PREPARATION OF WELL-DEFINED POLYMERS BY POLYMER-COUPLING REACTION .6. SIDE REACTIONS IN THE GRAFTING REACTION OF LIVING POLYSTYRENE WITH POLYMERS HAVING PENDANT BENZYLIC HALIDES

The grafting reaction of living polystyrene with polymers having benzylic halides as pendants involves as the side reaction both the monomeric and dimeric terminations of polystyryl anions. The monomeric termination is considered to be the protonation of polystyryl anions and the dimeric termination the combination between polystyryl radicals which were generated from polystyryl anions by one-electron transfer to benzylic halide groups. The extents of the terminations were evaluated on the basis of the decrease in the polymer molecules after the reaction. The termination was almost dimeric when Li+ was used as the counterion of polystyryl anions in benzene whereas when K+ was used it was mostly monomeric. The drastic effect of the addition of polar solvents was observed on the extent of the dimeric termination in the reaction system of polystyryllithium-poly(chloromethylstyrene)-benzene, which increased to a maximum of 67% when a minute amount of tetrahydrofuran was added to the reaction medium, but further additions suppress the dimeric termination gradually and completely. The nature of the halogen atom of the pendant benzylic halides also markedly affects the reactions and the extent of dimeric termination was higher in the order Cl < Br < I, which was as high as 70% even if K+ was used as the counterion when benzylic iodomethyl groups were used as the pendants. © 1979, American Chemical Society. All rights reserved.