Preparation of grafted particles PGMA/SiO2 with a new surface-initiating system of mercapto group/BPO and their functionalization transformation

A new surface-initiating system for free radical graft-polymerization of lipophilic vinyl monomer was designed. The coupling agent γ-mercaptopropyl trimethoxysilane (MPMS) was first bonded onto the surfaces of silica gel particles, obtaining the modified particles MPMS-SiO₂. So a new surface-initiating system was constituted by mercapto group on the surfaces of MPMS-SiO₂ and dibenzoyl peroxide (BPO) in the solution. Through the proton transfer of mercapto groups to the decomposition product of BPO, a great deal of primary sulfur free radicals were produced on the surfaces of the particles, leading to the graft-polymerization of glycidyl methacrylate (GMA) on silica gel particles, obtaining the grafted particles PGMA/SiO₂ with a high PGMA grafting degree (about 26 g/100 g) . The effects of the main factors on the graft polymerization of GMA were examined and the corresponding mechanism was investigated. The functionalization transformations of the grafted particles PGMA/SiO₂ were conducted via ring-opening reaction of the epoxy groups with 5-aminosalicylic acid (5-ASA) and iminodiacetic acid (IDAA) as reagents, respectively, obtaining two functional composite materials, SA-PGMA/SiO₂ and IDAA-PGMA/SiO₂. The new route of surface-initiated graft-polymerization is feasible and effective. The suitable temperature is 55 °C and the appropriate used amount of BPO is 1.0 % of the monomer mass. The grafted particles PGMA/SiO₂ are easy to be transformed into functional composite particles via the ring-opening reaction of epoxy groups. SA-PGMA/SiO₂ particles have excellent extracting ability for alkaloids, and have an adsorption capacity of 87 mg/g for matrine; IDAA-PGMA/SiO₂ particles have strong chelating adsorption action for heavy metal ions, and have an adsorption capacity of 360 mg/g for Pb²⁺ ion.