Removal of ungrafted monomer from polypropylene-graft-maleic anhydride via supercritical carbon dioxide extraction

The removal of spent initiator, excess initiator and unbound monomer from newly synthesized polypropylene-graft-maleic anhydride (PP-g-MA) has typically been carried out using Soxhlet extraction. Standard solvents used in the Soxhlet process are xylene, toluene, acetone or methanol. These chemicals are not only hazardous to some degree, but also lead to undesirable maleic anhydride (MA) ring opening. This paper establishes that supercritical carbon dioxide (scCO(2)) extraction of residuals prevents anhydride ring opening and eliminates the need for post-extraction vacuum-drying of the copolymer product. An added benefit of this innovative process is that environmentally friendly carbon dioxide (CO2) is used in place of harmful solvents. The successful extraction of the residuals is established by thermogravimetric analysis (TGA), whereas FTIR spectroscopy is used to compare the anhydride content of Soxhlet-extracted PP-g-MA to that of scCO(2)-extracted copolymer. (C) 2004 Society of Plastics Engineers.