Chemical modification of polynorbornene. I. Sulfonation in dilute solution

The sulfonation of dilute solutions of polynorbornene (PN) in CCl4 has been carried out using SO3–triethylphosphate complexes of various stoichiometries dissolved in dichloroethane (DCE) or trifluoro‐trichloro‐ethane (TTE). This leads to an electrophilic substitution, with very few side reactions, yielding high sulfonation ratios (ca. 85%). The initial reaction is first order in both reactants (PN and SO3) and has an activation energy of 17.5 kJ mol−1. The reaction becomes diffusion‐controlled after ca. 30 min at room temperature due to the precipitation of the partially sulfonated polymer. The initial rate is almost independent of the isomeric structure (cis or trans) and the molecular weight of the polymer, as well as on the stoichiometry of the SO3–TEP complex; it is higher when TTE is used as solvent. The final sulfonation ratio is strongly dependent on the concentration of SO3 and seems to be controlled by the conditions of diffusion inside the precipitated solid.