Ni‐Catalyzed Polymerization of Poly(3‐alkoxythiophene)s

Abstract

The Ni-catalyzed polymerization of poly(3-alkoxythiophene)s (P3AOTs) was studied and compared with the controlled chain-growth polymerization of poly(3-alkylthiophene)s (P3ATs). By varying the ratio of the initial monomer concentration to the initiator concentration, no linear dependence of the molar mass was observed, revealing that the polymerization does not proceed via a controlled mechanism. This was also confirmed by analyzing the end-groups of the polymer with MALDI-TOF mass spectrometry. To acquire more information on the polymerization mechanism, the formation of the actual monomer and the polymerization reaction were studied into more detail. These experiments proved that the polymerization proceeds via a chain-growth mechanism, although not in a controlled way. a Supporting information for this article is available at the bottom of the article's abstract page, which can be accessed from the journal's homepage at http://www.macros.wiley-vch.de, or from the author.-2 - IntroductionPoly(3-alkylthiophene)s (P3ATs) are a class of conjugated polymers that has been intensively studied over the past decades. The discovery by McCullough and Yokozawa of the chain-growth polymerization mechanism of P3ATs has led to a renewed interest in the synthesis of these polymers.[1] This chain-growth mechanism is made possible by the 'ringwalking process' of the Ni-catalyst, whereby the Ni(0) species is transferred intramolecularly along a polymer chain to its end where it oxidatively inserts in the C-Br bond. [2] Due to this mechanism, all polymer chains are equipped with the same end-groups, being a bromine and a hydrogen atom (after quenching with acid). It also allows control of the molar mass by adjusting the feed ratio of the monomer to the Ni-catalyst, and the formation of block copolymers by successive monomer addition.[3]The versatility of the quasi-controlled chain-growth polycondensation has also been demonstrated by the use of other monomers, polymerized with Ni-as well as Pd-catalysts. In this way, polyfluorenes [4] , poly(para-phenylenes) [5] and polypyrroles [3d] have been successfully prepared.If the polythiophene backbone is substituted with an alkoxy instead of an alkyl side-chain, a polymer with different characteristics is obtained. Regioregular HT-coupled poly(3-alkoxythiophene)s (P3AOTs) are electronically different and show a significantly higher  max compared to P3ATs. [6] Their Faraday rotation is much larger (Verdet constant up to 3x10 6 T -1 m -1 ) [7] and their magnetic properties differ [8] . Although their properties are interesting, the polymerization behavior of P3AOTs has never been studied in detail.An important finding in this respect is that starting the polymerization of P3AOT with an otolyl nickel initiator complex results in polymers which mainly bear o-tolyl/hydrogen endgroups -as would be formed by a controlled chain-growth mechanism -but also otolyl/bromine and even small amounts of Br/Br, Br/H and H/H end-groups.[9] Although most -3 -polymers were equipped with the initiator u...

Kumada Catalyst‐Transfer Polycondensation: Mechanism, Opportunities, and Challenges

“…In another study, Van den Bergh et al investigated the KCTP of the ''reversed'' monomer 5-bromo-2-chloromagnesio-3-alkoxythiophene. [85] They observed polymerization in the presence of both Ni(dppp)Cl 2 and Ar-Ni(dppp)-Br. It is likely that a HH initiating dimer is possible here since the alkoxygroups are sterically less demanding than alkyl chains, as was already suggested earlier.…”

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

“…Especially for combinations of electron‐poor monomers and poor electron‐donating ligands, it is possible that the catalyst–polymer complex is not strong enough and dissociation of the catalyst from the polymer chain occurs prior to oxidative insertion . The catalyst can also dissociate from the polymer chain if the oxidative addition is too slow …”

“…A substituent ortho to the Ni‐bond slows down the reaction due to increased sterical hindrance, but is not a necessity for stability . It was also found that an alkoxy‐sidechain in the ortho ‐position hampers oxidative insertion due to its strong electron‐donating effect . Also, poly(fluorene)s, poly(cyclopentadithiophene)s, and poly(dithienosilole)s can all be polymerized in a living fashion, proving ortho ‐substituents are not necessary …”

“…[4][5][6] The catalyst can also dissociate from the polymer chain if the oxidative addition is too slow. [7] Even though the mechanism was discovered and developed for P3AT, it was rapidly applied to several other conjugated polymers. Presently several conjugated polymers can be synthesized by KCTCP, such as poly(p-phenylene), poly(3-alkylselenophene), poly(N-alkylpyrrole), poly(4-alkylthiazole), poly(dithienosilole), poly(cyclopentadithiophene), poly(bithienylmethylene), and poly(fluorenes).…”

“…[19] It was also found that an alkoxy-sidechain in the ortho-position hampers oxidative insertion due to its strong electron-donating effect. [7] Also, poly(fluorene)s, poly(cyclopentadithiophene)s, and poly(dithienosilole)s can all be polymerized in a living fashion, proving ortho-substituents are not necessary. [12,13,15] In this article, the polymerization of 3-alkoxy-meta-phenylenes is discussed.The authors declare no conflict of interest.…”