed higher stability and more homogeneous size distributions when obtained in the presence of silica nanoparticles. Under the experimental conditions required for obtaining polymer particles, both the contribution of the described interfacial reactions and the effect of silica adsorbed monomer on the initiation steps of the polymerization may be neglected. The importance of in situ adsorption of the oligomer/polymer chains to silica NP during the polymerization propagation steps in determining the particle morphology is discussed. winDirVariable="C:/WINDOWS"