Living Anionic Polymerization of 1,4-Diisopropenylbenzene

The anionic polymerization of diisopropenylbenzene (DIPB) derivatives was conducted in THF at −78 °C with a specially designed initiator system prepared from oligo­(α-methylstyryl)­lithium and an excess potassium tert-butoxide (KOBut) (2.7–5.0 equiv to the Li salt). Among the ortho-, meta-, and para-isomers of DIPB derivatives, it was found that the para-isomer (p-DIPB) successfully underwent the living polymerization in a selective manner through one of the two isopropenyl groups under the above stated conditions. With this living polymerization system, soluble polymers with controllable M n values ranging from 7620 to 31 500 g/mol and near monodisperse distributions (M w/M n ≤ 1.03) were obtained for the first time. The obtained living polymers were stable at −78 °C even after 168 h and at −40 °C after 6 h, in which the intermolecular addition reaction of the chain-end anion to the pendant isopropenyl group could be completely suppressed. In contrast, the living polymerization of either the ortho- or meta-isomer was not successful under the same conditions. The block copolymerization of p-DIPB with either styrene (S), 2-vinylpyridine (2VP), or tert-butyl methacrylate (tBMA) by the sequential addition of such monomers was conducted. Four new PS-block-P­(p-DIPB), P2VP-block-P­(p-DIPB), P­(p-DIPB)-block-P2VP, and P­(p-DIPB)-block-PtBMA containing reactive P­(p-DIPB) segments were synthesized. On the basis of the block copolymerization results, it is understood that p-DIPB is comparable to 2VP and located between S and tBMA in monomer reactivity. The reactivity increases as follows: S < 2VP ∼ p-DIPB < tBMA, while the nucleophilicity of the living chain-end anion decreases in the following order: PS– > P2VP– ∼ P­(p-DIPB) – > P­(tBMA) –.