Synthesis of sulfonated natural rubber neutralized with Mg, Pb and Zn acetates

Abstract

Dry natural rubber (NR) was sulfonated with acetyl sulfate in chloroform at 35"c. The concentration of sulfonic acid groups onto the rubber chain ranged from 0.18 to 0.82 mole7o. After sulfonation the modified NR was neutralized with zinc, lead and magnesium acetate to form an ionic bridge between the polymer chains. The viscosity-average molecular weight (M^) revealed that polymer degradation occurred during sulfonation up to a sulfonic concentration of 0.30 mole7o. After the My leveled off, which would suggest, either that chain scission has ceased and the formation of hydrogen bonding took place, or that a balance between a viscosity increase due to sulfonation and degradation as a result of bond scission. Determination of the water absorption and Wallace Number of the neutralized product indicate a different ion/covalent character between the cations. It was found that Mg + is more ionic than Zn which in turn is more ionic than Pb Due to the susceptibility of NR to degrade during the sulfonation, sulfonated natural rubber ionomers could not be developed. Instead, it obtained a sticky material which has good adhesion properties.