Combining living anionic polymerization and atom transfer radical polymerization (ATRP)

well-defined comb-like branched polymers having one branch in each repeating unit were successfully synthesized by the coupling reaction of living PS and PI anions with 1

1-diphenylethenyl (DPE) groups along PS backbone.ATRP of 4-vinylbenzyloxy benzophenone (Sc) carried out in diphenyl ether at 130℃ using PhCH2Cl as an initiator and CuCl/2

2′-bipyridine complex as a catalyst led to PSc with benzophenone pendant groups.The molar ratio of PhCH2Cl

CuCl and 2

2--bipyridine used in ATRP was 1∶1∶3.The PSc was then converted to the corresponding PSe bearing DPE pendant groups viaWittig reaction

and PSe was used as a polymer backbone.Finally the coupling reaction of living PSLi or PILi prepared by the polymerization of styrene or isoprene via living anionic polymerization using n-BuLi as initiator in THF with DPE groups of PSe was carried out at -78℃ to form the desired comb-like branched polymers PSe-g-PS or PSe-g-PI.The resulting comb-like branched polymers and precursors were characterized by IR

1H-NMR

GPC and SLS measurements in detail.The peak at higher molecular weight ascribed to the comblike branched polymer in the GPC profile of crude comb-like branched polymer was sharp monodal and very narrow

suggesting a homogeneous and clean grafting.The apparent molecular weight of the comblike branched polymers determined by GPC was not reliable due to its branching structure.The absolute molecular weights of these polymers were therefore determined by SLS measurements.The values were much closed to the corresponding theoretical ones calculated assuming all the living chains were coupled with DPE groups (living chains were lack or equal) or all the DPE groups were consumed (living chains were excess)

suggesting that the grafting is nearly complete.The grafting efficiency could be calculated by comparing the molecular weights by SLS and the corresponding theoretical ones.Furthermore

the grafting efficiency was also proved to be almost quantitative by comparing 1H-NMR spectrum of comb-like branched PSe-g-PS and PSe.The effect of living chains and DPE groups molar ratio ([PSLi]0/[DPE]0) on grafting efficiency was discussed.When [PSLi]0/[DPE]0 varied from 0.7 to 1.2

the grafting efficiency increased from 65.5% to 101%.The results showed the coupling reaction of living chains and DPE groups was highly effective and proceeded until all the DPE groups were consumed

and the grafting efficiency could be controlled viachanging the feed molar ratios of living chains and DPE groups.Moreover

when excess living polymers were used

the effect of molecular weights of PSe and PSLi or PILi on graft efficiency was also discussed.When the Mw of PSe was smaller than 10000 s

and the Mw of PSLi varied from 4200 to 11200

almost quantitative grafting efficiency could also be achieved.When living chains was PILi

the similar results were obtained.In conclusion

all the results demonstrate that the method by coupling reaction of living polymer anion with DPE groups along backbone is very effective for the synthesis of well defined comb-like branched polymers.