The crosslinking of partially brominated poly(isobutylene-co-4-methylstyrene) elastomer 1 by phenolic resin crosslinkers was investigated. The curing was modeled using small molecule analogs of the elastomer and the phenolic resin. In order to mimic the conditions that prevail within the highly aliphatic rubber, the study was carried out in isooctane using catalysts such as coated ZnO that are compatible with such low polar media. In situ NMR analysis was used to probe the reaction between the molecular analogs. p-Isopropyl benzyl bromide was used as the elastomer analog and hydroxymethyl phenols were used as the resin analogs. Isotopic labeling allowed for independent yet simultaneous monitoring of the reactivity of the elastomer and resin analogs. The resin analog reacted with the elastomer analog via an electrophilic aromatic substitution, leading to the formation of a dibenzyl type ether and benzyl-phenyl type ethers as reaction intermediates. At lower temperatures the elastomer analog reacted with itself in a competing "self-cure" process that may be suppressed by increasing the homogeneity of the reaction mixture or by increasing the temperature of the reaction. The applicability of the mechanism was confirmed by successful model cure experiments involving a low molecular weight sample of elastomer 1 and the phenolic resin analog.