All-Conjugated ABC-block-copolymer Formation with a Varying Sequence via an Unassociated Catalyst

Abstract

This manuscript consists of two parts which focus on enhancing control over the polymerization of conjugated polymers. In the first part, the controlled chain-growth character of the polymerization of poly(selenophene) using Pd(Ruphos) as a catalyst system is demonstrated. Next, all-conjugated thiophene−fluorene−selenophene triblock-copolymers are synthesized in all possible orders using this catalyst. Subsequent, the properties of these advanced structures are assessed using GPC chromatography and 1 H NMR, UV−vis, and fluorescence measurements. DFT calculations were performed to explain the unusual independence of the monomer sequence during the polymerization, traditionally observed in other chain-growth protocols for conjugated polymers. ■ INTRODUCTIONπ-Conjugated polymers are well-studied materials during the last decades because of their optoelectronic properties and their potential in low-cost electronics resulting from their conductivity and easy processing. 1−10 The quest toward complex and tailored polymeric structures to improve the performance and usability was the topic of research in the recent past and continues nowadays. 11 This quest starts with obtaining as much control as possible over the polymerization mechanism, hereby turning it into a controlled chain-growth mechanism with control on end-group functionalization and molar masses. 12−15 Moreover, this enables block-copolymerization by successive monomer addition, in which the next monomer is added after the previous monomer is completely consumed. The research groups of McCullough and Yokozawa simultaneously discovered the chain-growth character of poly(3-hexylthiophene) with Ni(dppp)Cl 2 (dppp = diphenylphosphinopropane) as a catalyst. 16−19 Further research resulted also in control over other conjugated polymers that were formed in a chain-growth fashion using the same or other Ni-and Pd-based catalysts. 20−34 The controlled nature of the polymerization relies on the association of the catalyst with the π-system of the propagating polymer chain after the reductive elimination (catalyst-transfer polycondensation, CTP). 35 As a consequence, termination and transfer reactions are avoided and a controlled chain-growth polymerization mechanism is obtained. In principle, if the controlled polymerization of two different monomers is obtained under the same conditions, allconjugated block-copolymers (π-BCPs) are accessible by sequential monomer addition. Nevertheless, since the mechanism relies on the association of the catalyst with the propagating polymer, the synthetic direction is fixed from the monomer with the lowest catalyst affinity to the one with the highest catalyst affinity, as reported by the groups of Yokozawa and Wang. 30,32 As a consequence, the number of all-conjugated block-copolymers composed of electronically different blocks prepared by successive monomer addition remains scarce, e.g.

Role of Solution Structure in Self-Assembly of Conjugated Block Copolymer Thin Films

“…This goal has been met by BCPs where either one block has a conjugated backbone and the other has an insulating backbone with pendant conjugated molecules, [29][30][31][32][33][34][35][36][37] or by structures where both blocks have conjugated backbones (CBCPs). [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] Because of the relative stiffness of conjugated backbones, the phase separation of their BCP is complex due to energetic interactions between blocks, the volume fraction of the blocks, and potential crystallization.…”

Comparing blends and blocks: Synthesis of partially fluorinated diblock polythiophene copolymers to investigate the thermal stability of optical and morphological properties

“…With thin-film microstructure playing such a key role in the optoelectronic and charge transport properties of conjugated polymers, block copolymers naturally appear as useful tools for tailoring the thin-film morphology [1–5]. The propensity of some block copolymers to phase segregate at the nano-scale is of particular interest in the field of organic photovoltaics (OPV), where separation of the electron donor and acceptor domains on the order of the exciton diffusion length (5–10 nm) is required [1,6–9].…”

Access to (Hetero)arylated Selenophenes via Palladium‐catalysed Stille, Negishi or Suzuki Couplings or C−H Bond Functionalization Reaction

“…This reaction proceeds via the formation of a thiophen‐2‐ylmagnesium bromide intermediate. The polymerization of a 2‐bromo‐3‐octylselenophen5‐yl zinc bromide for the synthesis of a poly(3‐octylselenophene) via palladium‐catalysis has also been described …”