Homogenous Synthesis of Monodisperse High Oligomers of 3-Hexylthiophene by Temperature Cycling

Abstract

Whereas monodisperse polymers are ubiquitous in Nature, they remain elusive to synthetic chemists. Absolute control over polymer length and structure is essential to imparting chemical functionality, reproducible properties, and specific solid-state behavior. Precise polymer length has proven to be extremely difficult to control. The most successful examples are generally similar to solid-phase oligo nucleotide or peptide synthesis, wherein the polymer is built up one unit at a time with each sequential monomer addition requiring purification and deprotection (or other functional group activation) step. We have discovered a stepwise homogeneous catalyst-transfer polymerization to prepare monodisperse oligo(3-hexylthiophene) using temperature to limit additions to one unit per chain per cycle. This is the first reported example of a one-pot synthesis of monodisperse oligomers that requires no additional purification or intermediate steps. It is our hope that the strategy of temperature cycling to "freeze" intermediates will be generalizable to other living polymerization techniques, such as other catalyst-transfer polymerization systems, and those where a resting state involves an association between the catalyst and growing chain.

Isolation of Living Conjugated Polymer Chains

“…This observation seems to contradict previous discoveries of the Ni(II)-dithienyl complex as the catalyst resting state in analogous polymerizations. 20,21,26 However, we need to keep in mind that the Ni(II)-dithienyl complex can be observed only at low temperatures 27 and the Ni(II)-thienyl halide reported here is observed when the polymerization is complete 20,21,26 or when the polymer is isolated. Further support for this NMR assignment is provided when magnesium bromide is added to the solution, causing the two original peaks at 42.7 and 55.8 ppm to disappear while peaks at 44.7 and 59.1 ppm become strengthened (Figure 1c; full spectrum in Figure S4, Supporting Information).…”

Properties and applications of precision oligomer materials; where organic and polymer chemistry join forces

“…Given the flexibility in the chain end chemistry obtainable with this approach, the oligomers with terminal olefins at each terminus could be further polymerized using acyclic diene metathesis polymerization. Seferos and coworkers synthesized discrete oligo(3‐hexyl thiophene) (o3HT) containing up to 18 units 56 . A stepwise catalyst transfer polymerization was employed to form oligomers in a homogenous one‐pot approach using temperature cycling to control the elementary steps of the reaction.…”

“…Seferos and coworkers synthesized discrete oligo(3-hexyl thiophene) (o3HT) containing up to 18 units. 56 A stepwise catalyst transfer polymerization was employed to form oligomers in a homogenous one-pot approach using temperature cycling to control the elementary steps of the reaction. First, the bromothiophene monomer was deprotonated with lithium diisopropylamide in the presence of a nickel catalyst at low temperatures to generate a kinetically stable intermediate.…”

Examining the Spin State and Redox Chemistry of Ni(Diimine) Catalysts during the Synthesis of π‐Conjugated Polymers

“…(KCTP), was discovered to follow a quasi‐controlled chain‐growth mechanism by the McCullough and Yokozawa groups while working in independent laboratories. [ 15,16 ] Despite being the first reported example of a quasi‐controlled π‐conjugated polymerization mechanism, and in spite of significant efforts to expand the catalyst and monomer scope of KCTP, this system remains the most well‐controlled π‐conjugated polymerization to date allowing for the formation of well‐defined block copolymers, [ 17 ] polymers with complex architectures, [ 14 ] and even discrete high oligomers [ 18 ] and isolated living polymer chains. [ 19 ]…”