Furanized rubber studied by NMR spectroscopy

The double bonds of natural rubber latex (stabilized by a nonionic surfactant) were reacted with an approximately equimolar amount of performic acid at room temperature with a limited amount of formic acid present. Product analysis by 1H‐NMR during the course of the reaction showed that 69–90% epoxidation occurred before the advent of ring opening and ring expansion to produce furanized rubber; hence the rate of epoxidation was greater than the rate of furanization. Indeed, at lower concentrations of formic acid and rubber latex, epoxidation occurred to 90% and furanization was prevented; it was subsequently brought about by the addition of a catalytic amount of orthophosphoric acid. Increased formic acid concentration caused early coagulation of the modified rubber latex. By 1H‐ and 13C‐NMR, it was found that the furanized rubber probably consisted of tetrahydrofuran rings linked together by CC bonds at positions adjacent to the hetero atom and contained a terminal hydroxy group. The number average sequence length was 2–9, but only the sample with an average sequence length of 9 was effective as a cation binder.