Tuning the Electrical Conductivity and Self-Assembly of Regioregular Polythiophene by Block Copolymerization: Nanowire Morphologies in New Di- and Triblock Copolymers

Abstract

Over two decades ago the discovery of electrical conductivity in conjugated polymers spurred a tremendous amount of effort aimed at the development of practical conducting plastics. [1] One of the primary motivations was the hope of fabricating inexpensive, lightweight conducting materials. Those efforts have been coming to fruition in recent years with the development of polymer-based light-emitting diodes, [2] field-effect transistors, [3] elements for active matrix displays, [4] and all-polymer integrated circuits. [5] The synthesis and study of regioregular polythiophenes has produced conjugated polymers that self-assemble into well-defined superstructures and has furthered the use of these materials in the aforementioned applications. [6] Formation of ordered supermolecular structures in these regioregular materials correlates strongly with their excellent electrical conductivities (thousands or hundreds of S cm À1 in comparison with a few S cm À1 for regiorandom polymers). Nevertheless, regioregular polythiophenes still have poor mechanical and processing properties relative to typical flexible polymers.One approach to solving this problem is to synthesize block copolymers that contain conducting polymer or oligomer units. [7] Such a block copolymer [8] could self-assemble into a number of nanoscale morphologies, such as lamellar, spherical, cylindrical, and vesicular structures, which would lead to the possibility that new electronic/structural copolymers could be designed, synthesized, and assembled as components in new nano-devices. Here we present a very easy synthetic method to produce a large number of well-defined block copolymers and polyurethane elastomers containing regioregular polythiophenes. Despite having low percentages of regioregular polythiophenes, these new copolymers have very high conductivities (of the order of a few S cm À1 ) and form very well defined nanowires that reach lengths in the micron range. In addition, we have found that simply changing the solvent or evaporation conditions allows us to control the nanowire formation and the electrical conductivity of the block copolymer.The synthesis of diblock copolymers of head-to-tail-coupled poly(3-alkylthiophenes) (HT-PATs) can be accomplished by first preparing a well-defined PAT (polydispersity index (PDI) 1.2) with 95 % of its end groups [9] containing one proton and one bromine atom (2; Scheme 1). The method [10] shown in Scheme 1 is an important modification of methods previously published by our group. [6,11] The reaction was optimized and the polymer end groups were characterized by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS).Since PATs are chemically stable polymers, the ability to modify the end groups on one side of the polymer is similar to polymer-or bead-supported organic synthesis. Excess of reagents were used to drive the modification reactions to completion to give > 95 % yield for all of the steps subsequent to the synthesis of the HT-PHT. The purification of the products from all th...

Simultaneous Electronic and Ionic Conduction in a Block Copolymer: Application in Lithium Battery Electrodes

“…In contrast, the nanofibrils in the block copolymer AFM image are separated by distinct dark regions (Figure 1 b), which could indicate the location of the PEO block. These observations are consistent with previously reported data on P3HT‐containing block copolymer thin films 10. Figure 1 c shows small‐angle X‐ray scattering (SAXS) profiles obtained from bulk samples of both neat P3HT‐PEO and a P3HT‐PEO/lithium salt mixture.…”

Crystalline–Crystalline Donor–Acceptor Block Copolymers

“…The orientation of the cylinders is random, and dotlike and elongated structures suggest vertically and horizontally oriented cylinders. This is in contrast to fibrillar structures commonly observed in films of P3HT and P3HT block copolymers 25. Here, the bright domains are due to aggregation of perylene bisimide.…”

Air–Liquid Interfacial Self-Assembly of Conjugated Block Copolymers into Ordered Nanowire Arrays

“…13À17 McCullough and co-workers first showed that P3HT block copolymers form locally ordered short nanofibrils in drop-cast films. 18 In a later study, they found that reducing the bulkiness of the coil block improved the ordering in drop-cast films of P3HT block copolymers with 17 wt % P3HT. 19 Dai and co-workers have demonstrated that ordered assemblies of P3HT block copolymers can be formed through thermal annealing when P3HT block content was less than 70 wt %.…”