Diels–Alder polymerization: a versatile synthetic method toward functional polyphenylenes, ladder polymers and graphene nanoribbons

Abstract

The Diels-Alder reaction has been widely employed in synthetic organic chemistry since its discovery in 1928. The catalyst-free nature, functional group tolerance and high efficiency of the Diels-Alder reaction make it also promising for the fabrication of functional polymeric materials. In particular, a large variety of functional polyphenylenes (polymer structures mainly consisting of phenylenes) and ladderpolymers (double stranded polymers with periodic linkages connecting the strands) have been achieved by this method, showing potential applications such as polymer electrolyte membranes and gas separation. More recently, tailor-made polyphenylenes prepared by Diels-Alder polymerization have been utilized as precursors of structurally well-defined graphene nanoribbons (ribbon-shaped nanometer-wide graphene segments) with different widths, demonstrating large length (>600 nm) and tunable electronic band gaps. This article provides a comprehensive review for the use of Diels-Alder polymerization to build functional polyphenylenes, ladder-polymers and graphene nanoribbons.

Synthetic Applications of Oxidative Aromatic Coupling—From Biphenols to Nanographenes

“…Figure presents the structures of the two exemplary carbon nanoribbons 163 and 164 obtained in excellent yields by Feng, Müllen, and co‐workers from the corresponding polymeric precursors using FeCl 3 as an oxidant in a CH 2 Cl 2 /CH 3 NO 2 mixture. The precursor for nanoribbon 163 was obtained by Diels–Alder polymerization of an appropriate acetylene‐functionalized tetraarylcyclopentadienone monomer. The weight‐average molecular weight ( M w ) of the resulting polymer reached 640 kg mol −1 .…”

“…Their syntheses have been extensively reviewed recently. [5,155,156] Figure 11 presents the structures of the two exemplary carbon nanoribbons 163 [157] and 164 [158] obtained in excellent yields by Feng, Müllen, and co-workers from the corresponding polymeric precursors using FeCl 3 as an oxidant in aC H 2 Cl 2 /CH 3 NO 2 mixture.T he precursor for nanoribbon 163 was obtained by Diels-Alder polymerization [159] of an appropriate acetylene-functionalized tetraarylcyclopentadienone monomer.T he weight-average molecular weight (M w ) of the resulting polymer reached 640 kg mol À1 .F eCl 3 -promoted planarization of the polymer furnished the nanoribbon with ac ove-type edge structure and width of 0.7-1.1 nm. [157] Thep oly-para-phenylene scaffold of the precursor for nanoribbon 164 was constructed by Suzuki polymerization.…”

Polycyclic aromatic hydrocarbons in the graphene era

“…The readers are recommended to refer to previous reviews on bottom-up synthesized GNRs for a comprehensive analysis of the history and recent advances [6,16,62,63,66,67,124,125]. In the following, we only select typical examples to illustrate the close interaction between PAH and GNR chemistries.…”

Spiers Memorial Lecture : Carbon nanostructures by macromolecular design – from branched polyphenylenes to nanographenes and graphene nanoribbons

“…Notably, the concept of repetitive Diels-Alder cycloadditions has also been extended to the synthesis of polyphenylene dendrimers. [141][142][143][144] Therefore, the diene and dienophile functions have been combined with the AB 2 moiety, which serves as a branching unit. The second critical issue in GNR synthesis is cyclodehydrogenation by a Scholl reaction.…”