Synthesis of sulfonated rubber ionomers by the ring-opening reaction of epoxidized styrene–butadiene rubber, their characterization, and their properties

A novel method for the synthesis of the sulfonate ionomer of styrene-co-butadiene rubber (SBR) was developed. SBR was first epoxidized by performic acid formed from hydrogen peroxide and formic acid in situ in solution, and this was followed by a ring-opening reaction with an aqueous solution of NaHSO3. The optimum conditions for the epoxidation of SBR in the presence of a phase-transfer catalyst and for the ring-opening reaction of epoxidized SBR with an aqueous solution of NaHSO3 were studied. During the epoxidation of SBR, a phase-transfer catalyst, such as poly(ethylene glycol), could enhance the conversion of double bonds to epoxy groups. During the ring-opening reaction, both the phase-transfer catalyst and ring-opening catalyst were necessary to enhance the conversion of the epoxy groups to ionic groups. The addition of Na2SO3 to the reaction mixture was important to obtain 100% conversion. The products were characterized with Fourier transform infrared spectrophotometry, 1H-NMR spectroscopy, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). DSC showed that the sodium sulfonate SBR ionomer possessed a dissociation temperature of ionic domains at 110°C, which appeared as black spots under TEM, after the sodium ions of the ionomer were substituted by lead ions. Some properties of the sodium ionomer, such as the water absorbency, oil absorbency, and dilute solution behavior, were studied. With increasing ionic groups, the water absorbency of the ionomer increased, whereas the oil absorbency decreased. The dilute solution viscosity of the ionomer increased abruptly with increasing ionic group content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3090–3096, 2006