Mechanism of Radical Chain Polymerizations Initiated by Azo Compounds Covalently Bound to the Surface of Spherical Particles

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The kinetics and mechanism of a radical chain polymerization reaction initiated from a self-assembled monolayer of an azo initiator attached to the surfaces of silica particles are investigated. The rate of the decomposition of the surface-attached initiator is followed by differential scanning calorimetry and volumetry. The kinetics of formation of the terminally attached polymer is studied by dilatometry. After polymerization the polymer is removed from the surfaces and the molecular weight averages and molecular weight distribution of the degrafted polymer are studied as a function of reaction parameters during polymerization. From the molecular weight, the mass of the attached polymer, and the specific surface area, the number of polymer molecules per area (or the distance between the anchoring sites) can be calculated and compared to the corresponding values of the initiator monolayers. The mechanism of a polymerization with surface-attached radicals is compared to that of conventional radical chain polymerization in solution.