Cationic Graft Polymerization onto Silica Nanoparticle Surface in a Solvent-Free Dry-System

For the purpose of the prevention of the environmental pollution and the simplification of reaction process, the scale-up synthesis of polymer-grafted silica nanoparticle by surface initiated cationic ring-opening graft polymerization of 2-methyl-2-oxazoline (MeOZO) in a solvent-free dry-system was investigated. The introduction of iodopropyl groups onto the silica surface as initiating group was carried out by the reaction of silanol groups with 3-iodopropyl- trimethoxysilane in a solvent-free dry-system. The graft polymerization of MeOZO onto silica nanoparticle surface in a solvent-free dry-system was initiated by spraying the monomer onto the surface having iodopropyl groups and the polymerization was conducted in powder fluid system under nitrogen. After the polymerization, unreacted MeOZO was readily removed under high vacuum. It was found that the cationic ring-opening polymerization of MeOZO was successfully initiated in the solvent-free dry-system to give polyMeOZO-grafted silica nanoparticles. The maximum grafting of polyMeOZO obtained from the polymerization initiated by iodopropyl groups on the surface reached 47.7 %. The percentage of grafting and grafting efficiency during the cationic ring-opening graft polymerization in the solvent-free dry-system were considerably larger than those in solution system. This suggests that chain transfer reaction from surface growing cation to monomer was effectively inhibited in the solvent-free dry-system.