Maleic anhydride modified oligo(isobutylene) : Effect of hydrogen bonding on its associative strength in hexane characterized by fluorescence spectroscopy

The intermolecular associations of an oligoisobutylene with a maleic anhydride (MA) function at one of its ends were investigated in hexane by carefully monitoring the fluorescence response of a pyrene dye attached onto the MA moiety via an imide bond. Two pyrene-to-MA linkers were used. One consisted of a single methylene unit, and the other of an amide bond followed by three methylene units. Comparison of the fluorescence data obtained with the two pyrene-labeled oligoisobutylenes showed that very strong polar associations are obtained in hexane between modified oligoisobutylenes displaying an amide bond. The fluorescence decays were analyzed in a quantitative manner using two models, which yield the fraction of associated polar ends. Above an oligomer concentration of 40 g/L, more than 95% of the polar ends of the modified oligoisobutylenes displaying an amide bond are associated in hexane compared to less than 60% of the polar ends of the oligomer displaying no amide bond. In an apolar solvent, the amide bond can share its hydrogen with other imide moieties via an intermolecular process, which favors association. In more polar tetrahydrofuran, only 21% of the polar ends of both OIB-Pys are associated. These associations occur intramolecularly and are due to OIB chains displaying more than one MA moiety.