Radical polymerization initiated from a solid substrate. 2. Study of the grafting layer growth on the silica surface by in situ ellipsometry

摘要

Kinetics of the grafting free radical polymerization of styrene from the surface of Si wafers with a top silica layer was studied by in situ ellipsometric measurements of the grafted amount (A). Wafers uncovered and covered by physisorbed azo- or peroxide macroinitiator or covalently bonded with the substrate azo-initiator were used. Additional initiator of the same chemical nature was added to the bath solution (bulk). It was found that the grafted amount approaches a plateau value depending on the rate of grafting polymerization. At low rates, the plateau A values are on the order of 1-2 mg/m2, whereas at high rates, they are typically 10-15 mg/m2. Two kinetic regimes were studied where (1) the surface-attached chains terminate by chain transfer to the bulk or (2) the grafted chains terminate with the bulk free radicals. The rate of polymerization for the both regimes is linearly proportional to the surface density of the initiator. Within regime 2, the rate of polymerization has inverse square root dependence on the concentration of the initiator in the bulk. Two models were applied to explain the kinetics, which provide good agreement with the experimental data.