Radical coupling reactions of both 1,1-diphenylethylene (DPE)-chain-end- and DPE-in-chain-functionalized polymers with potassium naphthalenide have been studied under the conditions mainly in THF at –78°C. Chain-end-functionalized polymers having M̄n values of less than 10 kg/mol were very efficiently coupled in more than 90% yield to afford the polymeric dianion that were dimeric coupled products with two 1,1-diphenylalkyl anions in the middle of the chains. However, the dimer yield decreased with increasing the molecular weight. The dimer was obtained in 59% yield with use of the chain-end-functionalized polymer having M̄n of 33.9 kg/mol. Well-defined in-chain-functionalized polymers with two benzyl bromide and DPE moieties each have been successfully synthesized by the reaction of the polymeric dianion thus obtained with 1-(4-bromobutyl)-4-(tert-butyldimethylsilyloxymethyl)benzene and 1-[4-(4-bromobutyl)phenyl]-1-phenylethylene, respectively. The radical coupling reaction of in-chain-functionalized polymers with DPE (M̄n ca. 20 kg/mol) with potassium naphthalenide also proceeded efficiently to afford the coupled products that were A2A′2 and A2B2 four-arm star-branched polymers with well-defined structures (M̄n ca. 40 kg/mol).
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Higashihara et al. (2002) studied this question.