SYNTHESIS AND CHEMICAL STRUCTURE OF NATURAL RUBBER ADDUCT WITH SO2 AND STUDY OF THE THERMAL STABILITY

Natural rubber (NR, cis-1,4-polyisoprene) was reacted in solution with SO2 at room temperature in different solvents (tetrahydrofuran, CHCl3, CH2Cl2 and tetralin). The reaction product consisted of an adduct between NR and SO2. The chemical structure of the adduct was studied by Milk spectroscopy, by thermogravimetry coupled with FT-IR (TGA-FT-IR), by differential thermal analysis (DTA) and by derivative thermogravimetry (DTG). The maximum SO2 uptake from NR was 21% as determined by TGA. The TGA of the NR-SO2 shows that the adduct decomposes in two steps initially releasing SO2 at lower temperature and then decomposing at higher temperature like common NR. It is proposed that the chemical structure of the NR-SO2 adduct consists Of SO2 molecules added to the double bonds of the isoprene units forming a sulfone derivative with three-membered rings known as thiirane-1,1-dioxide. On heating the thiirane ring decomposes releasing SO2 in an extrusion reaction giving back the NR macromolecule.