Anionic Polymerization of 2‐Hexyl[3]dendralene

Abstract

studies have reported the addition poly merization of [3]dendralene derivatives. [10] Previously, our group has reported the anionic polymerization of 2phenyl [3]den dralene (P3D) and 2(4methoxyphenyl) [3]dendralene (MP3D). [11] In both cases, anionic polymerization smoothly pro ceeds in polar solvents at low tempera ture, affording a polymer with a narrow mole cular weight distribution and a conjugate addition chain structure com prising conjugated carbon-carbon double bonds in the polymer chain, as shown in Scheme 1. However, a bimodal molecular weight distribution was observed when the poly merization mixture was stand still for a long duration after the monomer was completely consumed, presumably because of the nucleophilic addition of the propagating carbanion to the conjugated double bond in the polymer chain, as shown in Scheme 2. Hence, it is crucial to select the polymerization conditions to obtain polymers with controlled chain structures.This side reactions, nucleophilic addition of propagating chain end to the polymer chain, can also be prevented via the lowering of the reactivity of conjugated carbon-carbon double bond in the polymer chain by changing the double bond sub stituent. The carbon-carbon double bond in the polymer chain is conjugated by the phenyl group (Scheme 2), which facilitates easier nucleophilic attack of the propagating carbanion to the double bond compared with the case of an unsubstituted double bond. Hence, the polymerization behavior of [3]den dralene derivatives with a nonconjugating substituent on the C2 carbon of the [3]dendralene framework is interesting. Hence, 2(nhexyl)[3]dendralene (H3D) is selected as a candi date to compare the effect of substituents on its polymerization behavior with that of P3D.Notably, the microstructure of the resulting polymers is also interesting. As expected, the 2substituted[3]dendralene Dendralene In this study, the polymerization behavior of 2-hexyl[3]dendralene (H3D), which is an alkyl-group-derived [3]dendralene, is examined. The polymerization of H3D in tetrahydrofuran (THF) at −78 °C with potassium naphthalenide as the initiator affords poly(H3D) with a narrow molecular weight distribution, although a small shoulder peak is observed at a high molecular weight even before the monomer is completely consumed. The molecular weight distribution of poly(H3D) prepared in heptane is broader than that prepared in THF, indicating that the nucleophilic addition of a propagating carbanion to the carbon-carbon double bond in the polymer chain occurs in addition to polymerization. Furthermore, the microstructure of poly(H3D) is investigated by NMR. Signals corresponding to the conjugate addition structure, that is, 1,4-and 4,6-structures, are exclusively observed. Poly(H3D) prepared in heptane contains a higher content of the 4,6-structures compared with those prepared in THF.

Diene-Transmissive Diels–Alder Sequences with Benzynes

“…We presume that the nucleophilic addition of n -BuLi to either terminus of a 1,3-butadiene moiety of 1a generates the pentadienyl-lithium 7a or the phenylpropenyl-lithium 7b , which undergoes the nucleophilic substitution of bromobutane. Organolithium-initiated 1,4-addition polymerizations of dienes and dendralenes are known, but to our knowledge, 1,4-addition/substitution is without precedent for unsaturated hydrocarbons . Attempts to generalize this three-component, two C–C bond-forming process are underway.…”

Quo Vadis Carbanionic Polymerization?

“…Many synthetic groups were focused on discovering and studying new vinyl monomers compatible with anionic polymerization, leading to the synthesis of novel materials with exciting properties. − Ishizone’s − and Ma’s , groups, reported the synthesis of several novel styrene and 1,3-diene derivatives bearing various substituents. For example, the anionic polymerization of styrene derivatives with bulky adamantyl groups generated well-defined polymers exhibiting higher T g values (>200 °C) than PS .…”

Stable and Highly Regioselective Anionic Polymerization of (Z)-1-Phenyl[3]dendralene

“…Since all dienyl structures can potentially undergo polymerization similar to 1,3-butadiene, a variety of microstructures can be formed in the resulting polymer. Earlier, we reported the successful polymerization of several 2-substituted [3]­dendralene derivatives (Figure c–e) to afford well-defined linear polymers with predictable molecular weights and narrow molecular-weight distributions using anionic initiators such as potassium naphthalenide (K-Naph) and sec -butyllithium ( s -BuLi). , In the case of poly­(P3D), two conjugate addition structures (1,4 and 4,6 structures) were observed, and their ratio was constant regardless of the polymerization conditions, while the vinyl addition structure was not detected. This indicated that the [3]­dendralene derivatives underwent conjugate addition during anionic polymerization and that the polymerizabilities of the two conjugated systems contained in P3D are similar to those in anionic polymerization.…”