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 anhydr ide (MA) function at one of its ends were investigated in hexane by careful ly monitoring the fluorescence response of a pyrene dye attached onto the M A moiety via an imide bond. Two pyrene-to-MA linkers were used. One consist ed of a single methylene unit, and the other of an amide bond followed by t hree methylene units. Comparison of the fluorescence data obtained with the two pyrene-labeled oligoisobutylenes showed that very strong polar associa tions are obtained in hexane between modified oligoisobutylenes displaying an amide bond. The fluorescence decays were analyzed in a quantitative mann er using two models, which yield the fraction of associated polar ends. Abo ve 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 h exane compared to less than 60% of the polar ends of the oligomer displayin g no amide bond. In an apolar solvent, the amide bond can share its hydroge n with other imide moieties via an intermolecular process, which favors: as sociation. In more polar tetrahydrofuran, only 21% of the polar ends of bot h OIB-Pys are associated. These associations occur intramolecularly and are due to OIB chains displaying more than one MA moiety.