Effect of polymerization conditions on the molecular weight of polystyrene grafted onto silica in the radical graft polymerization initiated by azo or peroxyester groups introduced onto the surface

The effect of polymerization conditions on the molecular weight of polystyrene grafted onto silica obtained from the radical graft polymerization initiated by azo and peroxyester groups introduced onto the surface was investigated. The molecular weight of polystyrene grafted onto silica obtained from the radical graft polymerization initiated by surface azo and peroxyester groups decreased with decreasing monomer concentration and polymerization temperature. The molecular weight of polystyrene was found to be controlled to some extent by the addition of a chain transfer agent. The molecular weight of grafted chain on silica surface obtained from the graft polymerization initiated by surface radicals formed by photodecomposition of azo groups was considerably smaller than that by thermal decomposition. The number of grafted polystyrene in photopolymeriztion, however, was much larger than that in thermal polymerization. These results are explained by the blocking of surface radicals formed on the silica surface by previously grafted polymer chain: when the decomposition of surface azo and peroxyester groups proceed instantaneously at the initial stage of the polymerization, the number of grafted polymer chains increased.