Diphenylethylene living polymer capping

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). 

The living anionic polymers of protected functional methacrylate monomers herein introduced are very similar in reactivity and stability to those of MMA. Accordingly, these living polymers can initiate the polymerization of MMA, tBMA, and other protected functional methacrylate monomers, resulting in block copolymers with tailored chain structures. Complete aossover block copolymerizations among these methacrylate monomers are possible. Furthermore, living anionic polymers of styrene, a-methylstyrene, isoprene, and 1,3-butadiene initiate the polymerization of protected functional methacrylate monomers to afford well-defined AB diblock copolymers. In order to avoid ester carbonyl attack by the chain-end anions, the living anionic polymers should be end-capped with 1,1-diphenylethylene... 

It is important to end-cap the living carbosilane polymer with 1,1 -diphenylethylene to decrease the reactivity of the living center in order to obtain the block copolymer successfully. The diphenylethylene thus provides a milder carbanion for initiation of the methacrylate monomer. With this modification, efficiency of the end-capping by an electrophile (quenching) has reached 0.95 <2001PSA86, 1998PSA2699>. 

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