(217am) Grafting of Maleic Anhydride Onto Natural Rubber Via Free Radical Initiation in Supercritical Carbon Dioxide

The grafting of maleic anhydride (MA) onto a polymer backbone is a popular method to expand the properties and processing options of that polymer.  The MA function helps to impart hydrophilicity as well as improve compatibility between components in polymer blends.  Many studies have been carried out in which natural rubber (NR) has been maleated in either the molten state or solution phase to produce NR-g-MA copolymers that can be used as compatibilizers in blends and composites containing NR as the main or minor phase.  In this work, MA was grafted onto the NR polymer in supercritical carbon dioxide (scCO₂).  ScCO₂ is an effective medium for polymerization because while most polymers do not dissolve, they tend to swell in scCO₂, allowing for diffusion of reactive monomer into the swollen polymer.  In addition, the density of the CO₂ can be easily tuned by changing pressure and/or temperature, and the reaction can take place under ideal conditions without the harsh organic solvents utilized in solution grafting or high temperatures employed in molten state grafting.  Azobisisobutyronitrile (AIBN) was chosen as the free radical initiator in this process.  The effect of monomer and initiator concentrations, reaction temperature, and reaction time on the graft level were studied.  Confirmation of MA grafting and determination of graft amount were achieved by FTIR and ¹H NMR techniques.