Anionicpolymerization of two phenyl-substituted trienes containing cross-conjugatedcarbon–carbon double bonds, 2-phenyl[3]dendralene (P3D) and 2-(4-methoxyphenyl)[3]dendralene (MP3D), was carriedout in THF under a variety of different conditions. Poly(P3D) of controlled molecular weight with a narrow molecular weight distributionwas obtained when the polymerization reaction was carried out at −78°C for 30 min. Broadening of the molecular weight distributionto the higher-molecular-weight side was observed if the polymerizationmixture was left to stand for 20 h at −78 °C, presumablybecause of the attack of the propagating chain-end carbanion at theconjugated diene structure in the polymer chain. Similar broadeningoccurred if the polymerization was performed at a higher temperature.However, under identical conditions, no such a broadening was observedin the polymerization of MP3D. Block copolymers of predictablemolecular weights and compositions containing a poly(2-vinylpyridine)segment were obtained by the sequential addition of P3Dand/or MP3Dto potassium naphthalenide and then 2-vinylpyridine.Only the conjugate addition structure was found in the resulting polymers. [ABSTRACT FROM AUTHOR]