Grafting of methyl methacrylate onto natural rubber in supercritical carbon dioxide

The grafting of the methyl methacrylate (MMA) monomer onto natural rubber (NR) was carried out by supercritical carbon dioxide (scCO(2)) swelling polymerization with benzoyl peroxide (BPO) as an initiator. Fourier transform-infrared spectroscopy (FT-IR) was used to confirm the formation of graft copolymers with the characteristic bands of symmetric C=O and C-O-C stretching vibrations at 1728cm(-1) and 1147cm(-1), respectively. The effects of the rubber-to-monomer ratio, amount of initiator, reaction time, and pressure on the monomer grafting level (GL) and grafting efficiency (GE) were investigated, and the optimum conditions for the preparation of NR-g-MMA were found to be 70:30 of the rubber-to-monomer ratio, 1.2% of the initiator content, and the reaction pressure of 23 MPa for 6 h. The thermal behavior of the NR and the different NR/MMA molar ratio grafted copolymer samples was studied by differential scanning calorimetry (DSC). The observed glass transition temperature (Tg) was consistent with the GL. The tensile strength, modulus of elasticity, elongation at break, hardness, and oil resistance of graft copolymers were determined and compared with the values of NR and that of polymerization products prepared in traditional toluene solution. The results showed that the tensile strength, modulus of elasticity, hardness and oil resistance were greatly improved after modification in scCO(2). Copyright (C) 2007 John Wiley & Sons, Ltd.