Synthesis and chemical structure of natural rubber adduct with SO_2 and study of the thermal stability

摘要

Natural rubber (NR, cis-1,4-polyisoprene) was reacted in solution with SO_2 at room temperature in different solvents (tetrahydrofuran, CHCl_3, CH_2Cl_2 and tetralin). The reaction product consisted of an adduct between NR and SO_2. The chemical structure of the adduct was studied by FT-IR spectroscopy, by thermogravimetry coupled with FT-IR (TGA-FT-IR), by differential thermal analysis (DTA) and by derivative thermogravimetry (DTG). The maximum SO_2 uptake from NR was 21% as determined by TGA. The TGA of the NR-SO_2 shows that the adduct decomposes in two steps initially releasing SO_2 at lower temperature and then decomposing at higher temperature like common NR. It is proposed that the chemical structure of the NR-SO_2 adduct consists of SO_2 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 SO_2 in an extrusion reaction giving back the NR macromolecule.rnThe possible potential applications of the NR-SO_2 adduct which is cheap and easy to prepare are outlined.