Polystyrene, living polymer capping reaction

Further support for the proposed mechanism is provided by the results of experiments involving phenylbromide instead of ethylbromide (Jj6). The polarizable TT electrons of this aryl compound allow it to effectively compete with styrene for the sites on the lithium surface and thus the Wurtz coupling reaction becomes dominant. Similar results were obtained with ethyltosylate. Although the reaction of tosylate with living polystyrene is rapid and quantitative, yielding ethyl capped polymers, its reaction with the monomer and metallic lithium produces only 10% of the ethyl capped polymers, the remainder being evolved as butane. Again, the aromatic nature of tosylate allows it to compete with styrene for the lithium sites. 

Another approach involves the end-capping reaction of living polystyrene with propylene oxide and the subsequent treatment of the alkoxide with bicyclo [2.2.1] hept-5-ene-2,3-rra s-dicarbonyl chloride to provide a macromonomer having a double bond in the middle of the polymer chain [88], as is shown in the following reaction (Scheme 33). 

A structure resembling that of the dumbbell polymers was made by Frechet et al. In this case the connector is linked with polyether dendritic groups [272, 273]. The synthetic approach involved the preparation of a difunctional polystyrene chain in THF using potassium naphthalenide as initiator. The living polymer was end-capped with 1,1-diphenylethylene (DPE) to reduce its nucle-ophilicity and avoid side reactions with benzylic halomethyl groups. Addition of the fourth generation dendrimer [G-4] -Br led to the final product (Scheme 100). 

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