PPV Polymerization through the Gilch Route: Diradical Character of Monomers

Abstract

Despite various studies on the polymerization of poly(p-phenylene vinylene) (PPV) through different precursor routes, detailed mechanistic knowledge on the individual reaction steps and intermediates is still incomplete. The present study aims to gain more insight into the radical polymerization of PPV through the Gilch route. The initial steps of the polymerization involve the formation of a p-quinodimethane intermediate, which spontaneously self-initiates through a dimerization process leading to the formation of diradical species; chain propagation ensues on both sides of the diradical or chain termination occurs by the formation of side products, such as [2.2]paracyclophanes. Furthermore, different p-quinodimethane systems were assessed with respect to the size of their aromatic core as well as the presence of heteroatoms in/on the conjugated system. The nature of the aromatic core and the specific substituents alter the electronic structure of the p-quinodimethane monomers, affecting the mechanism of polymerization. The diradical character of the monomers has been investigated with several advanced methodologies, such as spin-projected UHF, CASSCF, CASPT2, and DMRG calculations. It was shown that larger aromatic cores led to a higher diradical character in the monomers, which in turn is proposed to cause rapid initiation.

Gilch Synthesis of Poly(ortho -Phenylene Vinylenes): A Powerful Access to High-Molecular-Weight Blue-Emitting Polymers

“…In particular, we analyze the significance of competitive Diels–Alder reactions of ortho ‐quinodimethane monomers depending on the substitution pattern. We correlate the findings with latest mechanistic insights into the Gilch synthesis and validate the potential of the reported method with related approaches such as cyclopolymerization of 1,7‐octadiynes …”

In Situ Generation of Fullerene from a Poly(fullerene)

“…The former would explain the formation of crystals in the studies above, while the latter are known to be unstable and are typically considered as intermediates in the formation of larger species, for example, poly(phenylene vinylene) and [2.2]‐1,4‐cyclophane, or with C 60 to form small molecular bridged species (their structures are shown in the Supporting Information Fig. S19) …”

Thioalkyl- and sulfone-substituted poly(p-phenylene vinylene)s

“…The polymerization is initiated by diradicals, usually formed by thermal dimerization of the active monomers. 3 Besides the above mentioned advantages, Gilch polymerization is also an economical method for the industrial scale preparation of O-PPVs. 1 The industrial interest arises from the low price and the convenient accessibility of the starting materials and reagents, as well as from the simple preparation and purification of the polymers.…”

“…Poly(p-phenylene vinylene)s (PPVs) have shaped the field of organic electronics and had a strong impact on many other fields of research. Nevertheless, despite their status as the materials of choice for fundamental research on conjugated polymers, [1][2][3] the synthetic chemistry of this interesting class of polymers is still "far from being mission accomplished" (as we highlight by this work). 1 Furthermore, exciting new applications like in bioimaging and drug delivery are emerging, making use of the excellent fluorescence properties, the low toxicity, and the biocompatibility of PPVs.…”

“…1 Furthermore, exciting new applications like in bioimaging and drug delivery are emerging, making use of the excellent fluorescence properties, the low toxicity, and the biocompatibility of PPVs. [3][4][5] For most applications of PPVs, substituents are attached to the conjugated polymer backbone. The substituents not only render the polymers soluble, but they are also useful to adjust the electronic, spectral, morphological, and self-assembly properties.…”