Managing Local Order in Conjugated Polymer Blends via Polarity Contrast

Abstract

The optoelectronic landscape of conjugated polymers is intimately related to their molecular arrangement and packing, with minute changes in local order, such as chain conformation and torsional backbone order/disorder, frequently having a substantial effect on macroscopic properties. While many of these local features can be manipulated via chemical design, the synthesis of a series of compounds is often required to elucidate correlations between chemical structure and macromolecular ordering. Here, we show that blending semiconducting polymers with insulating commodity plastics enables controlled manipulation of the semiconductor backbone planarity. The key is to create a polarity difference between the semiconductor backbone and its side chains, while matching the polarity of the side chains and the additive. We demonstrate the applicability of this approach through judicious comparison of regioregular poly(3-hexylthiophene) (P3HT) with two of its more polar derivatives, namely the diblock copolymer poly(3hexylthiophene)-block-poly(ethylene oxide) (P3HT-b-PEO) and the graft polymer poly[3-but(ethylene oxide)thiophene] (P3BEOT), as well as their blends with poly(ethylene oxide) (PEO). Proximity between polar side chains and a similarly polar additive reduces steric hindrance between individual chain segments by essentially 'expelling' the side chains away from the semiconducting backbones. This process, which has been shown to be facilitated via exposure to polar environments

A Low‐Swelling Polymeric Mixed Conductor Operating in Aqueous Electrolytes

“…To give an example, the glass transition temperature, T g , of poly[3‐tetra(ethylene glycol)thiophene]—a material comprised of a polythiophene backbone and oligo(ethylene glycol) side chains—is notably affected by exposure to a humid environment. [ 13 ] In turn, the torsional backbone order and, hence, optoelectronic features significantly vary with temperature. [ 13 ] Structural [ 14 ] and mechanical properties also will be affected, rendering systematic establishment of structure/property relations intricate.…”

“…[ 13 ] In turn, the torsional backbone order and, hence, optoelectronic features significantly vary with temperature. [ 13 ] Structural [ 14 ] and mechanical properties also will be affected, rendering systematic establishment of structure/property relations intricate. In this communication, we demonstrate that in poly[3‐(6‐hydroxy)hexylthiophene] (P3HHT, see inset in Figure a for chemical structure), hydroxylated alkyl side chains introduce mixed conduction when operated with aqueous electrolytes, as work on random copolymers of poly(3‐hexyl thiophene) (P3HT) and P3HHT already indicated, [ 15 ] but without excessive swelling and/or unwanted plasticizing effects observed in materials with oligoethylene‐glycol side chains.…”

“…In this communication, we demonstrate that in poly[3‐(6‐hydroxy)hexylthiophene] (P3HHT, see inset in Figure a for chemical structure), hydroxylated alkyl side chains introduce mixed conduction when operated with aqueous electrolytes, as work on random copolymers of poly(3‐hexyl thiophene) (P3HT) and P3HHT already indicated, [ 15 ] but without excessive swelling and/or unwanted plasticizing effects observed in materials with oligoethylene‐glycol side chains. [ 13,16–18 ] The synthetic procedure and chemical characterization of the P3HHT are given in the Scheme S1 and Figures S1–S8, Supporting Information.…”

Repurposing Poly(3‐hexylthiophene) as a Conductivity‐Reducing Additive for Polyethylene‐Based High‐Voltage Insulation

“…for a polythiophene with tetraethylene glycol side chains blended with poly(ethylene oxide). [ 33 ] For the lowest measured composition of c P3HT = 0.0005 wt% the PL emission spectrum shows both features of aggregated and nonaggregated P3HT. It can be concluded that the conjugated polymer partially aggregates even at low compositions c P3HT < 0.01 wt%, which approach the monotectic composition, albeit likely as a single, self‐aggregated chain due to the high degree of dilution in LDPE.…”

Charge-Transfer Intermediates in the Electrochemical Doping Mechanism of Conjugated Polymers

“…This mode red-shifts during the first redox process (SI Figures S14, S16), representing a relaxation of the Cα=Cβ(-O) bond as it adopts a more single-bond character. In P3HT films, a shifting of this mode to lower frequencies has been attributed to greater torsional order and enhanced delocalization of π-electron, which again suggests that the early stages of doping are characterized by enhanced chain planarity [59][60][61]. Similarly, mode 9 (~1515 cm -1 , corresponding to the Cα=Cβ(-O) asymmetric stretch) also red shifts upon the initial oxidation of the polymer and then blue-shifts after the onset of the second redox process (SIFigureS12, S13).…”