The Synthesis of Poly(thiophene-co-fluorene) Gradient Copolymers

The copolymerization of thiophene and fluorene starting from a mixture of both monomers is investigated. It is shown that these monomers are incapable of copolymerizing using a Kumada catalyst transfer polycondensation. However, when the Pd(RuPhos)-protocol is used, this copolymerization is enabled and gradient copolymers are obtained. This protocol is applied to synthesize a series of 6 polymers with varying monomer feed and the properties of these gradient copolymers are investigated. This new class of materials, which was previously inaccessible using other catalysts, shows unique properties compared to the block copolymer analogues.status: publishe

Chirality in conjugated polymers: when two components meet

Chirality is a well-studied feature in the auspicious class of conjugated polymers. Proper use allows us to study and to control the behavior of the polymers which make them very valuable in many applications. Mostly chiral homopolymers are considered, but what happens when the chirality originates from the interplay between multiple components? This review summarizes different approaches to implement multicomponent chirality in conjugated polymers and their properties. © The Royal Society of Chemistry 2012.status: publishe

Synthesis of conjugated copolymers by combinin different coupling reactions

©2017 The Royal Society of Chemistry. Despite the significant progress in the controlled synthesis of conjugated polymers using a Catalyst Transfer Condensative Polymerization, the possibilities regarding random and gradient copolymers remain very limited. Therefore, a novel concept is introduced, in which different organometallic functions are placed on the monomers in a copolymerization, meaning that different types of coupling reactions are combined. By using combinations of Grignard, organozinc, organoboron, organotin and organogold functional groups, the goal is to tune the reactivity ratio of the monomers. As such, it enables to tune the polymer structure without having to intervene during the polymerization, something which was impossible up to now. In this study, two randomly copolymerizing thiophene monomers are considered, whose reactivity is varied by altering the organometallic function. Despite the significant difference in reactivity between the chosen functional groups, it is found that most combinations nevertheless result in the formation of a random copolymer. However, the combination of the organotin and organogold monomer shows a gradient in the monomer consumption, with a preferential incorporation of the organogold monomer at low conversion. Although the copolymerization is not controlled, it is an indication that the use of different organometallic functions is a viable strategy to tune the gradient in a copolymerization.status: publishe

Evidence for catalyst association in the catalyst transfer polymerization of thieno[3,2-b]thiophene

The performance of catalyst transfer polymerization (CTP) reactions which depend on catalyst association was studied on 3,6-dioctylthiothieno[3,2-b]thiophene (TT) monomers. This monomer was selected because a strong association of the catalyst is expected, since the aromaticity of thienothiophene is largely maintained when the catalyst and thienothiophene associate. This study includes both reported and unreported Ni- and Pd-catalyst systems. It is found that no polymer formation can be observed using Ni-catalysts, whereas Pd-catalysts show a similar behavior as for other monomer systems. During the study of the Ni-catalyzed CTPs, the π-associated Ni0-complex has been isolated in situ and displayed a high stability in solution. It is shown that the associated complex interferes with the polymerization reaction and even prevents polymer formation. Furthermore, this complex prevented any Kumada-coupling reaction in the presence of the TT unit, as it serves as a “trapping site” for free Ni0 catalyst entities. Ni0-trapping 2 does not occur during polymerization of 3-alkylthiophene, confirming the presence of the π-associated Ni0-complex in this polymerization. This introduces a new convenient method of probing Ni0-association during all Ni-catalyzed reactions. Furthermore, these results establish the presence of an upper limit to the catalyst association strength -above which oxidative addition is prevented and the polymerization is inhibited- and they therefore add extra considerations for optimal catalyst design.status: publishe

Conformational Behavior of Conjugated Polymers With Oligo(phenylene vinylene) Side Chains

The synthesis and chiroptical properties of a series of meta-arylenes, equipped with chiral oligo(phenylene vinylene) (OPV) side chains, are presented. How the OPV side chain contributes to the optical properties of the polymer is investigated. Secondly, the influence of the distance of the chiral moieties, placed on the OPV side chain, to the polymer main chain is investigated, which shows that, in order to induce any chiral effects, these chiral moieties need to be placed in the ß-position near the polymer main chain. Finally, it is shown that long (a)chiral, lateral alkoxy chains on the OPV side chain prevent the polymers from adopting a helical conformation and result in the formation of lateral (a)chiral stacks of different polymer chains. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.status: publishe

Steering poly(thiophene) properties by incorporation of phenyl groups

In order to tune the optical properties of poly(3-alkylthiophene)s, varying amounts of phenyl groups were incorporated more or less randomly along the backbone of this polymer. Because a living random copolymerization of thiophene and phenyl monomers is not possible in standard conditions, a specially designed biaryl monomer was used. The degree of randomness of this incorporation could be estimated by an in-depth 1H NMR analysis. The effect on the bandgap was remarkable, since a linear relation between the bandgap and the percentage of introduced phenyl rings was observed. This enables the synthesis of conjugated polymers with tunable and predictable bandgaps. Aggregation and crystallization behavior were also affected by the introduction of phenyl rings. Aggregation was still possible with 20% of phenyl rings, albeit in a small extent, while crystallization was already completely inhibited at that point.status: publishe