Polypropylene (PP) was swelled with a solution of monomers in supercritical carbon dioxide (SC CO2), and was grafted with acrylic acid (AA), methyl methacrylate (MMA) and maleic anhydride (MAH) via free radical polymerization leading to PP-g-(AA-MMA-MAH). During monomer selection, combination of soft monomer and hard monomer was used in order to tune flexibility of grafted polymer. The effects of different experimental conditions such as impregnation conditions, reaction conditions and ratio of monomers on grafting reaction were studied. The results indicated that the maximum grafting degree and grafting efficiency of PP with AA, MMA and MAH reached 4.31% and 71.83% respectively under the optimal swelling conditions at 7.74 MPa and 47 ℃ for 5 h, and reaction conditions at 75 ℃ for 3 h. After being grafted, the monomers were uniformly distributed in the PP substrate; the water contact angle of the grafted PP decreased, indicating the improvement of hydrophilicity; thermal stability of the product was improved because of introducing the grafted monomers.

Key words: supercritical CO2, polypropylene, ternary monomer, grafting polymerization