The Influence of Substituents in the 3‐Position on the Polymerization of Metaphenylenes

Leysen, Pieter; Mannaerts, Astrid; Koeckelberghs, Guy

doi:10.1002/macp.201700630

Cited by 1 publication

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References 24 publications

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“…Within the past decade, much work has been carried out to understand the underlying mechanisms, ,− develop design rules for specific monomer-catalyst systems, − and optimize polymerization conditions to tune properties of the resultant polymers. For example, the influences of halogens and side chains on polymerization kinetics were elucidated by systematically varying the monomer structure. , Density functional theory (DFT) modeling of the KCTP catalytic cycle ,, and computational studies of ligand steric and electronic effects , have increased our understanding of the factors that enhance polymerization control. This Account serves to highlight some key developments in controlled KCTP over the past decade, including our group’s contributions toward overcoming challenges such as the limited monomer scope, sequence control, dispersities restricted by the Poisson distribution, and living chain isolation, which are all still active areas of work today.…”

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confidence: 99%

Precision Synthesis of Conjugated Polymers Using the Kumada Methodology

2021

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Conspectus Since the discovery of conductive poly(acetylene), the study of conjugated polymers has remained an active and interdisciplinary frontier between polymer chemistry, polymer physics, computation, and device engineering. One of the ultimate goals of polymer science is to reliably synthesize structures, similar to small molecule synthesis. Kumada catalyst-transfer polymerization (KCTP) is a powerful tool for synthesizing conjugated polymers with predictable molecular weights, narrow dispersities, specific end groups, and complex backbone architectures. However, expanding the monomer scope beyond the well-studied 3-alkylthiophenes to include electron-deficient and complex heterocycles has been difficult. Revisiting the successful applications of KCTP can help us gain new insight into the CTP mechanisms and thus inspire breakthroughs in the controlled polymerization of challenging π-conjugated monomers. In this Account, we highlight our efforts over the past decade to achieve controlled synthesis of homopolymers (p-type and n-type), copolymers (diblock and statistical), and monodisperse high oligomers. We first give a brief introduction of the mechanism and state-of-the-art of KCTP. Since the extent of polymerization control is determined by steric and electronic effects of both the catalyst and monomer, the polymerization can be optimized by modifying monomer and catalyst structures, as well as finding a well-matched monomer–catalyst system. We discuss the effects of side-chain steric hindrance and halogens in the context of heavy atom substituted monomers. By moving the side-chain branch point one carbon atom away from the heterocycle to alleviate steric crowding and stabilize the catalyst resting state, we were able to successfully control the polymerization of new tellurophene monomers. Inspired by innocent role of the sterically encumbered 2-transmetalated 3-alkylthiophene monomer, we introduce the treatment of hygroscopic monomers with a bulky Grignard compound as a water-scavenger for the improved synthesis of water-soluble conjugated polymers. For challenging electron-deficient monomers, we discuss the design of new Ni(II)diimine catalysts with electron-donating character which enhance the stability of the association complex between the catalyst and the growing polymer chain, resulting in the quasi-living synthesis of n-type polymers. Beyond n-type homopolymers, the Ni(II)diimine catalysts are also capable of producing electron-rich and electron-deficient diblock and statistical copolymers. We discuss how density functional theory (DFT) calculations elucidate the role of catalyst steric and electronic effects in controlling the synthesis of π-conjugated polymers. Moreover, we demonstrate the synthesis of monodisperse high oligomers by temperature cycling, which takes full advantage of the unique character of KCTP in that it proceeds through distinct intermediates that are not reactive. The insight we gained thus far leads to the first example of isolated living conjugated polymer chains prepar...

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