Aluminum-Mediated Polymerization of Allylic Ylides toward α,ω-Functionalized C3 Polymers with Enhanced Nontraditional Intrinsic Luminescence

Allylic ylide polymerization is an unconventional method for synthesizing polymers with unique allylic repeat units. However, in contrast to significant efforts to develop new monomers, the development of new catalysts for this realm is scarce. Thus far, only organoboranes have been explored and proven to be efficient catalysts. Here, we demonstrate that aluminum-based catalysts, triethylaluminum (AlEt₃), aluminum chloride (AlCl₃), and aluminum bromide (AlBr₃), are efficient for 2-methylallyl triphenyl arsonium ylide polymerization, affording poly(propenylenes) with high 1,3-monomeric insertion selectivity (>97.7%) and trans-configuration (>92.5%). The aluminum-mediated polymerizations proceed in an immortal manner, as evidenced by the controlled molecular weights (DP_NMR), narrow polydispersities, and chain extension experiments. Interestingly, in the AlEt₃-mediated polymerization, each Al atom produces three polymer chains, whereas in the cases of aluminum halides, one polymer chain per Al atom is observed due to the weak migration ability of halogen. On the basis of experimental results, an aluminum-mediated ylide polymerization mechanism is proposed. This mechanism involves halogen and [1,3]-aluminum migrations, which dictate the catalyst activity and product structures. Moreover, all C3 polymers exhibit nontraditional intrinsic luminescence. Incorporation of halogen atoms at the chain end significantly enhances the photoluminescence properties due to the improved stacking of polymeric segments through halogen-π interactions. This study presents a new approach for synthesizing α,ω-end-functionalized C3 polymers and also expands the potential for the rational design of efficient catalysts for ylide polymerizations.