SYNTHESIS OF END-FUNCTIONALIZED POLYMERS BY MEANS OF LIVING ANIONIC-POLYMERIZATION .8. REACTIONS OF LIVING ANIONIC POLYMERS WITH ALPHA,OMEGA-DIHALOALKANES

In order to prepare well-defined polymers with halogen end groups, ani onic living polymers of isoprene and styrene were allowed to react wit h excess amounts of alpha,omega-dihaloalkanes in THF at -78 degrees C. The monosubstitution reactions of 1,3-dichloropropane with these anio nic living polymers proceeded cleanly to afford quantitatively the pol ymers with chlorine end groups that possessed controllable molecular w eights and narrow molecular weight distributions. On the other hand, t he reactions of the anionic living polymers with either alpha,omega-di bromoalkanes or alpha,omega-driodoalkanes proceeded competitively with side reactions leading to dimer formation of the starting living poly mers. Thus, the bromine- and iodine-terminated polymers were obtained in 12-93% yields along with undesirable dimers. As side reaction candi dates, we speculated on metal-halogen interchange and/or single electr on transfer pathways followed by coupling reactions between the reacti on intermediates generated by both pathways. By end-capping the polyst yryl anion with 1,1-diphenylethylene, one could almost suppress the di mer formation, and the end-functionalized polystyrenes with bromine an d iodine were successfully obtained in more than 95% yield.